A LONGITUDINAL STUDY OF THE STABILITY OF 'I'IIE
DENTITION FOlLOWING ORTHODON'I1C TRFATMENT
VOLUMEl
PAUL EMILE ROSSOUW
Thesis submitted to the Faculty of Dentistry,
University of Stellenbosch
in fulfilment of the requirements
for the degree of Doctor of Philosophy
DECLARATION
I hereby declare that this thesis entitled:
A longitudinal study of the stability of the dentition
following orthodontic treatment,
is my own work, and has not previously in its entirety or in
part been submitted at any university for another degree by
myself.
Sig
Date
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is cheap,
gives you
kind. It is
The greatest gift is the passion for reading. It
it consoles, it distracts, it excites, it
knowledge of the world and experience of a wide
a moral illumination.
--- Elizabeth Hardwick.
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DEDICAtIQH
This thesis is dedicated firstly to my wi.fe HEIDE, and
children CHARL, PATRIC and AILEEN who patiently supported
~nd encouraged me to achieve this important milestone in my
career, and to my father-in-law, DR G.J.J. WATERMEYER, who
tremendously influenced my orthodontic career by his
positive suppor~ and encouragement.
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The patients:
They co-operated willingly and their contribution made this
study possible.
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ACKNOWLEDGEMENTS
I am deeply indebted to those who contributed generously,
directly and indirectly, enabling me to accomplish a task
I could not have completed without their help.
My wife, Heide, and children, CharI, Patrie and Aileen, who
supported me and who were patient with me when this project
separated me from them for extended periods.
University of the witwatersrand:
Prof C.B. Preston (Promotor) - My conceptual leader, whose
knowledgeable help, constructive criticism without giving
offence, and impact on this work and in the field of
orthodontics is highly regarded and appreciated. I am deeply
indebted to him for his thorough supervision and guidance
during the preparation of this thesis.
Prof W.G. Evans - A friend and confidant whose enthusiasm
and ideas were a source of inspiration.
University of Stellenbosch:
Prof C.J. Hortje (Co-promotor) - Continual help, advice and
interest shown in the progress of the stUdy is greatfully
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literature summaries and
the thesis in a most
acknowledged. Your accommodating and considerate
staff-members, Mrs A.M. Roux and Mrs C.A. van Zijl,
assisted me tremendously in obtaining the radiographs.
Prof H.S. Breytenbach, Prof W.P. Dreyer and Prof C.W. van
wyk - The help and encouragement received during the initial
planning of the project was highly appreciated and your
dedication to research served as a strong stimulus to
complete the study.
Drs H.C. Bruwer, H.J. Burger, A.M.P. Harris and V.P. Joseph,
my post-graduate orthodontic students, supported me in the
search for the elusive answers so critical to the stability
of the orthodontically treated occlusion.
Mrs B. Kriel and her assistant Miss D.V. Julies, Mrs J.W.
Bartlett, Miss J. van Romburgh and oral hygienist, Mrs A.
Wolfaardt, conscientiously assisted me with the patient
recall and preparation of the records to be analysed. Their
efforts of encouragement were much appreciated.
Mrs L. Bester for typing the
assisting with the preparation of
efficient and prc~essional manner.
Mr G.H. Bruwer, dental technician, for the fabrication of
the retention appliances and Mr N.J. Fredericks, laboratory
assistant, for the casting and preparation of the dental
casts.
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Mr M.V. Jooste and Miss G.C. Truter for the compiling of the
photographic records.
Mr A. Louw, graphic artist, for his assistance in the
preparation of the figures illustrating the methods employed
during the study.
University of Pretoria:
Prof J.J.G.G. de Meulenaere, Prof J.E. Seeliger and Dr A.
Hennig Their unselfish attitude in allowing me access
to some pertinent subject material and for assisting me in
furthering my orthodontic knowledge.
Colleagues in private practice:
Dr J.P. Eloff, Dr R. Ginsberg, Dr R.G. Melville, Dr C.L.
steyn and Dr P. van der Walt I am indebted to these
orthodontists and their staff who provided me with the
necessary material for this study. They not only played a
tremendous part in my orthodontic post-graduate education,
but their invaluable support during this project is hereby
sincerely acknowledged.
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Colleagues abroad:
Dr R.G. Behrents (Head, Department of Orthodontics,
University of Tennessee, Memphis, Tennessee, USA), Dr J.e.
Boley (Richardson, Texas, USA), Dr J.G. Dale (Private
practice, Toronto, Canada), Dr R.S. Fisher (private
practice, Tucson, Arizona, USA), Dr J.C. Gorman (Private
practice, Marion, Indiana, USA) and Dr W.C. Sandusky, Jr.
(private practice, Memphis, Tennessee, USA). Their
dedication to orthodontics is a challenging example to
follow.
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Institute
Tygerberg:
for Biostatistics, Medical Research COuncil
Dr C.J. Lombard and Miss J.W. Truter - Their invaluable
advice and assistance in the statistical analysis of the
data were imperative to the success of this project. The
support from the Institute for Biostatistics is accepted
with gratitude.
Elida Pond's (Pty) Ltd:
The Elida Pond's Fellowship award enabled me to purchase a
cephalometric analysis computer program and digitizer.
These components were essential for the assessment of the
longitudinal changes in the sample.
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SUMMARY
The maintenance of dental alignment following orthodontic
treatment has been, and continues to be, a challenge for the
orthodontist (McReynolds and Little, 1991). Orthodontists
should endeavour to establish normal occlusions and
function to the end that physiologic balance and retentive
stability may be achieved (Goldstein, 1953). Many
philosophies and theories have been formulated in response
to this challenge, but few have successfully withstood the
test of rigorous post-orthodontic evaluation.
The present study comprises longitudinal assessments of
dentofacial changes which occurred in South African
Caucasian subjects during their orthodontic treatment as
well as a mean of 7 years following active treatnent. The
sample consists of 88 Caucasian subjects; 33 males and 55
female sUbjects who have undergone conventional edgewise
orthodontic treatment (Lindquist; 1985). The treatment
includes extraction (56%) and nonextraction (44%) therapy.
Due to the intricate structure of the craniofacial complex,
it is deemed important to discuss the major components of
this complex separately and then to compare the variables
describing the area with post-orthodontic lower incisor
crowding. Lower incisor crowding or irregularity, most
often referred to as relapse when occurring in the
post-orthodontic dentition, is a phenom~non that is
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clinically visible and easily assessed using the Little
Irregularity Index (Little, 1975). A variety of orthodontic
study cast and cephalometric variables represent the changes
which occur at the three time intervals selected for this
study, namely pre-treatment (T1), post-treatment (T2) and
following active treatment (T3). statistical analysis of th~
data was undertaken by the Institute for Biostatistics of
the Medical Research Council, Tygerberg, RSA utilising the
SAS (1985). The significance level of the results of this
study is set at p = 0.05.
x
No previous study has documented the
evaluated and described the various
craniofacial skeleton in this format.
literature
parts
or has
of the
The thesis is divided into thirteen chapters.
CHAPTER 1: INTRODUCTION
Chapter 1 is a general introduction to this longitudinal
study, documenting relevant literature and stating the
all-encompassing purpose of the study which was to record
the changes occurring in the dentition during and following
orthodontic treatment, and to evaluate certain parts of the
craniofacial skeleton and soft tissue profile in respect to
stability of the post-orthodontic occlusion.
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CRAPTER 2: TERHINGLQGY
Chapter 2 lists and defines various terms which have been
used in the literature to describe post-treatment changes
in the dentition. This is necessary in view of the widely
held opinion that all post-treatment changes are referred to
as relapse of orthodontic treatment. The immediate
understanding of this terminology is that of a badly treated
occlusion, but not all post-treatment changes are within
the orthodontist's control. Hence the introduction of terms
such as "rebound" and "physi~logic settling!l.
CHAPTER 3: MATERIALS AND METHODS
In comparison to other studies described in the literature,
the present study examines one of the largest longitudinal
samples. Various other professed elite studies in the world
used smaller samples. These studies are referred to in this
thesis. No other study has evaluated so many parameters in
such an encompassing manner as the present study. When
undertaking a study of this nature one has to plan to
compare the data and the conclusions with other studies in
this regard. Therefore, similar methods as described in the
literature were used to compile the data of the present
study. A combination of the best methods described are
utilised, a procedure not yet previously applied.
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The materi.als and methods utilised during the study are
described in Chapter 3. Each landmark and var1p,~le us.d is
defined. Relevant figures support these descriptions.
The essence of the thesis is described in Chapters 4-12.
Each chapter comprises a number of sections or subdivisions.
An introductory discussion offers a literature review and
ends with the statement of tha objectives of that part of
the study. Natural changes are included where applicable to
give insight to those occurring not only in the untreated
dentition, but also in the orthodontically treated
dentition. The measurements are described, results are set
out in tables, discussed and conclusions are drawn
regarding the stability of the treated occlusion.
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This study is
evaluated or
manner.
unique in this regard as no other study has
described relapse and stability in this
CHAPTER 4; NASOMA,XILLABY COMPLEX
The nasomaxillary complex which is attached to the cranial
base via sutures, is described and discussed in this
chapter. It i.s apparent that care must be exercised when
distalizing the maxilla as this retrusive disp~acement could
influence the post-orthodontic stability of the lower
incisor teeth. This is especially true when concommitant
forward growth of the mandible is occurring.
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CHAPTER 5: MANDIBLE
The mandible and its rela'tionship to post-orthodontic lower
incisor irregularity are described and discussed in Chapter
5. The forward growth and closing rotation of the mandible,
also experienced in the untreated individual, can influence
the alignment of the lower incisor teeth.
CHAPTER 6: AN~EROPOSTERIORDIMENSION
The anteroposterior dimension, as described and discussed in
this chapter, forms an integral part of the orthodontic
evaluation. Malo~clusions have been cla~gified according to
this dimension since the late nineteenth century (Angle,
1899). In the sample under study, the well-known ANB angle
was found Lo record a consistent decrease through the
period under review. The post-treatment changes of this
angle are mostly growth related and in particular to growth
of the mandible. The dental arch length shows a continual
decrease in size. It is obvious that these decreases must
influence the anterior dental alignment detrimentally.
CHAPTER 7: OCCLUSION
The goal of every orthodontist is to achieve a functional
and stable post-treatment occlusion. The static and
functional ideals are described in this chapter. An example
of a significant conclusion is that the arch dimensions
should be kept unaltered throughout treatment. During the
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post-orthodontic period, the intercanine width decreased to
a value smaller than the original value. This i9 similar to
changes occurring in untreated dentitions. Such decreases
could playa role in post-treatment relapse.
Numerous occlusal variables are studied in respect of their
changes during the various time intervals. The reader is
referred to the particular text for the relevant detail.
CHAPTER 8: ANTERIOR BORDER OF THE DENTITION
In Chapter 8 the longitudinal changes are described of the
anterior border of the dentition. Cephalometric norm values
published in the literature are taken as acceptable clinical
goals. The stability of the post-orthodontic dentition of
this study, and especially the stability of the an.terior
alignment, can be ascribed to the achievement of these
i~eals.
CHAPTER 9: VERTICAL DIMENSION
Vertical control .uring treatment is essential as
unwarranted opening or closing of the bite may result in
relapse of a treated occlusion. The vertical changes are
described and discussed in this chapter. The vertical
dimensions of the treated subjects in -this study were not
significantly altered during treatment. This effective
coatrol contributed to the stability of the treated
dentition as is shown by the stable overbite measurement
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recorded during the post-orthodontic period.
reported an increase in the overbite
post-orthodontic interval.
Other studies
during the
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CHAfTER 10: EXTRACTION VERSUS NQNEX~CTION TREATHBNT
Extraction treatment has been controversial since the
introduction of orthodontic therapy. The extraction of teeth
does not necessarily guarantee stability of lower incisor
alignment. In this study no significant difference is shown
between the extraction and nonextraction groups regarding
post-treatment lower incisor crowding when the pooled male
and female sample is evaluated. This is in accordance with
other studies reported in the literature. There is, however,
a difference when the males and females are separately
assessed as noted in Chapter 12. Th~.s factor must be
seriously taken in consideration when pli.'n:'.ing the treatment
of a malocclusion.
CHAPTER 11; SOFT TISSUE PROFILE
Many orthodontists assess the excellence of their treatment
only by the achievement of a sound soft tissue profile.
This confirms its importance in orthodontics. The soft
tissue changes are extensively discussed in Chapter 11. It
is largely growth and maturity changes which occur
post-treatment. The lower third of the soft tissue profile
becomes more retrusive during this time. This profile change
occurs simultaneously with the forward growth of the
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mandible as well as the lower incisor uprighting during the
post-treatment period. All these changes could influence the
post-orthodontic lower incisor alignment.
CHAPTER 12: SEXUAL DIMORPHISM
A longitudinal evaluation of the orthodontically treated
dentition is not complete without assessing sexual
dimorphism. These differences are described and discussed
in Chapter 12. Dimensional differences recorded in this
study are similar to those des~ribed in the literature with
the males showing the larger dimensions. Males have more
retrusive lips relative to the various profile lines. It is
reported that extraction and nonextraction treatment
ultimately end with the sarne amount of relapse. The present
study reports the contrary. The female sample shows bettp-r
maintenance of post-orthodontic lower incisor alignment. It
is also within the female sample that a larger percentage of
extractions were performed during orthodontic treatment.
CRAPTER 13: GF~\L DISCUSSION AND CONCLUSIONS
A general discussion, and conclusions are presented in this
chapter. Although many authors have reported the importance
of the lower incisor position, it was shown in the present
study that the maxillary incisor position is as important in
respect to long-term stability of the treated occlusion.
Groyth, especially post-pubertal mandibular growth, appears
to play a major role in the changes of the post-orthodontic
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dentition. The excecution of a well-founded treatment
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plan and the control of the facial dimensions and tooth
positions as part of a sound orthodontic technique seem to
be important in the achievement of a stable result.
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OPSQMMING
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Die instandhouding van tandbelyning na voltooiing van
ortodontiese behandeling was en sal nag steeds in die
toekoms 'n uitdaging bied vir ortodontiste (McReynolds en
Little, 1991). Die ortodontis se strewe moet wees am 'n
normale okkli'lsie in die ortodontiese pasient te veE)tig,
waartydens die funksie van die kake herstel word, asook
fisiologiese harmonie en stabiliteit van die okklusie
gevestig ~lOrd (Goldstein, 1953) • Menige filosofiee en
teoriee is al voorgestel om hierdie doelwitte te kan bereik,
maar baie min het nag daarin geslaag.
Tydens die huidige longitudinale studie is gepoog om In
ondersoek te doen van die veranderinge wat plaasvind in die
dentofasiale omgewing van agt-en-tagtig Suid-Afrikaanse
Kaukasiese pasiente tydens hulle ortodontiese behandeling,
asook na die verloop van 'n gemiddeld van sewe jaar sedert
die behandeling voltooi was. Die monster het uit 33 manlike
en 55 vroulike pasiente bestaan wat met 'n konvensionele
vierkantsdraad ("edg~wise") ortodontiese tegniek behandel
was (Lindquist, 1985). Die behandeling het 56% ekstraksie en
44% ni~-ekstraksie behandelingsbeplannings ingesluit.
Weens die baie komplekse kraniofasiale omgewing is dit
besluit am elke deel waaruit hierdie omgewing bestaan,
afsonderlik te beskryf en te bespreek. Die veranderlikes wat
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en die
in hierdie
elke deel beskryf is vervolgens gekorreleer met die
na-behandelings ondersnytand-bondeling. Ondersnytand­
bondeling is 'n verskynsel wat klinies sigbaar is en meestal
na verwys word as terugval indien dit voorkom in die
na-behandelings resultaat. Dit kan maklik gemeet word met
behulp van die "Little Irregularity Index" (Little, 1975).
'n Verskeidenheid van ortodontiese studiemodelle en
kefalometrie~Je verander.likes is tydens die voor-behandelings
(T1), na-behandelings (T2) asook na verloop van 'n gemidd.eld
van sewe jaar na afhandeling van die behandeling (T3)
gemeet. Die statistiese verwerkinge is deuI' die Institu,ut
vir Biostatistiek van die Mediese Navorsingsraad,
Tygerberg, R.S.A. gedoen deur middel van die SAS (1985). Die
betekenisvolheidsperk van die studie is op P = 0.05 gestel.
Geen studie het al voorheen die literatuur
gedefineerde areas van die kranio-fasiale skelet
formaat ondersoek of be~kryf nie.
Die proefskrif bestaan uit dertien hoofstukke.
HOOFSTUK 1: INLEIDING
In Hoofstuk 1 word 'n algemene inleiding gegee tot hierdie
longitudinale studie, waartydens die relevante literatuur
aangehaal word en die doelwit van die studie gestel word.
Die doelwit is om die veranderinge te bestudeer en te
beskryf wat plaasvind in die kranio-fasiale skelet en
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sagteweefsel profiel tydens en na voltooiing van
ortodontiese behandeling, asook hulle verband met langtermyn
stabiliteit van die okklusie aan te dui.
Die oorkoepelende doelwit, naamlik om vas te stel watter
faktore die na-behandelings okklusie laat terugval en watter
faktore die behandeling stabiel laat bly, is soortgelyk aan
studies wat in hierdie verband gedoen is. Sekere van hierdie
studies het optimistiese en ander negatiewe gevolgtrekkings
gemaak ten opsite van ortodontiese behandeling en veral die
na-behandelings resultate. Weens hierdie uiteenlopende
gevolgtrekkings bly dit dus belangrik om voort te soek na
data wat een van hierdie wee ondersteun, asook na parameters
wat nog nie voorheen vergelyk is met terugval nie. In
hierdie opsig is die huidige studie uniek, want geen studie
is egter nog in soveel detail bespreek en beskryf nie. Daar
is ook nog nie voorheen op een tydstip na al die
verskillende parameters soos in die huidige studie gemeet
en beskryf is, verwys nie.
HOOFSTUK 2; TEBMINQLOGIE
In hoofstuk 2 is verskeie terme wat in die literatuur
gebruik word om na-behandelings veranderinge te beskryf,
gedefinieer. nit is nodig geag aangesien die algemene
aanname is dat na-behandelings veranderinge terugval is of
dat dit dan, in die algemeen gesien, na verwys word as
onsuksesvolle behandeling. AIle na-behandelings veranderinge
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kan egter nie deur die ortodontis beheer word nie, vandaar
die verwysing na terme soos die terugspring en die
fisiologiese in~ok van tande.
HOOFSTUK 3: MATERIALE EN KETODES
Tydens hierdie studie word in vergelyking met andere in die
literatuur beskryf, een van die grootste monsters
longitudinaal ondersoek. Verskeie van die sogenaamde
vooraanstaande studies in die w@reld en wat volledig
aangehaal is in die proefskrif. het kleiner monsters
gebruik. Meer veranderlikes is nog nie gesamentlik tevore in
hierdie vorm ondersoek nie. Om die data en die
gevolgtrekkings van die huidige studie sinvol te kan
vergelyk met ander studies in die verband, moas soortgelyke
meetmetodes, soos in die literatuur beskryf, gebruik word.
In Kombinasie van die beste metodes is gebruik, 'n prosedure
wat nog nie voorheen aangewend is nie.
Die materiale en metodes wat tydens die studie gebruik is,
word in Hoofstuk 3 beskryf. Elke landmerk en veranderlike
gebruik se beskrYWing is met figure ondersteun.
In Hoofstukke 4 tot 12 is die grondbestandele van die
proefskrif heskryf. Elke hoofstuk bestaan uit 'n aantal
afdelings. Die inleiding bestaan hoofsaaklik uit die
literatuur oorsig en eindig met die stelling van die doelwit
van die deel van die studie. Natuurlike veranderinge is ook
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ingesluit, waar toepaslik, aangesien dit insig gee ten
opsigte van die verhouding daarvan in behandelde en
onbehandelde pasiente. Die verskillende metings van die
veranderlikes is beskryf, die resultate is in tabelle
uiteengesit, die resultate is bespreek en verskeie
gevolgtrekkings is gemaak ten opsigte van die stabiliteit
van die okklusie.
Hierdie studie is uniek in die verband aangesien nog geen
studie terugval en stabiliteit van ortodontiese behandeling
in hierdie formaat ondersoek en beskryf het nie.
HOOFSTUK 4: NASQMAKSILLeRE KOMPLEKS
Die kompleks, wat deur middel van nate aan die kraniale
basis geheg is, is in hierdie hoofstuk beskryf en bespreek.
Versigtigheid moet aan die dag gele word wanneer die
maksilla deur middel van die ortodontiese behandeling
distaal beweeg word, aangesien hierdie beweging die
stabiliteit van die ondersnytande kan beinvloed. Dit is
veral belangrik indien die voorwaartse groei van die
onderkaak ook in ag geneem word.
HOQFSTUK 5: HANDIBULA
Die mandibula en sy verhouding met die na-behandelings
ondersnytand-bondeling is beskryf en bespreek in hierdie
hoofstuk. Die voorwaartse en anti-kloksgewyse groeibeweging
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van die onderkaak, soos ook waargeneem in die onbehandelde
individu, beinvloed die na-behandelings ondersnytand
belyning.
HOOFSTUK 6: ANTERO-POSTERIOR VERHQUPING
Hierdie verhouding, soos beskryf en bespreek in die
hoofstuk, maak t n belangrike deel uit van die ortodontiese
evaluering. Wanokklusies word al sedert die laat negentiende
eeu (Angle, 1899) geklassifiseer. Die ANB hoek, een van die
hulpmiddels nodig vir die skeletale klassifikasie van t n
individu, het gedurende die projek afname in waarde getoon.
Hierdie verandering is nou gekoppel aan groei en in die
besonder aan die van die onderkaak. Die booglengte van die
tandboog vertoon ook aanhoudende afname in waarde. Hierdie
veranderinge kan die ondersnytand belyning nadelig
beinvloed.
HOOFSTUK 7: OKKLUSIE
Die doelwit van elke ortodontis is om toe te sien dat 'n
funksionele en stabiele na-behandelings okklusie gevestig
word. Die statiese en funksionele doelwitte is in hierdie
hoofstuk beskryf. Voorbeelde van betekenisvolle
gevolgtrekkings is:
i) tandboog dimensies moet so min as moontlik verander word
tydens behandeling, want veranderlikes soos die
inter-hoektand wydte verminder in die na-behandelings
periode na waardes minder as die oorspronklike afmetings.
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ii) molaar en hoektand verhoudings bly stabiel nadat
behandeling voltooi is.
Hierdie gewaarwordinge is soortgelyk aan die wat plaasvind
in die onbehandelde gevalle en speel sekerlik 'n rol in die
na-behandelings stabiliteit van die ondersnytand belyning.
Verskeie ander okklusale metings is geneem gedurende die
studie. Die leser word n~ die inhoud van die hoofstuk verwys
vir die relevante detail.
HOOFSTUK 8: ANTERIOR GRENS VAN DIE TANDBOe
In Hoofstuk 8 is die longitudinale veranderinge van die
anterior grens van die tande ·beskryf. Kefalometriese
standaardwaardes is in die literatuur te vind en hierdie
norme is steeds klinies bruikbaar. Die stabiliteit van die
okklusie in hierdie studie, en veral die anterior tand­
belyning, kan toegeskryf word aan die bereiking van hierdia
kefalometriese doelwitte.
HOOFSTUK 9: VERTIKALE VEBHQUDING
Vertikale beheer tydens ortodontiese behandeling is
belangrik aangesien hierdie verhouding vergroot kan word
tydefis behandeling. Die na-behandelings naiging is vir
hierdi~ vertikale verhouding am te verklein. So 'n
verandering sal lei tot die bondeling van die ondersnytande.
Die vertikale afmetin~p is nie betekenisvol verander tydens
die behandeling van die individu nie en het bygedra tot,
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onder andere, die stabiele oorbyt. Ander bekende studies
beskryf 'n verdieping van die oorbyt na verloop van tyd. Die
vertikale vcranderlikes is beskryf en bespreek in Hoofstuk
9.
HCQFSTUK 10: EKSTRAKSIE EN NIE-EKSTHAKSIE BEHANDELING
Ekstraksie behandeling is steeds 'n kontroverEiele
onderwerp. Die ekstraksie van tande as deel van
ortodontiese behandeling verseker nie noodwendig 'n stabiele
resultaat nie. Geen betekenisvolle veranderinge is
aangetoon, tussen ekstraksie en nie-ekstraksie groepe in
terme van die na-behandelings ondersnytand bondeling, waar
die geslagte gesamentlik beskou is nie. Hierdie
gevolgtrekking ondersteun die resuitate van ander studies.
Daar is egter weI 'n betekenisvolle verskil in laasgenoemde
verhoudings getoon wanneer die gesiagte afsonderlik evalueer
word en die belangrike bydrae in hierdie verband moet in ag
geneem word tydens behandelingsbeplanning.
HOOFSTUK 11: SAGTE WEEFSEL PROFIEL
Baie ortodontiste meet hulle sukses aan die bereiking van t n
estetiese sagte-weefsel profiel wat die belangrikheid van
hierdie veranderlike beklemtoon. D1e sagte w62fsel
veranderinge is in Hoofstuk 11 beskryf en bespreek. Dit is
hoofsaaklik na-behandelings groei en maturasie-veranderinge
wat die ondernytand belyning beinvloed. Die onderste een
derde van die sagte weefsel profiel word meer konkaaf as
xxv
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gevolg van die voorwaartse groei van
hierdie laasgenoemde veranderillge
ondersnytand bondeling veroorsaak.
HOOFSTUK 12: GESLAGSVERSKILLE
die
kan
onderkaak. Beide
na-behandelings
xxvi
In Longitudinale evaluasie van die ortodonties-behandelde
gebit is nie volledig indien die geslagsverskille nie
beskryf en bepreek word nie. Hierdie verskille is in
Hoofstuk 12 gedokumenteer. Mans vertoon grater dimensies wat
1n ooreenstemming is met verslae wat in die literatuur
gepubliseer is. Mans het meer retrusiewe lippe gemeet ten
opsigte van die verskillende profiel-lyne. Vroue het beter
na-behandelings belyning van ondersnytande vertoon. oit is
ook die vroulike groep waarin meer ekstraksies deel van die
behandeling uitgemaak het. Hierdie is in teenstelling met
die huidige denke in die literattlur.
HOOFSTUK 13: ALGEHENE BESPBEKING EN GEVOLGTREKKINGS
In Algemene bespreking en gevolgtrekkings is te vind in
Hoofstuk 13. Alhoewel baie outeurs die belang van die
ondersnytand posisie beskryf, word dit in die huidige studie
getoon dat die maksill@re snytand 'n ewe belangrike rol
speel in die stabiliteit van die behandelde okklusie. Oit
kom voor asof groei 'n belangrike oorsaak van
na-behandelings veranderinge in die dentofasiale omgewing
is. Oie uitvoering van 'n goeddeurdagte behandelingsplan, en
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xxvii
die beheer van gas~gsdimensies, asook tandposisi•• a. d••l
van in goale ortodonti8s8 tagniak, is belangrike eien.kappe
wat bydraes lewer tot In stabiele resultaat.
Stellenbosch University http://scholar.sun.ac.za
3.2.2
VOLUME 1
VOLUME 2 :
CHAPTER 1
CHAPTER 2
CHAPTER 3
CONTENTS
Chapters 1 - 7
Chapters 8 - 13
References
INTRODUCT ION .............•.•.••.....••.
1.1 General overview of longitudinal
orthodontic changes .
1.2 Objectives of the present study ..•
1.3 Presentation of the thesis .
TERMS USED TO DESCRIBE POST-ORTHODONTIC
TREATMENT CHANGES IN THE DENTITION .
2.1 Relapse .
2.2 Physiologic recovery •.....••..••..
2.3 Developmental changes ........••.••
2 • 4 Rebound...........................
2.5 Post-retention settling ..........•
2 • 6 "Ree idief" .
2.7 Crowding or recrowding .......••...
2 .8 Imbrication w, _ ••••
2.9 Stability .
2. 10 Retention .
MATERIALS AND METHODS ..••.•••••••.•..•.
3.1 Sample description ..............••
3.2 Orthodontic study model analysis
3.2.1 Molar and canine
relationships .........•.
Incisor overjet .
xxviii
1
1
5
7
9
10
11
11
11
12
12
13
13
13
14
15
15
19
22
26
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3.~:.3
3.2.4
3.2.5
3.2.6
3.2.7
Incisor overbite •••••.••
Anterior openbite •••.•••
Anterior crossbite .•.•..
Posterior crossbite •....
Maxillary and mandibular
xxix
26
26
30
30
crowding ...••.••..•.•..• 30
3.2.8 Mandibular intercanine
width ,. . 33
3.2.9 Maxillary intercanine
3.2.10
3.2.11
3.2.12
width ',", .
Rotations .., ..........•.
Curve of Spee ••••..••...
Total malocclusion
37
37
37
score 41
3.2.13
3.2.14
3.2.15
3.2.16
3.2.17
3.2.18
Bolton tooth-size
discrepancy ..•..........
Arch length .......••....
Extraction .....•••••••..
Teeth present .••••••...•
Classification •.•••..•..
Little Ir:-:-egularity
41
42
42
45
45
49
3.3.2
index 47
3.3 Cephalcmetric measurements •••••••• 48
3.3.1 Definitions of radio-
graphic landmarks used
as seen on a lateral
cephalometric radiograph.
Definitions of the
variables measured 64
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3.3.3
3.3.3.1
Radiographic technique ..
The cephalometric
xxx
64
67
67
68
74
75
75
66
64
65
radiograph •••.......•...
3.3.3.2
3.3.3.3
The enlargement error ••.
Calculation of the
enlargement factor ..••••
3.4 Third molars present post-
retention -: .
3.5 Retention appliances ...........••.
3.6 Intra-observer error .....•..•••...
3.7 Statistical analysis of data .••.. c
3.7.1 Descriptive statistics .•
3.7.2 Inferential statistics
LONGITUDINAL CHANGES IN THE NASOMAXILLARY
COMPLEX AND ITS RELATIONSHIP TO LOWER
CHAPTER 4
INCISOR ", . . . . . . . . . . . 77
4.1 Introduction................. • • • . • 77
4.2 The nasomaxillary complex and
related anatomy................... 79
4.3 Theories of nasomaxillary complex
growth 83
4.3.1 Sicher and Brodie's
4.3.2
theory .
The nasal septum growth
83
theory 84
4.3.3
4.3.4
The septo-premaxillary
ligament theory •.•......
Moss's functional matrix
theory .
86
87
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xxxi
4.3.5 Theory of genetic
influence .....••••••••.. 88
4.3.6 A modern composite
(Ranly, 1980) ....•...•.. 88
4.4 Dimensional changes of the Naso-
maxillary complex during growth ••• 89
4.5 Treatment effects on the Naso-
maxillary complex ...•....•.•••.... 89
4.6 Objectives 61....... 93
4.7 Materials and methods .......••.... 94
4.7.1 Criticisms of SNA and
CHAPTER 5
CHAPTER 6
ANS-PNS ..••.•...........
4 .8 Results .
4.9 Discussion ..........•.•..•.••••.••
4.10 Conclusions .••......•......•...•••
LONGITUDINAL CHANGES IN THE MANDIBLE AND
ITS RE~~TIONSHIP TO THE STABILITY OF
ORTHODONTICALLY TREATED DENTITIONS ..•..
5.1 Introduction •••••••••..••••••..•••
5.2 The mandible and related anatomy •.
5.3 Dimensional changes of the mandible
dur ing growth ,,. .
5.4 Objectives ~ , .
5.5 Materials and methods .....•......•
5.6 Results .
5.7 Discussion .
5.8 Conclusions .
A LONGITUDINAL EVALUATION OF THE
ANTEROPOSTERIOR RELATIONSHIP OF THE
95
96
99
101
103
103
105
109
114
114
116
121
125
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xxxii
127
127
133
133
135
137
143
150
MAXILLA TO THE MANDIBLE IN
ORTHODONTICALLY TREATED SUBJECTS •.••..•
6.1 Introduction •••••••..••.•..••..•••
6.2 Dimensional changes of variables
during normal growth .•••.•••••••••
5.3 Objectives .
6.4 Materials and methods .......••••••
6.5 Results .
6.6 Discussion .
6.7 Conclusions .•••.•...........••..••
A LONGITUDINAL EVALUATION OF POST­
ORTHODONTIC TREATMENT OCCLUSAL CHANGES
AND THEIR RELATIONSHIPS TO LOWER
INCISOR CROWDING ......•.......•.... ~... 151
7.1 Introduction .•...........•..•....• 151
CHAPTER 7
7.1.1 Development of the
occlusion •.•.....••.•••• 151
7.1.2
7.1.3
7.1.4
Characteristics of a
static occlusion •••••..•
Functional occlusion .•••
Concepts of functional
155
156
occlusion .............•• 158
7.1.5 Requisites for an ide;.l
functional occlusion at
the end of orthodontic
treatment ......••.•••... 159
7.2 Normal growth of the dental
arches
7.2.1
............................
Arch width ••....•.••••••
163
163
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7.2.2
7.2.3
Arch length or depth •••.
Arch circumference or
xxxiii
167
7.2.4
7.2.5
perimeter ........•.•.••• 169
Incisor crowding/
irregularity............ 170
Dimensional changes
during orthodontic
treatment ......••••..••• 173
7.2.5.1 Comparison of untreated
to treated subjects •••.• 174
7.2.6 Overbite and overjet .... 174
7.3 Correlation of untreated normal
occlusion with other d~ntofacial
and skeletal dimensional variables
(Predictability) ..••....•..•...... 175
7.4 Dentofacial growth and tooth
position changes .•................ 178
7.4.1 Incisor positions 178
7.4.2 Molar positions 179
7.5 Longitudinal occlusal stability... 180
7.5.1 Lower incisor relapse 181
7.5.2 Growth cessation and
relapse -I • • • • • • • • • 183
7.5.3
7.5.4
7.5.5
Spacing of teeth and
relapse .
Maxillary crossbite
correction and relapse ••
Mandibular arch
expansion and relapse
184
184
187
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xxxiv
7.5.6
7.5.7
7.5.8
The relapse of overbite
and overjet correction ..
The effect of third
molars on relapse ...••.•
Oxytalan fibers and
188
192
relapse .....•••••••..•.. 195
7.5.9 Oral habits and
relapse •.•.•..••••.••.•• 196
7.5.10 The influence of muscle
function on r~lapse ••••• 196
7.6 Aetiology of relapse of ortho-
dontically treated occlusions .•... 197
7.7 Tooth-size discrepancies in
relation to stability (Bolton
discrepancy) .
7.8 Anterior component of force •••••••
7.9 Objectives .
7.12 Discussion .
7.13 Conclusions .•.•.•••••••••.........
A LONGITUDINAL EVALUATION OF THE
7.10 Materials and methods ....•...•.•••
7.10.1 Maxillary teeth ...••••••
7.10.2 Mandibular teeth ••••••••
7.10.3 Maxillary and mandibular
teeth in occlusion ...•••
197
199
200
200
201
201
202
205
205
208
211
215
238
Maxillary teeth ...••••..
Mandibular teeth ••••••.•
Occlusion .••.•••••.....•
.... ~ ......................7.11 Results
7.11.1
7.11.2
1.11.3
cm..PTER 8
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CHAPTER 9
CP..APTER 10
ANTERIOR BORDER OF THE DENTITION AND
ITS RELATIONSHIP TO LOWER INCISOR
IRREGULARITY ••...•...••••... "....•••..•
8.1 Int.roduction .....•..•.•....•......
8.2 Objectives .
8.3 Materials and methods .
8.4 Results .
8.5 Discussion .
8.6 Conclusions ••••••••..............•
A LONGITUDINAL EVALUATION OF THE
VERTICAL DIMENSION OF THE CRANIOFACIAL
SKELETON IN ORTHODONTICALLY TREATED
SUBJECTS AND ITS RELATIONSHIP TO POST­
ORTHODONTIC LOWER INCISOR CROWDING ...•.
9.1 Introduction •••...................
9.2 Objectives .
9.3 Materials and methods .
9 .4 Results 41 .
9.5 Discussion ••...•••••••••••••.•••..
9.6 Conclusions .
LONGITUDINAL EVALUATION OF EXTRACTION
VERSUS NONEXTRACTION TREATMENT WITH
SPECIAL REFERENCE TO POST-TREATMENT
IRREGULARITY OF THE LOWER INCISORS ••..•
10. 1 Introduction ...........••••••••...
10.2 Objectives .
10.3 Materials and methods ...•••••••.••
10.4 Results r:- , ..
10.5 Discussion .
xxxv
240
240
244
244
246
252
255
257
257
263
263
266
269
274
275
275
287
287
288
310
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CHAPTER 11
xxxvi
10.6 Conclusions ••••..•••••.••.•..•.•.• 310
SOFT TISSUE PROFIf..E CHANGES RESULTING
FROM ORTHODONTIC TRF~TMENT AND THEIR
RELATIONSHIP TO LOWER INCISOR
IRREGULARITY
11.-1 Introduccion •.• ~ ••.•....• < ••••••••
312
312
11.1.1
11.1.2
Longitudinal changes in
the soft tissue profile ••
Changes in the components
of the soft tissue
317
prof i Ie .. ~ ., .. e _
11.1.2.1
11.1.2.2
11.1.2.3
11.1.2.4
Glabella .•..••
Nose
Lips
Chin
318
318
318
319
320
11.1.3
11.1.4
Soft tissue changes
influencing the
dentItion ............•.. 322
The effect of ortho­
dontic treatment on soft
tissue ~ ... ..... . .. ...... 323
11.1.4.1 Vertical
changes ...•.. ~ 323
11.1.4.2 Lip thickness
and strain •.•. 324
11.1.4.3 Thickness of
soft tissue of
lips .......... 324
11.1.4.4 Nasolabial
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326
328
11.1.4.5
11.1.4.6
11.1.4.7
xxxvii
angle .......•• 325
Hard tissue and
soft tissue •••
Lip changes
Orthognathic
11.2 Objectives .
11.3 Materials and methods .........•••.
11.4 Reslllts ~~ .
11.5 Discussion .~ .
11.6 Conclusions .
A LONGITUDINAL ASSEf,SMENT OF SEXUAL
DIMORPHISM IN ORTHODONTICALLY TREATED
CHAPTER 12
11.1.5
11.1.6
11.1.7
surgery ...•...
11.1.4.8 cephalometric
standard .
Lip strength and its
effects on the
denti tion .
Soft tissue analysis ....
Ethnic differences in
soft tissue profile .....
329
329
330
331
334
335
336
338
340
348
CHAPTER 13
!=;UBJ'ECTS •••••••••••••••••••••••••••••••
12.1 Introduction .•••••.•..............
12.2 Objectives .
12.3 Materials and methods .
12.4 Results .
12.5 DiscusEion .
12.6 Conclusions e _ ••••••
GENERAL SUMMARY AND CONCLUSIONS .
350
350
362
363
364
375
391
393
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xxxviii
·'
13.1 Introduction •••••.••••...•.....••• 393
13.2 Discussion ••••••••••••..••••...... 399
13.2.1
13.2.2
Changes in maxilla,
mandible and supporting
structures ........•••••• 401
Anteroposterior maxillary
versus mandibular
Extraction versus non-
relationship .....•.•••••
13.2.3
13.2.4
13.2.5
Occlusal changes
Vertical changes .. ......
403
404
409
REFERENCES ......••. 4\ •••••••••••••••••••
13.3 Conclusions .......•.•••••••.••....
13.2.6
13.2.7
extraction treatment .
Soft tissue changes .
Sexual dimorphism .
411
412
413
415
421
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yxxix
TABLE 0
LIST OF TABLES.
A Comparison of the Angle Dental
and ANB skeletal classification
23-24
20
21
parameters ' .
Description of the sample ......••.•
Data sheet for recording measure-
ments derived from dental casts •...
Descriptive statistics of intra-
observer error calculation 70
TABLE III
TABLE I
TABLE II
TABLE IV Level of significance (p) of
Wilcoxon signed ranks to indicate
differences between measurements
repeated three time to test for
intra-observer error . 71-73
TABLE V Age related mean values of certain
maxillary dimensions for :nales and
females ,.... 90
TABLE VI Age related mean values of the
palatal plane angle for males and
females. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
TABLE VII
TABLE VIII
TAB::'E IX
Age related mean values of certain
cranial base dimensions for males
and females .
Descriptive statistics for metrical
data in respect to the
nasomaxillary complex .
Spearman correlation coefficients
comparing the relationship of the
92
97
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TABLE X
i£",130m~_..xillary and cranial base
,...Jmensions to the lower incisor
irregularity index at T3 •..•...•••.
Age related mean values of certain
mandibular anteroposterior spatial
positional changes for males and
98
xl
TABLE XI
females 110
Age related changes in mandibular
growth direction - angular and
linear values for males and
females If • • • • • • • • • • • • • • 111
TABLE XII
TABLE XIII
TABLE XIV
Age related mean values of
mandibular gonial angle growth
changes for males and females •..•.•
Age related mean values of
mandibular corpus length growth
changes for males and females .
~ge related mean values of
mandibular ramus height changes for
112
112
TABLE XV
males and females 113
Age related mean values of
mandibular chin button/taper
change 113
TABLE XVI
TABLE XVII
Descriptive statistics for metrical
data in respect to the mandible •...
Spearman correlation coefficients
comparing the relationship of the
mandibular dimensions to the lower
117-118
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TABLE XVIII
incisor irregularity (L-Irreg) •...•
Age related mean values of changes
of the ANB angle for males and
119
xli
females 134
TABLE XIX
TABLE XX
Descriptive statistics for metrical
data in respect to the antero­
posterior relationship of the
maxilla to the mandible .......•....
Frequency of the severity of molar
and canine anteroposterior cusp
relationships recorded pre­
treatreent, post-treatment and
138
141
140
TABLE x""r!
TABLE XXII
TABLE XXIII
post-retention...................... 139
Spea~~an correlation coefficients
comp~ring the relationship of the
irregularity of the mandibular
incisors at T3 to the variables
depicting anteroposterior dimension
at T1, T2 and T3 .•.•.••••.••••••••.
Kruskal-Wallis test indicating
whether significant relationships
existed between molar and canj.ne
anteroposterior relationships at Tl,
T2 and T3 and the irregularity of
the lower incisors at T3 .
Age related mean values of
mandibular intercanine dimension
(mm) for males and females 168
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TABLE XXIV
TABLE XXV
Age related mean values of maxillary
bimolar dimension (mm) for males and
f emales .-.
Age related mean values of
mandibular arch length change (mm)
measured mesial of the first
168
xlii
molars 168
TABLE XXVI
TABLE XXVII
TABLE XXVIII
TABLE XXIX
Age related mean values of overbite
change (mm) for males and females ..
Age related mean values of overjet
change (mm) for males and females ••
Descriptive statistics of metrical
data in respect to the occlusion..•.
Frequency distribution (prevalence)
of Angle classification (molar
relationships) and Bolton tooth-
176
176
216-217
size discrepancy ..................• 218
TABLE XXX
TABT....E XXXI
Frequency distribution of crowding
and occlusal parameters ..•.....•.•.
Frequency of maxillary and
mandibular third molars present at
219-220
T3 c:. • • • • • • • 221
TABLE XXXII
TABLE XXXIII
Spearman correlation coefficients
comparing the relationship of the
measured occlusal variables at Ti,
T2 and T3 to the irregularity of the
mandibular incisors at T3 .
Kruskal-Wallis test comparing
222
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significant relationships of
occlusal variables ~t Tl, T2 and T3
to the irregularity of the lower
incisors at T3 •.................... 223
xliii
TABLE XXXIV
TABLE XXXV
TABLE XXXVI
TABLE XXXVII
Descriptive statistics for metrical
data in respect to the anterior
border of the dentition ......•.....
Spearman correlation coefficients
(r) comparing similar measurements
depicting the anterior border of
the dentition for the three phases
of evaluation .
Spearman correlation coefficients
comparing the relationship of the
irregularity of the mandibular
incisors at T3 to archwidth, arch­
length and incisor position at Ti,
T2 and T3 . . :: .
Longitudinal comparison of the
Spearman correlation coefficients
for the Little Irregularity Index
(Little, 1975) ....••••••••.••••.•..
247
248
249
250
TABLE XXXVIII Descriptive statistics for metrical
data in respect to the vertical
dimension 267
TABLE XXXIX Spearman correlation coefficients
comparing the relationship of the
irregularity of the mandibular
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TABI.E XL
xliv
incisors at T3 to the variables
dppicting the vertical dimension at
Tl, T2 and T3 ••••••••••••......•.. 268
Differences between extraction and
nonextraction groups for a number
TABLE XLI
TABLE XLII
TABLE XLIII
TABLE XLIV
TABLE XLV
of variables .
Differences between extraction and
nonextraction groups for maxillary
variables .
Differences between extraction and
nonextraction groups for maxillary
to mandibular variables ..........•.
Differences between extraction and
nonextraction groups for soft tissue
variables .
Differences between extraction and
nonextraction groups : descriptive
statistics for the Little
Irregularity Index (Little, 1975) ..
Age related changes of cephalometric
parametp.rs describing soft tissue
289-291
292-293
294-295
296-297
298
change 321
TABLE XLVI
TABLE XLVII
Descriptive statistics for metrical
datu in respect to the soft tissue .
Spearman correlation coefficients
comparing the relationship of the
lower incisor irregularity at T3
against the measured variables at
341
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TABLE XLVIII
T1, T2 and T3 .
Sexual dimorphism in craniofacial
342
xlv
patterns 361
TABLE XLIX
TABLE L
TABLE LI
TABLE LII
Differences between male and female
groups for age variable .....•••..••
Differences between male and female
groups for a number of mandibular
variables .
Differences between male and female
groups for a number of maxillary
variables .
Differences between male and female
groups maxillary to mandibular
variables .
366
367-369
371-372
373-374
378
376-377
TABLE LIII
TABLE LIV
TABLE LV
Differences between male and female
groups for soft tissue variables .••
Differences between male and female
groups for initial Angle
classification and for extraction
and nonextraction treatment .
Differences between male and female
groups : descriptive statistics for
the Little Irregularity Index
(Little, 1975) ••.............•...•• 379
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xlvi
FIGURE 1
LIST OF ILLUSTRATIONS
Ideal intercuspation in buccal
view 25
Assessment of crowding/space
Anterior open bite .... ' ............•
Overjet in sagittal view .....•••....
Overbite in sagittal view ....••..•..
FIGURE 2
FIGURE 3
FIGURE 4
FIGURE 5
FIGURE 6
FIGURE 7
Anterior cross bite
Posterior crossb1~e .................
27
28
29
31
32
shortage 34
FIGURE 8
FIGURE 9
FIGURE 10
FIGURE 11
Little Irregularity Index .
Mandibular intercanine width •••.••••
Maxillary intermolar width
Mensuration of rotation;
Deviation from mid-fossa occlusal
35
36
38
Bjork/Jarabak analysis ........•....•
Ricketts analysis •..•..............•
Landmark location necessary for use
of Oliceph Cephalometric
Mandibular arch; Curve of Spee •.•.•.
Conventional arch length •.......•...
Little arch length •••..••.........•.
Basic Cephalometric analysis ...•....
39
40
43
44
50
51
52
53..... . . ... ~ ........
.......... ~ ...........line (degrees)
Holdaway and more
FIGURE 12
FIGURE 13
FIGURE 14
FIGURE 15
FIGURE 16
FIGURE 17
FIGURE 18
FIGURE 19
analysis 54
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1CHAPTER 1
INTROpUCTION
1.1 ~eral Qverview Qf lqngitudinal QrthQQQntic changes
A great deal of research intQ craniofacial develQpment is
undertaken to prQvide a more complete understanding Qf those
aspects which tQuch Qn the Qrthodontic prQfession. The need
tQ Qbtain develQpmental and morphQlogic hQmeQstasis has
become Qne Qf the mQst significant challenges in
orthodontics. Notwithstanding these research effQrts, a
workable cQncept which takes intQ account the complex
circumstances dealing with equilibrium and stability, versus
imbalance and relapse, are largely lacking. At the present
time no mechanical instrument is available to determine or
to predict the stability of a dentition. Although attempts
in this regard have been reported in the literature, no
method presently exists to predict accurately the future
status of the post-treatment orthQdontic occlusion
(Lombardi, 1972; Peck and Peck, 1972a; Keene and Engel~
1979).
OrthQdontists are largely cQmmitted to treatment excellence,
not only because of ethical respQnsibilities, but alsQ
because the profession, in many ways, aims tQ improve the
quality of life. Edward Hartley Angle (1899, 1907) defined
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2a normal occlusion according to a number of criteria still
in daily use. It was his belief that a normal occlusion
required a full compliment of teeth. In response to Angle's
work, Tweed (1944) proposed a philosophy of good orthodontic
treatment. He stressed the principle of the lower incisors
being positioned over mandibular basal bone. According to
Tweed the objectives of orthodontic therapy viz. i) good
facial aesthetics, ii) efficient masticatory function, iii)
healthy investing tissues to assure longevity of the
dentition and, iv) permanency of tooth position, required
extractions in more than 50% of all orthodontically treated
subjects (Tweed, 1944).
These principles have been elaborated on in a series of
"classic" articles which proposed certain "keys of' normal
occlusion" (Andrews, 1972, 1976). In order to attain
occlusal stability following orthodontic treatment and to
limit the use of retainers, certain criteria ~~st be met.
These criteria focus on the position of the lower incisor
and canine teeth (Williams, 1985). Failure to achieve the
high standards demanded by the profession is not acceptable
and leaves Q feeling of personal defeat ~1ith the operator.
Notwithstanding the real risk of failure, the challenge of
providing excellent orthodontics should not be evaded
(Little, 1990). The additional effort and commitment
required to obtain the best possible end result goes with
the territory. It is certainly satisfying to document and
display those cases that remain excellent, despite the
passage of time, as examples of our prowess and skill.
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3Quality orthodontics reflects well not only on the
individual orthodontist, but on the profession in general.
The sense of failure caused by well-treated occlusions which
deteriorate with time can lead to feelings of frustration.
Given the recognisec problems associated with treatment,
certain relapse changes may be anticipated. The original
problems, unfavourable cooperation, and poor growth, are
factors which may give a warning that relapse is a
possibility. At other times relapse will occur unexpectedly
and for no obvious reason.
Occlusal stability following orthodontic treatment should be
considered to be a primary goal for every orthodontist
(Sandusky, 1983). In the search for post-orthodontic
treatment stability it may be necessary for an orthodontist
to review his diagnosis, change his treatment regime, or
even to vary his overall treatment philosophy. The ability
to recognise weaknesses in orthodontic diagnosis and
treatment, and to adapt treatment modalities to improve
occlusal function, facial aesthetics, long-term dental
health and stability of treatment results is an integral
part of the profession of orthodontics.
The quest to understand the fin~ balance which exists
between stability and relapse has led to many attempts to
identify some significant factor(s) which are responsible
for post-treatment relapse (Sanin and Savara, 1973;
Siatkowski, 1974; Little, Wallen and Riedel, 1981; Owman,
Bjerklin and Kurol, 1989). Every time an orthodontist treats
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a malocclusion it is assumed that the odds will favour
success. The possibility of failure is, however, very real.
There are many pitfalls which lead to treatment problems
and no orthodontist is immune to them (strang, 1954). It is
important that clinicians learn from their mistakes and in
that respect they should from the outset assume that
stability is not always achievable (Rubin,1988).
Fortunately, endeavours to improve knowledge and treatment
methods in orthodontics have resulted in many excellent
investigations into aspects of relapse (Sadowsky and Sakols,
1982; Sandusky, 1983; Little, 1990). Despite these important
studies many causes of orthodontic relapse are not fully
understood (King, 1974). The following statements are
frequently made: "because the bite was deep to start with,
it is likely to relapse"; "overbite relapses significantly
following correction"; "everything is Class I now, but the
buccal segments will probably slip" (Bresonis and Grewe,
1974). The question arises whether these somewhat
pessimistic statements are based on sound facts?
It has been said, "Knowledge is what you learn from others;
wisdom is what you teach yourself." It is not such a tragic
fault to make a mistake for the first time. It is, however,
tragic to repeat the same mistake time and again. The
present study arose out of a desire to eliminate mistakes
which prejudice against long-term stability following
orthodontic treatment.
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51.2 Objectives of the present study
The main purpose of the present study was to identify those
factors which contribute to post-orthodontic treatment
relapse. In general this does not differ from other studies
which were conducted on this subject, but no other study has
however been reported which documents its objectives in
such an encompassing manner as the present study. The
present study is unique in the sense that objectives are
set not only to try to confirm the results of other studies,
bu~ also to evaluate the different areas of the craniofacial
skeleton in a variety of combinations with the purpose of
attempting to show whether new knowledge could be added to
the field of stability of the post-treated occlusion.
Stability of treated occlusions is the ultimate goal which
every orthodontist strives to achieve. Some reports in the
literature seem to make this a very elusive target and
others seem to be more optimistic. It is thus important to
keep on searching for those factors which are responsible
for changes in the post-orthodontic occlusion and also to
identify those factors which will contribute to long-term
stability.
The craniofacial skeleton is divided into several areas
which are covered by soft tissues. In order to identify the
causes of post-orthodontic treatment relapse, it was deemed
necessary to study specific craniofacial areas and their
relationships to post-treatment relapse with specific
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The objectives of the
and record pre-, and
6
reference to lower incisor crowding.
present study were thus to assess
post-orthodontic treatment changes in:
a) the nasomaxillary complex,
b) the mandible,
c) the relationship of the maxilla to the mandible,
d) the occlusion,
e) the anterior border of the dentition,
f) the vertical dimensions of the face,
g) the soft tissue of the facial profile,
h) the extraction and nonextraction groups, and
i) the pooled and separated male and female sample (this
was deemed essential as reports in the literature
reflect both).
Clinically, most complaints are normally in respect to
crowding of the mandibular incisors as this is visible to
patients. Other changes do occur, but are not as visible.
Therefore, the longitudinal changes in the abovementioned
areas were examined in relation to post-treatment lower
incisor imbrication. The aim was to establish correlations
between the variables which described the different areas
evaluated and the lower incisor irregularity.
Some of the abovementioned areas have been described
individually in orthodontic literature, a few have also been
described in combination, but nowhere are the objectives of
a study in respect to the longitudinal changes in the
occlusion of the orthodontic subject described in such
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7detailed format. The uniqueness of the present study is
reiterated by the manner in which the objectives are
achieved and documented in the various chapters.
It is hoped that the insight gained from this study will
not only assist orthodontists in their search for excellence
in treatment and post-treatment stability, but that it will
also complement the various other studies which have been
done in this important facet of orthodontics.
1.3 Presentation of the thesis
Following the introductory chapter, a variety of terms
which have been cited in the literature to describe
post-treatment changes are discussed (Chapter 2). An account
is given of the sample used in this study including details
pertaining to sexual dimorphism, age distribution and
whether extractions were performed as part of the
orthodontic treatment provided (Chapter 3). A description is
given of the methods and techniques used in the present
study. The latter are discussed under two headings:
A. Metrical techniques and data gathering.
B. statistical methods.
Chapters four to eleven are used to discuss the
relationships between the longitudinal changes in the
various craniofacial dimensions and post-treatment
stability. This format has not previously been documented.
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8The final chapters encompass a general discussion, a
referral to retention and a compilation of the conclusions.
The list of references cited is arranged alphabetically and
chronologically.
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9CHAPTER 2
TERMS USED TO DESCRIBE POST-ORTHODONTIC TREATMENT CHANGES IN
THE DENTITION
The choice of a term to describe the changes which may occur
in a dentition following orthodontic treatment has received
a fair amount of attention in the literature. Hellman (1944)
distinguised between failure (operator-incompetence) and/or
factors outside the control of an operator and relapse
(changes in succesfully treated dentitions). Horowitz and
Hixon (1969) used the term relapse to describe detrimental
changes which occur following active orthodontic treatment.
There are many factors which may influence treated, as well
as untreated occlusions. The same terms are used to describe
the changes which can occur in both situations. The question
may thus be asked: "How clearly are the terms relapse and
failure really defined?". Theoretically and practically it
is important to distinguish between these two entities as
post-treatment and "aging" changes can be due to one or more
aetiologic factors (Moyers, 1988; proffit, 1986). Objective
examination in order to determine the exact aetiologic
factor is extremely difficult. The literature in respect of
terms describing relapse is incomplete (Dermaut, 1974).
Hence it was thus deemed necessary to define some of those
terms here.
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10
i) Relapse,
ii) Physiologic recovery,
iii) Developmental changes,
iv) Rebound,
v) Post-retention settling,
vi) "Recidief",
vii) Crowding,
viii) Recrowding and
ix) Imbrication.
2.1 Relapse.
Relapse is the return to a former condition,
especially after improvement or seeming improvement.
Riedel (1976) believes that the word is too harsh a
description of the changes that follow orthodontic treatment
and he prefers the term "post-treatment adjustment" for
these changes. A mutiplicity of factors cause
post-treatment adjustment.
The Shorter Oxford English Dictionary (1975) defines relapse
as follows "to fall back into or to revert to a former
habit or state, a falling back into error, heresy or
wrong-doing; back-sliding; the fact of falling back again
into an illness after a partial recovery".
Horowitz and Hixon (1969) define relapse in general as
changes in tooth position after orthodontic treatment.
They do also mention that these changes can take place even
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11
though no treatment was instigated. It is thus necessary to
distinguish between relapse, physiologic recovery and
developmental changes.
2.2 Physiologic recovery
Physiologic recovery is a return to a normal condition which
is characteristic of normal functioning living organisms.
Horowitz and Hixon (1969) explain physiologic recovery as
the change to the original physiologic state after
completing treatment.
2.3 Developmental changes
Developmental changes are those which occur irrespective of
whether orthodontic treatment was implemented or not. These
changes could easily be overlooked when assessing
post-treatment relapse. The developmental changes occuring
in subjects who have not undergone any orthodontic treatment
are well documented in the literature (Riolo, Moyers,
McNamara and Hunter, 1974; Broadbent, Broadbent and Golden,
1975; Moyers, van der Linden, Riolo and McNamara, 1976;
Sinclair and Little, 1983, 1985).
2.4 Rebound
TO spring or bounce back after hitting or colliding with
something; a recoil. This phenomenon can be ascribed to the
elasticity of tissues. The retraction of the upper incisors
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12
can be responsible for a variety of changes in the
morphology of the upper lip. The upper lip may become more
retrusive in the absence of lip strain, when the lip is thin
or in adult subjects. The opposite effect is also possible,
resulting in no lip retraction or in the upper lip becoming
more protrusive. The upper lip and upper incisors are thus
of key-importance when deciding on a treatment plan. In
planning a soft tissue visual treatment objective the
rebound of the upper lip, during the post-orthodontic
period, should be taken into account when the upper incisor
position is determined (Holdaway, 1984).
2.5 Post-retention settling
Settling can be described as the establishment of a desired
position. It leads to the arrangement of the teeth in a
final or satisfactory form which may be of more or less
permanent or of an unvarying configuration. The teeth "sink"
into occlusion and thus become comfortably adapted to a new
environment or situation. Retention appliances should
preferably be passive devices which allow the teeth to
settle into their final positions during function. In this
way post-retention settling will be maximized.
2.6 "Recidief"
Recidivism is described in The Shorter Oxford English
Dictionary (1975) as "a tendency to relapse into a former
pattern of behaviour". The concept is more applicable to
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13
behavioural patterns; for example a tendency to return to
criminal habits as is defined in the above dictionary. The
term "r~cidief" has been used to describe changes which
occur from the end of treatment back to the original
situation (Dermaut, 1974).
2.7 Crowding or recrowding
Crowding means to force tightly together. Lower incisor
crowding (recrowding) is normally the main problem noted in
a post-orthodontic evaluation. Crowding as a result of
post-treatment changes were fully described by Little (1975,
1990).
2.8 Imbrication
Imbrication refers to a regular overlapping of edges often
seen as with tiles on a roof or the scales of a fish. This
overlap is often used to describe incisor irregularity or
c:"~"Nding whether seen pre- or post-treatment.
Two other terms used in respect of relapse are stability
and retention.
2.9 Stability
The Shorter Oxford English Dictionary (1975) defines
stability as "the condition of maintaining equilibrium".
This refers to the quality or condition of being stable; the
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14
fixity of position in space or the capacity for re.i.tance
to displacement. Some orthodontists may be .£eluctant to
evaluate their patients in the post-~etention pha.. of
treatment. It is, however! only through a retrospective view
of treatment that factors which cause undesirable
po~t-retention changes can be identified. Such discoveries
could lead to greater occlusal stability following
orthodontic treatment.
2.10 Retention
stability is not retention. Joondeph and Riedel (1985)
explain retention as "the holding of teeth in ideal
aesthetic and functional positions". Retention is
accompli~hed by a variety of mechanical appliances.
Retention is defined in The Shorter Oxford English
Dictionary (1975) as "the action or fact of holding or
keeping in a place or position; retaining in a fixed
position; the condition of being retained, the capacity to
remember".
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15
CHAPTER 3
MATERIALS AND METHODS
3.1 Sample description
Alongitudinal study i.s a tedious undertaking which tests
the patience of all involved. One of the goals of such a
study is to use the largest sample possible which would
statistically provide accurate and representative results.
Numerous factors impede the achievement of this feat.
Longitudinal studies in respect to long-term stability and
with varying sample size have been reported. Some of the
more recent studies are as follows (sample size and minimum
post-retention interval in parentheses):
i) Simons and Joondeph (1973) (70, 10 years).
ii) Shapiro (1974) (80, 10 years).
iii) Gardner and Chaconas (1976) (103, ±5 years).
iv) El-Mangoury (1979) (50, 2 years).
v) Little, Wallen and Riedel (1981) (65, 10 years).
vi) sadowsky and Sakols (1982) (96, ±20 years).
vii) Uhde, Sadowsky and BeGole (1983) (72, ±20 years).
viii) Shields, Little and Chapko (1985) (54, 10 years).
ix) Glen, Sinclair and Alexander (1987) (28, 3 years}.
x) Little, Riedel and Artun (1988) (31, 10-20 years).
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16
The original sample of this study consisted of 102 Caucasian
subjects who had undergone conventional edgewise
orthodontic therapy followed by varying periods of
retention and eventual removal of all retention. A decrease
in the sample size occurred in order to make the starting
ages of the subjects, who had undergone orthodontic
treatment, more uniform. The final sample of the study thus
consisted of 88 subjects, including extraction and
nonextraction groups of both sexes. The edgewise arch
mechanism was Edward H. Angle's last and greatest
contribution to orthodontics r after almost a lifetime
devoted to the development of orthodontic appliances
(Angle, 1928). Lindquist (1985) gave an excellent
description of the conventional edgewise appliance and its
application in the treatment of malocclusions (In:
Orthodontics. Current Principles and Practice; Graber and
Swain, 1985).
The subjects included in the study were drawn from the
private practices of qualified orthodontists and from a
University Dental School clinic where post-gra4uate
orthodontic students treated patients under the supervision
of these orthodontists in their capacity as part-time
lecturers. The distribution of subjects amongst the
abovementioned clinicians were as follows:
Practice 1 - 13.63%
Practice 2 - 7.96%
Practice 3 - 2.27%
Practice 4 - 2.27%
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17
rractice 5 - 56.82%
University - 17.0~%
Orthodontic plaster casts and cephalograms representing
three stages of treatment, being pre-treatment (Tl),
post-treatment (T2) and a mean of 7-years (6.73 years,
range 5.09 10.70 years) post-treatment (T3), were
analysed. The active treatment period (Tl-T2) involved the
wearing of fixed orthodontic appliances for a mean period of
2.82 years. The post-orthodontic period (T2-T3) included
the period during which the subjects were instructed to
wear retention appliances. The m~an post-retention period
(no appliances present) was 5-years (4.90 years, range 0.08
17.17 years). During the retention period four subjects
used prefinishers, two subjects had no retention appliances
fitted and the remaining sUbjects had a maxillary Hawley
appliance and fixed lower intercanine retention. The
records of the subjects used were randomly selected from
those of some 3000 patients. The quality of the
post-treatment result did not influence their inclusion in
the study. Only subjects with complete initial and final
records could be included in the study. Practical problems
such as inability to reach sUbjects many years after active
treatment eliminated them from the study.
The sample included Angle Class I (27.3%), Class II (70.4%)
and Class III (2.3%) malocclusions. The sample was also
evaluated according to the skeletal classification using:
i) the angle ANB (Class I: 0.5 - 3.5 degrees; Class II: >
3.5 degrees; Class III: < 0.5 degrees) (Holdaway, 1956
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18
for Class Idegreesof 2describes an average
malocclusions),
ii) the wits analysis (Jacobson, 1975), and
iii) the point A convexity (Ricketts, 1982).
The ANB and convexity correlate strongly when compared to
each other (r = 0.94), but both correlate weakly with the
Wits (r = 0.26 ANB, r = 0.27 convexity) (Nel, 1991). The
skeletal classification gives an indicaLion of the severity
of the discrepancy between the anteroposterior positions of
the maxillu and the mandible. The information obtained in
this manner allowed for the exclusion of malocclusions
treated by orthognathic surgery. Class III orthodontic
mechanics are the opposite to that being used in the
treatment of Class r and Class II malocclusions, but
depending on the situation Class III elastics may be used in
a Class II malocclusion and vice versa. It may also be asked
why the inclusion of the Class III subjects in the sample
(Table I). Malocclusions are normally classified according
to the dental relationships (Angle, 1899; Dewey, 1942) and
it was also done for the present sample. The two Angle Class
III subjects included in the sample were classified by the
Angle maxillary/mandibular first molar relationship (1899,
1907), but when assessing them in respect to the angle ARB,
they showed angles of 5.01 and 5.68 degrees respectively.
They were in fact Class II skeletal malocclusions, but
possibly ended up with a Class III molar relatior~hip as a
consequence of molar drift. Four of the Angle Class I group
shewed skeletal Class III tendencies with angle ANB
measuring -2.89, -1.11, -0.50 and 0.42 degrees respectively.
It was deemed in order to include them in the sample. Only
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19
five Class II division 2 malocclusions were recorded as part
of the sixty-two Class II malocclusions. The majority of
the Class III subjects which were included during the
random selection of the sample, were subsequently
excluded as they were treated partly by orthognathic
surgery.
It appears that the degree of difficulty of the
malocclussions remain practically the same irrespective of
which way the sample is classified. The comparison of the
Ar.gle molar and ANB classification for the present sample is
represented in Table O.
No overt oral habits were present at the post-treatment
follow-up assessment (T3).
A description of the sample is set out in Table I.
3.2 Orthodontic study model analysis
The static occlusal features of the three stages of
treatment were evaluated through measurements made with a
SYLVAC digital vernier caliper (Sylvac SA, Manufacturers of
Precision Measuring Instruments, Rue du Jura 2, 1023
Crissier, Switzerland) with a resolution of 0,01 rom. The
dimension of the different variables were measured on
orthodontic study plaster casts of the pre-treatment,
post-treatment and post-retention records of the sample. The
points of the caliper were sharpened to permit access and to
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TABLE 0
A COMPARISON OF THE ANGLE DENTAL AND ANB SKELETAL
CLASSIFICATION PARAMETERS
ANB CLASSIFICATION
20
ANGLE MOLAR
CLASSIFICATION
I
II
III
N
I
11
12
o
23
II
9
50
2
61
III
4
o
o
4
N
24
62
2
88
N = Sample size
I = Class I
II = Class II
III = Class III
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21
TABLE I
DESCRIPTION OF-THE SAHPLE
Male(33) Female(55)
ANGLE
CLASSIFICATION Class 1(24) Class 11(62) Class 111(2)
SKELETAL
CLASSIFICATION
(angle ANa) Class 1(23) Class 11(61) Class 111(4)
~
(years)
T1
11,92 (range 10,10-14,20)
T2
~~,74 (range 11,11-24,20)
T3
21,47 (range 16,20-33,50)
EXTRACTION Extr -.ction(56%) Nonextraction(44%)
T1, T2 and T3 refer to the pre-treatment, post-treatment and
post-treatment follow-up orthodontic evaluations
respectively.
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22
make measurements more accurate according to the methods
suggested by Bolton (1958, 1962), steadman (1961), Little
(1975) and Sadowsky and Sakol~ (1982).
Dental impressions of the subjects (T3) were taken with
impression alginate material and poured within one hour of
gathering. A wax bite was also taken in centric occlusion.
The individual sets of study casts of each stage of
treatment of each patient were studied in occlusion as well
as with the upper and lower models separated.
The following measurements were obtained by
examiner (Table II):
a single
3.2.1 Molar and canine relationships
The relationships for the left and right sides of each set
of study models were recorded according to the system of
Angle (1899, 1907). Less than a cusp deviation from a Class
I relationship was regarded as being normal and given a
score of zero (0) ideal range. Deviations of a full cusp
(edge-edge) or more than a full cusp (Class II or III) were
given scores of 2 and 3 respectively.
Class I ideal molar and canine relationships are shown in
figure 1.
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23
TABLE II; DATA SHEET FOR RECORDING MEASUREMENTS DERIVED FROM
DENTAL CASTS
NAME; ••••••••••••••••••••••••• FILE NO: •••••••••••••••••••••
VARIABLE SCORE(S) PRE- P08T- POST-
TREATMENT TREATMENT ORTHODONTIC
MOLAR 0
LEFT AND RIGHT 2
3
CANINE 0
LEFT AND RIGHT 2
3
ANTERIOR OPENBITE
NONE 0
WITH OVERBITE 1
0.0-3.0 2
3.0+ 3
ANTERIOR CROSSBITE
NONE 0
1-2 TEETH 1
3-4 TEETH 2
OVERJET
0.0-3.0mm 0
3.5-6.0mm 2
6.5-9.0mm 3
9.5+ rom 4
OVERBITE
0.0-3.0mm 0
3.5-5.0mm 2
5.5+ rom 3
POSTERIOR CROSSBITE
NONE 0
UNILATERAL 1
BILATERAL 2
MAXILLARY CROWDING
0.0-3.0 0
3.5-6.0 1
6. 5+ mm 2
MANDIBULAR CROWDING
0.0-3.0mm 0
3.5-6.0mm 1
6.5+ rom 2
ROTATION
0° 15° 0
15.5° 90· 1
90.5° 135 0 2
135.5° 180· 3
CURVE OF SPEE
0.0 1.5mm 0
2.0 4.0mm 1
4.5+ rom 2
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LOWER INTERCANI~~ wIDTH
L3-3I
L3-3B
UPPER INTERMOLAR WIDTH
U6-6I
U6-6B
TOTAL HALOCLQSSIQN SCORE
BOLTON: Initial anterior
Final
SPACE ANALYSIS
ARCH LENGTH
EXTRACTION
TEETH PRESENT
CLASSIFICATION
WISDOMS PRESENT Final
RETENTION APPLIANCES
.........
24
posterior ......•••••.•
11 / 21 41 / 31
12 I 22 ~2 / 32
13 / 23 43 / 33
14 / 24 44 / 34
15 I 25 45 / 35
16 / 26 46 / 36
ANTERIOR
POSTERIOR
SPACE ANALYSIS
LITTLE IRREGULARITY INDEX
LITTLE ARCH LENGTH
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Fig. 1: ~deal intercuspatian in buccal view
(Angle Class I occlusal relationship)
25
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3.2.2 IncisQr overjet
26
Measured in millimetres as the distance parallel to the
occlusal plane from the incisal edges of the most labial
maxillary central incisor to the corresponding most labial
mandibular central incisor (OJB) (Fig. 2). The normal range
was represented by a score of 0 while scores of 2, 3 and 4
represented overjets of 3,5 6,Omm, 6,5 - 9,Omm and 9,Omm
or more respectively.
3.2.3 IncisQr overbite
Measured in millimetres as the deepebt vertical overlap of
the maxillary and mandibular central incisors (OBB) (Fig.
3). The ideal range was considered to be 0,0 - 3,0 mm and
given a score of 0. Scores of 2 and 3 represented overbites
of 3,5 - 5,Omm and 5,5mm or more respectively.
3.2.4 Anterior openbite
Measured in millimeters as the amount of space in the
vertical plane between lower and upper incisors or palatal
mucosa, with the study models in centric occlusion, but
witho~t the bite wax (Fig. 4). The ideal for this parameter
was considered to be O,Omm which was represented by a score
of o. If an overbite existed with an openbite present a
ncore of 1 was given. Openbites of 0,0 - 3,Omm and 3,Omm or
more, were given scores of 2 a~d 3 respectively.
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I-
o
0-
I­
G,)
...
c
C1S
27
- - --]--
:..._..-..:_~ .... -.a~ .. -.
Q)0-
'-
G,)
>o
1D
o~
G,)
>o
..
N
o
D)
u:
:
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28
Q)
:::
.c
...
Q)
>o
1 I
I- . ­
I I
I I
I
~
.s;
-CO
:=
.-C)
CO
en
c
.-
S
.-
.c
...
Q)
>o
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(a)
Maxillary teeth
mandibular teeth
(b)
Posterior
A B
Fig. 4: Anterior openbite (a) Anterior view (b) Sagittal view
A - Normal incisor relationship
B - Openbite without incisor overbite
C - Openbite with incisor overbite
C
Anterior
N
\0
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3.2.5 Anterior crossbite
30
Recorded according to a syst~m which recognises three
sub-categories (Sadowsky and Sakols, 1982):
i) none (score 0)
ii) 1-2 teeth (score 1)
iii) 3-4 teeth (score 2)
NO teeth in crossbite was regarded as ideal (Fig. 5).
3.2.6 PQsteriQr crQssbite
RecQrded by a system which recognises this feature as being
(SadQwsky and SakQls, 1982):
i) absent (scQre 0)
ii) unilateral (score 1)
iii) bilateral (score 2)
NO consideration was given tQ the actual number of teeth
invQlved or the presence Qf a functional shift. Absence of
crossbite was regarded as ideal (Fig. 6).
3.2.7 Maxillary and mandibular crowding
Measured in millimetres as the difference between the space
available in the dental arch to accommodate the secondary
teeth (from first molar to first mQlar) and the sum of the
mesiodistal widths Qf the secQndary teeth (frQm first molar
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(a) Mlxillary teeth
Mandibular teeth
(b)
Posterior
(i)
(i) (ii)
anterior
i
Fig. 5: Anterior crossbite
(I) Anterior view
(i) Anterior crossbite (ii) Normal overbite
(b) sagittll view _.
(i) Normal overbite/overjet (ii) Crossbite (reversed or negative overbite/overjet) w
....
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(a)
Maxillary teeth
Mandibular teeth
A B C o
(b)
Buccal Lingual
Fig. 6: Posterior crossbite
(a) Sagittal view with canine in normal relationship and premolars and molar in crossbite
(b) Transverse view of molars '.
A - Normal bucco-lingual relationships
B - Buccal crossbite
C - Lingual crossbite
0- Complete lingual crossbite (scissorsbite)
W
N
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33
to the opposite first mc·:~~). The method described by Moyers
(1988) was used to establish the crowding (Fig. 7). The
millimetre difference between the arch length and the sum of
the tooth measurements was given a score value which
represented the degree of crowding present. The ideal range
was considered to be 0,0 3,Omm and this was regarded as
the norm. Most of the crowding occurred in the lower
anterior segment of the dental arch and therefore the
amount of anterior irregularity was also measured according
to the method described by Little (19'75). Little expressed
this measurement as the Little Irregularity Index (Fig. 8).
The crowding was represented by certain score values:
i) 0,0 - 3,Omm (score 0)
ii) 3,5 - 6,Omm (score 1)
iii) 6,5mm or more (score 2)
3.2.8 Mandibular intercanine width
Two different measurements were recorded and the values
scored as actual millimetre measurements (Fig 9):
a) the distance measured in millimetres at the gingival
margins on the mid-axis of the labial surfaces of the
canines (L3-3B) (Seedat, 1984).
b) the distance between cusp tips or estimated cusp tips
in the cases of wear facets (L3-3I) (Walter, 1962;
Little and Riedel, 1989).
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aa = mm b = mm(a + b) - (Mesiodistal dimentions of teeth in a + b)
=space shortage for one quadrant
Fig. 7: Assessment o~ crowding/space shortage
w
~
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A + B + C + 0 + E = IRREGULARITY INDEX
-.
Fig. 8: Little Irregularity Index (Angle Orthodontist 60:257, 1990)
w
U"I
~l:
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, III .... ~'",."........' __...lII'li"'i......L.IIa.J.PI_. ...--..-ra.. I ,InasUE dill' .,""~';~""''''."
36
•
•2»
u.
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3.2.9 Maxillary intermQlar width
37
TWQ different measurements were recQrded and the value.
sCQred as actual millimetre measurements (Fig. 10):
a) the distance measured at the gingival margins Qf the
mesiQbuccal cusps Qf the first mQlars present (U6-68)
(Seedat,1984).
b) the distance measured at the cusp tips of the
mesiobuccal cusps or estimated cusp tips in ca.e. of
wear facets (U6-61). Similar measurements were made
of mandibular bimQlar widths (Walter, 1(')62).
3.2.10 Rotations
Rotation of a tooth or teeth were recorded as the deviation
from a line through the central mid-fossae area (Fig. 11).
The ideal range was taken to be 0 - 15 degrees and this nora
was represented by a score of 0 (Fig. 11). A score of 1, 2,
and 3 correlated ~ith rotations between 15,5 - 90 degr... ,
90,5 - 135 degrees and 135,5 - 180 degrees respectively.
Measured
bet'Ween 'i
posterior
mandibular
premolar
3.2.11 Curve of Spee
in millimetres as the perpendicular distance
line connecting the distal cusp of the go.t
mQlar and the interproximal contact of the
central incicors and the deepest point Qf the
area (Fig. 12). The ideal range was O,J - 1,5..
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38
.-..
.c.c
.... ­
"'CS ....
.- ~3:(1)
'-E
SCI>
0' ­e::J
'-0Cl>CU
.... CI>
.= E
~caCU(,)
=(,)
.- :::s)(00CU
:5Ci
.. -o
~
.
en
.-u.
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39
~-
o
-C\'S
o
~
-(,)
(,)
o
C\'S
U)
U)
.s
I
"C
.-
E
E
'0
' ­
'0-
r:::
o
-..---
.....
CIS
.:;
(1)
C
.'"C
o
.-
......
CO
..,
e
.....
o
c
o
.-.,
f!
::J
tn
-.-Q)
:E
.....
,..
•
.2'
LL
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40
Stellenbosch University http://scholar.sun.ac.za
which was represented by a score of o.
were given to curves of spee between 2,0
or more respectively.
41
Scores of 1 and 2
- 4,Omm and 4,5..
3.2.12 TQtal malQcclusiQn SCQre
The tQtal malQcclusiQn SCQre was assessed according to a
method which was similar to that advocated by Sadowsky and
SakQls (1982). It was recorded as an additional metrical
character tQ determine whether an orthodontic correction of
a dentition had remained stable. The tQtal score was an
aggregate Qf the SCQres Qf:
i) the mQlar and canine relatiQnship
ii) anteriQr openbite
iii) anterior and posterior crossbite
iv) Qverjet and overbite
v) maxillary and mandibular crowding
vi) rotations
vii) curve of Spee
as well as the actual numerical measurements of:
i) lower intercanine buccal measurement
ii) upper intermolar buccal measurement
3.2.13 Bolton tooth-size discrepa~
The Bolton tOQth-size ratio analysis gives an indication Qf
the degree Qf interarch discrepancy in the tQtal as well as
the aute~iQr mandibular versus maxillary tooth-size ratiQs.
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42
These ratios help to estimate ~he overbite and overjet
relationships which will likely be o'btained after treatment
is completed, the effects of concempl"lted extraction. on
the posterior occlusion and incisor relationships, and the
degree of occlusal misfit produced by interarch tooth-size
incompatibilities. A total mean ratio of 91,3% and anterior
mean ratio of 77,2% were described as the acceptable norms
(Bolton, 1958, 1962).
3.2.14 Arch length
Two different methods were used to measure this parameter:
a) the distance measured in millimetres between the most
anterior mandibular incisor and the line connecting
the mesial of the mandibular first molars (ARCHL)
(Gardner and Chaconas, 1976) (Fig. 13).
b) the sum of the right and left distances from mesial
anatomic contact points of the permanent molars to
the contact point of the central incisors or, if
spaced, to the midpoint between the central incisor
contacts (LITTLE-A) (Little and Riedel, 1989; Little,
Riedel and Engst, 1990) (Fig. 14).
3.2.15 Extractl.on
Te3th which were extracted as part of the orthodontic
treatment were recorded. It was also noted when
nonextraction treatment was performed. Any extraction spaces
remaining after active treatment, or recorded in the
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111111. I
43
.c
..
C)
C
Q)
-
.c
~
«
II
X
.c
..
C)
c:
Q)
-
.c
(J
~
ca
-ca
c
o
;:
C:
Q)
>
c:
o
o
M
,...
.
C)
u::
Stellenbosch University http://scholar.sun.ac.za
A + B = Arch length
Fig. 14: Little arch length (Angle Orthodontist 60:257, 1990)
IIloo
IIloo
5
P;t
i
,
.
i
•
l
~~
I
,
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45
post-retention phase, were monitored in order to a•••••
whether these spaces close according to the philosophy of
anterior drifting of teeth (Moyers, 1988).
3.2.16 Teeth present
All teeth present during the various phases were recorded.
3.2.17 Classification
according to the position of
system of classification was
1907). Modifications were later
The dentition was classified
the first molars. This
described by Angle (1899,
added by Dewey (1942).
All occlusions were thus divided into one of three classes:
a) Angle Class I:
The normal mesiodistal (antero-posterior) relation of
the dental arches, represented by the mesiobuccal cusp
of the maxillary first permanent molar fitting in the
buccal grove of the mandibular first permanent molar
(Lischer, 1928 - Neutroclusion).
Dewey modifications to Class I:
Type I - crowded incisors; the canines frequently labial.
Type II - protrusion of the maxillary incisors.
Type III one or more of the maxillary incisors in
linguoversion to the mandibular incisors (anterior
cross-bite) .
Type IV - mnlars alone or molars and premolars in buccal or
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46
linguoversion to the mrndibular teeth (posterior
cross-bi.te) .
Type V - mesial drifting of molars resulting from premature
loss of teeth.
b) Angle Class II:
The mandibular arch is distal to normal in its relation to
the maxillary arch as characterized by the position of the
mesiobuccal cusp of the maxillary first permanent molar
fitting into the buccal embrasure between the mandibular
first permanent molar and second premolar (Lischer, 1928­
Distoclusion) .
i) division 1 bilaterally distal with protruding
maxillary incisors.
ii) division 2 bilaterally distal with retruding
maxillary incisors.
The addition to the abovementioned two divisions, the term
subdivision, indicates a unilateral malocclusion.
c) Angle Class III:
This category is characterized by the mesial relation of
the mandibular arch to the maxillary arch and it may be
identified by the position of the mesiobuccal cusp of the
maxillary first permanent molar fitting into the buccal
embrasure between the first and second mandibular permanent
molars (Lischer, 1928 Mesioclusion). Dewey also added
modifications to the Class III occlusion to fu~ther describe
this classification.
Dewey modifications to Class III:
Type I - maxillary and mandibular teeth in good alignment
with the incisors in an edge-to-edge bite.
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47
good alignment; mandibular
incisors but definitely
teeth in
maxillary
maxillary
lingual to
Type II
incisors
crowded.
Type III - maxillary teeth at times crowded; mandibular
teeth in good alignment; but the mandibular incisors are
labial to the maxillary incisors.
As noted previously, each classification was also compared
to a cephalometric skeletal classification utilising amongst
others the ANB angle (Steiner, 1953, 1959, 1960) and the
WITS appraisal (Jacobson, 1975, 1976).
3.2.18 Little Irregularity Index
This index was measured in millimetres according to the
method described by Little (1975). It gives an indication of
anterior crowding (L-IRREG) (Fig. 8).
~ '.e scoring method in'~"olved measuring the linear
displacement of the a.natomic contact points (as
distinguished from the clinical contact points) of each
mandibular incisor from the adjacent tooth anatomic contact
point, the sum of these five displacements representing the
relative degree of anterior irregularity. Perfect alignment
from the mesial aspect of the left canine to the mesial
aspect of the right canine was given a score of 0, with
increasing crowding represented by greater displacement and,
therefore, a higher index score. The following scores were
allocated as described by Little:
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48
o Perfect alignment
1-3 Minimal irregularity
4-6 Moderate irregularity
7-9 Severe irregularity
10 Very severe irregularity
The Little Irregularity Index represents the distanc~ that
the anatomic contact points had to be moved to gain ideal
anterior alignment (Little, 1975). Each of the five
measurements was obtained directly from the mandibular study
cast rather than intraorally, since proper positioning of
the caliper is essential for consistent accuracy. The
caliper was held parallel to the occlusal plane while the
beaks were lined up with the contact points to be measured.
Each of the five measurements represented a horizontal
linear distance between the verti.cal projection of the
anatomic contact points of adjacent teeth. Contact points of
anterior teeth can vary in the vertical plane, but
correction of vertical displacement will not appreciably
affect anterior arch length; therefore, all vertical
discrepancies of contact points may be disregarded
(Little,1975). By holding the caliper consistently parall~l
to the occlusal plane the evaluator ensured each measurement
was reflected only in a horizontal displacement.
3.3 Cephalometric measurements
The cephalometric measurements were performed by digitizing
various landmarks on a cephalogram utilising a digitizer
(Hipad DT-II digitizer, Houston Instuments, Austin, Texas.
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49
U.S.A.) connected to an IBM compatible microcomputer
(Multitech Mac-PC 1, Multitech Industrial Corp., aep. of
Taiwan) and using the OLI Cephalometric Soft,"are package
(Orthodontic Logic, Incorporated, P.O.Box 22473, Kan8ae
City, Missouri 64113, U.S.A.) incorporating the following
analyses:
i) Basic cephalometric analysis.
ii) Ricketts analysis.
iii) Bjork/Jarabak analysis.
iv) Holdaway soft tissue analysis.
v) Wits appraisal.
vi) Analysis of upper incisor to Facial axis, A-pogonion
and to Frankfurt horizontal.
Plotted examples of the abovementioned
portrayed in Figures 15, 16, 17 and 18.
analyses are
3.3.1 Definitions of radiographic landmarks used as seen
on a latera~ cephalometric radiograph
The landmarks are portrayed in Figure 19.
1. IX1 Index point 1:
The fir5t of three index points used to relate the plotter
drawing to the x-ray film. Located outside the anatomical
perimeter in front of soft tissue nasion. Selected
arbitrarily (Oliceph, 1983).
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FIG i5
II
-_ ,.1""0'---,
B1.6
AO.
1.
AN.A.L_ YS I S
_•... - .._.. - ---- -_." ---'_'_._-..._'. " .•_,~,. ~..~.,-~.,,--~.,.~-_.-
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_ ····;.; .. -r _-
jLJ -
CEPHALOMETRIC
Patient Ncn-Ext~act Model
88.2 8S 88
7~.7 76 76
-2.9 -3.2 -3.2
13 11.7 11.7
-1.2 -1.5 -l.S
WILSEN. KATHY # 1
PRE-TREATMENT
12. 3 Female
06/24/88
84-3228-7
DEPT.OF ORTHODONTICS
Ideal
B5-95
6S-SB
-1 te a
25
..
BASIC
Patient
Status
Age/Sex
X-Ray
ID
Doctor
4cceptable IMPA Window is B5 to 95 deQ
Prerotation Incisor Intrusien is 0 mm
Incisor Retation Canter is 15 mm FrOID Tip
IMPA
FHIA
/1 to APe
/1 to NS
/1 to NS (IIID)
4rch Length !.Jcrapancy -Within Limits
SCale: 107.51
CJ'
o
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Stellenbosch University http://scholar.sun.ac.za
----------- --------------------------
R I C.:t<.El-TS ANALYSIS
Patient
status
Age/Sex
X-Ray
ID
Doctor
WILSEN, KATHY * 1
PRE-TREATMENT
12. 3 Female
06/24/88
84-3228-7
DEPT.OF ORTHODONTICS
NORMS
So'Sn' to FH 22-30 deg.
NPo to FH 8"-90 deg.
PtGn' to Nel 87-93 deg.
N-Gn'-6o' 6~-71 deg.
PM-Xl-DC 22-30 deg.
ANS-Xl-PM "3-S1 deg.
A tl NPo 0 to .....
/1 to APo 18-26 deg.
/1 to APo -1 to 3 .
6/ to PlV 1.. to 19 .
/M LIP to E -.. to 0 .
rU
36." 1!5.6
---
)
SCale: 107.51
FIG 16
UI
...
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800RK/0ARABAK ANALYSIS
Patient
Status
Age/Sex
X-Ray
ID
Doctor"
WILSEN, KATHY f 1
PRE-TREATMENT
12. 3 Female
06/24/88
84-3228-7
DEPT.OF ORTHODONTICS
NORMS
NSAr 118-128 deg. 0
SArGo' 137-149 deg. b'8.ArGo tHe 123-137 deg. .
SN 68 to 74 u.
SAr 29 to 35 mao
ArGotN 52-55 deg.
NGotHe 70-75 deg.
ArGot 39 to 49 ...
Go'Me 66 to 76 u.
SGo' 70 to 85 .
NNe 105 to 120 .
SSo'/NNe 63 to 68 I.
SotMe/SN 1.
SNPo 77-80 deg.
Post-Ant FH 60 to 64 I.
118.5
/
ble: 101.!I
FIG 17
U'I
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, .~ Q> ... ~~ ..1 ...~lIiio',,}(H.._ h -~- ••- .........'-~,••
Stellenbosch University http://scholar.sun.ac.za
HOLDAWAY AND MOFiE
PRE-TREATMENT
12. 3 Female
06/24/88
84-3228-7
DEPT.OF ORTHOD~NTICS
Status
Age/Sex
X-Ray
ID
Doctor'
lSSl ERIlP A
Var illl1. Value
Soft Tissue Facial 92.3 de;.
Nose PpollIinerice (a) 19.3 lalB.
superior Sulcus Depth -3.7 IDI.
SO ft Ato HLine (a1 1.3 III.
4 PtJint Convuxity -.5 11I11.
Upper Lip Thickness 13.6 111'11 \ r , f 11 \ __ \ L--I MY J FIG 18\Upper Lip TdPer B.3 III.
Upptr Lip Strain 5.3
It-Angll 5.8 de;.
lOwer Lip to It-Line -1.4 ••.
Inf. Sulcus tu ij-line 3.6 '1.
Soft Tissue Chin (II) 12 III'.
WITS Analysis -1.8 ...
1/ to Frlnkfort Hariz 112.6 de;.
1/ to Facial Axil 11•.4 de;.
1/ to 4Pu 1..1 4.3 ••
,,~.
Stale: 107.51
UI
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ee) 1987 bV orthodontic L.cglc. Inc. 5.G PC Typ.n~7!SA UNIVERSITY OF STELJ..EteOSCH 002112-48 02: 00 010001-1110
-------------------'"
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'.
Fig.19: Landmark locations necessary for use of Oliceph Cephalometric Analysis
.1
Dental cast landmarks
not used for present
study, but digitization
essential for operation
of analysis
-
51 52 53 54 55 58
• • • • • •
57 58 58 80 61 62
• • ••• •
113 114 I , /"V~ ./ U'I• • ....
-"'-"-'.......__~_..._. ,'-,,, ••._......-..-~."'"_ .......~.·'F •••. "'.,._"', ...""'_~: •. ~~'Ql;'~' .~~
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55
2. IX2 Index point 2:
The second of three index points llsed to relate the plotter
drawing to the x-ray film. Located outside the anatomical
perimeter in front of soft tissue chin. Selected arbitrarily
(Oliceph, 1983).
3. IX3 Index point 3:
The third of three index points used to relate the plotter
drawing to the x-ray film. Located near the geometrical
centre of the odontoid process of the axis (second cervical
vertebra). Selected arbitrarily (Oliceph, 1983).
4. N Nasion:
This midsaggital point marks the most anterior limit of the
nasofrontal suture (Hrdlicka, 1920). It is also described as
the junction of the frontonasal suture at the most posterior
point on the curve at the bridge of the nose (Riolo et 01.,
1974, 1979).
5. Posterior Horizontal Point:
A point in the "true horizontal plane" passing through
Nasion. Located posterior to Nasion at a distance equal to
the length of the film image of the magnification scale
(Oliceph, 1983).
6. S Sella:
The centre of the pituitary fossa of the sphenoid bone as
seen in a cephalometric radiograph. Located by visual
inspection (Riolo at 01., 1974, 1979). It takes into
consideration the antero-posterior, as well as the
sup9ro-inferior midpoint of the sella turcica (preston,
1986).
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56
7. Or Orbitale:
The lowest point on the average outline of the left and
right bony orbits (Riolo et al., 1974, 1979). It is also
described as the lowest point on the outline of the inferior
or infraorbital margin of the left bony orbit (Preston,
1986).
8. Po Anatomic Porion:
The most superior point on the radiographic outline of the
left external auditory meatus. If not discernible, the most
superior point on the left ear rod of the cephalostat may be
used (machine porion) (Oliceph, 1983).
9. A A Point:
This landmark is also referred to as point subnasale. It is
the most posterior point on the bony outline of the maxilla
(radiographic contour) between the Anterior Nasal Spine and
Supradentale (Downs, 1948; Riolo et al., 1974, 1979). This
point is assumed to lie in the mid-sagittal plane of the
face (preston, 1986).
10. B B Point:
The point furthest posterior from a line joining
Infradentale and Pogonion on the anterior surface of the
symphyseal outline of the mandible (radiographic contour)
(Downs, 1948). This point should lie within the apical third
of the incisor roots. When there is no curvature in this
region and identification is not possible using the
abovementioned method, preceding or succeeding films may be
used to clarify the situation as erupting teeth obscure
mandibular concavity on o;~casion (Riolo et al., 1974, 1979).
11-18. These landmarks are digitized using the 011 Template
Position Landmarks (Oliceph, 1983):
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57
11. Upper incisor incisal tip
12. Upper incisor root apex
13. Lower incisor incisal tip
14. Lower incisor root apex
15. Upper first molar mesial cusp tip
16. Upper first molar mesial root apex
17. Lower first molar mesial cusp tip
18. Lower first molar mesial root apex
19. Mesial tangent, lower first molar:
Located perpendicular to the occlusal plane. Average of left
and right sides (Oliceph, 1983).
20. Distal tangent, upper first molar:
Located perpendicular to true horizontal plane. Average of
left and right sides (Oliceph, 1983).
21. Pog pogonion:
The most anterior point on the contour of the bony chin as
seen on a lateral cephalometric radiograph. If this is an
area rather than a specific point, pogonion is the point at
which the anterior outline of the chin begins to curve
posteriorly (i.e. the lowest point on the area of tangency
determined by a tangent through Nasion) (Riolo et al., 1974,
1979; Oliceph, 1983). Pogonion is assumed to lie in the
median plane (Preston, 1986).
22. Gn Gnathion:
The most anterior-inferior point on the contour of the bony
chin sYmphysis as seen on a lateral cephalometric
radiograph. Located by projecting onto the chin the bisector
of the angle formed between the mandibular plane and the
Nasion - Pogonion plane (Riolo et al., 1974, 1979).
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passes through
outline of the
the mandible
58
23. Me Menton:
The most inferior point on the symphyseal outline of the
chin as seen on a lateral cephalometric radiograph (Riolo At
~., 1974, 1979). It is the point at which the mandibular
plane is tangent to the symphysis (Oliceph, 1983). It is
also described as the most caudal point in the median
sagittal outline of the mandibular symphysis (Krogman and
Sassouni, '.957) and corresponds to the craniological
gnathion (Preston, 1986).
24. posterior point on the mandibular plane:
An arbitrarily selected point on a line that
Menton and which is tangent to the average
left and right posterior-inferior border of
(Oliceph, 1983).
25. Ar Articulare (Articulare posterior):
The intersection of the average outline of the posterior
borders of the left and right condylar necks as seen on a
lateral cephalometric radiograph and the image of the
inferior border of the occipital bone (Inferior cranial
base) (Bjork, 1947; Riolo ~t al., 1974, 1979; Oliceph,
1983).
26. Inferior point on the posterior border line:
An arbitrarily selected point on a line that passes through
Articular~ above and is tangent to the average cephalometric
outline of the posterior borders of the left and right rami
below (Oliceph, 1983).
27. Go Gonion:
The midpoint of the angle of the mandible. Located by
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and right
(Broadbent,
59
projecting onto the radiographic outline of the mandible the
bisector of the angle between the mandibular plane and the
A~ticulare Inferior tangent ramus point (Riolo et al.,
1974, 1979; Oliceph, 1983).
28. Lingual symphyseal point:
The point at which the lingual surface of the symphysis as
seen on a lateral cephalometric radiograph is intersected
posteriorly by a line passing through Pogonion parallel to
the mandibular plane (Oliceph, 1983).
29. Ba Basion:
The most inferior and posterior midline point on the
anterior margin of the foramen magnum as seen on a lateral
cephalometric radiograph (Riolo ~ al., 1974, 1979). It is
alao referred to as the external basion or ectobasion
(Preston, 1986).
30. Bo Bolton point:
The highest point of the average of the left
postcondylar notches of the occipital bone
Broadbent and Golden, 1975; 01iceph, 1983).
31. Pt Point:
The inferior and posterior crest of the foramen rotundum.
Average of left and right images (Ricketts et al., 1979).
32. PHS Posterior nasal spine:
The posterior limit of the hard palate as seen on a lateral
cephalometric radiograph. This point is assumed to lie in
the midline (Riolo et al., 1974, 1979; Oliceph, 1983).
33. ANS Anterior nasal spine:
The tip of the median, sharp bony process at the anterior
limit of the maxilla. It is assumed to lie in the midline
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60
at the lower margin of the anterior nasal ()paning (Riolo.m;.
li., 1974, 1979). It corresponds to 'the craniological
acanthion (Rakosi, 1982).
34. Sd Supradentale:
The labial alveolar crest of the upper central incisor
(Oliceph, 1983) or the most anterior inflarior point on the
maxilla at its labial contact with the maxillary central
incisor (Riolo et 01., 1974, 1979).
35. Id Infradentale:
The labial alveolar crest of the lower central incisor
(Oliceph, 1983) or the anterior superiLor point on the
mandible at its labial contact with the mandibular central
incisor (Riolo et 01., 1974, 1979).
36. Gb Glabella:
The most anterior point on the outline of the frontal bone
ove~lying the frontal sinus as seen on a lateral
cephalometric radiograph at the level of the supra-orbital
rim. Where this point is not readily apparent, the overlying
soft tissue is used to locate it (Riolo ~t al., 1974, 1979;
Oliceph, 1983).
37. Co Condylion:
The most posterior-superior point on the average outline of
the left and right condylar heads. Located by projecting
onto the condyle the bisector of the angie formed between a
line parallel to the true horizontal plane that is tangent
to the superior curvature of the condyle and a line that is
tangent to the posterior curvature of the condyle above and
tangent to the posterior outline of the ramus below. The Co
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tangent to the
et al., 1979;
61
point is, therefore, located as the most superior-posterior
axial point of the condylar head rather than as the .cst
superior point on the condyle (Riolo at al., 1974, 1979).
38. Nose tangent point (of E-Line):
The nose point of a soft tissue line that is
nose above and the chin below (Ricketts
Oliceph, 1983).
39. Chin tangent point (of E-Line):
The chin point of a soft tissue line that is tangent to the
nose above and chin below (Ricketts et al., 1979; Oliceph,
1983).
40. Closest point on lower lip to E-Line:
Measured perpendicularly to the soft tissue nose-chin
tangent line (Ricketts et al., 1979; Oliceph, 1983).
41. Closest point on upper lip to E-Line:
Measured perpendicularly to the soft tissue nose-chin
tangent line (Oliceph, 1983).
42. Pm Protruberance menti:
The point on the anterior outline of the SYmphysis as seen
on a lateral cephalometric radiograph between B Point and
Pogonion where the curvature changes from concave to convex.
If not discernable, use midpoint of the outline of the
SYmPhysis between B Point and Pogonion (Ricketts et al.,
1979).
43. Point Xi:
The geometric centre of the left ramus. It is derived by
locating the centre of a rectangle, the top side of which is
parallel to Frankfurt horizontal and tangent to the deepest
point of the sigmoid notch, the two vertical sides of which
are tangent to the narrowest dimension of the anterior and
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62
posterior contours of the ramus and the bottom side of which
intersects the inferior (external) contour of the mandible
directly below the point at which the top side of the
rec~angle is tangent to the sigmoid notch (Ricketts et 01.,
1979) .
44. Point DC:
Thg midpoint of that portion of the Nosion-Bosion line thot
crosses the neck of the condyle (Ricketts et 01., 1979).
45. Point vcc:
palate (Oliceph,
Geometric centre of
visual inspection
hard
millimetre arc from PP1
the
a 5
condyle.
of
of
Visualized centre of the left
the head of the condyle. Located by
(Oliceph, 1983).
46. PP1. Palatal point 1:
The most anterior-superior point on the inferior outline of
the hard palate. Located by projecting onto the inferior
outline of the palatal contoyr the bisector of the angle
formed between the posterior palatal plane and the anterior
palatal plane. The posterior palatal plane is selected by
visual inspection to represent the inferior surface of the
posterior hard palate. The anterior palatal plone is
selected by visual inspection to represent the slope of the
inferior surf-ace of the anterior palatal contour in the
vicinity of the rugae (Oliceph, 1983).
47. PP2. Palatal point 2:
The posterior intersection
with the inferior outline
1983).
48. PP3. Palatal point 3:
The anterior intersection of a 5 millimetre arc from PP1
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63
with the inferior outline of the hard palate (Oliceph,
1983).
49. D Point:
The geometric centre of the bulbous portion of the symphysis
as seen on a lateral cephalometric radiograph. Located by
visual inspection (steiner, 1953).
50. MC60. Mandibular Corpus 60 millimetre point:
The intersection of a 60 millimetre arc from D Point with
the inferior aspect (average of left and right sides) of the
mandibular canal (Oliceph, 1983).
POINTS 51-64 are needed for the DENTAL CAST TECHNIQUE. These
were digitized randomly in the bottom corner of the
digitizing pad as they were not used in this study, but were
needed by the 011 programme to analyse the cephalogram.
65. Soft tissue Point Nasion:
The point where the Sella-Nasion line crosses the soft
tissue profile (Holdaway, 1983; Oliceph, 1987).
66. Soft tissue Point A:
The soft tissue point overlying the skeletal Point A
previously described (Holdaway, 1983; Oliceph, 1987).
67. Soft tissue Point B:
The soft tissue point overlying the skeletal Point B
previously described (Holdaway, 1983; Oliceph, 1987).
68. WITS Premolar point on Functional Occlusal Plane:
Location by inspection of a point on the occlusal plane
where the premolars occlude (Jacobson, 1975; Oliceph, 1987).
69. WITS Molar point on FUnctional Occlusal Plane:
Location by inspection of a point on the occlusal plane
where the molars occlude (Jacobson, 1975; Oliceph, 1987).
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64
70. Upper incisor buccal point:
Most anterior point on the buccal surface of the upper
central incisor (Holdaway, 1983; Oliceph, 1987).
3.3.2 Definitions of the variables measured
The various linear and angular cephalometric measurements
are described in Figures 15, 16, 17 and 18. These figures
represent the analyses included in the Oliceph cephalometric
computer programme. The variables are defined in the
corresponding chapters.
3.3.3 RadiQgraphic technigue
The lateral cephalograms used in this study had tQ be
Qbtained from different orthodontic offices in order to
fulfil the requirements Qf the sample size Qf this project.
The cephalograms were, however, all taken by radiQgraphers
familiar with the technique. The enlargement factQr for each
x-ray machine was cal~ulated~
the cephalometric radiogrAph
The lateral cephalometric x-ray film was taken with the
subject's head h~Jd in a commercial cephalQstat and
exposures were ~, e. The target to film distance was
standardized at 152,4cm (five feet). The left side of the
subject's head was positioned against the film cassette. All
subjects were x-rayed with their teeth fully Qccluded and
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with the mid-sagittal plane perpendicular to
the Frankfurt horizotal plane parallel to
lips were held together.
the
the
65
floor and
floor. The
Three cephalometric radiographs were necessary in order to
determine the longitudinal dentofacial changes. The
pre-treatment (Tl) and post-treatment (T2) cephalometric
radiographs were part of the active orthodontic treatment.
Special permission was granted by the Ethical Committee of
the University of Stellenbosch to attain the
post-orthodontic (T3) cephalometric radiograph. This
permission was granted on the basis that:
i) a study of this magnitude has not previously been
performed on a South African sample,
ii) certain dental adjustments were to be executed during
this post-orthodontic period which included
interproximal approximation, fitting of spring
retainers, sectional bandings and also the removal of
third molar teeth, and
iii) the subjects included in the sample were informed
regarding the purpose of the ~~oject and given the
opportunity to refuse should they not want to be
futher exposed to any x-rays.
3.3.3.2 Enlargement error
The radiographic image is always larger than the original
SUbject due to the inherent property of x-rays to proceed in
radiating straight lines from the anode (Thurow, 1977).
Enlargement factors become meaningful when the linear error
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66
exeeds the limit of what is considered acceptable, which
limit depends on the natural variation in the aize of the
anatomic region being studied. The sample in thi••tudy
consisted of subjects of various ages and sizes which mean.
that the enlargement factor could not only have varied from
subject to subject and from age-group to age-group, but
could also have varied between the different x-ray machines.
Midline cranial structures would tend to be slightly further
away from the film when comparing a young small head to an
older, bigger head on a radiograph. It was thus deemed
necessary to calculate an average enlargement factor for the
purpose of accurate measurem2nts. The enlargement correction
of 7,5% was applied to all the measurements on the lateral
cephalometric radiographs.
3.3.3.3 Calculation of the enlargement factor
A 100 millimetre radiopaque magnification scale of stainless
steel was positioned in the midsagittal plane vertically and
parallel to the film plane and a radiograph was taken. The
dimension of the scale was periodically checked during this
procedure with the same vernier caliper (Sylvac digital
vernier caliper) used to measure the plaster casts. The
percentage enlargement for the cephalometric set-up was
calculated by de~ermining the mean size increase of the
images of the magnification scale as seen on the resultant
raciographs. The enlargement factor was found to be 7,5%
which is in accordance with acceptable norms found with most
conventional cephalometers (Broadbent ~t al.,1975). Bjork
(1947) described the difficUlty of calCUlating, with
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67
accuracy, measurements of diagonal linear di.tanc••
traversing different sagittal planes. The pre.ent .tudy
utilised, amongst others, midline sagittal points and thi.,
comhined with the fact that the minimum practical
object-film distance was used, ensured relative accuracy of
the measurements made on these films. In the instances where
bilateral landmarks were used, the mid-values between
measurements made on the left and on the right images were
used (Bergersen, 1980).
In addition to the mensuration of the study casts and
cephalometric radiograph~, a simple assessment was done of
the third molar status. The type of retention appliance
utilised following the active treatment was noted.
3.4 Third molars present post-retention
The presence of third molars was noted in order to assess
the possible influence they may have had on the stability
and alignment of the dental arches. The mode of treatment
(extraction or nonextraction) was also studied in this
context.
3.5 Retention ARPliances
The types of retention appliances used were noted as well as
4he period of the time these were in place following active
treatment. The purpose of this observation was to evaluate
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not only the long-term
assess the changes that
phase.
68
stability post-l~tention, but to
took place during the retention
3.6 Intra-obseryer et~
The degree of intra-observer variation was calculated.
Measurements of ten sets of study models and ten
cephalograms were repeated at three different intervals, on
separate days, without reference to prior measurements.
These study records, as well as the variables measured, were
randomly selected from the sets of records available in the
sample. Descriptive statistics of the data are set o~t in
Table III. The Wilcoxon signed-rank test (nonparametric
statistics) was used to evaluate the significant differences
between measurements (Table IV).
The study model variables were:
a) mandibular intercanine width in millimetres, buccal
measurement (L3-3B) and incisal measurement (L3-3I)
(Fig. 9),
b) maxillary intermolar width measured in millimetres,
mesiobuccal measurement (U6-6B) and mesiobuccal
incisal measurement (U6-6I) (Fig. 10), and
c) arch length in millimetres, conventional (ARCHL)
(Fig. 13) and described by Little (1990) (LITTLE-A)
(Fig. 14),
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69
(FMA) (Tweed, 1954). Similar to Go'Gn' to PH in figure
16,
h) facial angle measured in degrees (FAC-ANGL) (Ricketts,
1981) (MPo to FH, Fig. 16),
c) facial-axis angle measured in degrees (FAC-AXIS)
(Ricketts, 1981) (PtGn' to NBa, Fig. 16),
d) facial taper or chin button taper measured in degrees
(FAC-TAPER) (Ricketts et ale , 1979) (M-Gn' -Go' , in
Fig. 16),
e) mandibular arc measured in degrees (MARD-ARC)
(Ricketts, 1981) (PM-Xi to Xi-DC, Fig. 16),
f) lower facial height measured in degrees (L-FACH)
(Ricketts, 1981) (ANS-Xi-PM, Fig. 16),
g) the maxillary convexity at point A measured in
millimetres (A-CONVEX) (Ricketts, 1981; Holdaway,
MPO, Fig. 16 or A Point convexity,to1983) (A
Fig. 18),
h) mandibular incisor position to point A-Pogonion line,
millimetres (/I-APO-MM)angular (/I-APO-DEG) and
(Ricketts, 1981) (Fig. 16),
i) maxillary molar position measured in millimetres
between pterygoid vertical (PTV) and distal aspect of
the upper first molar (UM-PTV-MM) (6/ to PTV, Fig.
16), and between the centre of the face (CCV) and the
distal of the upper first molar (UM-CCV-MM) (Ricketts
et al., 1979), and
(Ricketts, 1981) (/M lip to E, Fig. 16).
j) lower lip
\L-LIPE-MM)
to E-plane measured in millimetres
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TABLE III
DESCRIPTIVE STATISTICS OF INTRA-OBSERVER ERROR CALCULATION
1 2 3
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D.
L3-3I 27.07 0.97 27.07 1.06 26.96 0.97
L3-3B 31.39 1.13 31.32 1.23 31.38 1.03
ARCHL 22.74 3.08 22.73 3.11 22.71 2.91
LITTLE-A 59.31 5.73 59.16 5.69 59.18 5.70
U6-6I 52.05 2.19 52.09 2.22 52.00 2.22
U6-6B 54.78 2.22 55.03 2.19 55.03 2.20
FHA 18.45 4.74 18.62 5.39 18.93 5.17
FAC-ANGL 91.04 2.64 90.96 2.61 91.11 2.65
FAC-AXIS 88.76 2.75 88.79 2.82 88.88 2.71
FAC-TAPE 70.08 4.99 69.97 5.60 69.48 5.32
MANn-ARC 34.47 5.45 35.05 5.20 34.42 5.48
L-FACH 42.95 2.33 42.96 2.44 42.72 2.15
A-CONVEX 2.14 3.47 2.13 3.49 2.15 3.55
II-APO-MM 1.34 1.89 1.39 1.89 1.65 2.06
II-APO-DEG 30.53 4.66 30.77 5.15 29.64 6.09
UM-PTV-MM 19.94 3.71 20.36 4.17 20.52 3.66
UM-CCV-MM 18.68 3.85 19.07 4.34 19.17 3.69
/M-LIPE-MM -0.45 3.69 -0.81 3.81 -0.72 3.67
S.D. = Standard deviation
1, 2, 3 = Measurements of variables repeated three times
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TABLE IV
LEVEL QF SIGNIFICANCE (p) or WILCOXON SIGNED RANKS TO
INDICATE DIFFERENCES BETWBElI MEASURBMIJITS REPEATED THREE
TIMES TO TEST FOR IURA-OBSERVER ERBOR
VARIABLE: L3-3I
1 2 3
1 1.00
2 0.41 1.00
3 0.03 0.07 1.00
VARIABLE: L3-3B
1 2 3
1 1.00
2 0.51 1.00
3 0.72 0.92 1.00
VARIABLE: ARCHL
1 2 3
1 1.00
2 0.77 1.00
3 0.79 0.88 1.00
nlUABLE: LITTLE-A
1 2 3
1 1.00
2 0.51 1.00
3 0.17 0.59 1.00
VARIABLE: U6-6I
1 2 3
1 1.00
2 0.68 1.00
3 0.72 0.19 1.00
VARIABLE: U6-6B
1 2 3
1 1.00
2 0.08 1.00
3 0.17 0.48 1.00
71
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VARIABLE; PMA
1 2 3
1 1.00
2 0.1. 1.00
3 0.15 0.23 1.00
VARIABLE: FAC-ANaL
1 2 3
1 1.00
2 0.06 1.00
3 0.67 0.16 1.00
VARIABLE: FAC-AXIS
1 2 3
1 1.00
2 0.87 1.00
3 0.31 0.61 1.00
VARIABLE: FAC-TAPE
1 2 3
1 1.00
2 0.1'7 1.00
3 0.14 0.11 1.00
VARIABLE: MANP-ARC
1 2 3
1 1.00
2 0.33 1.00
3 0.72 0.68 1.00
VARIABLE: L-FACH
1 2 3
1 1.00
2 0.95 1.00
3 0.37 0.39 1.00
72
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1VARIABLE: A-CONVEX
2 3
73
1
2
.,
1.00
1.00
0.94
1.00
0.86 1.00
1
VARIABLE; II-APQ=HH
2 3
1
2
3
1.00
0.61
0.06
1.00
0.19 1.00
VARIABLE: II-APQ-DEG
1
2
3
1
1.00
0.72
0.31
2
1.00
0.20
3
1.00
VARIABLE; UK-PTV-MK
1
2
3
1
1.00
0.14
0.01
2
1.00
0.20
3
1.00
VARIABLE; UK-CCV-MK
1
2
3
1
1.00
0.16
0.02
2
1.00
0.24
3
1.00
VARIABLE: IM-LIPE-MK
1
2
3
1
1.00
0.04
0.16
2
1.00
0.48
3
1.00
p = Level of significance, 0.05
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74
No significant difference could be ahown between the
variables measured except for the following four,
intercanine width (L3-3I), upPer first molar position
(UM-PTV-MM and UM-CCV-MM) and lower lip PO.ition
(L-LIPE-MM). For L3-3I, UM-PTV-MM and UM-CCV-MM there were
significant differences between 1 and 3, and for L-LIPE-MM a
significant difference existed between measurement 1 and 2.
When the mean values of these differences were observed, it
became apparent that the differences although significantly
different, would from a clinical point of view not influence
the interpretation of the data. In every instance the
intra-operator error was less than 1,0% of the value of the
parameter being studied except where one of the measurements
was different from the other two as previously mentioned.
The la~dmarks of these four variables were difficult to
pinpoint and thus extreme care was taken with its
assessment. Having determined the intra-operator error, it
became clear that it was a sensible decision to measure more
than one variable of similar description.
It was thus concluded that intra-operator errors did not
have a material effect on the outcome of the present study.
3.7 Statistical analysis of data
All analyses of the present data utilised the &AS
(Stat1stical Analysis System, University of North Carolina,
USA, 1985) programs available at the Institute for
Biostatistics, Medical Research Council, Tygerberg, Republic
of South Africa.
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75
The subjects comprising the sample in this atudy were of
different ages while undergoing, having completed
orthodontic treatment or being re-examined for
post-treatment changes. A varying number of variables were
recorded during the study at the pre-treatment,
post-treatment and post-orthodontic time intervals. During
the data reduction inferential testing was d.e.ed
nescessary in order to evaluate the numerous longitudinal
changes that took place during the time span of the study.
3.7.1 Descriptive Statistics
Descriptive statistics were calculated for the complete
sample, as well as for males and females, and extraction and
nonextraction groups separately. The following statistics
were calculated:
1. Mean.
2. Standard deviation.
3. Minimum and maximum range.
3.7.2 Inferential Statistics
More complex analyses were necessary in order to
characterize the differences between the pre-treatment (Tl)
and post-trea~ent (T2) orthodontic records, and between
the post-treatment (T2) and post-orthodontic (T3)
or'c.hodon'c.~~ records. 'Ine !ried1\\an t.est.. "ilcQ1on. t.est..
Chi-square test and Spearman Correlation. coefficient test
were performed in order to make the necessary conclusions
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76
regarding the•• different orthodontic change. (Zar, 19&4).
The.. te.t. were perfo~ at a .1gnlflcance level of p •
0.05.
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77
CHAPTER ..
LONGITUDINAL CHANGES IN THE NASQMAXILLABY COMPLEX AID ITS
RELATIQNSh,.1P TO LOUR INCISOR IRREGULARITY
4.1 IntroductiQn
For as lQng as QrthQdQntics has been a dental speciality a
significant prQblem facing the QrthQdQntist has been the
relapse Qf carefully treated and well finished dentitiQns
(Hellman, 1940; Hahn, 1944; Nance, 1947). The QrthodQntic
literature suggests that CQrrect diagnQsis and prQperly
developed treatment plans, fQllQwed by execellent
mechanQtherapy designed tQ place the teeth in certain
predetermined positiQns, in its turn followed by retention
for a certain amount of time, minimizes or eliminates
relapse (Behrents, Harris, Vaden, Williams and Kemp, 1989).
Stark reality, hQwever, suggests that Qver two-thirds of
QrthQdontically treated subjects have unacceptable dental
alignment 10-20 years following orthodontic therapy (Bell,
Proffit and White, 1980; I,ittle, Riedel and Artun, 1988).
Less relapse has been documented in other studies , but none
the less relapse is a universally accepted phenomenon and
problem (Sadowsky and Sakols, 1982; Sandusky, 1983; Uhde,
Sadowsky and BeGele, lq83).
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78
It has been suggested that relapse is under the influence
of evolutionary or genetic control, such that a certain
amount of relapse is inevitable and should be expected
during development. There is, however, little scientific
evidence to support this point of view (Chung, Niswander,
Runck, Bilben and Kay, 1971; Corruccini and Potter, 1980;
Harris and Smith, 1980; Harris and J'ohnson, 1991). In spite
of all attempts to control and limit relapse it is probably
still true that we are alRlost complete ignorant of the
etiological factors which cause relapse (Behrents at 01.,
1989). Other schools of thought are based on various
clinically-derived guidelines (strang, 1949; Tweed, 1954;
Mills, 1967; Williams, 1985). These guidelines suggest
that relapse can be controlled if certain aspects of active
treatment are controlled and adhered to. Failure to do so
will be prejudicial toward stability. Whatever the cause,
malocclusion is an important problem in our dentally aware
contemporary society. Although it is difficult to know the
precise aetiology of any specific malocclusion, certain
general possibilities are known (Proffit, 1986).
There appears to be a fairly strong association (r = 0.53)
between the irregularity index and the space analysis of
Merrifield (1978). This relationship was shown to be
sensitive to different occlusal parameters (Harris, Vaden
and Williams, 1987). It must be noted, however, that no
dental or skeletal parameters appear to correlate with
observed post-treatment relapse (Shields, Little, Chapko,
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79
1985; Little, Riedel and Artun, 1988). Similar conclu.ion.
have been made for dental changes seen in untreated
individuals (Carmen, 1978).
Growth of the craniofacial skeleton has been implicated a. a
possible factor involved in post-treatment relapse
(Litowitz, 1948; Huckaba, 1952; Kelly, 1959: BjOrk and
Skeiller, 1972; Behrents, 1984; Behrents et al., 1989). A
statistically significant correlation was reported to exi.t
between the maxillary length (Sella-A Point distance) and
the crowding of the lower incisors. It was observed that the
Little Irregularity Index decreased with an increase in the
maxillary length (Little, 1975; Behrents et al., 1989).
The suggestion is that relapse may occur as a result of
tooth movement which occurs as part of the growth process.
It is therefore imperative to understand not only treatment
effects on the dentitions, but also the anatomy and normal
growth changes of the craniofacial components. These
factors must be taken into consideration when attempting
to study post-orthodontic relapse of the dentition.
4.2 The Nasomaxillary complex and related anatomy
The midface consists of the orbits and their contents, the
nasal structures, the maxillary sinuses
processes and the teeth (Graber 1966).
and alveolar
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The largest, and probably the .cst important, bone in the
upper face is the maxilla. It consists of a body and the
frontal, zygomatic, alveolar and palatine processes. Other
contributions to the face are made by the nasal, frontal,
ethmoidal, vomer, lacrimal, conchae, palatine and zygomatic
bones.
The intricate anatomical structure of the nasomaxillary
complex can be appreciated when the related anatomy of the
various surfaces of the maxilla are studied (Van Rensburg,
1981; Longmore and McRae, 1985; DuBrul, 1988).
The anterior surface of the maxilla shows the undulating
ridges of the alveolar process formed by the roots of the
maxillary teeth, the most prominent being that formed by the
canine teeth. The inferior border is formed by the alveolar
process which carries the teeth, the medial ridge ends in
the anterior nasal spine CANS), the lateral border, as seen
in the anterior view, is the zygomatic process while the
superior border follows the infra-orbital ridge cranially to
the frontal process.
The posterior surface is laterally related to the
infra-temporal fossa and medially to the pterygo-palatine
fossa. The infra-teaporal surface contains various small
foramina allOWing the posterior superior alveolar nerves and
blood vessels to reach the molar teeth. The maxillary
tuberosity, which articulates with the pyramidal process of
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the palatine bone, is found at a more
palatine bone is wedged between the
pt.er~F';0id process of the sphenoid bone.
81
inferior level. the
tUberosity and the
~.Lh' llasal surface of the maxilla has the opening of the
maxillary sinus which is overlapped posteriorly by the
vertical plate of the palatine bone. The lacrimal bone
closes the sinus anteriorly and superiorly. The lacrimal
groove is formed by this articulation between lacrimal bone
and maxilla. Superiorly, the ethmoid labyrinth also helps
with the sealing of the maxillary sinus. Inferiorly, the
sinus is closed by the inferior concha. The middle meatus
receives the opening of the sinus.
The orbital surface of the maxilla forms the greater part of
the floor of the orbit. The frontal process runs upwards and
articulates with the frontal bone superiorly, the nasal bone
anteriorly and the lacrimal bone posteriorly. The lacrimal
fossa, housing the lacrimal gland, is found on the orbital
surface of the frontal process of the maxilla, partly on the
maxilla and partly on the lacrimal bone.
The zygomatic process articulates with
while the alveolar processes form the
houses the maxillary teeth.
the zygomatic bone
dental arch which
The pala~ine process, pointing in a medial direction, forms
two thirds of the hard palate. The two palatine processes
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82
puberty. The anterior part of this groove leads to the
incisive foramina found posterior to the incisor teeth. The
greater palatine artery passes from the mouth to the no•• ,
and the terminal branches of the nasopalatine nerve and
blood vessels from the nose to the mouth, through these
foramina. A groove from the incisive foramina run. through
the interdental space between the lateral and canine teeth
on both sides of the maxilla, in the young skull, seParating
the premaxillary part from the main body of the maxilla. The
very intricate nature of the anatomy of the nasomaxillary
complex is emphasised by its attachmentl to the vitlaUI
bones noted. According to Brodie (1940b, 1941, 1953) the
sutures involved in attaching the mid-face to the cranium,
are all orientated in such a way that growth at these
sutures results in a downward and forward movement of the
midface. The sutures are:
i) Fronto-maxillary
ii) Zygomatico-temporal
iii) Zygomatico-maxillary
iv) Pterygo-palatine
This alignment allows the midface to maintain its
antero-posterior relationship to the growing anterior
cranial base and at the same time increase its vertical
dimension. The growth is excellently illustrated and
documented in the literature (Riolo et AI., 1974; Broadbent,
Broadbent and Golden, 1975; Bebrents, 1984).
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It was thought for many years that primary growth occurred
at these sutures in the midface. It has, however, not been
possible to demonstrate autonomous expansive growth of
these sutures, nor the perfect alignment of them for the
growth needed. This theory thus fell away. Today the sutur••
are seen as areas of adaptive growth and are described as
being "growth adjusters" rather than "growth initiator."
(Coben, 1955; Ranly, 1980).
4.3 Theories Qf HasQmaxillary cQmplex grQwth
VariQus hyPOtheses in respect Qf nasomaxillary growth have
been develOPed in order to assist clinicians in their quest
for excellent orthodontic diagnQsis and treatment. Exactly
what determines the growth of the jaws remains largely
unclear. The following theories attempt to give some insight
intQ this complex growth process.
4.3.1 Sicher and Brodie's theohY
In Sicher and Brodie's view all bone forming ele..nts
(cartilage, sutures and Periosteum) are growth centre.
(Ranly, 1980). The "theory of sutural force" was developed
because bone is pressure sensitive. Different researchers
including Enlow (1968) prQposed that myofibroblasts in the
sutures are responsible for producing a type Qf joint which
creates an action causing slipPage of bones seParated by
sutures and due to the tension of the myofibroblast on
the bone margins, growth occurs in the sutures.
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They claimed that the nasomaxillary complex grows forwards
and downwards due to active growth of the fronta-nasal,
zygomatico-maxillary, zygomatico-temPQral, and
pterygo-palatine sutures. They described these sutures as
centres of active growth. Brodie found that certain
anatomical planes are in constant correlation with each
other throughout growth e.g. the mandibular, palatine and
oc~lusal planes and the skeletal base.
The theory does not seem to apply in cases of hydrocephaly
where if the sutural growth was genetically determined then
the calvarium would not cover the rapidly expanding cranial
contents.
4.3.2 The nasal septum growth theQry
Scott (1948, 1953) intrQduced the "nasal septum growth
theory". He claimed that cartilage is specially developed
to prQduce pressure while growing at the same time.
Although the nasal cartilage provides only a saall part of
the endQchQndral growth of the skull, it forms the basis for
the above theory. Accordingly expansiQn Qf the nasal
cartilage produces pressure which initiates grQwth in the
maxillary sutures.
This theory classifies cartilage areas (especially nasal)
as grQwth centres and classifies sutures as being Passive
and secondary growth areas (Ranly 1980). Accordingly, the
sphenQ-ethmoidal, palatQ-maxillary and pterygo-palatine
sutures form part of the intregal circum-maxillarj auture
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sy~tems which makes it possible for the nasal cartilage to
push the maxilla away froa the sphenoid bone. It is claiaed
that this whole system s~ops growing at seven years of age
which becomes the end of the first phase of growth. The
second phase of growth is said to commence after 7 years of
age .3cott, 1953).
Removal of the nasal septae of animals results in
underdevelopment of the nasomaxillary complex. Such animal
experiments attempt to prove the importance of the nasal
septum as a growth centre (Sarnat and Wexler, 1966). Koski
(1968) claimed that there was general consensus concerning
the role of the cartilaginous nasal septum in providing a
thrusting force which carries the maxilla forwards and
downwards during growth. storey (1972) suggested that
failure of the nasal cartilage to grow normally results in
a lack of maxillary growth with the resultant develo~nt of
a Class III jaw relationship. The importance of the nasal
septum is not so much that it is a growth centre which
controls the forward growth of the maxilla, but that it i.
an important growth point (Babula, sailey and Dixon, 1970).
On the other hand the potential of the septa. to act as a
growth centre is linked to the growth potential of the
cartilage cells, which are genetically program.ed and which
will respond to various demands.
Experimental excision of the nasal septum markedly affects
the growth of the upper face. Such experiments are not
conclusive as the malfOl."lll&tions which result could also be
due to the surgical procedures.
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Observations in chlldren with agenesis of the nasal ••ptua
indicates that the septum is important for antero-posterior
growth of the upper face, presumably because of endochondral
growth occurring at its posterior border, but not for
vertical development of the face.
On the basis of all the evidence it may be concluded that
the septo-ethmoidal junction acts as a growth centre during
postnatal life (Ranly, 1980).
In summary, Scott (1953) claimed that the soft tissues o~
the face keep pace with the sutural separation achieved by
the enlarging nasal septum. Thus as the bones of the
midface move ar.ead of the expanding septum, corresponding
additions of bone at the various facial sutures
passively functioh to maintain the bones in continuo1Js
sutural contact and to enlarge them in a linear manner.
4.3.3 The septo-premaxillary ligament theory
The nasal septum lies inferior11J' '.n the vomerine groove,
separated from the vomer by a fat layer. Anteriorly the
septUIi. is attached to the premaxilla in the area of the
nasal spine by a tlfibrous tissue" (septa-premaxillary
ligament) (Latham, 1969, 1970). This fibrous ligament is
said to extend frem the antero-inferior border of the nasal
septum in a postero-inferiorly direction to the anterior
nasal spine (ANS) and the intermaxillary suture of the
premaxillary region.
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septum and the fibrou.
prenatal and in early
an influence on the
1969, 1970).
It is claimed that the nasal
septo-premaxillary ligament, in
postnatal maxillary growth, has
direction of facial growth (Latham#
Latham claims two mechanisms which affect growth of the
naso-maxillary complex:
i) In foetal life the pUll of the septa-maxillary
ligament.
ii} In post-natal life the maxilla has the intrinsic
capability _0 remodel itself in an upwards and
backwards direction.
studies in experimental animals show that severing the
septa-premaxillary ligament retards maxillary growth
relative to the rest of the cranium (Gange and Johnson,
1974). These authors postulate that in future the severing
of this ligament may be of clinical importance in treating
Class II malocclusions.
4.3.4 Moss's Functional Matrix theory
This theory (Moss, 1962) claims that bone grows in response
to the sum of tha accumulated forces placed on it by ~ne
expansion of the soft tissue surrounding it. The theorz
claims equal importance for cartilage and sutures in
craniofacial growth.
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Accordingly no one entit} .. lch as the nasal septum, ha. the
ability to move a complex structure such as the mid-face.
Na30m~illary growth resul ts . in an expaAlsion of the facial
muscles, subcutaneous, and submucosal tissue, oral and nasal
epithelium as well as blood uessels and nerves.
The question as to whether the functional matrix theory and
the concept of nasal septum growth can be combined has not
been answered (Banly, 1980). Speculation on whether the
nasal cartilage controls the growth of the midface or
whether the cartilage is controlled by means of a capsular
matrix remains contentious.
4.3.5 Theory of genetic influence
This is basically a combination of Scott's and Moss's
theories and is possibly the most accepted one. Local
epigenetic factors (brain and eyes) appear to play an
important role according to this theory which suggests that
skull growth is under genetic influence (Van Limborgh,
1970).
4.3.6 A modern composite (Ranly 1980)
complex can be
factors inclUding
press'lre during
familial genetic
trauma, loss of
The development of the nasomaxillary
influenced by a wide range of
developmental abnormalities, postural
pregnancy, pressure of the birth canal,
factors, and environmental factors such as
teeth, caries, muscle functio, and habits.
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4.4 Dimensional changes Qf the NasomoxillatY complex
during growth
Dimensional changes must be studied in subjects who have not
undergone orthodontic treatment in order tQ assess normal
longitudinal growth changes. These changes will enable
orthodontists to distinguish between treatment and other
influences on occlusal stability.
Normal growth of the nasomaxillary complex is well described
in the literature (Enlow, 1968; Proffit, 1986; Moyers,
1988). Some of these growth changes are set out in Table V,
VI and VII (Adapted from Riolo, Moyers, McNamara Jr. and
Hunter, 1974).
4.5 Treatment effects Qn growth of the Nasomoxiliary
complex
Treatment can lead to positional change in some of the
facial landmarks. During a description Qf the use of the
visual treatment objective (VTO), the examples were given
for changes in point A as a result of various treatment
procedures (Ricketts et al., 1979):
Mechanics Moyement caused
i) Headgear
- 8mm
ii) Class II elastics - 3mm
iii) Activator
- 2mm
iv) Torque - 1-2mm
v) Class III elastics + 2-3mm
vi) Facial Mask + 2-4mm
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TABLE V
AGE RELATED MEAN ",u.l~'IJ~S OF CERTAIN MAXILLARY DlMEI'SIOJIS
FOR MALES AND FEMALES
HaJ& Female
Sella-Nasion-A point (SIAl(Population sample from Riolo at AI" 197.) :
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
6 37 81.9 3.3 6 25 80.7 3.0
10 46 80.8 3.1 10 35 80.7 3.7
13 43 81.2 3.4 13 29 81.0 3.8
16 23 81.4 4.4 16 9 81.8 3.7
Sella-Nasion-Basioo (SNBa)
!fQpulation sample from Riolo et al., 1974):
A,ge(X) N Degrees(X) S.D. Age(X) N Degrees (X) S.D.
6 37 129.3 5.0 6 25 129.6 5.0
10 4.6 129.2 4.7 10 35 129.7 4.5
13 43 129.2 5.3 13 29 130.3 4.7
t6 23 128.9 5.9 16 9 131.1 4.1
Convexity at point A(Population sample from Ricketts. 1981):
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
6 37 5.2 2.3 6 25 4.5 2.2
10 46 3.9 2.5 10 35 3.5 2.8
13 43 3.2 2.6 13 29 2.7 2.6
16 23 2.6 3.4 16 9 1.7 2.9
X == Mean
N == Sample size
S.D. :=: Standard deviatioo
90
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TABLE VI
AGE RELATED MEAN VALUES QF THE PALATAL PLANE AHGLE FOR
MALES AID FEMALES
(Pqpulation sample from Riolo et 01., 197.)
Palatal plane angle (ANSfNS-SN):
HAJ& Female
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
6 37 5.2 2 ... 6 24 7.0 2.6
10 46 6.1 2.6 10 35 7.5 2.8
13 43 7.1 3.2 13 29 8.2 2.9
16 23 7.0 3.0 16 9 8.0 2.2
X = Mean
N = Sample sizeS.D. = Standard deviation
91
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TABLE VII
AGE RELATED MEAN VALUES OF CERTAIN CRANIAL BASE DIMENSIONS
FOR MALES AND PEMALES(Population sample from Riolo et 01 .. 1974)
Ha.J& Female
Sella-Nasion (S-N) :
Age(X) N mm(X) S.D. Age(X) N mm(X) S.D.
6 37 72.7 2.8 6 25 70.3 2.7
10 46 76.8 3.2 10 35 73.9 2.8
13 43 79.5 3.8 13 29 75.5 3.1
16 23 83.3 3.8 16 9 76.9 3.9
Sella-Nasion/Frankfort plane (SN-FH) :
Age(X) N Degrees(X) S.D. Age(X) N Degrees (X) S.D.
6 21 6.1 3.0 6 12 6.5 4.7
10 25 5.4 2.7 10 14 . 6.1 3.9
13 23 4.0 3.6 13 9 6.2 3.3
16 13 3.1 3.6 16 5 4.8 2.9
sella-Articulare, posterior (S-Ar):
Age (X) N mm(X) S.D. Age(X) N mm(X) S.D.
6 37 29.5 2.8 6 25 28.4 3.1
10 45 33.7 3.1 10 35 32.6 3.4
13 43 36.9 3.5 13 29 34.6 3.8
16 23 38.2 3.1 16 9 34.0 2.9
X = Mean
N = Sample size
S.D. = Standard deviation
92
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Positive values (+) indicate protrusive movements and
negative values (-) indicate retrusive movements.
Although general orthopaedic responses in the mandible are
variable, depending on facial growth type, maxillae tend to
respond in a more predictable way to forces directed at a
level of, or below, the rotational centre of the maxillae.
When a distal force is applied to the maxillary dentition,
the maxillary complex rotates in a clockwise direction
around a point which roughly approximates the top of the
pterygomaxillary fissure. This rotation accounts for a
reduction in maxillary protrusion and a downward canting of
the palatal plane (ANS-PNS). There is a reciprocal clockwise
rotation of the mandible, an opening of the facial axis and
the mandibular plane and a retrusive effect on the chin
(Ricketts et al., 1979).
The various changes described above could contribute to
relapse of a malocclusion following orthodontic treatment.
4.6 Objective~
There exists no longitudinal growth data for the
nasomaxillary complex as defined for this or another similar
sample (Table I). There is also no data in respect to
orthodontic treatment available to enable one to compare the
changes occurring in the nasomaxillary complexes of this
sample during orthodontic treatment, as well as changes
occurring following orthodontic treatment, to other studies
noted previously.
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Hence, the objectives of this part of the study were:
i) to assess the longitudinal changes occurring in the
nasomaxillary complex and cranial base during
treatment and growth and,
ii) to determine whether any of these changes affected
long-term post-treatment stability of the dentition.
4.7 Materials and methods
The description of the materials used
employed to assess the data are documented
and the methods
in Chapter 3.
For this part of the study the Little Irregularity Index
(Little, 1975) was correlated with the cephalometric
nasom~~illary dimensions. The Little Irregularity Index
provides an indication of the lower incisor crowding and
was measured with a digital calipers capable of measuring to
O.Olmm (Sylvac S.A., Rue du Jura 2, 1023 Crissier.
Switzerland). The cephalometric measurements were obtained
with the use of the Oliceph computer programme (Oliceph,
Kansas City, Missouri, USA) and for this part of the study
comprised the following:
1. The maxillary morphology as described by:
i) the SNA angle (SNA) (Steiner, 1953).
ii) the maxillary convexity at point A (A-CONVEX)
(Ricketts, 1981).
2. The angle measured between the palatal line (ANS-PNS) and
the SN line (ANSPNS-SN).
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3. Some cranial bas. dimensional changes (Bjork, 1947;
Jarabak and Fizzell, 1972; Oliceph, 1987). The K-S-Ar angle
(SADANGLE), S-N length in millimetres (SK-MM) and the S-Ar
length in millimetres (SAR-MM).
4. The angle between the 8N line and the Pranfkfurt
horizontal line (8N-PH) (Oliceph, 1987).
4.7.1 criticisms of SIA and ANS-PNS
The use of the angle 8NA to measure maxillary prognathism
has been criticised by a number of authors (Baumrind and
Frantz, 1971; van der Linden, 1971; Jacobson, 1975, 1976;
Jacobson and Jacobson, 1980). The criticism has been based
mainly on problems which may be experienced in locating
point A on lateral cephalometric radiographs (Jacobson and
Jacobson, 1980). The size of the angle SMA is affected by
the cant of the anterior cranial base, as well as by the
anteroposterior position of the maxilla relative to the
rest of the face (Jacobson, 1975, 1976).
Because the majority of cephalometric analyses use 8NA to
measure tte relative position of the maxilla (Jacobson and
Jacobson, 1980), its use has been retained in the present
study.
It has been suggested that in a lateral cephalometric
radiograph a line through the most radio-opaque outline of
the palate may best represent the palatal plane (Jacobson,
1976). This approach is in keeping with Blafer's (1971)
contention that the anterior nasal spine has no consistent
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96
shape and that its position is quite ~ndependent of the
horizontal trend of the re~t of the palate. In the pre.ent
study of the palatal plane angle (ANSPNS-SM) the
conventional landmarks (ANS and PNS) were, neverthele•• ,
employed to make possible ready comparison with results from
previous studies of the palatal plane.
4.8 Results
The findings are set out in Tables VIII and IX.
The pairwise comparisons indicated that SNA remained
constant during the post-orthodontic period (T2-T3). A
significant change (p = 0.0001) was measured, however, for
the entire period of the study, being pre-treatment to
post-orthodontic time interval (Tl-T3). The palatal plane
angle (ANSPNS-SN) re~ained stable from Tl-T3. The saddle
angle (SADANGLE) and the angle SN-FH showed no significant
change (p > 0.05) from T1-T3. The convexity measured at
point A (A-CONVEX) decreased significantly (p = 0.0001)
throughout the study (Tl-T3). The cranial base length
measurements (SN-MM and SAR-MM) also showed a significant
change (p = 0.0001) from T1-T3, increasing throughout the
study (Table VIII).
According to the correlation analysis (Table IX) only the
maxillary anteroposterior position (SMA) at T3 showed a
weak significant correlation with the Little Irregularity
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TABLE VIII
DESCRIPTIVE STATISTICS FOR METRICAL DATA IN RESPECT TO THEJASQMAXILLARI COMPLEX
(Friedman test included)
Tl T2 T3 Tl-T2 Tl-T3 T2-T3
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D. p-value P~irwise differences
SNA 81.31 3.56 79.55 3.50 80.07 3.53 0.0001 + + x
ANSPNS-SN 7.53 2.89 8.17 3.22 7.86 3.21 0.03 - Yo x
SADANGLE 123.48 4.67 123.94 4.82 123.82 5.15 0.34 x x x
SN-FH 10.35 2.51 10.64 2.60 10.45 2.73 0.85 ,.. x x
A-CONVEX 4.16 2.95 1.98 2.71 1.12 2.99 0.0001 + + +
SN-MM 71.84 3.20 73.90 3.30 75.95 4.13 0.0001
SAR-MM 35.02 3.47 36.59 3.49 37.49 3.93 0.0001
L-IRREG 4.21 3.57 0.43 0.66 1.71 1.64 0.0001
S.D. = Standard deviation
+ = Significant, p < 0.05 (Tl > T2, T3)
= Significant, p < 0.05 (Tl < T2, T3)
x = Not significant, p > 0.05
".~" ... , ....,~.,...,...,.~ ...... ..."." ... ,,,,,,,,,,,,_.'(> ,"'.. ~'
.0
~
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TABLE IX
SPEARMAN CORRELATIQN COEFFICIENTS COMPARING THE
RELATIONSHIP OF THE NASQMAXILLARY AND CRANIAL BASE
DIMENSIONS TO THE LOWER INCISOR IRREGULARITY INDEX AT T3
LOWER IRREGULARITY INDEX (L-IRREG)
T1 T2 T3
VARIABLE r p r p r p
SNA -0.13 0.22 -0.15 0.16 -0.24 0.03
ANSPNS-SN 0.14 0.18 0.15 0.16 0.20 0.06
SADANGLE 0.04 0.69 0.11 0.31 0.10 0.38
SN-FH 0.09 0.42 -0.09 0.38 -0.01 0.92
A-CONVEX 0.04 0.72 0.04 0.75 -0.02 0.84
SN-MM 0.11 0.32 0.09 0.40 0.19 0.07
SAR-MM 0.10 0.36 0.15 0.15 0.11 0.32
r = spearman correlation coefficient
p = Probability values, Significance level 0.05
98
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Index at T3 (r. -0.24; p. 0.03). No other significant
correlations could be shown with the post-treatment lower
incisor irregularity (p > 0.05).
4.9 Discussion
Growth (Behrents et al., 1989) and treatment (Gardner and
Chaconas, 1976; Little, Wallen and Riedel, 1981) have been
shown to affect the stability of the post-treatment
occlusion.
The SNA remains basically unchanged during normal growth
(Table V). The SHA was reduced during treatment (T1-T2) by
1.76 degrees, but showed a small rebound (relapse) during
the post-orthodontic treatment phase (T2-T3) of 0.52
degrees. This rebound was not clinically significant and for
all purposes the SNA stayed stable following the active
orthodontic treatment (Table VIII).
The dimensions of the anterior and posterior part of the
cranial base increase in length during normal growth, but
this increase does not influence the cranial base angle
(angle BaSH) and the palatal plane angle which remain
basically unchanged (Tables V, VI and VII). Similar data was
recorded during orthodontic treatment. The palatal plane
angle (ANSPNS-SN), the cranial base angles (NSAR, SADANGLE)
and the angle between the cranial base reference lines,
Sella-Nasion (anterior cranial base) and Frankfurt
horizontal (SH-FH) remained virtually constant from Tl-T3 (p
> 0.05) (Table VIII). It appears that cranial base changes
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100
had little, if a 1 'i. effect on the degree of post-treatment
relapse. The stable palatal plane angle (ANSPNS-SN)
following orthodontic treatment indicates a high degree of
vertical control of the maxil~ary position during the use of
Class II and Class III orthodontic mechanics. Class II and
Class III intermaxillary traction are necessary to enabie
the orthodontist to correct anteroposterior occlusal and
midline discrepancies, and to enhance anchorage requirements
when indicated.
Convexity at point A (A-CONVEX) was reduced concomitant with
the reduction of the angle SNA (T1-T2), but the convexity
continued to decrease following the removal of active
appliances (T2-T3). The reduction from T2-T3 could be
classified as part of normal growth as is indicated in Table
V, and may in part have been due to growth at the mandibular
symphysis. Mandibular growth causes the facial plane angle
(Ricketts et al., 1979) to increase. The facial plane thus
moves anteriorly as a result of this growth, more at the
chin (the mandible normally grows in a forwards and
closing rotational direction (Tables X and XI» than at the
maxilla measured at point A, which results in a reduction of
the convexity at point A. The significant reduction of the
SNA angle during treatment (Tl-T2) and the consistency of
th~s angle following active treatment (T2-T3) (Table VIII),
in accompanyment with late forward growth of the mandible
(T2-T3) (5MB, SND, FAC-ANGLE, FAC-AXI5, Table XVI) may have
contributed to the post-treatment lower incisor crowding
as measured by the increase in the Little Irregularity
Index (Table VIII). This observation would be in
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agreement with the findings of Behrents et AI. (1989) who
showed that lower incisor crowding is less in subjects in
whom the maxillary length (measured from Sella to point A)
increased after orthodontic treatment.
The anterior, (8M) and posterior (8AR) cranial base lengths
continued to increase during the study (Tl-T3). These
dimensions increased as a result of normal growth of the
cranial base (Table VII) which has the nasomaxillary complex
attached to its anterior component. It could be speculated
that although these dimensions increased (Tl-T3), the
forward growth of the mandible was greater than that of the
maxilla as witnessed by the decrease of the convexity
measured at point A (Table VIII).
The changes which took place as a result of treatment
(TI-T2) remained largely stable during the follow-up period
(T2-T3) which had a mean duration of nearly seven years.
Growth changes are reflected in Table VIII. During the
active treatment period (TI-T2) 1(; is difficult to
distinguish growth changes from tha~ occuring as a result
of treatment, but during the post-orthodontic period (T2-T3)
mostly growth and maturity changes (Behrents, 1984) occur
and it is possible that these growth changes could
contribute to relapse incidences.
4.10 Conclusions
1. There was a reduction of the 8NA angle as a result of
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the orthodontic treatment (SNA decreased and SKB reaained
practically constant), suggesting a more retrusive
maxillary anteroposterior position which could in turn
contribute to lower incisor crowding in the post-orthodontic
period.
2. Maxillary retrusion in combination with forward growth of
the mandible, partially borne out by a continued reduction
of the convexity at point A, could enhance post-treatment
crowding of the lower incisors.
3. Retrusion of point A during treatment must be done with
due considerat1on being given to mandibular growth (as well
as to upper incisor torque).
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CHAPTER 5
LONGITUDINAL CHANGES IN THE MANDIBLE AND ITS RELATIONSHIP TO
THE STABILITY OF QRTHODONTICALLY TREATED DENTITIONS
5.1 Introduction
The morphology of the face as a whole, as well as of its
component parts, largely determines the direction which will
be taken by the face during growth (DuBrul, 1988). The
writings of Brodie (1941, 1953), Bjork (1947), Lande (1952),
Behrents (1984) and Behrents et ale (1989) indicate that the
success or failure of a treated malocclusion may be
influenced by growth.
Extreme mandibular rotation (Bjork, 1969) and complicated
facial development (Bjork and Skieller, 1972) may be
responsible for increased lower arch crowding. Late lower
arch crowding is also claimed to be caused by a specific
pattern of growth and a type of skeletal pattern which is
susceptible to crowding at the beginning of adolescence
(Sakuda, Kuroda, Wada and Matsumoto, 1976). Mandibular
growth, which occurs predominantly by downwards and forward
(protrusive) mandibular rotation, is thought to be a factor
which could contribute to late crowding of the lower
anterior teeth (Richardson, 1986).
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Changes in the shapes and positions of the jaws are mostly
dependant on growth (Holdaway, 1956). Holdaway believed
that when treatment reduced the size of the angle ANB, most
of the change was due to the angle SNA becoming more acute.
This was the result of an inhibition of maxillary alveolar
growth and a change in the position of point A as a result
of the upper incisors being retracted. In most cases,
even when favourable mandibular growth was observed, the
angle SNB became only slightly more obtuse, or remained
static. This finding can be attributed to a bite opening
movement due to orthodontic treatment or to lingual movement
of the lower incisors which can alter the relationship of
point B to the body of the mandible.
Growth also tends to cancel out some of the unfavourable
side effects which result from wearing ort.hodontic
appliances. For example the simple placing of fixed
appliances may cause teeth to extrude sligthly from their
alveolar processes (King, 1960). The flattening of the curve
of Spee during orthodontic treatment and most Class II
treatment modalities may cause further dental extrusion.
In nongrowing patients the nett effect of this was to cause
the mandible to tip downwards which in turn caused pogonion
to move posteriorly relative to the anterior cranial base.
With active growth, however, many of the unfavourable side
effects of the appliances could be corrected by the growth,
while in some instances, growth made the situation worse.
If the mandible does swing downwards as a result of
treatment, forward growth following the therapy could result
in a recovery of the mandibular position (King, 1960). If
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this downwards tipping of the mandible occurred in the
absence of growth, sUbsequent recovery after treatment could
contribute to some unfavourable sequelae such as incisor
crowding (King, 1974).
In theory, with a forward displacement of the mandibular
symphysis as a result of growth, as indicated by the SHB
angle becoming more obtuse, the lower incisors may be placed
forwards relative to the upper incisors. This change is
resisted by the lower incisors occluding with the upper
incisors and which may result in crowding of the mandibular
incisors (Perera, 1987).
Increased lower dental crowding has been reported following
active orthodontic treatment (Haavikko and Backman 1973;
Shapiro 1974; Little, Wallen and Riedel, 1981; Ronnerman and
Larsson 1981; Little, 1990). Similar findings were also
reported in untreated normal subjects (Sinclair and Little,
1983).
In order to study the effects on the dentition of mandibular
dimensional changes during and following orthodontic
treatment an understanding of the intricate anatomy and
growth changes of the mandible is necessary.
5.2 The mandible and related anatomy
Each half of the mandible develops in membrane from a single
centre which is formed in the first pharyngeal (mandibular)
arch on the outer side of Meckel's cartilage. Meckel's
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cartilage, by the sixth week, extends down from the otic
capsule to meet its other half in the midline of the foetal
face. At birth the mandible consists of two halves joined
at the symphysis by cartilage and fibrous tissue. At this
stage the mandible differs in some respects from its adult
appearance in that the body has a large alveolar component
full of unerupted deciduous teeth. This results in the
mandibular foramen lying close to the inferior
border. As the permanent dentition is established the
foramen moves to a higher position halfway between the
upper and lower border. During the first year of life
the two halves fuse. The other secondary cartilages
present at birth are the bilateral coronoid and condylar
cartilages. The coronoid catilage become ossified during
the first year of life. The condylar cartilage which
appears in the twelfth intra-uterine week, above and
lateral to the bony part of the condylar process, forms a
conical mass which is gradually replaced by bone by about
the fifth month. A zone of cartilage is, however, left
beneath the articular surface of the condyle which allows
for limited growth of the m~ndible as well as for moulding
of the condyle to fit the articular area on the growing
temporal bone (Longmore and McRae, 1985).
The mandible forms the lower part of the skeleton of the
face and carries the mandibular teeth. Unlike the other
skull bones, it is mobile and consists of a
horseshoe-shaped body and each half has a ramus. The
mandible gives insertion and origin to some important muscle
groups, notably the muscles of mastication and of the tongue
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(Longmore and McRae, 1985; DuBrul, 1988). The upper end of
the ramus is divided into the condylar and coronoid
processes by the sigmoid notch. The condylar process has a
constricted part, the condylar neck which carries the
condyle with its articular surface (DuBrul, 1988).
In growing children the mandible appears to grow
essentially downwards and forwards. Vital staining
experiments (Brash, 1924) as well as the recognition of
condylar growth centres (Charles, 1925; Brodie, 1941) have
shown that the predominant direction of mandibular growth is
actually posteriorly. It is thus evident that the
predominant growth directions and displacement directly
oppose each other. This phenomenon is responsible for the
anterior and inferior projection of the jaw which is a
consequence of displacement that occurs during the growth
which proceeds largely in a superior and posterior
direction. Thus, the mandible becomes projected forward,
notwithstanding the fact that actual forward growth at the
chin itself is relatively slight. Mandibular elongation
involves additions of bone at each condyle (endochondral
bone formation) and along the posterior border of the ramus
(bone remodeling). This results in a linear mode of growth
somewhat comparable to that found in typical long bones. The
overall enlargement of the mandible, however, is accompanied
by a complex series of major regi~nal bony remodeling
changes that serve to adapt each individual area to a total
pattern cf growth (Enlow,1968). The process of relocation of
a former portion of the mandible into a part of the new
anatomical region is the key factor that underlines the
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basis for continued remodeling as the mandible increa.e. in
in both forward and backward
size. :~etal implant studies
changes occur in the mandible
have shown that structural
processes occur simultaneously with growth activity
growth rotations 1969; Bjork andmandibular
Skieller, 1983). These
(Bjork,
intricate mandibular growth
in the
maxilla, the cranial base and facial soft tissue. These
changes are progressive and sequential, and they repeat
themselves
(Enlow,1968) .
continuously until growth terminates
The growth curve of the mandible, shown against the
background of Scammon's curves (Scammon, 1930), follows
general body growth more closely than does the maxilla. A
pubertal acceleration in general body growth affects the
jaws and parallels a dramatic increase in sexual
development. Males reach puberty on average two
chronological years (Broadbent, Broadbent and Golden, 1975)
or one and a half chronological years (Lewis, Roche and
Wagner, 1982) later than females. Skeletal maturity
indicators (SMI) show that the male mandibles attain a
maximum growth spurt one 8MI later than do those of females
(Fishman, 1982). It is generally believed that growth ceases
in the late teens (Riolo et al., 1974; Greulich and Pyle,
1976; Moyers et al., 1976). Behrents (1984) in a treatise
on the cvntinuum of growth, showed that in the aging
craniofacial skeleton a variety of morphological changes
occur beyond this age. Late mandibular growth changes may
thus affect an orthodontically treated dentition.
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variation in mandibular morphology and size contribut•• more
significantly to most malocclusions than does maAillary
variability (McNamara, 1983). The mandible is for example
more apt to be at fault in both Class I and Class III
malocclusions than is the maxilla. When there are
significant variations in mandibular morphology, both the
upper and lower dentitions have to adapt during development
(Moyers, 1988).
When bones such as the maxilla and mandible are "abnormal"
in shape, size or position, it is usually due to changes in
the composite of local morphogenic and functional
conditions. The bones themselves may actually have develoPed
normally were it not for these conditions. If a bone is
altered as a result of clinical intervention, but the
functional environment that produced it is not, subsequent
growth will continue to comply with the unchanged
environment and "relapse" may follow (Enlow, 1986).
5.3 Dimensional chaAlges of the mandible during growth
In order to understand how orthodontics affects facial
growth it is important to study facial growth which takes
place in the absence of orthodontic treatment. Male and
female parameters are presented in Tables X, XI, XII, XIII,
XIV and xv. The differences between the sexes are well
illustrated (Adapted from Riolo, Moyers, McNamara and
Hunter, 1974). These differences can be compared to those of
this study (Table XVI).
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TABLE X
AGE RELATED MEA..-J VALUES OP CERTAIN MAlfDIBULAR
ANIERQPOSTEBIQR SPATIAL poSITIONAL CHANGES lOR MALIS AID
EEMALES !population sample from Riolo et al •• 1974)
MA.le Pemale
Sella-Hasion-Point B (SNB) :
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
10 45 76.5 2.5 10 35 76.6 3.5
12 44 77.3 2.7 12 27 77.7 3.4
14 40 77.3 3.1 14 25 77.9 3.8
16 23 78.2 3.9 16 9 79.2 2.3
Sella-Nasion-Pogonion (FACPLANEl:
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
10 45 76.9 2.4 10 35 77.2 3.5
12 44 77.9 2.6 12 27 78.4 3.4
14 40 78.2 3.0 14 25 78.8 4.1
16 23 79.3 3.5 16 9 80.2 2.5
Frankfurt Plane/Hasion-Pogonion (FAC-ANGL) :
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
10 24 82.1 3.4 10 14 84.0 3.5
12 24 82~6 3.8 12 14 85.0 3.0
14 20 83.3 3.7 14 9 86.7 3.7
16 13 82.5 3.9 16 5 86.0 2.5
X = Mean
N = Sample size
S<D. = Standard deviation
110
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TABLE XI
AGE RELATED CHANGES IN MANDIBULAR GROWTH DIRECTIQH ­
ANGULAR AID LINEAR VALUES lOR MALES AID PBMALES(pqpulation sample from Riolo et 01., 1974)
bJ& Female
Sello-NasiQu/Gonion-Gnothion (GOGH-SN) :
Age(X) N Degrees (X) S.D. Age(X) N DegreeB(X) S.D.
10 45 34.4 4.5 10 35 35.0 4.8
12 44 33.5 4.8 12 27 34.0 5.1
14 40 32.9 5.0 14 25 33.5 6.0
16 23 32.6 5.2 16 9 31.1 3.1
Franfurt Plane/Mandibular Plane (FHA) :
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
10 24 29.6 5.0 10 14 28.9 4.2
12 24 29.4 5.5 12 13 28.1 5.2
14 20 27.7 5.8 14 9 24.8 5.8
16 13 28.7 5.2 16 5 25.8 3.0
Condylar Plane/Nasion-a Point (FAC-AXIS) :
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
10 45 83.6 3.4 10 35 84.3 3.1
12 44 84.5 3.3 12 27 84.8 3.0
14 40 84.9 3.5 14 25 84.5 3.3
16 23 84.7 3.7 16 9 87.7 3.1
Nasion-Menton (ABTFACH-MM) :
Age(X) N mm(X) S.D. Age(X) N mm(X) S.D.
10 45 118.7 5.7 10 35 115.1 6.7
12 44 123.3 6.3 12 27 118.3 6.0
14 39 130.3 7.9 14 25 122.3 5.9
16 23 136.8 7.9 16 9 123.2 5.1
Sella-Menton (POSFACH-MM) :
Age(X) N mm(X) S.D. Age(X) N mm(x) S.D.
10 45 73.6 4.6 10 35 70.2 4.1
12 44 77.6 5.3 12 27 73.7 5.1
14 40 82.9 5.6 14 25 76.6 5.5
16 23 88.2 5.9 16 9 79.1 4.3
X = Mean
N = Sample sizeS.D. = Standard deviation
111
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TABLE XII
AGE RELATED MEAN VALUES OF· MABDIBULAB GONIAL ANGLE GROWTH
CHANGES FOR KALES AND FEMALES(population samgle from Riolo et 01,. 1974)
112
Female
Menton-Gonial Intersection Articulore Posterior (GQHANGLE):
Age(X) N
10 46
12 44
14 39
16 23
Degrees (X) S.D,
12d.0 4,9
126.5 5,2
124.0 5,3
123.5 5,9
Age(X) N
10 35
12 27
14 25
16 9
Degrees (X) S.D,
127.5 4.5
126.2 4.2
125.0 4.7
122.2 4.2
x = Mean
N = Sample size
S.D. = Standard deviation
TABLE XIII
AGE RELATED MEAN VALUES OF MANDIBULAR CORPUS LENGTH GROWTH
CHANGES FOR HALES AND FEMALES(PQpulation sample from Riolo et 01,. 1974)
HAJ& Femole
GoniQn-Gnathioo (GOGH-MK) :
Age(X) N mm(X) S.D. Age(X) N mm(X) S.D.
10 46 74.4 2.8 10 35 73.4 4.4
12 44 77.9 3.2 12 27 75.9 4.1
14 40 62.4 3.8 14 25 78.9 4.0
16 23 86.3 3.6 16 9 81.0 4.0
GQoiQo-MentQn (CORL-MK) :
Age(X) N mm(X) S.D. Age(X) N mm(X) S.D.
10 46 69.6 3.0 10 35 69.0 4.2
12 44 73.1 3.5 12 27 71.5 4.0
14 39 77.4 3.9 14 25 74.8 4, ~
16 23 80.9 3.6 16 9 77.6 ,
X = MeanN = Sample sizeS,D. = Standard deviation
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naLE XIV
AGE RELATED MEAN VALUES OF MANDIBULAR RAMUS HEIGHT CIWfGES
FOR MALES AND PEMALES(Papulation sample from Riolo et al .. 1974)
HA.l.e Female
Gonion-Condylion (GOCO-MM) :
Age(X) H nun(X) S.D. Age(X) N mm(X) S.D.
10 46 54.0 3.5 10 35 51.5 2.7
12 44 57.2 3.9 12 27 54.6 3.9
14 40 61.6 4.4 14 25 56.8 3.5
16 23 66.1 4.1 16 9 60.5 2.4
Articulare-Gonion (RAHH-MM) :
Age(X) H nun(X) S.D. Age(X) N wm(X) S.D.
10 46 44.2 3.4 10 35 41.6 3.2
12 44 46.7 3.8 12 27 44.9 3.9
14 40 49.8 4.6 14 25 46.4 4.6
16 23 54.3 4.1 16 9 49.6 3.9
X :: Mean
N :: Sample size
S.D. = Standard deviation
TABLE XV
AGE RELATED MEAN VALUES OF MANDIBULAR CHIN BUTTON/TAPER
CHANGE (Papulation sample from Riolo et a1 •• 1974)
113
Female
Nasion-PogonionlNandibular Plane (FAC-PLANE) :
Age (X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
10 45 68.3 3.8 10 35 67.5 3.0
12 44 68.2 3.7 12 27 67.5 2.9
14 39 68.6 3.4 14 25 67.5 2.6
16 23 67.8 3.7 16 9 68.6 2.3
X :: Mean
N = Sample sizeS.D. = Standard deviation
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114
5.4 Objectiyel
There exists no longitudinal growth data for the mandibular
dimensions as defined for this or another similar sample
(Table I). There is also no data in respect to orthodontic
treatment available to enable one to compare the changes
occurring in the mandibles of this sample during orthodontic
treatment, as well as changes occurring following
orthodontic treatment, to other studies noted previously.
Hence, the purpose of this chapter was to:
i) study some longitudinal mandibular changes which occur
during and following orthodontic treatment and
ii) study the relationships of the observed
mandibular changes to post-treatment lowe~' incisor
irregularity.
5.5 Materials and methods
The basic description of the materials used
employed to assess the data are documented
this thesis.
and the methods
in Chapter 3 of
For this part of the study the only metrical parameter
measured on the study models, for comparison with the
cephalometric mandibular dimensions, was the Little
Irregularity Index (Little, 1975).
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The cephalometric measurements
use of the Oliceph computer
following:
115
used were obtained with the
programme and included the
1. The mandibular antero-POsterior position (degrees):
i) SNB (Sella-Nasion-Point B) (Steiner, 1953).
ii) SND (Sella-Nasion-Point D) (steiner, 1953).
iii) FACPLANE (S~lla-Nasion-Pogonion) (Bjork/Jarabak:
Jarabak and Fizzell, 1972).
iv) FAC-ANGL (Facial angle: FH/Nasion-Pogonion)
(Ricketts, 1981).
2. Mandibular growth direction:
a) Angular values:
i) GOGN-SN (Sella-Nasion/Gonion-Gnathion) (Steiner,
1953).
ii) FMA (Frankfurt mandibular plane angle)
(Tweed, 1954).
iii) FAC-AXIS (Facial-axis angle) (Ricketts, 1981).
iv) MANn-ARC (Mandibular arc) (Ricketts, 1981).
v) L-FACH (Lower facial height) (Ricketts, 1981)
b) Linear values (millimetres):
i) ANTFACH-MM (Nasion-Menton, Anterior facial height)
(Bjork/Jarabak: Jarabak and Fizzell, 1972).
ii) POSFACH-MM (sella-Gonion, Posterior facial height)
(Bjork/Jarabak: Jarabak aud Fizzell, 1972).
iii) SGO-NME (Anterior to posterior facial height ratio)
(Bjork/Jarabak: Jarabak and Fizzell, 1972).
3. Mandibular growth rotation (degrees) as described by
Bjork/Jarabak (Jarabak and Fizzell, 1972):
i) ART ANGLE (Articular angle: S-Ar-Go).
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116
ii) GOH ANGLE (Gonion angle: Ar-Go-Me).
iii) SUMANGLE (Aggregate of N-S-Ar, S-Ar-Go, Ar-Go-!·jn).
4. Gonial angle dimension (degrees) as described by
Bjork/Jarabak (Jarabak and Fizzell, 1972):
i) GONSLING (Gonial sling: Ar-Go-N).
ii) CORSLING (Corpus sling: N-Go-Me).
iii) GONANGLE (Summation of above: Ar-Go-Me).
5. Corpus length dimension (millimetres) as described by
Bjork/Jarabak (Jarabak and Fizzell, 1972):
i) GOGN-MM (Gonion-Gnathion).
ii) CORL-MM (Gonion-Menton).
6. Ramus height dimension (millimetres) as described by
Bjork/Jarabak (Jarabak and Fizzell, 1972):
i) GOCO-MM (Gonion-Condylion).
ii) RAMH-MM (Articulare-Gonion).
7. Chin button size/taper (degrees) as described by Ricketts
et a1. (1979);
FAC-TAPE (Facial Taper/N-Gn'-Go')
8. Corpus dimension ratio to cranial base as described by
Bjork/Jarabak (Jarabak and Fizzell, 1972):
CORLCRAN (Go-Me/SH)
9. Mandibular length relationships (millimetres) as
d~scribed by Oliceph (1987):
i) GOGNGC (GOGH minus GOCO)
ii) GOGH-GOeo (mandibular length from Condylion to
Gnathion)
5.6 Results
The results are set out in Tables XVI and XVII.
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TABLE XVI
DESCRIPTIVE STATISTICS FOR METRICAL DATA IN RESPECT TO THE MANDIBLE
(Friedman test included)
Tl T2 T3 TI-T2 TI-T3 T2-T3
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D. p-value Pairwise Differences
SNB 76.81 1.34 76.49 3.43 77.37 3.68 0.0006 x x
SNP 73.72 3.18 73.99 3.35 75.32 3.62 0.0001 x
FACPLANE 77.52 3.37 77.76 3.56 79.05 3.83 0.0001 X
FAC-ANGL 88.37 3.00 88.90 3.41 89.99 3.58 0.0001 x
GOGN-SN 33.44 4.93 34.05 5.76 32.19 6.24 0.0001 x + +
FMA 23.09 4.69 23.39 5.52 21.46 7.11 0.0001 x + +
FAC-AXIS 88.94 4.11 88.36 4.46 89.43 5.13 0.0001 + x
NAND-ARC 29.91 5.47 30.76 5.95 33.90 5.91 0.0001 x
L-FACH 43.56 4.44 44.62 4.83 44.03 5.01 0.0001 - x +
ANTFACH-MM 115.91 5.94 122.65 7.34 126.49 7.90 0.0001
POSTFACH-MM 74.44 4.89 78.89 6.27 85.01 7.98 0.0001
Soo-NNE 64.32 4.39 64.50 4.93 67.25 5.17 0.0001 x
ARTA:"JLE 146.11 7.11 146.08 7.43 146.10 7.62 0.58 x x x
ooNANGLE 124.31 6.34 124.44 6.54 121.83 6.81 0.0001 x + +
SUMANGLE 393.89 5.38 394.46 5.98 391.78 6.36 0.0001 x + +
l-'
....
~
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GONSLING 52.03 4.26 51.02 4.52 49.63 4.28 0.0001 x + +
CORSLING 72.27 4.56 73.42 4.76 72.20 5.30 0.0001 - x +
GOGN-MM 72.84 4.37 76.04 4.71 78.68 5.39 0.0001
CORL-MM 70.97 4.29 74.08 4.47 76.72 5.79 0.0001
GOCO-MM 56.26 3.91 59.83 4.57 63.66 8.65 0.0001
RAMH-MM 42.94 4.16 46.12 5.25 51.49 6.82 0.0001
FAC-TAPE 68.57 4.06 67.78 4.26 69.18 4.59 0.0013 x x
CORLCRAN 1.00 0.13 1.00 0.06 1.01 0.06 0.0006 - - x
L-IRREG 4.21 3.57 0.43 0.66 1.71 1.64 0.0001 + +
S.D. =
Friedman
+ =
=
x =
Standard deviation
test:
Statistically significant, p < 0.05 (TI > T2, T3)
statistically significant, p < 0.05 (TI < T2, T3)
Statistically not significant, p > 0.05
....
....
(Xl
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TABLE XVII
SPEARMAN CORRELATION COEFFICIENTS COMPARING THE RELATIQNSHIP
OF THE MANDIBULAR DIMENSIQHS TO THE LOWER IBCISQR
IRREGULARITY (L-IBREG)
L-IRREG
Tl T2 T3
VARIABLE r p r p r p
SNB -0.23 0.03 -0.24 0.02 -0.25 0.01
SND -0.23 0.03 -0.21 0.05 -0.27 0.01
FACPLANE -0.17 0.12 -0.17 0.11 -0.22 0.04
FAC-ANGL -0.15 0.16 -0.22 0.04 -0.27 0.01
GOGN-SN 0.04 0.73 0.04 0.74 0.008 0.94
FHA 0.01 0.89 0.08 0.46 0.02 0.89
FAC-AXIS -0.09 0.39 -0.07 0.50 -0.10 0.35
NAND-ARC -0.05 0.66 -0.16 0.14 0.05 0.63
L-FACH 0.13 0.23 0.06 0.59 0.10 0.34
ANTFACH-MM 0.001 0.99 -0.02 0.84 0.17 0.12
POSTFACH-MM -0.03 0.81 -0.07 0.53 0.02 0.87
SOO-NME -0.04 0.74 -0.05 0.62 -0.06 0.60
ARTANGLE -0.02 0.82 -0.04 0.69 0.01 0.91
GONANGLE 0.04 0.73 0.08 0.46 0.04 0.71
SUMANGLE 0.06 0.61 0.05 0.63 0.06 0.59
GONSLING 0.07 0.52 0.07 0.54 -0.01 0.95
CORSLING 0.01 0.90 0.00 0.99 0.01 0.94
OOGN-MM -0.09 0.40 -0.05 0.63 0.03 0.75
CORL-MM -0.12 0.27 -0.07 0.54 0.11 0.30
GOCO-MM 0.04 0.70 -0.06 0.57 0.19 0.07
RAMH-MM -0.07 0.54 -0.18 0.09 -0.01 0.89
FAC-TAPE 0.06 0.59 0.06 0.59 0.09 0.43
CORLCRAN -0.23 0.04 -0.15 0.15 -0.07 0.54
r = Spearman Correlation Coefficient
p = Probability value, significance level 0.05
119
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The purpose of the measurements in this part of the 8tudy
was to assess the longitudinal changes in the size and
spatial position of the mandible. The observed changes were
subsequently correlated with the Little Irregularity Index
(Little, 1975).
Changes noted during the treatment period (T1-T2) varied
depending on whether they were influenced by the orthodontic
treatment or were mostly due to growth. The variables
changing significantly were the FAC-AXIS, L-FACHL,
ANTFACH-MM, POSTFACR-MM, CORSLIHG, GOGH-MM, CORL-MM,
GOCO-MM, RAMH-MM, CORLCRAN and L-IRREG (Table XVI).
Practically all the mandibular dimensions changed
significantly (p < 0.05) from the end of treatment to the
final observation (T2-T3). The exceptions (p > 0.05) were
the articular angle (ARTANGLE) and the ratio comparing the
corpus length to anterior cranial base (CORLCRAN) (Table
XVI).
The r-values were all small (Table XVII). However, ce~tain
variables did show significant correlations (p < 0.05). The
clinically significant correlations were those correlating
the changes occurring during the post-orthodontic period
(T2-T3). The treatment period (Tl-T2) represented the
active orthodontic phase and although a Little Irregularity
Index mean value of 0.43 was attained at the end of
treatment (T2), indicating well aligned mandibular anterior
teeth, the final observation (T3) value is the real
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indicator of success (Table XVI). The end
post-orthodontic period (T3) was measured a
approximately 7 years post-treatment.
5.7 Discussion
121
of the
_an of
The mandible, the most highly mobile of the craniofacial
bones, is singularly important, for it is involved in the
vital functions of mastication, maintenance of the airway,
speech and facial expression. The modes, mechanisms and
sites of mandibular growth are complicated and much argued
in the literature (Moyers, 1988).
The growth movements of the mandible (Tables X, XI, XII and
XIII), in general, are complemented by corresponding changes
occurring in the maxilla (Chapter 4). As the maxilla becomes
displaced anteriorly and inferiorly, a simultaneous
displacement of the mandible in equivalent directions and
approximate extent occurs. The mandible does, however, lag
behind the growth of the maxilla and reaches its growth
spurt approximately one and a half chronological years later
(Lewis, Roche and Wagner, 1982). The mandible also continues
to change deep into adulthood (Behrents, 1984).
For the purpose of a better understanding of the effect of
mandibular change, as well as the accompanying treatment
effects on the long-term stability of the post-orthodontic
dentition, it was deemed essential to discuss the mandible
as a separate entity.
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The mandibular anteroposterior position changes to a more
prognathic situation during growth. This was indicated by
the norms in Tables X and XI, and amply supported by the
values in Table XVI. The 8MB, SND (Steiner, 1953), FACPLANE
(Bjork, 1969) and the FAC-ANGL (Ricketts, 1981; Holdaway,
1983) did not show any significant change during treatment
(T1-T2). Significant changes were, however, measured during
the post-orthodontic period (T2-T3). All four variables,
at both the end of active orthodontic treatment (T2) and at
the final observation (T3), were within the accepted norms
found in the literature. These changes were all growth
related and were expected (Riolo et al., 1974). Moreover,
a.ll these changes can influence the stability of the
dentition. The Spearman correlation coefficients were small,
but did correlate significantly (p < 0.05) with the Little
Irregularity Index (Little, 1975) (Table XVII). This finding
supports similar data reported by Richardson (1986) and
Perera (1987).
Mandibular growth direction and growth rotation gives an
indication of the forwards and/or downwards displacement of
the chin in space (Bjork, 1969; Ricketts, 1981; Bjork and
Skieller, 1983). The mandibular plane angle decreases with
growth (Table XI) (Riolo et al., 1974). This is supported by
the measurements recorded in this study. The GOGN-SN
(Steiner, 1953), ~MA (Tweed, 1962, 1966) and HAND-ARC
(Ricketts, 1981) all changed significantly (p = 0.0001)
during the period studied (Tl-T3) (Table XVI)~ The GONANGLE
and SUMANGLE (Bjork, 1969) also changed significantly (p =
0.G001) indicating a closing rotation of tha manaible from
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123
the start of the orthodontic treatment to the final
observation (T1-T3). The FAC-AXIS and L-FACH (Rickett.,
1981) did not change meaningfully with growth (Table XI).
Any change thus occurring here must be ascribed to treatment
mechanics. The angles did, however, remain practically
unchanged throughout the period studied (T1-T3) (p ) 0.05),
indicating sound orthodontic technique. King (1960, 1974)
reported that insufficient vertical control during
orthodontic trealment could lead to lower incisor crowding.
The significant change, although not clinically important,
of these two dimensions (p = 0.0001) occurred as a closing
rotation during the post-orthodontic period (T2-T3). No
significant correlation could, however, be shown between
the Little Irregularity Index and these variables (Table
XVII). The Bjork/Jarabak cephalometric analysis (Oliceph,
1987) measured the posterior to anterior face height ratio.
The values of ANTFAC~-MM, POSTFACH-MM and SGO-HME portrayed
in Table XVI showed a continued increase from the start of
treatment to the final observation (T1-T3) (p. 0.0001).
Similar measurements are recorded during normal growth
(Table XI). The SGO-HME (67.25%) measured at the final
observation (T3) is a larger value compared to the suggested
norm (60--64%). This supports the forward closing rotation of
the mandible. The GONANGLE representing the summation of the
GONSLING and CORSLIHG also decreased below the norm (121.83
< 123-137 degrees) which is an indication of a closing
rotation, but no significant correlation could be shown with
lower incisor irregularity (Table XVII). The fact that the
mandible rotated clockwise during treatment prevented the
bite from opening, an occurance which played a significant
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124
role in preventing the lower incisor crowding side-effect.
noted by King (1960, 1974).
It is generally accepted that the mandible rotates clockwise
or anti-clockwise during growth (Tabl~s XI and XII). This
occurs especially during the pubertal growth spurt (Schudy,
1965). These rotations have also been demonstrated by BjOrk
(1969) and Bjork and Skieller (1983). The lower incisor is
functionally related to the upper incisor, a fact that is
illustrated by the small changes occurring in the
interincisor angle during the growth rotation of the
mandible. The rotation also has an anteriorly displacing
effect on the maxillary teeth (Bjork, 1969; Bjork and
Skieller, 1983). The closing rotation of the mandible can
affect the overbite-overjet situation and subsequently lead
to relapse with resultant incisor irregularity.
Mandibular dimensional changes occurred throughout the
period studied (T1-T3). Continued increase of the corpus
length (GOGN-MM , CORLH-MM) and ramus height (GOCO-MM,
RAMH-MM) is shown in Table XVI. These increases also occur
during normal growth (Table XIII). These mandibular changes
occurred simUltaneously with the abovementioned variables
and could thus in combination affect the dentition. No
significant correlation between lower incisor crowding and
these four variables could be determined (Table XVII).
Other variables, however, also give an indication of
mandibular anterior displacement, being SNB, SND, FACPLAHE
and FAC-ANGL. These show significant correlations as shown
in Table XVII.
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Although numerous authors (Haavikko and Bickman, 1973;
Shapiro, 1974; Little, Wallen and Riedel, 1981; Rannerman
and Larsson, 1981; Little, 1990) reported mandibular incisor
crnwding following orthodontic treatment, they did not
record the variables in this format. Associations between
lower incisor crowding and certain mandibular dimensions
were reported in the literature (Richardson, 1986; Behrents
et al., 1989). The forward growth of the mandible during
the post-orthodontic period (T2-T3) as noted previously and
also described by Behrents (1984) thus appears to influence
the late lower incisor crowding. This phenomenon is
illustrated by the small, but significant correlations
between the Little Irregularity Index at the
post-orthodontic assessment (T3), and the SNB, SND, FACPLANE
and FAC-ANGL variables which indicate forward mandibular
growth (Table XVII). These are the only significant
correlations at T3.
5.8 Conclusions
1. Growth of the mandible occurs within the norms quoted in
the literature.
2. In this study orthodontic treatment complimented the
growth. No adverse effects such as mechanical OPening of the
bite which could lead to relapse of treated dentitions took
place.
3. Forward and closing rotation of the mandibular growth arc
took place.
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4. All variables from Tl to T3 corresponded with published
norms.
5. The closing and forward" displacement of the mandible
post-treatment, could be mostly responsible for the increase
in the irregularity of the lower incisors.
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CHAptER 6
A LONGITUDINAL EVALUATION OF THE ANTEROpoSTERIOR
RELATIONSHIP OF THE MAXILLA TO THE MANDIBLE IN
QRTHODQHTICALLY TREATED SUBJECTS
6.1 IntrQductiQn
The first texts that systematically described QrthQdQntics
appeared after 1850 and in this respect NQrman Kingsley's
Oral DefQrmities is a mQst nQtable example (PrQffit, 1986).
Despite the cQntributiQns Qf Kingsley and his cQntemporaries
the emphasis in QrthQdQntics remained Qn the alignment Qf
teeth and the cQrrectiQn Qf SQme facial prQportiQns. The
functiQning QcclusiQn did nQt attract great attentiQn, and
it was CQmmQn practice to remove teeth tQ CQrrect tooth
alignment. This philQSQphy was severily critisized in later
years (Angle, 1907).
Edward H. Angle (1907), the "father Qf mQdern Qrthodonics",
can be credited with much Qf the develQpment Qf a cQncept Qf
QcclusiQn in the natural dentitiQn. This wQrk subsequently
led tQ the develQpment Qf the Angle classificatiQn Qf
malQcclusiQn (Angle, 1899, 1906, 1907) which represented an
important step in the grQwing field Qf QrthodQntics. This
classificatiQn prQvided the first clear descriptiQn Qf a
nQrmal natural QcclusiQn and subdivided the majQr types Qf
malQcclusion. The classificatiQn described three classes Qf
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malocclusion based on the occlusal relationship. of the
first molars. Although mention is usually only made of the••
three classes, the Angle classification actually provide.
for four major divisions of occlusion: normal, Class I,
Class II and Class III occlusions. Case (1922), Simon
(1924), and others (Moyers, 1988) have taken issue with
Angle's classification based on a molar relationship, but
its usefullness as a ready descriptor of malocclusion has
outlasted most critics (Ackerman and Proffit, 1969;
Magazini, 1974).
Numerous other concepts in respect of the ideal occlusion
have subsequently been pUblished (Bolton, 1958, 1962;
Andrews, 1972, 1976; Ricketts et al., 1979; Roth, 1981). It
has, however, become clear that even an excellent occlusion
is unsatisfactory if it is achieved at the expense of proper
facial proportions (Holdaway, 1983, 1984).
The introduction of cephalometric radiography in
orthodontics (Broadbent, 1931; Hofrath, 1931) has enabled
orthodontists not only to measure the changes of tooth and
jaw positions, but also to study facial growth and to
evaluate their treatment results. The study of cephalometric
radiographs soon made it clear that many Angle Class I,
Class II and Class III malocclusions were due to faulty jaw
relationships and not just to malposed teeth (proffit,
1986). cephalometries showed how jaw growth could be
affected by both functional jaw orthopaedic appliances as
well as extraoral traction appliances which are commonly
used to control and modify facial form.
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Malocclusion is the result of an interaction between jaw
position and dental compensation or adaptation. It i.
possible to have a normal occlusion in spite of an
underlying jaw discrepancy or vice versa. A variety of
cephalometric analyses are available for case evaluation
(Downs, 1948; Steiner, 1953; Tweed, 1954; Ricketts, 1981;
Holdaway, 1983; McNamara, 1983).
Although the Angle classification of malocclusion has been
used for nearly a century, it refers primarily to those
occl~~al characteristics which are manifested in the
anteroposterior or sagittal plane of space. At the same time
it does not distinguish between the skeletal and dental
components of a malocclusion. It is of great importance to
to be able to distinguish between the various components of
a malocclusion when subjects with dishar~onies are being
evaluated. An important facet of any cephalometric analysis
is its ability to evaluate the anteroposterior
maxillo-mandibular relationship in a malocclusion. This
dimension can be measured, amongst others, by the ARB angle
(Steiner, 1953), the Wits analysis (Jacobson, 1975), the
anteroposterior dysplasia indicator (APDI) (Kim and vietas,
1978), the linear measurement of the distance between points
A and B projected onto the Frankfurt horizontal plane
(AF-BF distance) (Chang, 1987) or the A point convexity
(Ricketts, 1981). These analyses while probably being
sufficient for analysis purposes could be augmented by
similar information provided by the McNamara Nasion vertical
(McNamara, 1983), as well as the AO-BO difference
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130
measurements (McIver, 1973). High correlations were shown by
Oktay (1991) amongst the ARB angle, "Wits" appraisal, Al"-Bl"
measurement and the APDI indicator. No one cephalometric
analysis will evaluate the entire dento-facial environment
completely and it is thus essential to combine measurements
to obtain all the relevant information to study an
orthodontic problem. Investigations indicate that the ARB
angle (Steiner, 1953) is influenced by the locations of
Sella and Nasion, the mandibular plane angle and the
rotation of the jaws relative to the anterior cranial base.
The "Wits" analysis may be used to exclude, to some degree,
these facial disharmonies (Jacobson, 1975).
Other parameters are also available to assess
longitudinal anteroposterior changes. They are the
length, overjet and incisor positions.
the
arch
Arch length decreases with age (Brown and Daugaard-Jensen,
1951; Moyers et al., 1976) and this decrease could cause the
lower incisors to crowd (Lundstrom, 1969; Carmen, 1978;
Perera, 1987).
One of the most common procedures in orthodontics is to
correct an excessive overjet. Overjet, after being
orthodontically corrected, tends to return to its original
value irrespective of whether extraction or nonextraction
treatment was performed (Amott, 1962; Bishara, Chadha and
Potter, 1973; Bresonis and Grewe, 1974; Little, Wallen and
Riedel, 1981; Uhde, Sadowsky and BeGele, 1983; Hellekant,
Lagerstrom and Gleerup, 1989).
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Lower incisor position is important and should be placed
one millimetre ahead of the APO line (Williams, 1985). If
the lower incisor root apices are all in the same
bucco-lingual plane, if interproximal flat surfaces are
created by enamel stripping and if the canines are placed
correctly (Williams, 1985), then no lower retainer is
necessary post-treatment. Upper incisor stability may be
enhanced by keeping its angUlar relationship to within five
degrees to the Rickett's facial axis (Engel et al., 1980).
What constitutes an ideal incisor position has been the
subject of ongoing debate. It was proposed by Tweed (1941),
Margolis (1943) and Speidel and stoner (1944) that ideally
the lower incisor long axis should form an angle of near to
90 degrees to the lower mandibular border. Tweed (1953,
1954) also suggests the use of the Tweed triangle including
the FMA, IMPA and FMIA angles, for determining the correct
incisor position. A method which directly relates the lower
incisor to the chin point is suggested in the Holdaway
ratio whicr requires that the distance between the lower
incisal edge and the NB line be equal to the distance
between hard tissue pogonion and the NB line (Steiner,
1953). Lower incisors must be in a definite relationship to
the soft tissue in order to produce facial aesthetics and
this should be taken into consideration when planning
treatment (Lindquist, 1958). Various cephalometric incisor
position guidelines have been documented in the literature
(Downs, 1948; Steiner, 1953; Tweed, 1954; Ricketts, 1981).
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In spite of certain weaknesses, cephalometric measurements
do enable orthodontists to obtain more consistant and
stable results.
The goals of modern orthodontics are largely to create the
best possible occlusion, facial aesthetics and occlusal
stability. Harmony between anteroposterior occlusal
relationships, jaw position and jaw growth ultimately
det~rmines the quality of the orthodontic result achieved
(King, 1974; Uhde, Sado~sky and BeGele, 1983; Sandusky,
1983; Little, 1990). Riedel (1950) recommended the use of
the SNA, SNB and ANB angles to measure anteroposterior
relationships. The ANB angle is recognized as a sagittal
discrepancy indicator and is widely used in cephalometric
analyses (Riedel, 1950; steiner, 1953; Brown, 1981;
Freeman, 1981; Hussels and Nanda, 1984; Jarvinen, 1986).
Little (1990), however, could not show any correlation
between his Irregularity Index and various dento-facial
parameters in the post-orthodontic period. Moreover the
complexity of the post-orthodontic situation makes it seem
that retention needed to be more or less permanent (parker,
1989). This pessimistic picture makes it imperative to
further research in this regard, especially when different
samples can be used and the results compared to those that
have already been described and published in the literature.
Anteroposterior dimensional cl&anges which occur during
normal growth affects orthodontic results and it is
therefore imperative for orthodontists to take cognizance of
oC' ",~':l growth during orthodontic treatment.
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6.2 Dimensional changes of variablea during normal growth
Anteroposterior dimensional growth changes have been well
described in the literature (Riolo at al., 1974, 1979;
Moyers at al., 1976). An indication of how the ARB angle
changes during normal growth is set out in Table XVIII
(Adapted from Riolo et al., 1974).
Certain measurements which may affect the anteroposterior
facial morphology have Leen described in the preceeding and
succeeding chapters of this thesis. The maxillary changes
(SNA and A-CONVEX) (Chapter 4), the mandibula= changes (SKP'
(Chapter 5), overjet (OJB), arch length (ARCHL and LITTLE-A)
(Chapter 7) and the loW'er incisor (I-NB-MM, I-Im-DEG and
I-APO-MM) , upper incisor (I-NA-MM, I-NA-DEG and I-FACAX)
and interincit. .. l angle (I-I) (Chapter 8).
6.3 Objectives
There exists no longitUdinal growth data for the
anteroposterior dentofacial dimensions as defined for this
or another similar sample (Table I). There is also no data
available to ',nable one to co.pare ~che changal occurring
in these dimensions during orthodontic treatment, al well
as changes occurring following orthodontic treatment, to
other studies noted preViously.
Hence, the purpose of this part of the stUd}" was to:
i) assess the longitUdinal changes in certain
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TABLE XVIII
AGE RELATED MEAN VALUES OF CHANGES OF THE ANB ANGLE FOR
MALES AND FEMAL.ES(population sample from Riolo et al, , 1ll4l
~ Female
Age(X) N Degrees (X) S.D. Age(X) N Degrees (X) S.D.
6 37 5.3 2.2 6 25 4.7 2.2
10 45 4.3 2.0 10 35 4.0 2.7
13 43 3.7 2.0 13 29 3.5 2.4
16 23 3.2 2.3 16 9 2.6 2.4
x = Mean
N = Sample size
S.D. = Standard deviation
134
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135
anteroposterior dentofacial dimen.ion. in
orthodontic subjects.
ii) determine possible relationships between growth,
changes induced by orthodontic treatment and
post-treatment lower inci~or crowding.
6.4 Materials and methQds
The basic descriptiQn Qf the materials used and the methods
employed to assess the data have been dQcumented in Chapter
3 Qf this thesis.
Cephalometric measurements were obtained with the use Qf the
Oliceph computer program included the following:
1. The maxillary pQsition as described by:
i) the Sella-Nasion A point angle (SNA) (steiner, 1953).
ii) the convexity of A point (A-CONVEX) (Ricketts, 1981).
2. The mandibular positiQn as described by:
i) the Sella-Nasion-Point Bangle (SNB) (steiner, 1953).
3. The maxillo-mandibular anteroposterior relationship as
described by:
i) the Point A-Masion-PQint B angle (ARB) (Steiner,
195Z).
ii) the Point A and Point B discrepancy relative to
the functional Qcclusal plane expressed as the wits
analysis (WITS-MM) (JacQbsQn, 1975).
4. The upper incisor position as des~ribed by:
i) the upper incisor position measured to the
Nasion-Point A line in millimetres (I-NA-MM) and
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measured with digital
0,01mm. The following
136
degrees (I-NA-DEG) (steiner, 1953).
ii) the upper incisor position measured to the facial
axis of Ricketts (1981) (I-?ACAX) (Engel et AI.,
1980) •
5. The lower incisor position as described by:
i) the lower incisor position measured to the Point
B-Nasion line in millimetres And degrees (I-NB-MM
and I-NB-DEG) (steiner, 1953).
ii) the lower incisor position measured to the Point
A-Pogonion line in millimeters (Ricketts, 1981).
6. The interincisor angular relationship (I-I) as described
by Steiner (1953).
The orthodontic study casts were
calipers capable of measuring to
variables were measured:
1. An indication of lower incisor crowding in millimetres
-che Little Irregularity Index (L-IRREG) (Little, 1975).
2. Arch length dimension measured in millimetres, being
the aggregate of the left and right measurement taken from
the mesial aspect of the mandibular first molar to the
interproximal contact of the central incisors (LITTLE-A)
(Little, Riedel and Engst, 1990).
3. The arch length (ARCHL) mensured in millimetres as the
perpendicular measurement from the mandibular mesial bimolar
line to the interproximal contact point of the lower central
incisors (Moyers et al., 1976).
4. The overjet (OJB) measured in millimetres as the upper
to lower incisor anteroposterior overlap (Moyers, 1988).
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137
The data wele subjected to de.criptive atatiatica auch aa
mean and stan1ard deviation for each of the three
evaluations. The Friedman test was used to test for
significant differences during the active treatment period
(T1-T2), during the post-orthodontic period (T2-T3) and in
general throughout the study (T1-T3). The Wilcoxon and the
Chi-square tests tested for significant differences amongst
the variables at the three time intervals. The Spearman
correlation coefficient and the Kruskal-Wallis tests were
used to test the relationships of the different variables
with the degree of lower incisor irregularity (Little, 1975)
at the final observation (T3) (Zar, 1984). The significance
level of this part of the study was set at 0.05.
6.5 Results
The longitudinal changes which were assessed in respect to
the anteroposterior relationship between the maxilla and the
mandible are recorded in Tables XIX and XX. These
changes were subsequently correlated with the Little
Irregularity Index (Little, 1975) (Tables XXI and XXII).
Although the mean SNA value was significantly reduced during
the active orthodontic treatment (T1-T2) and a similar trend
was shown throughout the observation period (Tl-T3), it
remained reasonably stable after removal of the appliances
(T2-T3). The mean SHB value did not change significantly
during the treatment period (T1-T2), but a significant
increase was measured after active treatment (T2-T3). The
metrical characters ANa and A-CONVEX were significantly
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TABLE XIX
DESCRIPTIVE STATISTICS FOR METRICAL DATA IN RESPECT TO THE ANTEROP(bSTERIOR
RELATIONSHIP OF THE MAXILLA TO THE MANDI~
(Friedman test included)
Tl T2 T3 Tl-T2 Tl-T3 T2-T3
~RIABLE MEAN S.D. MEAN S.D. MEAN S.D. p-value pairwise Differences
fA 81. 31 3.56 79.55 3.50 80.07 3.53 0.0001 + + x
fB 76.81 3.34 76.49 3.43 77.37 3.68 0.001 x x
fB 4.50 2.39 3.05 2.01 2.70 2.28 0.0001 + + +
-CONVEX 4.16 2.95 1.98 2.71 1.12 2.99 0.0001 + + +
[TS-MM 1.19 3.93 0.46 3.05 0.81 3.64 0.23 x x x
-IRREG 4.21 3.57 0.43 0.66 1.71 1.64 0.0001 + +
rB 6.21 3.29 2.85 0.85 3.17 1.23 0.0001 + + X
lCHL 23.50 2.37 20.75 3.19 20.01 3.52 0.0001 + + +
[TTLE-A 61.06 4.31 56.69 6.83 54.99 7.05 0.0001 x + +
-NA-DEG 22.99 9.09 22.60 8.44 22.35 7.48 0.83 x x x
-NA-MM 4.14 2.86 2.84 2.61 3.49 2,60 0.002 + x
-NB-DEG 27.22 6.41 28.43 5.08 26.71 4.72 0.03 x x +
-NB-MM 3.89 2.11 4.32 1.63 4.04 1.65 0.15 x x x
-I 126.40 11.05 127.05 9.34 129.38 7.79 0.03 - xx
-APO-MM 0.42 2.86 1.29 1.90 0.86 1.93 0.03 - x x
'-FACAX 4.02 8.65 5.57 7.29 6.19 6.08 0.19 x x x
,D. = Standard deviation
= Significant, p < 0.05 (TI > T2, T3)
= Significant, p < 0.05 (TI ( T2, T3)
= Not significant, p > 0.05
....
w
Q)
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TABLE XX
FREOUENCY OF THE SEVERITY OF MOLAR AND CANINE
ANTEROpoSTERIOR CUSP RELATIQNSHIPS RECORDED
PRE-TREATMENT, POST-TREATMENT AND POST-RETENTION
139
VARIABLE
MOLAR L
o
2
3
MOLAB R
o
2
3
CANINE L
o
2
3
CANINE R
o
2
3
Tl
N
43 (48.9%)
21 (23.9%)
24 (27.3%)
37 (42.0%)
25 (28.4%)
26 (29.5%)
17 (19.3%)
43 (48.9%)
28 (31.8%)
18 (20.5%)
45 (51.1%)
25 (28.4%)
T2
N
83 (94.3%)
3 (3.4%)
2 (2.3%)
82 (93.21)
4 (4.5%)
2 (2.3%)
83 (94.3%)
4 (4.5%)
1 (1.1%)
82 (93.2%)
6 (6.8%)
o
T3
N
80 (90.91)
5 (5.7%)
3 (3.4%)
82 (93.21)
3 (3.41)
3 (3.4')
80 (90.9%)
6 (6.81)
2 (2.31)
80 (90.91)
7 (8.0%)
1 (1.1%)
N = Sample size
o = Normal molar and canine relationship (Table II)
2 = Full cusp (edge-edge) deviation (Table II)
3 = More than a full cusp deviation (Table II)
Percentage representation in parentheses
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TABLE XXI
SPEARMAN CORRELATION COEFFICIENTS COMPARING THE RELATIONSHIP
OF THE IRREGULARITY OF THE MANDIBULAR INCISORS AT T3 TO THE
VARIABLES DEPICTING ANTEROpoSTERIOR DIMENSION AT Tt, T2 AND
n
LITTLE IRREGULARITY INDEX
T1 T2 T3
VARIABLE r p r p r p
SNA -0.13 0.22 -0.15 0.16 -0.23 0.03
SNB -0.23 0.03 -0.24 0.02 -0.25 0.02
ANB 0.15 0.17 0.09 0.39 0.03 0.79
A-CONVEX 0.04 0.72 0.04 0.75 -0.02 0.84
WI TS-MM 0.07 0.49 0.09 0.42 0.01 0.89
OJB 0.20 0.06 0.09 0.43 0.04 0.75
ARCHL -0.12 0.27 0.04 0.72 0.01 0.89
LITTLE-A -0.11 0.32 0.06 0.55 -0.01 0.94
I-NA-DEG -0.01 0.96 0.07 0.53 0.09 0.42
I-NA-MM 0.04 0.74 0.08 0.45 0.08 0.46
I-NB-DEG -0.16 0.14 -0.08 0.43 -0.06 0.59
I-NB-MM -0.07 0.50 0.13 0.23 0.03 0.75
I-I 0.06 0.61 -0.02 0.85 -0.09 0.39
I-APO-MM -0.19 0.06 -0.03 0.80 -0.07 0.51
I/-FACAX -0.03 0.81 -0.04 0.67 -0.09 0.39
r = Spearman correlation coefficient
p = Significance level, p < 0.05
140
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TABLE XXII
KRQSKAL-WALLIS TEST INDICATING WHETHER SIGNIFICANT
BBLATIQNSHIPS EXISTED BETWEEN MOLAR AND CARINE
ANTEROpoSTERIOR RELATIONSHIPS AT Tl.T2 AND T3 AND THE
IRREGULARITY OF THE LOWER INCISORS AT T3
LITTLE IRREGULARITY INDEX
T1 T2 T3
VARIABLE P P P
MOLAR L 0.34 0.55 0.45
MOLAR R 0.05 0.61 0.34
CANINE L 0.13 0.88 0.13
CANINE R 0.13 0.88 0.13
P = probability level for significance, p < 0.05
141
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142
reduced during the period Tl to T3. The WITS-.~ mea8urement
also showed a reduction throughout the study (T1-T3), but
this was not a significant reduction (Table XIX).
Overall the incisor positions measured to HA, NB , APO and
the facial axis were not significantly (p > 0.05) altered
during the period studied (Tl-T3), but the angular
relationship between the incisors (I-I) did increase
significantly. The mean millimetre measurement of the upper
incisor to the HA line as well as the millimetre value to
the APO line changed significantly (p < 0.05) during
treatment (Tl-T2). The upper incisor moved anteriorly
without changing its angulation and the lower incisor
uprighted significantly (I-NB-DEG) post-orthodontically
(T2-T3). The mean overjet (OJB) having been significantly
reduced during treatment (Tl-T2), showed a non-significant
increase after appliance removal (T2-T3). The mean arch
length (ARCHL and LITTLE-A) showed a significant decrease
throughout the study (T1-T3) (Table XIX).
active treatment (T2-T3) (Table
irregularity
treatment
The lower
signifi::antly
significantly
XIX) •
incisor
during
follol-J'ing
(L-IRREG)
(Tl-T2) and
decreased
increased
Practically all the Class I, II and III molar and canine
relationships, with minor exceptions, were treated to a
Class I relationship (T1-T2). The new positions remained
stable during the post-orthodontic period (T2-T3) (Table
XX) •
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Significant, but weak correlations were shown for the 8KA
and SNB angular changes compared to the degree of lower
incisor irregularity at the final observation (T3). The 8RB
angle, however, showed significantly weak correlations
throughout the study with the Little Irregularity Index
(Little, 1975) (Table XXI).
No significant Spearman correlations (Table XXI) or
Kruskal-Wallis test relationships (Table XXII) could be
shown between the other variables measured and the Little
Irregularity Index (Little, 1975).
6.6 Discussion
Succes~ful growth modification during treatment is possible
only in subjects who have a significant amount of growth
remaining (Proffit, 1986; King, Keeling, Hocevar and
Wheeler, 1990). ~ttempts at growth modification should begin
with girls at eight to nine years and boys at ten to eleven
years of age (King et al., 1990). Although jaw growth
continues after puberty, the magnitude is rarely enough to
allow for correction of significant skeletal jaw
discrepancies. If point A is distalized in a nine year old
and Nasion and Pogonion continue to grow normally then the
profile convexity will decrease in an anteroposterior
dimension. After thirteen years of age the convexity
~~ducticn in girls at point A is minimal (Ricketts et a1.,
1979; Ricketts, 1981) making it difficult to reduce the
profile convexity because Nasion and Pogonion are not
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144
growing forwa~d as much as iil the earlier years (King at
Al., 1990). This parameter shows similar decreases in both
sexes up to fifteen years of age (4.5mm to 1.7mm), but
thereafter it only decreases in males (1.7mm to -O.4mm)
(Ricketts, 1981). The ARB angle normally reduces during
growth (Table XVIII), but can also be reduced by a variety
of orthodontic treatment mcaalities which affect point A and
point B (Gianelly and Valentini, 1976; Ricketts et al.,
1979). The relatively small, but significant reduction of
SNA throughout the study (T1-T3) could possibly be
attributed to the relatively high starting mean age of
11.92 years (Table I and XIX). The mandible in contrast to
the maxilla showed significant growth, borne out by the
increase in the SNB angle, in the post-orthodontic period
(T2-T3) (Table XIX).
Changes in the apical bases during treatment have been shown
to be greatly dependent on growth. Holdaway in 1955 noted
that the greatest change which occurs in the reduction of
the ANE angle is due to a reduction of the SNA angle which
results after the inhibiting of maxillary alveolar growth
as well as a remodelling in the region of point A following
retraction of th~ upper incisors. This Observation was borne
out in the present study (Table XIX). The upper incisor was
significantly retracted during treatment (I-NA-MM 4.14mm to
2.84mm), which probably resulted in the significant
reduction of the SNA angle, which is in contrast to the SNB
angle which showed no significant change in this period
(T1-T2). In most subjects with favourable mandibular growth
who were evaluated by Holdaway (1956) the angle, SNB
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145
increased only slightly, or exhibited no change. The
latter finding could be due, either to a bite o~ning, or
to a lingual movement of the lower incisors. Either of t ••••
factors could alter the relationship of point B to the body
of the mandible.
Mean reductions in the parameters ANS, A-CONVEX and WITS-MM
reductions during the period T1 to T2 were thus mainly due
to treatment. Upper inci~or retraction appeared to play a
major role in the posterior movement of point A and
subsequently in the reduction of the angle SNA. This
reduction in the angle SNA appeared to influence the
reduction of the angle ANB as non-significant mandibular
growth and lower incisor proclination during treatment
(T1-T2) could not have influenced point B significantly,
hence the relatively unchanged 5MB value at the
post-treatment evaluation (T2). The mean ANB angle, A-CONVEX
and WITS-MM were all reduced following active treatment
(T2-T3), indicating that following orthodontic treatment,
growth caused the further reduction. It has been reported
that growth continues well into adulthood (Behrents, 1984)
and the present study appears to support this theory as the
post-treatment mean age was 21.47 years (Table I). Thus,
with the forward displacement of the mandibular symphysis
as a result of growth, the lower incisors would be pushed
forward relative to the upper incisors (Perera, 1987). The
mean interincisal angle increased throughout ~he study
(T1-T3) (Table XIX) which tends to support the above
observation. It may be postUlated that the upper incisor
moved anteriorly and that the lower incisc~ uprighted
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146
posteriorly because of this forward movement of the mandible
resulting in a slight, but non-significant increase in the
overjet during the post-orthodontic period (T2-T3) (Table
XIX). Although the overjet increased during T2-T3, it is
still within clinically acceptable norms (Moyers et al.,
1976) and it is a significant improvement in respect to the
initial measurement. The increaso showed a slight return
towards the original value which supports the data presented
by other authors (Amott, 1962; Bishara, Chadha and Potter,
1973; Bresonis and Grewe, 1974; Little, Wallen and Riedel,
1981; Uhde, Sadowsky and BeGele, 1983). During this latter
period the incisor positions remained within accepted
clinical norms (Steiner, 1953; Engel et al., 1980;
Ricketts, 1981). The lower incisor movement which results
from forward mandibular growth, is resisted by the occlusion
of the upper teeth, which may result in an incre&sed
crowding of the mandibular incisors (Perera, 1987). In the
present study, the Little Irregularity Index (Little, 1975)
measured an increase following the removal of the
orthodontic appliances (T2-T3) (Table XIX). The maxillary
incisors showed a slight anterior movement following
treatment which could be the result of this phenomenon. The
overall non-significant changes of the individual positions
of the upper and lower incisors during the period studied
show the tendency of the teeth to return towards their
original positions.
Physiologic
teeth, with
extractions,
drift is defined as
no applied force,
congenital absence
the natural migration of
into spaces cre~ted by
of teeth, dental decay,
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147
proximal attrition, or orthodontic tooth movement
(Creekmore, 1975). The term mesial drift is not new in
dental literature and means that the buccal teeth of a
dentition move in a mesial direction. It is said to be
present, in a normal dentition and to result from a natural
physiological force which becomes ~ifective as soon as the
first permanent molars erupt into occlusion (Downs, 1938).
Downs (1938) described four factors which could lead to a
reduction in dental arch length:
i} constitutional factors affecting the growth of the
maxilla and mandible.
ii) an anterior component of force.
iii) a restraining or distal force emanating from the
labial and buccal musc~lature.
iv) a lack of resistance to these two latter opposite
forces induced by the disturbance of the proximal
contact points of the teeth.
The significant reduction of the mean arch length ~easured
in the present study (Table XIX) is thus in accordance with
clinical observations made in previous publications (Downs,
1938; Brown and Daugaard-Jensen, 1951; Creekmore, 1975;
Moyers et aI, 1976). These reports were not as elaborately
supported with statistics. Lundstrom (1969), Carmen (1978)
and Perera (1987) reported that the decrease in arch length
could cause lower incisor crowding. The post-trea~ent (T2)
and post-orthodontic (T3) lower incisor crowding of the
present study is within clinically acceptable norms
according to Little (1975) (Table XIX). Although it is
possible that the significant decrease in the arch length
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148
co~l.d have contributed to the increase in the Little
Irregularity Index during the post-orthodontic interval, no
significant correlation could be shown between these
variables (Table XXI).
The attainment and maintenance of a Class I molar
relationship is commonly identified as being a prime goal of
orthodontic treatment (strang, 1943; Graber, 1966; Thurow,
1966; Tweed, 1966; 8egg, 1971, 1977; Moyers, 1988). A Class
I molar relationship has also been identified as being the
pre-eminent key to a normal occlusion (Andrews, 1972, 1976).
Molar malrelationships are rarely self-correcting (Arya,
Savara and Thomas, 1973), and it may be expected that they
will become more severe with time if left untreated (Harris
and Behrents, 1988).
In this study the indications are that the Class I molar and
canine relationships are indeed most stable. There were 176
molar and canine relationships treated and of those 94.3'
(left) and 93.2% (right) were changed to Class I molar and
94.3% (right) and 90.9% (left) were changed to Class I
canine relationships. The majority of these remained stable
in their corrected positions, 90.9% (left molar), 93.21
(right molar), 93.2% (right canine) and 90.9% (right canine)
(Table XX). It was reported that none of 69 untreated
patients starting in a Class I cusp-in-groove relationship
moved out of that relationship (Harris and Behrents,
1988). In contrast Harris and Behrents (1988) also believe
that for some unexplained reason Class II molar
relationships appeared to be intrinsically more stable in
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14:9
natural untreated occlusions. Angle's (1907) original
reason that the maxillary first molar is invariably in the
correct anteroposterior position when in a Cla.s I
relationship, appears to be no longer tenable.
According to the Little Irregularity Index (Little, 1975),
incisor positions as well as molar and canine relationships,
the malocclusions in this study were successfully treated.
The post-orthodontic results were clinically acceptable
and stable (Tables XIX and XX). The slight, but significant
increase in the crowding of the lower incisors during the
post-orthodontic period (T2-T3) (L-IRREG 0.43 to 1.71mrn) is
well within the acceptable limits (Little, 1975).
Although changes occurred in the anteroposterior dimensions
which possibly contributed to the small increase in the
L-IRREG during the post-orthodontic period, only weak
significant correlations could be shown for the angular
measurements SNA and SNB at ths final observation (T3)
when compared to the Little Irregul~rity Index (L-IRREG) at
T3. The other variables measu~ed showed no significant
correlations when compared to L-IRREG at this assessment
(Tables XXI and XXII).
A successfully treated dentition may show small
irregularities follOWing orthodontic treatment and patients
and parents shou~d be informed of this possibility at the
initial appointment.
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150
6.7 Conclusions
1. The anteroposterior dimensions (ARB and A-CONVEX)
decreased from T1 to T3, mainly due to a combination of
treatment effect on point A and growth effect on point B.
This was noted in the decrease of the angle SNA (T1-T2), and
as an increase in the angle SNB, following the active
orthodontic treatment (T2-T3).
2. The mandible continued its growth during the
post-pubertal period.
3. Continued decrease in the variables ARB and A-CONVEX
throughout the study (T1-T3) could affect lower incisor
irregularity, but no significant correlations were shown
between the Little Irregularity Index and these variables.
4. Molar and canine relationships once established in Class
I remained extremely stable and no significant
interdependence could be shown between these and lower
incisor crowding.
5. Weak, significant correlations were shown between the
angular change in the angle SNB at T1 to T3 and the lower
incisor crOWding at the final observation (T3), but a
similar observation was noted for the angle SNA only at the
final observation.
6. The measurement of the arch length decreased
be held partly
significantly throughout the stUdy. Although this change
from Tl to T2 was treatment related, growth and mesially
displacing occlusal forces could also
responsible for the post-treatment changes.
7. Post-treatment lower incisor irregularity appears to be
growth related.
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151
CHAPTER 7
A LONGITUDINAL EVALUATIQN QF PQST-ORTHODONTIC OCCLUSAL
CHANGES AND THEIR RELATIONSHIPS TO LOWER INCISOR CROwnIIG
7.1 Introduction
7.1.1 DeyelQpment Qf the occlusiQn
Orthodontists should have an in-depth understanding Qf
prenatal dental development which includes normal and
abnormal development of the teeth within the jaws (Moyers,
1988). Tooth development takes place over a relatively long
periQd of time. It begins in the seventh week Qf embryonic
life (primary dentition), and continues well into the late
teenage years (third mQlar of the secQndary dentition)
(Moss-Salentijn and Hendricks-Klyvert, 1985).
Embryonic development of both the mandibular and maxillary
dentitions proceeds through four stages. These are:
initiation of odotogenesis, bud stage, cap stage and bell
stage (Longmore and McRae, 1985; Moss-Salentijn and
Hendricks-Klyvert, 1985; Moyers, 1988). The twenty deciduous
tooth buds differentiate through the cap and bell stages at
rates that manifest recognizable sequence patterns, or
polYmQrphisms (Burdi et al., 1970). These variations in
embryonic sequence may be the prenatal antecedents of the
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152
polymorphisms of sequence which may be observed in postnatal
dentitions (Garn and Burdi, 1971). According to Moyers
(1988) examples of sequential polYmOrphism are:
i) the mandibular incisors which tend to precede their
maxillary counterparts in eruption.
ii) teeth closely positioned show stronger correlations
in crown size than those more widely spaced.
iii) the presence of sexual dimorphism in the
calcification and eruption of permanent teeth with
the exception of the third molars.
Throughout their development the tooth germs move, relative
to each other and relative to the developing bone of the
jaw. Once most of the crown has been formed and all crown
odontoblasts have differentiated, eruptive movements begin.
Nolla (1960), incorporating the previously noted four
stages, described ten stages of tooth development. Permanent
teeth do not begin to erupt until after their crowns are
complete (Nolla stage 6). Eruption may be described as a
predominantly vertical movement of teeth from their sites of
development inside the jaws, until their crowns eventually
establish a functional occlusion (Moss-Salentijn and
Hendricks-Xlyvelt, 1985).
Various theories which attempt to explain dental eruption
have been proposed, studied and debated (Melcher and
Beertsen, 1977). These include theories such as root growth,
pulp growth, tissue fluid pressure, bone growth and the
periodontal fibres creating a pulling force on the erupting
tooth (Longmore and McRae, 1985; DuBrul, 1988).
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Alveolar bone is formed during the development, and
especially during the eruption, of the teeth. Alveolar bone,
which comprises the sockets in which the roots of the teeth
are suspended, is part of the bone of the jaws. There is no
sharp line of division, and one can only designate bone
arbitrarily as being part of the alveolar or basal bone of
the jaws. This division is in fact based on clinical
experience. When an individual becomes edentulous his
alveolar bone is gradually lost or, in an anodontic sUbject,
is never formed. Only basal bone remains when the teeth are
absent and it is thus clear that alveolar bone is entirely
dependent on the presence of teeth for its existence.
Alveolar bone allows for movement of teeth, whether this
movement is due to active eruption, mesial drifting or
remodelling as part of orthodontic tooth movement. The
correct positioning of the teeth during orthodontic movement
is imperative as this will influence the morphology of the
interdental septae and shape of the alveolar crests,
parameters frequently used as indicators of periodontal
health (Moss-Salentijn and Hendricks-Klyvert, 1985).
The secondary dentition is made up of 16 upper and 16 lower
teeth. All teeth are longest mesicdistally near their
occlusal thirds while they tend to be broadest
buccolingually near their cervical thirds. The mesiodistal
dimension ensures a continuous line of interdental contact,
establishing the unity of the dental arch. At the same
time, the narrowing of the teeth in the cervical region
provides space for the interproximal alveolar bone and
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154
gingival soft tissues. The buccolingual bulging of the
dental crown near its cervical third provides a sheltering
overhang that protects both the thin crests of alveolar
bone and its covering gingivae which fit tightly around the
necks of the teeth (DuBrul, 1988).
The establishment of certain occlusal relationships have
been described by Baume (1950) and Friel (1927, 1954). They
related the establishment of a Class I occlusion (Angle,
1899, 1907) to the mesial movement of teeth and the forward
growth of the mandible. Diet can playa significant role in
this regard. A diet which includes coarse, rough food such
as is consumed by the Eskimos and North American Indians for
example, would tend to eliminate cuspal interferences and
thus permit an easier forward movement of the mandible. An
edge to edge incisor relationship can easily result in
ethnic groups which manifest severe dental attrition. Begg
(1977) based his treatment philosophy on the severe dental
attrition which may be found in the Australian Aborigines.
The concept of "normal occlusion" which implies variations
around an average or mean value, is fundamental to
orthodontic diagnosis (Moyer~, 1988). Any deviation from
this "normal occlusion" which is a hypothetical concept or
goal, has traditionally been termed a malocclusion (Moyers,
1988). Ideal occlusion rarely exists in nature, and is
therefore sometimes termed the imaginary "normal" (Proffit,
1986). As there is no universally acceptable definition of
"ideal occlusion", diagnosis in orthodontics is based on a
concept of the ideal. Occlusion can be defined as lithe
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normal fit of the teeth when they are brought together"
(The Shorter Oxford English Dictionary, 1975).
Articulation is therefore a function of feeding during which
opposing dental arches are ultimately brought into contact
by rhythmic cycles that prepare food for swallowing. A
fundamental understanding of all aspects of occlusion is
necessary to achieve orthodontic treatment goals which
include optimal facial aesthetics acceptable to the
subject's social environment, optimal dental aesthetics,
optimal functional occlusion, optimal oral health and
stability of treated results.
7.1.2 Characteristics of a static occlusion
Andrews (1972) described "six keys to normal occlusion" as a
measure of the static occlusal relationship which may be
used to evaluate the success of orthodontic treatment. The
keys included evaluation of the molar relationship, crown
angulation (mesiodistal tip) and inclination (labiolingual
or buccolingual "torque"), rotations, tight interproximal
contacts and a normal Curve of Spee. These qualities were
considered meaningful as they were all present in each of
120 non-orthodontic normals, and the lack of even one of the
six keys was a defect predictive of an incomplete end result
in treated subjects. Most orthodontists accept Andrew's
static tooth alignment as the primary objective in the
orthodontically treated dentition. A fUlther of this "normal
occlusion" is that the teeth reach maximum intercuspation
with the condyles in centric relation position (Andrews,
1972; Aubray, 1978).
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The relationship of the mesiobuccal cusp of the upper first
molar to the buccal groove of the lower first molar (Angle,
1899, 1907), irrespective of its shortcomings, is used to
classify dentitions in everyday orthodontic practice
(Chapter V). Ricketts et 01. (1979) provided a check list of
requirements to which an ideally treated dentition should
conform. Amongst these requirements are the occlusion of the
upper second premolar with the mesial marginal ridge of the
lower first molar as an indication of a Class I occlusion,
and the correct mesiobuccal rotation of the maxillary first
molar which allows for the alignment of the distobuccal and
mesiolingual cusp with the distal third of the respective
opposite maxillary canine. Ricketts (1969) also suggested
that the lower first molar should be rotated in a
mesiobuccal manner which would allow its distobuccal cusp to
contact the middle of the mesial marginal ridge of the lower
second molar.
7.1.3 Functional occlusiQn
FunctiQnal QcclusiQn refers tQ a state Qf the QcclusiQn in
which:
i) the Qcclusal surfaces are free Qf interferences to
allow fQr smoQth gliding mQvements Qf the mandible,
ii) there is freedQm for the mandible to clQse Qr tQ be
guided intQ maximum intercuspation in centric
occldsiQn, and
iii) Qcclusal CQntact relatiQns cQntribute to Qcclusal
stability (Ash and RamfjQrd, 1982).
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The movement of the mandible is dictated by the condyl•• ,
via the articular discs, against the slopes of the glenoid
fossae and the articular eminences. Any conflict l:ctween
condylar positions and tooth positions may induce
pathological responses in the neuromuscular system
surrounding the temporomandibular joint (AUbrey, 1978).
In order to achieve a functional occlusion, centric
occlusion and centric relation should coincide. Teeth should
function according to a mutually protected scheme with no
interferences which could cause the mandible to detour
excessively in order to prevent damage to teeth (Roth,
1981). centric relation should be the starting point for all
treatment decisions (AUbrey, 1978). Procedures to record
centric relation and to transfer measurements to
articulators were discussed by Chiappone (1975, 1977). The
manipulation technique described by Aubrey (1978) or any
other which is compatible with the neuromuscular system,
should be carried out at each orthodontic visit. When
initial contact is reached, manipulation stops and the
subject's true occ~.usal relationship, centric relation
occlusion, is observed.
All jaw movements take place within certain boundaries
which can be traced as envelopes of movement in the
sagittal and horizontal planes (Posselt, 1952).
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7.1.4 concepts of functional occlulion
158
Three major concepts of occlusion have been described in the
literature; bilateral balanced occlusion (Von Spee, 1890),
unilateral balanced occlusion (group function) (Mann and
Pankey, 1960; schuyler, 1935) and mutually protected
occlusion or canine disclusion (D'Amico, 1958; Williamson,
1976; Roth, 1981). Bilateral balanced occlusions, although
acceptable for complete dentures, are not easily accepted by
natural dentitions (Celenza and Nasedkin, 1978). Unilateral
balanced occlusion was introduced for application in
periodontics and restorative dentistry. The importance of
canine function or mutually protected occlusion only gained
popUlarity from the 1950's. The mutually protected occlusion
is considered the ideal not only for the natural untreated
dentition (D'Amico, 1958), but also for the post-orthodontic
occlusions (Roth, 1981).
While the anterior teeth are important for good occlusal
integrity (McHorris, 1979), the canines can be considered
nature's stress breakers as canine contact in lateral
excursion causes an immediate break in the tension of
temporal and masseter muscles. Canines have a higher minimal
lateral threshold than do the other teeth. There are
indications that canine-protected (mutually) occlusions have
signif' ~antly less periodontal trauma than the other
funtional groups. To achieve anterior disclusion all the
anterior teeth must be established in positions resistant to
change. Harmony between condylar disclusion and anterior
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disclusion results in effortless, physiologic mandibular
movements (~cHorris, 1979). Bell and Harris (1983) 8Ugg••tad
"that the angulation of the 'articular eminence may be u.ad
as a guide for the orthodontic placement of the maxillary
incisor teeth. Various ideal positions have been described
for the anterior teeth (Downs, 1948; steiner, 1953; Tweed,
1966; Moyers et al., 1976; Ricketts, 1981).
The posterior teeth must stop closure of the mandible when
in function and thus prevent hard contact of the anterior
teeth. McHorris (1979) described the various interocclusal
contacts and advocated elimination of the anterior component
of force by proper organization of these posterior
interocclusal contacts.
7.1.5 Regyisites for an ideal functional occlusion at the
end of orthodontic treatment as a
temporomandibular disorders
precaution against
The occlusal parameters essential for functional occlusion
may be described as follows (Dawson, 1974):
i) stable centric contact points on all teeth which
evenly distribute the stress
attrition will occur and
of occlusion. Less
the centric contact
points prevent over-eruption of teeth.
ii) anterior guidance which harmonises with the
functional border movements.
iii) disclusion of posterior teeth should occur in
protrusive movements.
iv) disclusion on the balancing side should occur
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during lateral mandibular movements.
v) no posterior interferences should be present on
the working side.
Three areas constantly creating occlusal interference are:
a hanging palatal cusp especially of the upper second
molar, the oblique ridge and hanging palatal cusp of an
upper first molar, and the mesiobuccal incline of the
lingual cusps of premolars (Dawson, 1974).
A stable jaw relationship should have slight freedom in
centric occlusion, i.e. the mandible should not slide when
closing in centric position, but should be able to move from
centric relation (CR) to centric occlusion (CO) (less than
lmm) (Timm, Herremans and Ash, 1976). Gnathologic
assessment of post-treatment orthodontic subjects produced
controversial findings. Orthodontists are often criticized
for failing to achieve a stable centric relation occlusion
(CO=CR). Equilibration is suggested as part of the
post-treatment detailing (Timm, Herremaps and Ash, 1976),
but care must be taken against indiscriminate equilibration
where ideal orthodontic detail was not achieved during
treatment (Roth, 1981). Roth (1981) noted that
equilibration should not be performed until growth is
completed. Research results are confusing d~ untreated
control groups show CO-CR differences (Sadowsky and BeGole,
1980; Sadowsky and Polson, 1984) and pre-treatment COaCR
differences returned after active orthodontic treatment
(Johnston, 1988). Studies in favour of orthodontic treatment
are those of Rinchuse and Sassouni (1983) which showed no
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differences in the number, location or severity of balancing
or protrusive contacts between the occlusions of .Ubject.
following orthodontic treatment and those subjects who had
no orthodontic treatment, but with ideal static occlusion.
No association between extraction treatment and posterior
condylar position was found following treatment (Gianelly,
1989).
In the 1980's, articles in various journals suggested that
orthodontic treatment might play a role in initiating
temporomandibular disorders. Litigation was the order of the
day. On the other hand, it was also claimed that orthodontic
treatment might be effective in alleviating the signs and
sYmptoms of temporomandibular disorders, but it is apparent
from the abovementioned that orthodontists should not
expect temporomandibular symptoms to disappear during
treatment (Machen, 1989). All the controversy surrounding
the occlusion and temporomandibular disorders resulted in
the initiation of a research program by the American
Association of Orthodontists to determine the risks and
responsibilities involved in orthodontic treatment. The
scientific evidence from this research program enabled
Behrents and White (1992) to make the following conclusions:
i) consistently significant associations between the
structure (dental and osseous) and
temporomandibular disorders do not exist,
ii) the development of temporomandibular joint disorders
cannot be predicted,
iii) no method of temporomandibular joint disorder
prevention has been demonstrated,
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iv) the prevalence of temporomandibular di8order8
increases with age: thus temporomandibular joint
disorders may originate during orthodontic
treatment, but may not be related to the treatment,
v) orthodontic treatment per se does not initiate
temporomandibular disorders,
vi) evidence favours the benefits of orthodontic
treatment; orthodonitcs, as a part of the regimen of
care, may assist in the lessening of the symptoms,
and
vii) once temporomandibular disorders are present, its
cure cannot be assumed or assured.
are closed, rotations are
are parallelled near extraction
proper cusp interdigitation is
vii)
According to Alexander (1986) active orthodontic treatment
is complete:
i) when there is coincidence of centric relation &~d
centric occlusion.
ii) when a Class I canine relation with normal canine
function is present.
iii) if the lower intercanine width is maintained.
iv) when normal inter-incisal angle, overbite, overjet
and correct anterior torque are established.
v) when normal posterior overbite and overjet al~
present.
vi) when there is a levelled curves of Spee in the
dental arches.
when all spaces
eliminated, roots
sites and when
achieved.
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AS teeth will move after appliance removal. orthodontists
must incorporate a certain measure of overcorrection of
tooth positions (Roth, 1981). Parameters which may change
after treatment include deepening of the curve of Spee,
mesial tipping of teeth (teeth distally tipped during
treatment will tend to settle better than teeth already
mesially inclined) , rotaOl' i.:»n and tipping of teeth into
adjacent extraction sites and the fact that maxillary
lingual cusps tend. to migrate downwards until they find an
occlusal stop against opposing teeth.
In order to understand the occlusal changes which occur
during orthodontic treatment, orthodontists must have
insight into dimensional changes which occur in dental
arches during the normal growth of individuals who have not
undergone orthodontic treatment.
7.2 Normal growth of the dental arches
7.2.1 Arch width
Arch width growth is almost totally due to alveolar process
growth since there is little skeletal width increase at the
time of tooth eruption (none in the mandible) (Moyers,
1988). Width changes are significantly different in the
maxilla and the mandible. Dental arch width increases
correlate strongly with vertical alveolar process growth,
the direction of which is different in the upper and in the
lower arches (Moyers et 01., 1976). The maxillary alveolar
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164
processes diverge while the mandibular alveolar proc•••••
are more parallel. These morphological features allow for
more maxillary increase in" width during growth. Maxillary
arches can thus be more easily altered during treatment
(Moyers, 1988). Dental arch width increases are closely
related to the events of dental development (Moyers et 01.,
1976).
The intercanine width in the mandible increases only
slightly as a result of a distal tipping of the primary
cuspids into the primate spaces when the secondary incisol'S
erupt. It does not widen significantly thereafter. The
maxillary cuspids are placed further distally in the arch
than their primary predecessors and erupt pointing mesially
and labially allowing for more widening than is possible in
the mandible (Moyers, 1988). Intercanine width and its
immutability have long been the sUbject of heated
discussions in the orthodontic literature (Angle, 1907;
Lundstrom, 1925; strang, 1949). Intercanine width was
investigated and found t~ show a rapid increase from six to
nine years of age, corresponding with permanent incisor and
canine eruption (Barrow and white, 1952; Moorrees, 1959 and
Sillman, 1964). From ten to twelve years there iB a decrease
in intercanine width, which then remaines stable according
to Moorrees (1959), but which, according to the other
authors continues to decrease. There were small decreases
in intercanine width, with the most significant change
occurring in females from thirteen to twenty years, but in
general this dimension was shown to be very stable in males
(Sinclair and Little, 1983). Post-retention studies of
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treated cases have typically shown marked reductions in
intercanine width (Shapiro, 1974; Gardner and Chaconas,
1976; Little, Wallen and Riedel, 1981) . In many cases the
intercanine widths reduced to below their original
dimensions, whereas in a few cases, some nett gain after
expansion was noted (Sinclair and Little, 1983).
Maxillary premolar width increases more than does its
mandibular counterparts as a result of the growth direction
of the alveolar processes noted ealier.
The mandibular first molars erupt with a lingual inclination
irrespective of the fact that i.n this jaw the alveolar
process growth is almost vertical. They do not upright until
after the eruption of the second molars. This uprighting
allows for an increase in bimolar width, but does not
signify an increase in the diameter of the mandible itself.
Furthermore, both first molars move forward at the time of
the late mesial shift to OCL _py any remaining leeway space
and thus assume a narrower diameter along the convergent
dental arch (Moyers, 1988). The mandibular intermolar width
was shown to increase between the ages of nine to fourteen
years in both sexes , but remained constant thereafter
(Moorrees, 1959) . Intermolar width in general appears to
remain very stable with some degree of sexual dimorphism
being present (Sinclair and Little, 1983). A distinct
difference in intermolar width was noted between
nonextraction and extraction therapy groups. The extraction
sample showed a decrease in intermolar width during
treatment which continued during retention, but the
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nonextraction sample maintained, and in some case. .howed
an increase, in intermolar width (Shapiro, 197.). The
nonextraction group resembled a sample of untreated subjects
from the Burlington Growth Centre at the University of
Toronto (Sinclair and Little, 1983).
The only postnatal mechanism for widening the mandibular
basal bony width other than orthognathic surgey is bone
deposition on the lateral borders of the body of the
mandible (Bell, Proffit and White, 1980). All bone growth
occurs by surface addition and orthodontic therapy will not
stimulate bone growth (Fairbank, 1948). Bone deposition
offers little help to clinicians who wish to widen
mandibular dental arches (Moyers, 1988). The same
observation is not true for the maxilla as a result of
differences which occur during alveolar process development.
Where a cross-bite is apparent, maxillary expansion may be
considered as part of a treatment aiming to co-ordinate the
maxillary and mandibular arches (Chaconas, De Alba and Levy,
1977). Maxillary expansion during active growth can be
accomplished with rapid midpalatal expansion appliances
(Haas, 1980) while orthognathic surgery is possible for this
purpose in the adult subjects. A debate has raged since the
nineteenth century between those advocating expansion by a
rapid method (Goddard, 1893) and those who claimed that
expansion should be gained by a slower process, which is
said to be physiologically less traumatic and possibly more
stable (Ferris, 1914). Few studies have followed patients
who were subjected to palatal expansion long-term out of
retention, yet Timms and Moss (1971) found histological
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167
evidence of bony changes as late as 2 years post- expansion.
Herold (1989) found that relapse occured in all patients
having had transverse expansion of the maxillary arch
irrespective of the type of appliance used.
Measurements of arch width dimensions determined in normal
untreated subjects are set out in Tables XXIII and XXIV
(Adapted from Moyers et al., 1976).
7.2.2 Arch length or depth
Although often measured and reported for research purposes,
this parameter does not have the clinical value of the
arch circumference measurement. Changes in arch length or
depth offer only coarse reflections of changes in the arch
perimeter. Sometimes one-half the arch circumference is
referred to as "arch length" (Moyers, 1988). Arch length
decreases with age in both sexes, with the greatest decrease
occurring between nine and fourteen years of age. This
decrease corresponds with the replacement of the deciduous
by the permanent dentition. Arch length remains more or less
constant after fourteen years of age. These observations
were made during a longitudinal study of developing
dentitions between the ages of three and eighteen years
(Moorrees, 1959). In a later study it was shown that the
arch length decrease commenced at age three, after
completion of the erution of the primary dentition, with the
tendency to decrease in length being greater in the mandible
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TABLE XXIII
AGE RELATED MEAN VALUES QF IWIDIBULAR INTEBCANlKE
DIMENSIOlf (mm> FOR MALES AIfD FEMALES(population sample from Moyers et 01 •• 1976>
IW& FEMALE
AGE MEAN S.D. MEAN S.D.
10 24.97 1.32 24.70 0.93
12 25.14 1.73 24.81 1.42
14 24.73 1.45 24.39 1.14
16 24.66 1.68 23.90 1.76
18 24.81 1.27 23.08 2.01
S.D. = Standard deviation
TABLE XXIV
AGE RELATED MEAN vALUES QF MAXILLARY BIMQLA2 DIMENSION (mro)
FOR KALES AND FEMALES(Population sample from Moyers et 01 •• 1976)
HAI& FEKALE
AGE MEAN S.D. MEAN S.D.
10 44.46 2.55 43.52 2.51
12 45.34 2.27 44.54 2.23
14 45.86 2.53 44.32 2.47
16 46.63 2.87 45.01 2.65
18 46.69 2.58 43.94 4.19
S.D. = Standard deviation
TABLE XXV
AGE RELATED MEAN VALUES QF MANDIBULAR ARCH LENGTH CHANGE
(mm) MEASURED MESIAL OF THE FIRST MOLARS(Papulation sample from Moyers et 01,. 1976)
~ FEMALE
AGE MEAN S.D. MEAN S.D.
12 23.75 1.87 23.82 1.38
14 23.93 1.35 22.92 1.89
16 23.42 1.68 21.87 1.68
18 23.02 2.45 21.84 2.37
S.D. = Standard deviation
168
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(Moorrees and Chadha, 1965; Moorrees, Lebret and Kent,
1979). Changes in arch length were determined in 3u~ject.
during adolescence and early adulthood and found to decrease
with age (Brown and Daugaard-Jensen, 1951). A decrease in
the incisor-canine circumference which was noted from three
to eighteen years was associated with a decrease in arch
length rather than a narrowing in arch width (Moorrees,
1959; DeKock, 1972). In another study a constant decrease in
arch length was shown from the mixed dentition phase into
early adulthood (Sinclair and Little, 1983).
Measurements of arch length changes related to different age
groups in normal untreated subjects are set out in Table XXV
(Adapted from Moyers et al., 1976).
7.2.3 Arch circumference or perimeter
The arch circumference dimension is important as it
provides the space to accommodate the dentition. An observed
continual reduction in mandibular arch circumference (Moyers
et al., 1976) during the different phases of dental
development is the result of:
i) a mesial shift of the first permanent molars into
the leeway space,
ii) mesial drifting of the posterior teeth throughout
life,
iii) interproximal wear of teeth due to diet and
function,
iv) lingual positioning of the incisors as a result of
differential mandibular-maxillary growth,
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v) the original tipped position of incisors and molar.
(Moyers, 1988),
vi) interproximal caries and early loss of primary
teeth (Northway, 1977).
vii) pressure from the third molars during their
eruption (Moyers, 1988).
A negative discrepancy between the sum of the mesiodistal
tooth dimensions and the arch circumference is noted as a
space shortage which is a common problem in many
malocclusion. The Little Irregularity Index is an
appropriate indication of lower incisor crowding (Little,
1975).
Incisor crowding/irregularity
Lower incisor crowding appears in 30,6' to 47,0' of the
population (Mansbach, 1938; Lieb, 1962). The incidence of
incisor crOWding as shown in a longitudinal study is
virtually zero in the maxilla at age six years, but
increases to 24% by the age of fourteen years. The frequency
of mandibular incisor crowding is said to increase from 14'
at six years to 51% at fourteen years of age (Barrow and
White, 1952). Cryer (1966) found an incidence of lower
incisor crowding of 621 at fourteen years of age and in 601
of these there was an increase in the severity of incisor
crowding after the age of eleven years. The cause of lower
incisor crowding is generally ascribed to a discrePancy
between mesiodistal tooth width and the size of the
available supporting bone (Doris, Bernhard and Kuftinec,
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171
1981; HOW6, McNamara and O'Connor, 1983). A cross-sectional
study (Foster, Hamilton and Lavelle, 1970) showed a
different pattern. They found spacing in the mandible at age
three, but by seven years of age there was a 701 incidence
of crowding and this value increased to 90% by fourteen
years and then decreased somewhat by age twenty-five, with
females having more crOWding than males despite the greater
average size jf the male dentition. Moorrees (1959) observed
a slightly different pattern, showin~ considerable crowding
in the eight to ten year age group. This phase corresponds
to the eruption of the permanent canines. According to
Moorrees (1959) the crowding decreases between twelve to
fourteen years of age and then increased again from fourteen
to eighteen years of age. Bjork and Skieller (1972)
suggested that incisor position may be correlated to the
amount and direction of facial growth. A significant
correlation was found between increases in incisor crowding
and decreases in arch length with age (Lundstrom, 1969).
Incisor irregularity increases from thirteen to twenty
years of age with females exhibiting more incisor
irregularity than males at the adult stage (Sinclair and
Little, 1983). Lower incisor crowding tends to occur in
malocclusions which are primarily dental in nature and in
those with atypical skeletal patterns (Miethke and
Behm-Menthel, 1988).
There are a number of factors which relate to lower incisor
irregularity (Wilson, 1967). An evaluation of the causes of
lower incisor irregularity points to the complexity of the
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factors involved in this important problem. The factor. are
as follows:
i) a disproportion of tooth to bone size relationship.
may occur.
ii) irregularity increases with an increase in bite
closure.
iii) oversized individual teeth reflect congestion in an
anterior direction and may thus cause irregularity.
iv) a reduction of intercuspid width due to a premature
loss of the deciduous cuspids, as well as a
supra-eruption of the lower cuspids due to a late
eruption of the upper cuspids causing lingual
deflection of the lower cuspid teeth.
v) a mesial, or lingual, inclination of the upper
cuspids which cause the lower cuspids to deflect
lingually.
vi) variations in lateral excursion of the mandible may
result in a lingual inclination of the lower
cuspids.
vii) in full cusp Class II cases the lower cuspids
assume an upright position with straight lower
incisors because of the greater width permitted by
the wider embrasures between the maxillary cuspid
and the first bicuspid in the Class II
relationship. In contrast, in a half cusp Class II
molar relationship the restriction in lower
intercanine width when the cuspids are in a cusp to
cusp occlusion, causes the lower cuspids to
occlude with the heavy cingulae of the upper
cuspids and in so doing reduce the lower
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173
intercuspid width by .everal millimetr••• A Cla••
I relationship places the cuspid in an upright
position because of the occlusion within the
embrasures which is similar to the full cusp Cla••
II.
viii) rotations of maxillary central and/or lateral
incisors have a restrictive effect upon the lower
incisor teeth.
ix) the presence of heavy anatomical ridge. on the
upper incisor teeth.
x) a deflection of anterior teeth due to a mentalis
hyperactivity or certain tongue habits.
xi) the presence of a marginal Class III tendency in a
Class I occlusion with the forward mandibular
pressure causing a slight condensation of the lower
incisors.
xii) a tight restrictive upper lip with
small upper lateral incisors
constriction of the upper arch in
the normal lower arch.
the presence of
resulting in a
the direction of
7.2.5 Dimensional changes during orthQdontic treatment
It is far easier to bring about changes in the maxilla than
it is in the mandible. An increase in maxillary dental arch
width and/or length is relatively simple to accomplish, but
difficult, if at all possible, to attain in the mandible.
There are a variety of means used to i.ncrease arch
perimeters in certain maloccIus ion"'_ , including lip bumpers,
utility arch wires, functional appliances and headgear wear.
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These appliances have limited application in the mandible
and success is usually only noted when specific condition.
favour the use of an appropriate appliance. Pew mandibular
arch circumferences can be lengthened permanently and there
are no magic appliances for doing so. Success is only
secured when alteration of muscle function and/or the
positions of teeth within the alveolar process is safely
possible (Moyers, 1988).
7.2.5.1 Comparison of untreated to treated subjects
Maturational changes in the permanent dentitions of a sample
of untreated individuals (Class I) appeared, in general to
be similar in nature, but significantly less in extent, than
changes observed in similar parameters examined in a
post-retention Angle Class I sample of treated subjects
(Little, Wallen and Riedel, 1981). Both samples were
examined by the same observer using the same methodology.
The treated group underwent first-premolar-extractions at a
mean age of thirteen years, followed by routine
comprehensive edgewise mechanotherapy and retention
(Sinclair and Little, 1983).
7.2.6 overbite and overjet
These variables undergo significant changes during the
development of the occlusion. From the early mixed dentition
phase to the completion of the adult dentition the average
overbite increases slightly and then tends to decrease
again, while the overjet shows a continual decrease (Moyers
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175
et 01., 1976) (Tables XXVI and XXVII as adapted from Moyer.
et al., 1976). Overjet and overbite typically increase from
nine to thirteen years of age, then decrease from thirteen
to twenty years of age, resulting in minimal overall
changes. These changes are in contrast to the post-retention
results of treated cases which show a tendency towards on
increase in overbite (Sinclair and Little, 1983). OVerbite
is correlated with a number of vertical facial dimensions
(e.g., ramus height), whereas overjet usually is a
reflection of the anteroposterior skeletal relationship
(Fleming, 1961). Overjet is also sensitive to abnormal lip
and tongue function (Proffit, 1986).
7.3 Correlation of untreated normal occlusions with other
dentofacial and skeletal dimensional variables
(Predictability)
Mandibular incisors that are more labially inclined
pre-treatment are associated with less long-term crowding
(Sanin and Savara, 1973; Gilmore and Little, 1984). While
being only a weak predictor (r = 0,45) of long-term
crOWding, the pre-treatment facial pattern that emerges as
having a tendency for greater long-term incisor irregularity
is a divergent face with wide, upright incisors (Gilmore and
Little, 1984). At post-treatment or over the long-term,
subjects that were less retrognathic tend to have less
lower incisor irregularity (Norderval, Wisth and Boe, 1975;
Gilmore and Little, 1984).
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TABLE XXVI
AGE RELATED MEAN VALUES OF OVERBITE CHANGE (gup)
FOR MALES AlfD FEMALES
(Population sample from Moyers et 01 .. 1976).
HAI& FEMALE
AGE MEAN S.D. MEAN S.D.
10 3.13 1.79 2.83 1.61
12 3.45 1.73 3.13 1.32
14 3.45 1.71 2.87 1.48
16 2.83 2.02 2.97 1.54
18 3.05 1.55 3.03 1.69
S.D. = Standard deviation
TABLE XXVII
AGE RELATED MEAN VALUES OF OVERJET CHANGE (gup) FOR MAI,ES
AND FEMALES (Pgpulation sample frgm Moyers et 01., 1976)
HAI& FEMALE
AGE MEAN S.D. MEAN S.D.
10 4.01 1.99 3.24 2.10
12 3.91 1.83 3.27 1.84
14 3.48 1.49 2.97 1.50
16 3.14 1.83 2.97 1.69
18 3.16 1.05 2.45 2.60
S.D. = Standard deviation
176
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177
A correlation between lower ant: 'oft lor crowding and the growth
vector of the mandible was ~itod by Fisk (1966). He believed
that a prediction of arch form, final tooth position, and
the available space is possible only if the relationship
between the skeletal growth pattern and development of the
dentition is known.
Lundstrom (1975), however, found no correlation amongst
arch dimension changes in the developmental stage, changes
in the incisor position within the mandible, and direction
of mandibular growth.
~~ny other factors are involved in the phenomenon of incisor
crowding. Biologic variability, however, may confound even
the most carefully executed study.
The results of a longitudinal study (Leighton and Hunter,
1982) showed that patients with severe mandibular arch
crowding mesial to the first molars (>4.0 mm) have steeper
mandibular planes, greater ANS-PHS to mandibular plane
angles, shorter mandibular bodies, shorter posterior
facial heights, less mandibular size increase between the
ages of nine and fourteen years, and a more clockwise
(downwards and backwards) growth of the mandible. The same
conclusion could be drawn from Bjork's (1963) implant
studies.
Carmen (1978) conducted a
anterior crowding, and its
cases at ages twelve and
serial study of
predictability,
eighteen years.
mandibular
in untreated
The study
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concentrated on data obtained from study models and included
only limited cephalometric measurements. The study showed
that there was no significant relationship between inci.or
crowding, gender nor the Angle classification. Arch length,
canine width and molar width changes were found to be
insignificant factors in controlling crowding, but may
contribute in small measure to a multifactorial relationship
associated with crowding. In the whole sample incisor
irregularity tended to increase with time, but nearly a
third of the cases showed an actual improvement in incisor
alignment. It was concluded thus that no single variable
measured at either observation time, or the change in any
single variable between observations, correlated
significantly with crOWding changes. Attempts to find
correlations between incisor crOWding and other dental and
skeletal features have been somewhat limited due to
difficulties in quantifying incisor crOWding and due to the
apparent multifactorial aetiology of malalignment (Sinclair
and Little, 1983). Sinclair and Little (1983) found that,
when changes in individual dental variables were compared,
no associations or predictors were of clinical value in
predicting incisor crOWding.
7.4 Dentofacial growth and tooth position changes
7.4.1 Incisor positions
with skeletal growth incisors undergo uprighting relative to
the facial plane (Subtelny, 1959). Anterior teeth appear to
be functionally stable within the facial environment and it
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179
was indicated that they did not correlatB with jaw rotation.
(Bjork and Skieller, 1972). Incisor angulation,
superimposed with the cephalometric tracings on the anterior
cranial base, appears to be relatively stable, showing
compensations for skeletal changes, which result in the
maintenance of acceptable occlusal relationships. These
compensating changes are limited to a slight proclination of
the mandibular incisors, while the maxillary incisors
displayed less compensatory movement. Mandibular incisors
show a significant degree of eruption, which correlates
closely with the amount of mandibular growth, during the
change from the mixed to the ~dult dentition. Mandibular
superimposition of cephalometric radiographs (Bjork and
Skieller, 1983) indicates that a forward movement of the
incisors may be correlated with a mesial movement of the
mandibular molars (Sinclair and Little, 1985).
No correlations were found betw6en the parameters reflecting
lower incisor position and factors relating to the amount
and direction of facial growth (Sinclair and Little, 1985).
7.4.2 Molar positions
The effect of positional changes in jaw relationships on the
dentoalveolar structures is considerable. Changes in the
molar position seem to be characteristic of the different
types of facial rotation. Generally a forward (bite-closing)
rotation of the maxilla and the mandible results in a more
mesial path of eruption of the molars (Sinclair and Little,
1985).
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There appears to be a relationship between the amount and
direction of dentofacial growth and changes in occlu.al
features such as overjet, intercanine width and incisor
crowding (Hasund and Sivertsen, 1970; Sanin and Savara,
1973; Lundstrom, 1975; Nordeval, Wisth and Boe, 1975; Nas.,
1981). No significant correlations could be found when
comparing maturational occlusal changes with a variety of
cephalometric variables (Sinclair and Little, 1983, 1985).
This do£s not imply that such correlations do not exist, but
rather, that they were not revealed despite extensive
analysis (Sinclair and Little, 1985).
7.5 Longitudinal occlusal stability
The modern concept of a dynamic individual occlusion
naturaly includes an interest in the stability of the
occlusion before, during and after orthodontic treatment. A
stable occlusion is dePendent on the resultant of all forces
acting on the teeth. Adjustment of tooth position occurs
throughout a person's lifetime in response to naturally
induced changes of occlusal forces associated with wear, in
response to pathologic changes in the support mechanism or
muscle tonicity, and following dental procedures such as the
placement of restorations. However, within the adaptive
capacity of the masticatory system, a balance of force is
maintained (Ramfjord and Ash, 1960).
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The patterns of forces that act on the teeth are far more
complex than usually conceived. Research in this regard t.a.
been directed toward magnitude of biting forces (Black,
1895; Adler, 1947; Anderson, 1956), the orthodontic a.pect.
of tooth mechanics (Halderson, Johns and Moyer., 1~53;
Burstone, Baldwin and Lawless, 1961), equilibriua of teeth
relative to their biologic environment (Haack and Wein.tein,
1963; Weinstein et al., 1963; Dempster and Duddle., 1964),
tooth mobility (Muhlemann, 1960; Parfitt, 1960) and tilting
movements (Picton, 1962). Few deductions can be made fra­
these studies that are of direct practical value for the
stabilization of teeth by occlusal adjustment or other
dental procedures (Ramfjord and Ash, 1966).
7.5.1 Lower incisQr relapse
studies evaluating interproximal enamel reduction also
report conflicting findings. Peck and Peck (1972a) coabined
mesiodistal (ND) and faciolingual (FL) dimension. into an
index (MD/FL X 100) and recommended mesiodistal width
reduction Qf incisors to place them in an ideal size range
to prevent future crowding. They stated that the aaxi.ua
faciQlingual dimensiQn of the mandibular incisQrs was Qften
found subgingivally and, therefore, plaster casts could not
be used tQ measure this dimension accurately (peck and Peck,
1972a; 1~10). A very close agreeMent between the intraoral
and study cast faciQlingual dimensiQns Qf the lower incisors
measurements were, however, indicated by Gilmore and Little
(1984). Edwards (1970) and Boese (1geO) suggested ~~at a
combination of reshaping of incisor contacts ~d an
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incising of 8upracrestal gingival fibre9 be used to prevent
post-treatment crowding, especially after the correction of
dental rotations. Rye (1983) found 23' rotational relapse in
a fiberotomized sample compared with a 39' relapse rate for
a nonsurgical group. Little, Riedel and Artun (1988) showed
in a study of mandibular incisor stability that 61' of
dental rotations which have been corrected do not relapse.
Their preliminary results indicate that rotations often
relapse in spite of circumferential supracrestal fiberotomy
(CSF) procedures and conversely that rotations might not
recur even in the absence of CSF. Slight reductions of the
mesiodistal dimensions of mandibular incisors to correct
in~isor irregularies may be a rational clinical procedure,
but some evidence (Gilmore and Little, 1984) suggests that
there is little reason to reduce incisor wilths to establish
long-term stability of mandibular incisor alignment.
statistical tests to show relationships between the
"irregularity index" (Little, 1975) and the "MD/FL index"
(Peck and Peck, 1972a) of the dimensions of the mandibular
central and lateral incisors clearly demonstrate that only
weak associations exist betwaen these variables (Gilmore and
Little, 1984).
Little, Wallen and Riedel (1981) concluded that stability
of the anterior mandibular se~nent (minimum of ten years
post-ret~ntion) '~as variable and unpredictable. Success
with the maintainance of satisfatory mandibular anterior
teoth alignment is lese than 30% with nearly 20% of the
cases likely to show marked crowding some years after
removal of retention appliances.
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studies which have incorporated cephalometric analy.e. in
combination with incisor measurements have not substantially
increased the predictability of incisor crowding (Sanin and
Savara, 1973; Norderval, Wisth and Bee, 1975; Keene and
Engel, 1979). During a cephalometric appraisal of subjects
who had undergone first-premolar-extraction treatment
Shields, Little and Chapko (1985) found that mandibular
alignment was unpredictable; no cephalometric parameters
such as maxillary and mandibular incisor proclination,
horizontal and vertical growth amounts, mandibular plane
angle, etc. were useful in establishing a prognosis for
relapse of lower anterior alignment.
Sadowsky and Sakols (1982) and Uhde, Sadowsky and BeGele
(1983) presented a more optimistic view of post-retention
results. The difference in opinion may be due to differences
in the appraisal of the mdasurement techniques by the two
research groups Little, Wallen and Riedel (1981) and Little,
Riedel and Artun (1968).
7.5.2 Growth cessation and relapse
Sinc~ orthodontists have assumed that once facial growth
ceases, dento-occlusal changes (relapse) wil~ be minimal and
therefore that continued retention may not be necessary.
Little, Riedel and Artun (1988) using the Little
Irregularity Index (Little, 1975) shows that changes in
the occlusion continue, at varying rates, we:l beyond the
point of growth cessation. They found that one factor was
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consistently predictable; the continuing decr~~.;e in
mandibular arch length which occurs with time following the
removal of retainers.
7.5.3 Spacing of teeth and relapse
In an ass~ssment of subjects who had been out of retention
for a minimum of ten years and who had displayed generalized
spacing of their anterior teeth prior to treatment, Little
and Riedel (1989) showed a consistent reduction of their
arch lengths and intercanine widths into their adult years.
The incidence of post-retention clinically unacceptable
malalignement was lower for the sample with pre-treatment
dental spacing.
7.5.4 Maxillary crossbite correction and relapse
The outcome of treatment with various types of appliances to
correct buccal crossbites by maxillary expansion and
separation of the maxillary halves are recorded by
Mossaz-Joelson and Mossaz (1989). The more physiologic
sutural adjustment produced by slow maxillary expansion
(SME) appliances result in a more stable increase in
maxillary width (Storey, 1973). Palatal expansion is more
stable when treatment is initiated at an early age
(Skieller, 1964; Melsen, 1972, 1975; storey, 1973; Mew,
1983), with slow expansion procedures (Skieller, 1964;
Storey, 1973; Cotton, 1978; Hicks, 1978; Mew, 1983) and with
prolonged retention (Thorne, 1960; Timms, 1976; Haas,
1980). Further, stability decreases with an increase in the
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width of the expansion (stockfish, 1969). Long-term studies
warn again of the effects of cumulative relap.e over
extended post-treatment periods (Krebs, 1964; Linder-Aronson
and Lindgren, 1979). A tendency towards a decrease in the
width of the dental arches, four to five years following
rapid maxillary expansion (RME), was reported by Krebs
(1964). Krebs (1964) found that with conventional
jackscrew appliances, skeletal (sutural) expansion was only
equal to half of the palatal expansion achieved by the end
of th~ active RME phase. Only 45% of the width of the
palatal expansion achieved with RME was maintained 5 years
post-retention (Linder-Aronson and Lindgren, 1979). These
findings are in agreement with the observations made by
stockfish (1969) who found a 50% relapse in width in his
sample within five years following appliance removal. Hicks
(1978) stipulated that only eight weeks of fixed retention
was required folloWing this type of expansion and did not
recommend removable retainers. Rocke et ale (1980) found
less relapses occurred in crossbites treated by executing
rapid maxillary expansion.
Mossaz-Joelson and Mossaz (1989) used removable retainers
for 12 weeks following palatal expansion. The correction of
the crossbite was maintained even though an average relapse
(30%) occurred. The slow rate of expansion, 8 mm during
three months, compared to 8 to 10 mm during one month for
conventional RME could be responsible for the post-expansion
stability achieved by Mossaz-Joelson and Mossaz (1989).
Their data, however, remain to be confirmed by a long-term
study. The studies of Krebs (1964) and Linder-Aronson and
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Lingren (1979) show that intercanine expnnsi~n rela~aes to
a greater extent than does the intermolar width. This
~inding was confirmed by a longitudinal ~tudy on eight
t'!acaca fascicularis monkeys (Vardimon, Gr~bf:::' and Voss,
1989). They used tantalum implants inserted along the facial
sutures and dental markers (0,018" s.s. wire) bonded along
the buccal crown surfaces of the upper canines and upper
molars in order to be able to make their conclusions. They
found that the gain in intermolar width exceedud the gain in
intercanine width by the end of the relapse phase. The
greater the buccal tip of the canine during expansion, the
greater the intercanina width relapse.
The last mentioned authors could not entirely explain why
buccal tooth tipping in the molar area, as a result of RME,
produced a stable intermolar width expansion. A second
factor which seems to determine the stabilty following
expansion is the selective activity of the circummaxillary
sutures.
Vardimon, Graber and Voss (1989) mention intercuspation and
muscular pressure as other causitive factors likely to
affect canine vs. molar interarch stability. Unlike molar
expansion, canine transverse expansion recieves no
antagonistic support from the lower arch. Additionaly, the
increase in tension of the circum-oral musculature, as a
result of the RME (Graber, 1972), essentially acts on the
intercanine width.
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A low force slow palatal expansion regimen can be of
substantial benefit in young patients with transverse
maxillary deficiency. Even with slow expansion a 401
overcorrection in intercanine expansion may be required
(Vardimon, Graber and Voss, 1989).
7.5.5 Mandibular arch expansiQn and relapse
The mandibular intercanine width remaines unchanged or
decreases during adolescent growth and can thus not be
changed during treatment without a tendency to relapse
(Strang, 1949; Magill, 1960; Gardner and chachonas, 1976;
Riedel, 1976; Berg, 1983). According to Moorrees(1959) the
mandibular intercanine width reaches its maximum with
eruption of the permanent canines and then decreases
slightly with increasing age. The mandibular intercanine
width seems to decrease over a long periQd of time a finding
which may be associated with late crowding, both in treated
cases (Haavikko and Backman, 1973; Shapiro, 1974; Little,
Wallen and Riedel, 1981; Ronnerman and Larsson, 1981; Glenn,
Sinclair and Alexander, 1987) and in untreated cases, where
a decrease Qf 0,7 mm was reported by Sinclair and Little
(1983). A decrease of 1,8 rom (treated group) and 1,0 rom
(untreated group) were found in a study by Owman, Bjerklin
and KurQl (1989). In contrast Richardson (1979) reported no
major changes in intercanine width in thirteen to eighteen
year old untreated individuals. Little, Wallen and Riedel
(1981) reported that more than 60% of an extraction sample
shewed an increase in mandibular intercanine width of more
than 1 mm during treatment. FQllowing treatment, however,
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60 out of 65 cases showed an intercanine width decrease. An
important finding of the Little, Wallen and Riedel (1981)
study was that many cases showed post-retention mandibular
intercanine widths which were less than they were at the
start of treatment.
The lower cuspid and molar widths should not be expanded
because of their tendency to relapse (Rocke et al., 1980).
Occasionally a malocclusion presents with extreme incisor
crowding and a narrow intercuspid width. In such an instance
the cuspids may be tipped distally, into the bicuspid
extraction space, which tends to increase the intercuspid
width. In general, if either the cuspid and/or the molar
width have to be expanded, to accommodate all teeth, the
case should be treated by extraction (Rocke et al., 1980).
7.5.6 The relapse of overbite and overjet correction
studies of the long-term results of overbite correction have
reported various degrees, ranging from improvement to
complete relapse, of post-treatment change (Berg, 1983). A
relapse in overbite and overjet of between 25% and 55% has
been reported with the length of the follow-up observation
period varying from one to more than ten years (Ludwig,
1967; Simons and Joondeph, 1973; Lagerstrom, 1980).
The position of teeth in relation to their supporting basal
bone has long been recognized as an important diagnostic
factor in treatment planning (Lundstrom, 1925; Tweed, 1944).
In discussing the stability of overbite correction, the
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mandibular incisor position ~~ays an important rolQ
(Steiner, 1960; Ricketts, 1964; Hasund and Ulstein, 1970).
Changes in position of the mandibular incisor position
relative to the mandibular symphysis, during growth, were
described by Bjork and Skieller (1972). They related this
change to a growth rotation of the mandible which
necessitates a compensatory adaptation in the eruption paths
of the teeth. This adaptation was termed the
dento-alveolar compensatory mechanism (Solow, 1980) and the
concept is used in clinical cephalometries and treatment
planning. By advocating different incisor inclinations for
different sagittal jaw relationships, clinical guidelines
have been developed to use in cephalometric analysis
(Steiner, 1959). As an example; the visualized treatment
objective (VTO) (Ricketts at al., 1979), relates the
mandibular incisor position to the APo line. By using a
cranial base referenced growth axis, the vertical dimension
could be adapted during VTO analysis (Ricketts, 1960;
Ricketts et al., 1979).
By means of a mUltiple regression statistical approach an
average incisor inclination, corresponding to various
combinations of sagittal and vertical jaw relations, was
calculated (Hasund and Ulstein~ 1970). The importancp. of
vertical jaw relationships as being primary factors in
post-treatment overbite and mandibular incisor crowding
relapse has been ascribed to late condylar growth which
occurs without compensatory posterior vertical
dento-alveolar development (Schudy, 1974). The equilibrium
which should exist between the activity of the intra- and
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extraoral muscles is another factor w~ich is of importance
in occlusal stability (strang, 1949; Brodie, 1954). The
form, and growth pattern of the mandible are factors which
influence the stability of overbite correction (Bjork,
1969).
Once incisor contact has been established, a factor which
influences overbite depth is the inclinations of the lower
incisor axes to the the palatal surfaces of the upper
incisor crowns. This relationship is known as the
interincisor angle (Ballard, 1948). Popovich (1955)
investigated the association between the interincisal angle
and overbite depth in class II division 2 subjects and
reported a positive correlation of r = 0,73. Similar
findings were reported by other authors (Backlund, 1960;
Solow, 1966; LUdwig, 1967; Simons and Joondeph, 1973).
Ludwig (1967) and Simon and Joondeph (1973) reported
significant positive correlations between these parameters
prior to treatment (r = 0,52 and 0,45 respectively) but
could only determine low or no correlations post-retention.
In a study of the stability of deep overbite correction
Berg (1983) found that when the interincisor angle was less
than 140 degrees after treatment, it became an important
factor in the amount of overbite stability achieved. Where
incisor contact is not achieved, either because of the size
of the overjet or because there is an open bite, these
dental factors are less important in determining overbite
depth (Houston, 1989).
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Hinrichsen and storey (1968) showed that maxillary expan.ion
could result in an increase of the overjet of the upper
incisors. In such instances a nett maxillary advancement as
a result of the treatment, after deducting growth changes,
was 3,5 mm (Vardimon, Graber and Voss, 1989). They used
interosseous magnetic lateral expansion. A collapse of 1,25
mm in incisor proclination during the relapse phase was
related to the lack of interincisor contact to support the
upper incisor's new position. A similar incisor relapse was
rep~rted by Wertz and Dreskin (1977). Where the incisors
do not meet, they will continue to erupt until a stable
contact which balances the forces of eruption of the teeth
is established. The stability of the incisor contact
ultimately depends on the size of the interincisor angle
(Houston, 1989).
In a Class II skeletal pattern an increased interincisal
angle is usually associated with a deep overbite. In a Class
III skeJ~tal pattern with a similar interincisal angle the
overbite, however, tends to be reduced (Houston, 1989). In
this respect the skeletal pattern is important in its
influence on incisor overbite. Variations in the lower
incis07 inclination may compensate for, or exaggerate, the
effects of the anteroposterior incisor apical relationship.
Houston (1989) suggests thus, in order to attain maximum
overbite stability, the upper root centroid should be at
least two millimetres behind the lower incisor edge. This
distance is represented as the distance between the
perpendicular projections of these points on the maxillary
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192
plane (ANS-PHS). The measurement is positive whenever the
lower incisor edge is in front of, and negative when it is
behind, the upper root centroid.
Overcorrection should be carried out as a precaution against
overbite and overjet relapse (Simon and Joondeph, 1973;
Berg, 1983).
Early treatment may be necessary in malocclusions with an
extreme overjet in order to prevent fracture of the upper
anterior teeth. Early treatment may result in a 10S8 of
patient co-operation due to the long treatment periods
usually involved (Rocke et al., 1980). It may also mask
the severity of a malocclusion due to limited tooth movement
when most of the permanent teeth are still unerupted. This
factor could lead to a nonext~'action treatment regime which
in turn could result in a bimaxillary protrusion at the end
of treatment and eventual relapse (Rocke et al., 1980).
7.5.7 The effect of the third molar on relapse
The role of third molars in post-orthodontic tooth alignment
was described by Dewey (1917). He commented that in some
SUbjects mandibular third molars become impacted due to a
lack of space. In others these molars create space for
their eruption by causing crowding of the anterior teeth.
Since then, numerous investigators have attempted to
determine whether such a correlation exists.
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The presence and eruption of third molars may have an
adverse influence on the stability in the mandibular
anterior region (Bergstrom and Jensen, 1960; Richardson,
1979; Lindqvist and Thilander, 1982). Bergstrom and Jens~n
(1961) studied sixty sUbjects with unilateral molar agenesis
and noted more crowding in the quadrants in which third
molars were present than in those in which third molars were
missing. Sheneman (1968) concluded that patients with
congenitally missing third molars showed a greater degree of
dental stability than those in whom third molars were
present. Schwartz (1975) found a significantly greater
forward movement of first molars, particularly in the
mandibular arch, when third molars were present. He
concluded that mandibular incisor crowding could result from
the sagittal force exerted by erupting third molars.
Several investigators have pUblished data to support their
belief that third molars play very little, if any, role in
causing long-term dental arch changes (stemm, 1961; Shanley,
1962; Lundstrom, 1969). In a post-retention study of 75
orthodontically treated patients Kaplan (1973, 1974) found
that some degree of lower incisor crowding occurred in the
majority of s\wjects. There was, however, no significant
difference in incisor crowding in subjects whose third
molars were bilaterally erupted, impacted, or congenitally
absent. In addition, he found that observed changes in
mandibular arch length and width and in molar and incisor
positions were not significantly different amongst the three
groups. In conclusion, Kaplan stated that the presence of
third molars did not influence post-retention changes in
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194
arch dimension, in tooth position, or in mandibular inci.or
crowding. In a critical review of Kaplan's article (1974),
Schulhof (1976) pointed out that, with a larger sample and
different statistical tests, Kaplan may have found
significant differences between his groups. Rocke et al.
(1980) do not assign much importance to the third molars
(upper or lower) when looking for the cause of relapse.
Mesially inclined lower third molars with the;r crowns
impacted under the distal aspects of second molars, are the
effect of crowding, not the cause. It may just be
coincidental that the third molars often erupt at the same
time that relapse occurs. Perhaps much of this is due to
molar mesial migration occurring at the same time as the
third molars erupt (Rocke ~~., 1980).
Richardson (1980, 1982) found significant mesial movement of
the first molars in a group of subjects with intact dental
arches and this movement correspcnded with an increase in
mandibular arch crowding, which occurred over the same time
period (13 to 17 years). No difference in the amount of
movement, however, was shown between the patients with
impacted, and the patients without impacted third molars.
In the majority of cases some degree of mandibular incisor
crowdiv3 occurs after retention, but the change was not
significantly different between subjects with or without
third molars, suggesting that third molar removal with the
objective of alleviating or preventing long term mandibular
irregularity may not be justified (Ades, Joondeph, Little
and Chapko, 1990).
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At present there is no unanimity of opinion or conclu.iva
experimental evidence as to tha role of third molar. in
upsetting mandibular incisor stability (Ades et al., 1990).
7.5.8 Oxytalan fibres and relapse
Oxytalan fibres were first described in 1958 by Fullmer. A
similarity between oxytalan fibres and elastic fibres was
demonstrated by using specific elastic-fir~e stains
(Fullmer, Sheetz and Narkates, 1974). Edwards (1968)
claimed that following rotational movements of teeth,
oxytalan fibres particularly in the supra-crestal area, were
more numerous and more clearly defined than in control
teeth which were not rotated. The tissue in the
interproximal region is a part of the apparatus that
supports the teeth in relation to the alveolar process, to
the neighbouring tooth as well as to the gingivae. Bowling
and Rygh (1988), however, found no evtdence to sustain the
claim that oxytalan fibres, situa~ed in the transseptal
bundles between adjacent teeth, provide any anchoring
effect. There seem to be no or very little increase in the
oxytalan fibres in the transseptal bundles following
orthodontic treatment. However, the area deep to the
transseptal bundles, but above the alveolar bone crest, was
found to be comparatively rich in oxytalan fibres (BoWling
and Rygh, 1988). The oxytalan fibres present appear to be
associated more with the blood vessels and it was the
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opinion of Bowling and Rygh (1988) that the oxytalan fibre.
were highly unlikely to be responsible for relapse of tooth
movements.
7.5.9 Oral habits and relAPse
A good reason for breaking oral habits, such as
finger-sucking, lies in the fact that they are seldom
conducive to occlusal welfare and little
self-correction (Hughes, 1949).
inclined to
7.5.10 The influence of muscle function on relAPse
Orthodontic failures frequently exhibit faUlty tongue
positions or function (Swinehart, 1950; Baker, 1954).
Normal tongue action plays an important role in the
formation of the permanent dentition. The co-ordinated
function of the tongue, lips, and cheeks maintains a proper
equilibrium of muscle forces during the early stages of
facial growth and this assures harmony in development of the
region. Arch dimension gained through the influences of
normal tongue function tends to remain stable (Swinehart,
1950).
There is no reason to believe that lip pressure influences
mandibular incisor crowding more in treated than in
uni:reated groups (Owman, Bjerklin and Kurol, 1989) • In
support of this contention it was shown that lower lip
res,ting pressure does not differ significantly among the
Angle classes (Thu~r and Ingervall, 1986).
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7.6 Aetiology of relORle following orthodontic treatMent
Many theories have been propoled to explain the aetiology of
relapse and many treatment and retention Itrategie. have
been devised to minimize undesirable post-treatment
changes (Joondeph and Riedel, 1985). U~fortunately many of
these theories and clinical guidelines are based on perlonal
experience and bias, with little or no objective
documentation to support them. The results of longitudinal
studies have started to cast some light on the
post-treatment and post-retention occlusal changes following
orthodontic treatment (Shapiro, 1974; Gardner and Chaconas,
1976; Johnston, 1977; Little, Wallen and Riedel, 1981).
The problem has been the inability to determine whether
these changes occur primarily as a result of the orthodontic
therapy or as part of the normal developmental maturation
process (Sinclair and Little, 1983). Perhaps Horowitz and
Hixon (1969) have best summarized the problem with their
statement, "The significant point is that orthodontic
therapy may temporarily alter the course of these continuous
physiologic changes and possibly, for a time, even reverse
them; however, following mechanotherapy and the period of
retention restraint, the developmental maturation process
resumes. II
7.7 Tooth-size discrepancies in relation to stability
(Bolton discrepancy)
Much research has been devoted to defining the causes of
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198
malocclusion and che prevention post-treatment relapse. One
area which has been examined over the years, with varying
conclusions, has been the association of tooth size with
crowding. It has been found that in cases with crowding
there is a tendency for the incisors to be wider
(Richardson, 1977, 1982) . In those studies in which
statistically significant differences in incisor dimensions
were found between crowded and uncrowded cases, the actual
mean difference has been in the range of 0.25 mm per incisor
(Peck and Peck, 1972b; Swanson, 1973; Norderval, W1sth and
Bce, 1975; Doris, Brenhard and Kuftinec, 1981). Other
similar studies have found no significant ~ifferences in
size between crowded and uncrowded incisors 'i·,.i.lls, 1964;
Keene and Engle, 1979). Correlation coefficients between
incisor dimensions and crowding have been uniformly low (r =
0.46 Lundstrom, 1955; r = 0.42 Fastlicht, 1970; r = 0.42
Lombardi, 1972; r = 0.24 Smith, Davidson and Gipe, 1982 ; r
= 0.42 Gilmore and Little, 1984). Most earlier studies used
samples which received no orthodontic treatment, or if
treated, the measurements were made from the pre-treatment
casts. Tne effects of orthodontic treatment were thus
excluded as well as the possibility that treated subjects
may represent a unique sample. The subjects in many of the
abovementioned studies were young and it is possible that
their well-aligned dentitions became crowded at an older age
(Sinclair and Little, 1983).
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A decrease in intercanine width in combination with larger
tooth size may account for the increased crowding which
occurs in the mandibular anterior region (Owman, Bjerklin
and Kurol, 1989).
A unilateral Class II problem may be a disguised tooth
discrepancy problem. These cases often show high anterior
Bolton tooth-size ratios of 80% or more (Bolton, 1958,
1962). If, in such patients a Class I molar relationship is
attained, the anterior edge-to-edge or slight overbite will
not hold and lower anterior crowding and deepening of the
overbite is likely to occur. This is more than relapse and
an inexperienced orthodontist may find it difficult to
explain the crooked teeth (Swain, 1980).
7.8 Anterior component of force
The importance of an anterior component of occlusal force
was first emphasized by Angle (1907) and Stallard (1923).
The influence of opposing teeth on mesial drift of monkey
teeth was reported by Joho (1973), who found that distally
directed forces on mandibular first molars caused distal
migration of opposing molars. Teeth are normally slightly
mesially tipped and occlusal biting forces may thus create
mesially directed forces on the teeth, a phenomenon known as
mesial drift (picton, 1962; Moss and picton, 1967, 1970;
Moyers, 1988). Orthodontic treatment in the upper jaw only
ending with a class II molar and class I canine
relationship, may create reciprocal forces which are
mesially directed in the posterior segments through
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200
interdigitation and occlusal forces, and are transmitted to
the mandibular arch with resultant increased crowding of the
incisors (OWman, Bjerklin and Kurol, 1989).
7.9 Objectives
There exists no longitudinal data in respect to growth or
orthodontic treatment for this or another similar sample
(Table I). No comparison can thus be made in this regard
with other studies noted previously.
Therefore, the objectives of this part of the study were to
assess the longitudinal changes following orthodontic
treatment in respect of:
i) changes in the occlusion (maxillary teeth to
mandibular teeth).
ii) a possible correlation of these changes with
irregularity of the lower incisors.
7.10 Materials and methods
The basic description of the materials used
employed to assess the data are documented
this thesis.
and the methods
in Chapter 3 of
A brief explanation of the measurements used during this
part of the stUdy follows.
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7.10.1 Moxilla~ teeth
201
The maxillary teeth were studied in terms of:
i) Space shortage in millimetres, in the maxillary arch
(MX CROWD) (Moyers, 1988). Similar measurements were
used in a study by Sadowsky and Sakols (1982).
ii) Bimolar width in millimetres measured between the
centres of the mesiobuccal cusps of the first molars
(U6-6I) as well as measured between the widest points
on the mid-long axes of the mesiobuccal cusp. of
the first molars (U6-6B).
iii) The distance in millimetres measured from the distal
aspect of the upper first molar,
(a) to pterygoid vertical or the most posterior aspect
of the maxilla (PTV) (UM-PTV-MM).
(b) to the centre of the face (CCV) along the facial
axis (UM-CCV-MM) (Ricketts et al., 1979).
iv) Upper incisor cephalometric position measured to:
(a) Nasion-Point A line, angular (I-NA-DE3) and
millimetres (I-NA-MM) (steiner, 1953).
(b) Frankfurt horizontal, angular (I/-FH) (Downs,
1948).
(c) Facial axis, angular (I/-FACAX) (Ricketts et al.,
1979; Engel et al., 1980).
(d) Point A-Pogonion line, millimetres (I/-APO-MM)
(Downs, 1948).
7.10.2 Mandibular teeth
i) Space shortage measured in millimetres to accommodate
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202
the mandibular teeth (MD CROWD) (Moyers, 1988).
Similar measurements were used in a study by Sadowsky
and Sakols (1982).
ii) Curve of Spee measured in millimetres (SPEE) (Moyers,
1988).
iii) Lower intercanine width measured in millimetres from
the centres of the cusp tips (L3-3I) as well as the
most prominent buccal aspects in the mid-axial
dimension (L3-3B) (Moyers et al., 1976).
iv) Irregularity of the lower incisors measured in
millimetres (L-IRREG) (Little, 1975).
v) Arch length/ arch depth measured in millimetres
(ARCHL) (Moyers et al., 1976) as well as the
measurement used by Little (1975) (LITTLE-A).
vi) Lower incisor cephalometric position measured to:
(a) Nasion-Point B line, angular (I-NB-DEG) and
millimetres (I-NB-MM) (Steiner, 1953).
(b) Point A-Pogonion line, angular (I-APO-DEG) and
millimetres (I-APO-MM) (Williams, 1969, 1985;
Ricketts, 1981).
(c) Mandibular plane, angular (IMPA) (Tweed, 1954).
(d) Frankfurt horizontal, angular (FMIA) (Tweed,
1954).
7.10.3 Maxillary and mandibular teeth in occlusion
The ~cclusion was assessed using the following parameters:
i) Overbite measured in millimetres as the vertical
distance between the incisal edges (OBB) and
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203
overjet measured in millimetres as the horizontal
distance between the buccal surfaces of the
maxillary and mandibular incisor teeth (OJB)
(Ricketts et al., 1979; Moyers, 1988).
ii} Cephalometric interincisal angle between the upper
and lower central incisors (I-I) (steiner, 1953).
iii) The Bolton discrepancy between the upper and lower
teeth, canine to canine (BOLTON A) and first molar
to first molar (BOLTON B) (Bolton, 1958, 1962).
iv) The cant of the occlusal plane as an angular
measurement to the Sella-Nasion line (OCC-SN)
(Steiner, 1953).
v) The molar (MOLAR L and MOLAR R) and canine (CANINE L
and CANINE R) relationship (Steiner, 1899, 1907;
Andrews, 1972, 1976) assessed according to a similar
method employed by Sadowsky and Sakols (1982) (Table
II). The variables were noted as described in the
literature being Class I, Class II and Class III.
vi) The malocclusion was classified according to the
Angle classification system (1899, 1907) with
additions as presented by Dewey (Dewey, 1942;
Anderson, 1948).
vii) Crossbite assessment of the anterior (ANTXBIT) and
the posterior (POSTXBIT) teeth (Moyers, 1988).
Parameters similar to Sadowsky and Sakols (1982)
were used (Table II).
viii) Total severity score (TMSCORE), a general overview
of the degree of severity of the situation (T1, T2
and T3), how it improved and relapsed. This was
recorded as a summation of the molar and canine
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204
relationship, openbite, crossbites and crowding
scores, as well as the direct intercanine and
intermolar width measurements. The change in the
value of this score is of significance and not the
actual numerical value. The change of the score
during active treatment is recorded and the
deviation from this end-of-treatment value following
treatment indicates whether relapse has taken
place.
ix) Assessment of the presence of the third molars.
x) Openbite was assessed according to the overbite
present. It was recorded as noncontact of incisors
or noncontact of the lower incisor with the palatal
mucosa (Sadowsky and Sakols, 1982; Moyers, 1988).
xi) Rotations were recorded as the degree of deviation
of the mesiodistal centre groove from the
mid-mesiodistal centre occlusal line.
The data were ~ubjected to descriptive statistics such as
mean and standard deviation for each of the three
evaluations. The Friedman test indicated significant
differences between the initial and end of treatment
observations (T1-T2), initial and final observations (Tl-T3)
and post-treatment and final observations (T2-T3). The
Wilcoxon and the Chi-square tests tested for significant
differences between the groups at the three time intervals.
Spearman correlation coefficients and the Kruskal-Wallis
test showed the relationships of the different variables
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with the lower incisor irregularity (Little, 1975) at the
final observation (T3) (Zar, 1984). The significance level
of this part of the study was 0.05.
7.11 Result~
The results are set out in Tables XXVIII, XXIX, XXX, XXXI,
XXXII and XXXIII.
7.11.1 Maxillary teeth
The maxillary variables which remained stable in the
post-orthodontic period (T2-T3), were those which showed
no significant change (p > 0.05) during this observation
period. They were upper molar buccal intermolar width
(U6-6B), upper incisor position measured to the BA line,
Frankfurt horizontal, the facial axis and the APo line
(I-NA-DEG, I/-FH, I/-FACAX ~nd I/-APO-MM). The variables
which changed significantly (p < 0.05) during this
post-orthodontic period were partly influenced by
post-pubertal growth changes and included the forward
movement of the upper first molars (UM-PTV-MM and
UM-CCV-MM) as well as the slight forward movement of the
upper incisor measured to the NA line (I-NA-MM) which may be
related to mandibular forward growth (Table XXVIII).
During the observation period (T1 to T3) a general
assessment was made of how the variables changed throughout
the study. Some of the variables showed no significant
change (p > 0.05) during this period. Those included the
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206
upper intermolar widths (U6-61 and U6-6B) and upper inci.or
~osition (I-NA-MM, I-NA-DEG, I/-PH and I/-PACAX). The
variables showing significant changes from Ti to T3 (p <
0.05) were the mesial migration of the upper first molars
(UM-PTV-MM and UM-CCV-MM) and the upper incisors measured to
APO (I/-APO-MM). The measurement I/-APO-MM indicated a
small forward movement of the upper incisors during T2-T3,
but this change, although not significant, corresponded with
the mesial drift tendency of the teeth and the impingement
of the lower incisors upon the upper incisors during forward
growth of the mandible as discussed in Chapter 5 (Table
XXVIII).
The period of active orthodontic treatment (Ti-T2) resulted
in various observed changes. Upper first molar inclination
or buccal crown torque was slightly increased. This
significant change measured a mean increase of 0.59 Mm,
practically negligible, but even this increase could have
affected the post-orthodontic occlusal stability as the
measurement at the final observation (T3) was smaller than
that at Ti, indicating a tendency to relapse in the
direction of the original value (Ti) after expansion. The
upper first molars were moved in a mesial direction,
possibly a combination of the normal tendency of mesial
migration and the forward movement due to the closing of
extraction spaces (p < 0.05). The upper incisors were
retracted during the active orthodontic treatment (I-NA-MM
and I/-APO-MM) (p < 0.05), but good torque control
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I/-APO-MM) (Table
maintained the axial inclinations
significant changes (I-HA-DEG, I-FH and
XXVIII).
which
207
showed no
Maxillary crowding was resolved during treatment.
Measurements of the crowding mesial of the upper first
molars of between 0 to 3.0 mm were taken as clinically
8cceptable. This measurement also gave an indication
whether acceptable incisor alignment was achieved. In all
the subjects (88) included in this study this goal was
achieved (Table XXX). The severity of the crowding measured
at the initial observation (T1) varied according to a scale
set out in Table II. Most of the subjects (64.8%)
presented with crowding of between 0 to 3.0 mm, while the
remaining subjects had more severe crowding measuring 3.5
to 6.0 mm (19.3%} and more than 6.5 mm (15.9%) (Table XXX).
The maxillary tooth alignment remained stable during the
post-orthodontic peeiod. This was borne out by the fact
that all eighty-eight subjects (100%) were categorized in
the 0 to 3.0 mm group at the final observation (T3) (Table
XXX) .
Spearman correlation coefficients indicated whether a weak
or strong correlation existed between the lower incisor
crowding and the maxillary parameters. The only
significant, b~t weak correlations of the maxillary
parameters with the post-orthodonti.c (T3) lower incisor
irregul~rity (L-IRREG», were the mesial migration of the
upper first molars following active orthodontic treatment
(T2) and at the final observation (T3). These correlations
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208
were UM-PTV-MM; r. -0.23, p • 0.03 and UM-CCV-MM; r·
-0.24, p • 0.02 at T2. Only one parameter (UM-PTV-MM)
showed a significant, but weak correlation with the Little
Irregularity Index (L-IRREG) at T3 (r = -0.23, P • 0.03)
(Table XXXII).
7.11.2 Mandibular teeth
Certain mandibular parameters were significantly (p < 0.05)
altered during the active orthodontic treatment. They were
the arch length (ARCHL and LITTLE-A), the Little
Irregularity Index (L-IRREG) as well as the lower incisor
position measured to the APo line (I-APO-DEG and I-APO-MM),
measured to the Downs (1948) mandibular plane and measured
to Frankfurt horizontal as part of the Tweed triangle
(Tweed, 1954) (IMPA and FMIA respectively) (Table XXVIII).
The non-significant changes (p > 0.05) included the lower
intercanine dimension (L3-3I and L3-3B) and the lower
incisor position measured to the NB line (I-HB-MM and
I-NB-DEG) (Table XXVIII).
Of the non-significant changes occurring during the period
Tl to T3, one is of special importance, the stable
intercanine dimension. This dimension measured at two
different positions (L3-3I and L3-3B) remained practically
unaltared. Mean changes of 0.2 mm (decrease in L3-3I) and
0.55 mm (increase in L3-3B) occurred from T1 to T2, while
both showed decreases during the post-orthodontic period
(T2-T3) to values less than the original intercanine
distance (0.42 mm and 0.64 mm respectively). The lower
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209
incisor parameters (I-HB-DEG, I-HB-MM, I-APO-MM, IMPA and
FMIA) remained practically the same as the post-treatment
values, indicating good stability during the period from Tl
to T3. The significant changes which occured throughout the
study (T1-T3) included the only lower incisor parameter
change I-APO-DEG (mean 3.53 degrees proclination). Other
significant changes were the arch length (AReHL and
LITTLE-A) measurements which showed a continual decrease.
Th5.s may be as a result of the closing of space between
teeth as well as in accordance with natural growth changes.
The Little Irregularity Index was significantly (p.
0.0001) reduced from a mean value of 4.24 rom to a value of
0.43 mm during treatment (T1-T2) which is within the ideal
alignment range described by Little (1975). The index,
however, relapsed subsequently during the post-orthodontic
observation period (T2-T3) to a mean value of 1.71 mm (p ~
0.0001). Although an increase in this value was recorded, it
still conformed with the normal value advocated by Little
(1975) (Table XXVIII).
Most of the variables measured during the post-orthodontic
period (T2-T3), showed non-significant changes indicating
good stability. Those that remained practically unchanged
were the L3-3I, L3-3B, I-NB-MM, I-APO-DEG, I-APO-MM and IMPA
(Table XXVIII). The significant changes (p < 0.05) included
the lingual uprighting of the lower incisor (I-HB-DEG; 1.72
degrees and FMIAi 1.94 degrees). This may be due to the
forward mandibular growth during the post-orthodontic period
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which probably also resulted in
Index showing a small (1.28 mm),
during this period (Table XXVIII).
210
the Little Irregularity
but significant increase
Mandibular crowding, although 100% corrected during active
orthodontic treatment, showed some return of crowding
during the post-treatment period as measured at T3. The
different categories at the intial observation period (T1)
were 87.5% of the sUbjects measured between 0 to 3.0 mm
crowding, 11.4% between 3.5 mm to 6.0 mm crowding and 1.1'
measured more than 6.5 Mm. Only 69.0% of the subjects
remained within the accepted range (0 to 3.0 rom) and
31.0% showed more than 3.5 mm at the final observation which
included the 13.8% lower arch crowding of more than 6.5 mm
(Table XXX).
The curve of Spee measured at the T3 (Table II), showed a
similar range to that measured at the initial observation
(Tl). The deepening of the curve following treatment is
illustrated by the 77.1% of subjects measuring a curve of
less than 1.5 rom at T2 and then changing to a value of 44.8%
of subjects in the normal range at the final observation.
The subjects measuring a curve of Spee more than 1.5 mm
(39.8%) were reduced to 22.9%, but this increased to 55.2%
of subjects at T3. This gives an indication that the curve
of Spee tends to return to the original pre-trea'tment value
(Table XXX).
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Only the lower incisor parameters I-NB-MM and I-APO-MM at
the pre-treatment evaluation showed weak, but significant
correlations with the L-IRREG at T3. No other statistically
significant correlations could be shown between the
mandibular variables (T1-T2, T1-T3, and T2-T3) and lower
incisor irregularity at T3 (Table XXXII).
7.11.3 Occlusion
An overview of the changes (T1-T3) show that the overbite
(OBB) , overjet (OJB) , interincisal angle (I-I) and the
occlusal plane angle measured to the Sella-Nasion plane
(OCC-SN) significantly changed (p < 0.05) during this
period. The OJB and OBB showed mean reductions of 3.04 mm
and 1.41 rom respectively during this period. The
interincisal angle increased by a mean value of 2.98
degrees. The occlusal plane angle although slightly
increased during active treatment, showed a nett reduction
of 1.56 degrees reduction during the period T1 to T3 (Table
XXVIII). The only occlusal parameter not changing
significantly (p > 0.05) during this period was the severity
score (TMSCORE) (Table XXVIII). Changes occur in untreated
subjects (Sinclair and Little, 1983). These changes may also
occur in treated subjects following treatment. The TMSCORE
which describes a combination of clinical variables may be
affected by these changes following treatment. There is a
normal tendency for teeth to return to their original
positions following treatment as is shown in the present
study. These changes may be the cause why a non-significant
change is shown by the TMSCORE the period T1 to T3.
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The observed changes during the active orthodontic treatment
~Tl-T2) indicate that the norms described in the literature
were attained. The overjet and overbite were significantly
reduced (p = 0.0001) to within the accepted range (0 mm to
3.0 mm) described in Chapter 3 (OJB a mean 2.85 mmi OBB •
mean 2.82 mm) (Table XXVIII). The TMSCORE indicated that the
corrected dentition had a mean score of 86.44, a significant
reduction from the initial value of 88.21 (Table XXVIII).
The non-significant changes (p > 0.05) included the
interincisal angle which increased by a mean of value 0.65
degrees and the occlusal plane angle which increased by a
value mean of 0.96 degrees (Table XXVIII).
A closer look at the critical period which indicates relapse
(T2-T3), however, showed most of these variables to remain
stable with no significant changes. The OJB increased by a
mean value of 0.32 mm, the OBB decreased by a mean value of
0.01 mm and the angle I-I increased from 126.40 degrees to
127.05 degrees. Only the occlusal plane and severity score
changed significantly (p = 0.0001 and 0.02 respectively)
during this time (Table XXVIII). The occlusal plane angle
remained practically unchanged during the active treatment
(T1-T2) and post-pubertal growth changes (T2-T3) may have
influenced this small reduction of 2.32 degrees. The
TMSCORE gives an overall indication of the post-orthodontic
ct-~nges as it was compiled by a variety of variables (Table
II and Chapter 3). The TMSCORE showed a change of 3.75%
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213
during this period which is a significant change, but is
negligible from a clinical point of view, illustrating the
acceptable stability of the .treatment result (Table XXVIII).
Table XXIX portrays the distribution of the Angle
classification, an indication of the severity of the
malocclusions included in this study. The larger percentage
of the subjects in this study was Class II (70.51). The
Bolton tooth-size discrepancy analysis indicates a slightly
larger anterior mean ratio of 78.57% (norm noted in the
literature by Bolton is 77.2%), but the posterior mean ratio
of 91.79% is practically the same as the described norm
(91.3%).
Molar and canine relationships remained very stable with
only a small percentage of individuals showing relapse. At
the pre-treatment observation (Tl) 51.2% of the left first
molars and 57.9% of the right first molars were not in a
Class I relationship. The canines showed much higher
percentages not in Class I (left 80.7% and right 79.51).
The molar and canine relationships were practically all
(MOLAR L 94.3%, MOLAR R 93.2% and CANINE L 94.3%, CANINE R
93.2%) corrected to a Class I rel~cionship during the
orthodontic treatment (T1-T2). At the final observation
(T3) all these parameters showed values of over 90% (Table
XXX) •
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A small percentage of individuals who showed an anterior
openbite (OPENBIT) at the pre-treatment observation (Tl)
showed a relapse of the corrected dentition, but a nett
improvement was recorded (22.8' with openbites at Tl, 5.6'
at T2 and 9.1% at T3) (Table XXX).
The anterior crossbites which were observed at the initial
observation (Tl) were all (100') corrected during the active
orthodontic treatment (T1-T2). A small relapse occurred
during the post-orthodontic period. Only 5.71 of individuals
measured one to two anterior teeth in crossbite at the final
observation (T3) (Table XXX). Posterior crossbites,
however, were not all corrected during treatment and 5.6' of
individuals still showed posterior crossbites followinfg
active treatment. The corrections (94.3% showing no
crossbite) remained reasonably stable with only a very
small percentage showing relapse (6.9%) (Table XXX).
Although practically all the rotations were corrected (T2:
92.0% of individuals with no rotations, 8.0' showing
rotations between 15 degrees and 90 degrees), relapses were
recorded at the final observation (T3). Of the ~orrected
rotations observed at the post-treatment assessments (T2),
57.5% of the individuals showed no rotations, 41.4' showed
rotations between 15 degrees and 90 degrees and only one
individual showed rotations of more than 90 degrees at the
final observation (T3) (Table XXX).
A large number (80.7%) of the third molars were not present
in the mouth at T3 (Table XXXI).
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The Spearman correlation coefficients set out in Table XXXII
showed no significant relationships (r < 0.2 and p > 0.05)
between the occlusal metrical variables (OJB, OBB, I-I,
BOLTON A, BOLTON B, OCC-SN and TMSCORE) at the various
observations (Tl, T2 and T3) and lower incisor irregularity
(L-IRREG) at the final observation (T3). The Kruskal-Wallis
test was used to indicate whether a significant relationship
existed between the non-metrical variables (MOLAR Land R,
CANINE Land R, ANTXBIT, POSTXBIT and WISDOMS) and the lower
incisor irregularity measured at the final observation (T3).
No significant relationships could be shown for these
parameters (p > 0.05) (Table XXXIII)
7.12 Discussion
Occlusal analysis is a vital part of the original diagnosis
and a necessary ongoing procedure in assessing treatment
progress or results. There is no diagnostic way to measure
or to accurately estimate malocclusion, nor to decide how
closely treatment has approached good end results, until we
have first decided what good occlusion is. Most
orthodontists focused on two areas only: molar
relationship and interincisal angle. The remaining
components of good occlusion have not been objectified; as a
result, there are almost as many static occlusal schemes as
there are orthodontists (Andrews, 1976).
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TABLE XXVIII
DESCRIPTIVE STATISTICS OF METRICAL DATA IN RESPECT TO THE OCCLUSION
(friedman test included)
Tl T2 T3 Tl-T2 Tl-T3 T2-T3
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D. p-value Pairwise differences
MAXILLA:
U6-6I 49.60 3.63 50.19 3.79 49.51 3.31 0.05 - x +
U6-6B 53.13 3.57 54.26 5.42 53.02 3.16 0.29 x x x
UM-PTV-MM 17.10 3.75 20.23 4.86 23.02 4.4:9 0.0001
UM-CCV-MM 15.96 3.72 18.86 4:.93 21.46 4:.64: 0.0001
I-NA-DEG 22.99 9.09 22.60 8.44 22.35 7.4:8 0.83 x x x
I-MA-MM 4:.14: 2.86 2.84 2.61 3.49 2.60 0.002 + x
I/-PH 114:.4:1 8.76 112.55 8.10 112.65 7.09 0.1,4: x x x
I/-PACAX 4:.02 8.65 5.57 7.29 6.19 6.08 0.19 x x x
I/-APO-~ 7.29 3.13 4.31 1.73 4.42 1.93 0.0001 + + x
IlUDIBLJ::
L3-31 26.19 1.72 25.99 1.69 25.77 1.88 0.08 x x x
L3-3B 30.52 1.90 31.07 3.14: 30.16 2.11 0.10 x :It x
ARCHL 23.50 2.37 20.75 3.19 20.01 3.52 0.0001 x :It x
LITTLE-A 61.10 4.31 56.69 6.83 54:.99 7.05 0.0001 + + +
L-IRREG 4:.21 3.57 0.43 0.66 1.71 1.64 0.0001 + +
I-MB-DEG 27.22 6.4:1 28.43 5.08 26.71 4:.72 0.03 x :It +
I-rm-MM 3.89 2.11 4.32 1.63 4:.04: 1.65 0.15 x x x
I-APO-DEG 23.75 5.17 27.71 4:.68 27.38 4:.65 0.0001 - - x
I-APO-MM 0.42 2.86 1.29 1.90 0.85 1.93 0.03 - x x
IMPA 96.79 10.68 98.54 6.64 97.79 6.68 0.05 - x x
FMIA 60.42 6.84 59.18 5.72 60.92 8.86 0.001 + x
N
~
0\
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'CCLUSIOH:
IJB 6.21 3.29 2.85 0.85 3.17 1.23 0.0001 + + x
IBB 4.22 1.48 2.82 0.97 2.81 1.09 0.0001 + + x
-I 126.40 11.05 127.05 9.34 129.38 7.79 0.03 x - X
ICC-SN 16.89 5.22 17.65 4.19 15.33 4.92 0.0001 7.- + +
'MSCORE 88.21 5.63 86.44 5.19 89.68 5.85 0.02 + x
1.0. :-
•
•
•
standard deviation
Significant, p < 0.05 (TI > T2, T3)
Significant, p < 0.05 (TI < T2, T3)
Not significant, p > 0.05
N
...
~
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TABLE XXIX
FREQUENCY DISTRIBUTIQN (preyalence) OF ANGLE CLASSIFICATIQN
(molar relationship) AND BOLTQN TQQTH-SIZE DISCREPANCY
i) Classification T1:
VARIABLE N
218
CLASS I
CLASS II
CLASS III
24 (27.31)
62 (70.5')
2 (2.31)
N = Sample size
Percentage representation (frequency) in parentheses
ii) Bolton tooth-size discrepancy T1:
VARIABLE
BOLTON A
BOLTON B
FREQUENCY
78.57' (2.141)
91.791 (2.041)
Standard deviation in parentheses
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TABLE XXX
FREOUENCY DISTRIBUTION or CROwnING AND OCCLUSAL PARAMETBRS
VARIABLE 1'1 T2 1'3
N N N
MXCRQWD:
a 57 (64.8%) 88 (100%) 88 (1001)
1 17 (19.3%)
2 14 (15.9%)
MDCRQWD:
a 77 (87.5%) 88 (100%) 61 (69.01)
1 10 (11.4%) 15 (17.21)
2 1 (1.1%) 12 (13.8%)
Sf9:
a 53 (60.2%) 68 (77.1%) 40 (4:4.8%)
1 33 (37.5%) 19 (21.81) 46 (52.91)
2 2 (2.3%) 1 (1.1%) 2 (2.31)
MOLAR L:
a 43 (4:8.9%) 83 (94.3%) 80 (90.91)
2 21 (23.9%) 3 (3.4%) 5 (5.71)
3 24 (27.3%) 2 (2.3%) 3 (3.4:1)
!JOI,AR R:
a 37 (42.0%) 82 (93.2%) 82 (93.21)
2 25 (28.4%) 4 (4.51) 3 (3.4:1)
3 26 (29.5%) 2 (2.3%) 3 (3.4:1)
CANINE L:
a 17 (19.31) 83 (94.3%) 80 (90.9%)
2 43 (48.91) 4 (4.5%) 6 (6.81)
3 28 (31.8%) 1 (1.11) 2 (2.31)
CANINE R:
0 18 (20.5%) 82 (93.2%) 80 (90.91)
2 45 (51.1%) 6 (6.8%) 7 (8.01)
3 25 (2~.4%) a 1 (1.11)
OPEHE.IT:
a 68 (77.3%) 82 (93.2%) 76 (86.4:1)
1 18 (20.51) 6 (6.8%) 11 (12.51)
2 2 (2.31) 1 (1.11)
219
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ANTXBIT:
0 72 (81.81) 88 (1001) 83 (94.31)
1 13 (14.81) 5 (5.71)
2 3 (3.41)
POSTXBIT:
0 58 (65.91) 83 (94.31) 80 (90.91)
1 21 (23.91) 4 (4.51) 5 (5.71)
2 9 (10.21) 1 (1.11) 3 (3.41)
ROTATE:
°
66 (75.01) 81 (92.01) 51 (57.5')
1 21 (23.91) 7 (8.0') 36 (41.4'~2 1 (1.1') 1 (1.11
H = sample size
Percentage representation (frequency) in parentheses
220
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TABLE XXXI
FREQUENCY QF MAXILLARY AND MANDIBULAR THIRD MQLARS PRESEHT
AT T3
221
VARIABLE
Third molars not present
Third molars present
N
71 (80.7%)
17 (19.3%)
N = Sample size
Percentage representation (frequency) in parentheses
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TABLE XXXII
SPEARMAN CORRELATION COEFFICIENTS COMPARING THE RILATIQlSHIP
OF THE MEASURED OCCLUSAL VARIABLIS AT Tl. T2 AIfD T3 TO THB
IRREGULARIty OF THE MANDIBULAR INCISORS AT %3
222
VARIABLE r
T1
p
L IRREG
T2
r p
T3
r p
MAXILLA:
MXCROWD
U6-6I
U6-6B
UM-PTV-MM
UM-CCV-MM
I-NA-DEG
I-NA-MM
I/-FH
I/-FACAX
I/-APO-MM
MANDIBLE:
MD CROWD
SPEE
L3-3I
L3-3B
ARCH-L
LITTLE-A
I-NB-DEG
I-NB-MM
I-APO-DEG
I-APO-MM
IMPA
FMIA
OCCLUSION:
OJB
OBB
I-I
BOLTON A
BOLTON B
OCC-SN
TMSCORE
0.13
0.03
0.002
-0.17
-0.18
-0.01
0.04
-0.03
-0.03
0.08
-0.22
0.06
0.05
-0.01
-0.12
-0.11
-0.16
-0.07
-0.20
-0.21
-0.07
0.07
0.20
0.11
0.06
-0.02
0.01
0.05
0.09
0.45
0.78
0.98
0.11
0.09
0.96
0.74
0.79
0.81
0.48
0.22
0.64
0.64
0.91
0.27
0.32
0.14
0.05
0.06
0.05
0.49
0.53
0.06
0.31
0.61
0.92
0.97
0.65
0.39
0.08
0.06
-0.23
-0.24
0.07
0.08
-0.04
-0.04
0.10
0.01
-0.01
-0.06
0.04
0.06
-0.08
0.13
-0.04
-0.04
0.01
-0.10
0.09
0.13
-0.02
0.10
0.01
0.49
0.59
0.03
0.02
0.53
0.45
0.71
0.69
0.34
0.93
0.91
0.58
0.72
0.55
0.43
0.23
0.69
0.69
0.91
'0.34
0.43
0.23
0.85
0.33
0.92
-0.08
0.09
0.08
-0.23
-0.17
0.09
0.08
-0.03
-0.09
0.11
0.04
-0.02
0.16
0.06
0.01
-0.01
-0.06
0.03
-0.05
-0.07
0.05
-0.10
0.04
O.lt
-0.09
0.03
0.03
0.11
0.12
0.56
0.42
0.46
0.03
0.11
0.42
0.46
0.79
0.39
0.32
0.81
0.87
0.14
0.58
0.89
0.93
0.57
0.75
0.63
0.52
0.65
0.37
0.75
0.29
0.39
0.80
0.80
0.33
0.26
r = Spearman correlation coefficient
p = Significance level, p < 0.05
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TABLE XXXI I I
KftUSKAL-WALLIS TEST CQMPARIBG SIGNIFICANT RELATIONSHIPS OF
OCCLUSAL VARIABLES AT Tl. T2 AJU) T3 TO 'rUE IRREGULARITY 01
THE LOWER IKCISQRS AT T3
L IRREG
223
VARIABLE
OCCLUSIOB:
MOLAR L
MOLAR R
CANllE L
CABlNE R
ANTXBIT
POSTXBIT
WISDOMS
Tl
p
0.34
0.05
0.13
0.13
0.69
0.85
T2
p
0.55
0.61
0.88
0.88
0.79
0.12
T3
p
0.45
0.34
0.13
0.13
0.79
0.07
0.51
p = Significance level, p < 0.05
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224
The implications of a wide diversity of opinion about
fundamental standards should disturb all orthodonti.ts. It
should be a matter of personal pride for orthodontists to
provide treatment which is directed toward known and well
founded objectives, and to deliver complete treatment, with
every tooth optimally positioned according to static and
anatomical occlusal standards which are entirely campatible
with the requirements of functional occlusion (D'Amico,
1958; Andrews, 1972, 1976; Dawson, 1974; Roth, 1976, 1981;
McHorris, 1979; Alexander, 1986). Orthodontists consider it
to be axiomatic that good occlusion is one of the benefits
patients recieve from orthodontic treatment. However, the
post-treatment maintenance of a healthy stomatognathic
system and the attainment of a stable post-orthodontic
treatment result are tasks which can not be taken lightly.
Attaining tooth alignment during treatment and then
maintaining this tooth alignment, as well as oral healt~l and
comfort in the post-orthodontic phase, depends on many
factors such as:
i) the physical and psychological state of the subject.
ii) oral and dental care.
iii) the quality of the orthodontic treatment in terms of,
not only aesthetics and anatomical norms, but also of
muscle balance, oral habits, functional ailway, the
periodontium and the functional harmony of the
occlusion and its effect cn the musculature and the
temporomandibular joints (Roth, 1976).
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225
Crowding of lower incisor teeth, following active
orthodontic treatment, is a problem encountered frequently
in orthodontic practi~~ (Little, 1990). Little, Riedel and
Artun (1988) noted that the lower incisor irregularity as
measured by Little (1975) continuously changed during a
period of ±20 years (mean values: pre-treatment. 7.41mm;
post-treatment = 1. 66rnm; 10 years post-retention. 5.25mm;
20 years post-retention = 6.02mm). It appears fram these
values that the :ower incisor irregUlarity does not
significantly change from a clinical point of view following
tae 10 vear post-retention period. The present study sho~gd
an iucreasc of 1.28rnm (L-IRREG: ~2 = C.43mm; T3 • 1.71mm)
(Taole XXVIII) in this parameter -~llowing a 5 year
post-retention period (7 'lear post-l .•:c.hodontic). A better
mean correction was attained for the malocclusions of the
present studt when judging the alignlRent of the lower
incisors (Little et al., 1988 L-IRREG T2 = 1.66mmi Present
study L-IRREG T2 = O.43mm). A prospective speculation in
respect to the Little Irregularity Index (Little, 1975) may
see this index increase ±39.22% during the post-orthodontic
interval if compared to the increase of the Little et ale
(1988) study. It is however doubtful whether this would
occur to the same extent seeing that better alignment was
attained at the end of the treatment. The latter more
positive conclusion is in agreement with some other studies
(Sandusky, ~J83; Udhe, Sadowsky and BeGcle, 1933). The
sYmptom of crt)wding (the phenomenon of post-treatment
crowding rLgard~d as an indication of relapse) has little
meaning, unless it is related to the other parameters
constituting the occlusion. Successful therapy may depend on
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the orthodontist's ability
contributing to the overall
to evaluate th•••
occlusal pattern.
226
Maxillary bimolar width remains virtually unchanged during
normal growth from ten to eighteen years (Table XXIV).
Maxillary arches can be more easily altered during
orthodontic treatment than can mandibular arches (Moyers,
1988). Maxillary molar width was increased sJ.1ghtly during
the period of active treatment (T1-T2). This mean widening
was in the the order of a 0.59mm (U6-6I) and 1.13mm
(U6-6B). Although on11 the incisal mensuration (U6-6I)
showed a significant difference in the period between T2
and T3, both returned to a mean of O.llmm of the original
measurment. During the post-treatment period (T2-T3) the
upper first molar rotated mesio-palataly as a result of the
continual mesial migration tendency attributed to the
dentition (Picton, 1962; Moss and Picton, 1967, 1972;
Moyers, 1988), thus causing the U6-6I variable to decrease.
This intermolar dimension was, however, increased as noted
in Table XXVIII during T1 to T2 and restriction by the
buccal alveolar cortical plate and buccinator muscles,
could be the cause for the slight relapse during the
post-treatment period to a value less than the original (p
< 0.05). The upper molars showed continual mesial movement.
The UM-PTV-MM and UM-CCV-MM distances increased in the
period from T1 to T3 (Table XXVIII). These findings are
closely linked with the decrease in arch length (Moyers ~
Al., 1976), mesial migration of teeth (Enlow, 1968; Moss and
Picton, 1972; Moyers, 1988) and although highly
controversial, also with the development and eruption of
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227
the third molars (Richarson, 1980). The result. of a .tudy
on untreated individuals (Sinclair and Little, 1985) .howed
that with a bite-closing rotation of the jaws similar
forward molar movements were experienced.
Various measurements of the upper incisor position were
assessed (Table XXVIII). All of the upper incisor. were
treated to within acceptable clinical parameters (Downs,
1948; Steiner, 1953; Riolo et al., 1974; Ricketts et al.,
1979; Engel et al., 1980). Small changes are to be expected
in an occlusion surrounded by a sound periodontium, but
although measurable changes were noted, none were
significant except the I-NA-MM and I/-APO-MM (Table
XXVIII). The I-HA-MM measurement changed 0.65mm during the
post-orthodontic period (T2-T3), which is clinically al~Qst
negligible. A similar small forward movement, which was noc
significant during this period (T2-T3), was portrayed with
the I/-APO-MM variable (mean 0.11 mm). A significant change
was shown in the overview from T1 to T3. It can, however,
be speculated that as the dentition migrates me.ially, a
slightly more protrusive meaeurement to the lines NA and APe
would be measured. Mandibular forward growth during the
post-orthodontic period may also have contributed to this
minimal forward movement ,f the upper incisor.
The variable which could contribute significantly to relapse
of treatment was the continual mesial movement of the upPer
molars. They not only moved mesially during treatment
(TI-T2), but continued in a forward direction following
treatment (T2-T3). The most significant incisor change as
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228
noted could have been the result of this molar drift. The
upper arch was treated to practically perfect alignment
(1001 achieved a crowding mean measurement of between 0 and
3. Omm) . This percentag.... of success was maintained at 1'3
(Table XXX). Findings in respect of the influence of these
changes on the lower incisor irregularity (T1-T3) showed
only upper molar mesial movement which significantly, but
weakly correlated with the Little Irregularity Index
(Little, 1975) at T3 (Tablp XXXII).
The mandibular intercanine dimension in the secondary
dentition rema~as constant with growth (Table XXIII). As is
recommended in the literature, the mandibular intercanine
width (L3-3I and L3-3B) was maintained during treatment
(Riedel, 1960; Schulof, Lestrel, Walters and Schuler, 1978).
Although not significantly (p > 0.05), it did decrese to a
value narrower than the original dimension at T3. This
finding is in keeping with studies by Dona (1952), Arnold
(1963), Welch (1965), Shapiro (1974), Gardner and Chaconas
(1976) and Little, Wallen and Riedel (1981). ~he
intercanine distance also decreased to a value narrower than
the original observation in untreated normal individuals
(Table XXIII). The report of the work of Shields, Little
and Chapko (1985) showed no correlation beTween this
measurement and lower inciso~ crowding post-treatment, but
according to the findings of the present and other studies
(Strang, 1949; Gardner and Chaconas, 1976) a stable
intercanine dimension could be a contributing factor to
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229
d~nture stability since it will keep the arch circumference
between the lower canines constant, and thus provide the
necessary space for uncrowded lower incisors.
The position of the lower incisor tip was treated to ideal
norms (Steiner, 1953; Ricketts, 1981). The axial
inclination mensuration (I-HB-MM, I-APO-DEG, IMPA and PHIA)
indicated, however, that the lower incisor was proclined
slightly beyond the upper limit of the norms (Steiner,
1953; Tweed, 1954 and Ricketts, 1981). These positional
measurements remained reasonably stable. No significant
changes, except for I-NB-DEG and FMIA were measured at the
final observation (T3) (Table XXVIII). The lower incisor
changed to a more upright position following treatment (T3)
which could decrease the arch circumference in the anterior
area. This decrease in arch circumference could cause the
lower incisors to relapse into a crowded situation. The
situation is aggravated by the co~tinual decrease (T1-T3)
in the arch length (ARCHL and LITTLE-A) (Table XXVIII). The
decrease in the arch length could be due to closing of
spaces during treatment as well as the natural pbe~non
of me~ial migration of the dentition noted earlier. This is
borne out by the mandibular dentition, having been ideally
aligned in all the patients during treatment, but showing
only 69.0' of subjects reaaining within clinically
acceptable alignment at T3 (13.8' of the subjects showed
lower incisor crowding of more than 6.5 mm at T3) (Table
}C{X). This continual decrease in mandibular arch length is
also observed during normal growth and maturation of the
dentition (Table XXV). ~n only 77.1% of the dentitions
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230
studied was the ideal curve of Spee, of Ie.. than 1.5am
(Andrews, 1972, 1976), achieved at the end of treat.ent
(T2). This morphological trait deteriorated so that
eventually only 44.8' of the subjects wera within the set
norm. It must, however, be mentioned that only a very small
percentage of the patients manifested with a very deep curve
(deeper than 4mmj at the end of treatment (T2) and even at
the final observation (T3) (Table XXX).
Rotations which were corrected during treatment also tend to
return towards ~riginal positions. Of the 92.0% success rate
achieved at the end of treatment (T2) only just more than
half (51.5%) remained stable (Table XXX). Crowding of the
lower incisors post-orthodontically, accounts partly for
the rotations observed i.n this phase. Rotated posterior
teeth take up more space in the dental arch (Andrews, 1972,
1976) and could have been a contributing factor towards the
increase in the lower incisor irregularity (Little, 1975)
which was noted post-treatment. No fiberotomies as described
by Edwards (1970), were performed in any of the cases
studied.
The uprighting of the lower incisors, a deepening of the
curve of Spee, the relapse of rotations in combination with
the continual decrease in arch length during
post-orthodontic growth (T2-T3), may largerly account for
the increase in the Little Irragularity Index (Little, 1975)
from a mean of 0.43 mm to one of 1.71 mm (Table XXVIII). It
will be noted that the mean value for this parameter at T3
is significantly better than the mean for the Little
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231
Irregularity Index recorded prior to the treatment (T1).
Although some relapse or rebound took place (L-IRREG froa
T2-T3, p < 0.05), the mean value for the Little Irregularity
Index at the final observation (T3), is still within
acceptable clinical norms (Little, 1975). Other studie.,
which also included assessments of untreated normals,
showed similar results (Barrow and White, 1952; Hoorrees,
1959; Lundstrom, 1969; Little, Wallen and Riedel, 1981;
Sinclair and Little, 1983). Bjork and Skieller (1972) and
Fisk (1966) referred to the forward growth of the mandible
as the cause of the lower incisor crowding. Similar
conclusions were made in Chapter 5 of this thesis.
All the mandibular variables were correlated with the
Little Irregularity Index at the end of the post-orthodontic
period (T3). No significant correlations were shown between
the lower incisor irregularity (L-IRREG) and the mandibular
metrical characters (p > 0.05) (Table XXXII). This is in
accordance with the study of Carmen (1978) and Little and
Sinclair (1983, 1985).
Pr.or to treatment the teeth in occlusion presented in the
folloWing Angle (1907) relationships: Class I = 27.3', Class
II = 70.5% and Class III = 2.3% (Table XXIX). As a result of
the orthodontic treatment a correction to a Class I molar
relationship was achieved in almost all the subjects (94.3'
left aA'i 93.2% right). The findings in respect of the canine
relationships were in close agreement with those recorded
for the molar teeth (Table XXX). More than 90% of both
molar and canine Class I relationships were maintained
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232
post-treatment which indicates good stability. Siailar
lults were recorded by Behrents et al. (1989) ••0
significant relationship (p ) 0.05) could be establiahed
betwe~n the Little Irregularity Index (Little, 1975) at the
final observation (T3) and the molar and canine
relationships at the various time intervals (Table XXXII).
The mean Bolton tooth-size discrepancy recorded in this
study (Table XXIX) was practically identical to the norms
described by Bolton (1958, 1962) for American Caucasians. No
significant correlation was shown for this measurement with
lower incisor irregularity (Table XXXII). The mean anterior
tooth-size discrepancy ratio was slightly larger (1.32%)
than Bolton's norm for this region and could, even in this
low value, have contributed to the lower incisor crowding
which was noted at the end of the post-orthodontic phase.
The overall finding, however, eliminates the abovementioned
variable as a cause of lower incisor crowding.
As a result of the treatment, overjet and overbite (OJB and
OBB) were significantly corrected to acceptable norms
(Ricketts et al., 1979; Moyers, 1988). The overjet and
overbite norms for various ages during growth are portrayed
in Tables XXVI and .XXVII. Overjet tends to decrease during
normal growth, but overbite shows an overall increase in
females and males up to fourteen years of age and then a
slight decrease in males with the females continuing to
increase (Tables XXVI and XXVII). These two parameters did
not change significantly after the removal of the appliances
(T2-T3) (Table XXVIII). It was shown in other long-term
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233
studies that overjet and overbite tend to improve or
degenerate completely following treatment (Ludwig, 1967;
Simon and Joondeph, 1973jLagerstrom, 1980; Berg, 1983).
Moyers et ale (19'/6) noted in untreat(-: i10rmals that the••
parameters increased initially , but dec:reased from t. T'teen
to twenty years of age, resultin~ in minimal overall
changes. Correct overjet and overbite in ..Jmbination with
acceptable upper incisor torque (axial incliration) values
and a normal interincisal angle (I-I) are imperative in
achieving a Class I occlusion (Andrews, 1972, 1976).
Positive correlations between these parameters were shown by
Popovich (1955), Backlund (1960), Solow (1966), LUdwig
(1961) and Simon and Joondeph (1973). In the present study
the interincisal angle was within prescribed norms for all
phases studied. An obtuse interincisal angle is often
associated with a deep overbite (Houston, 1989). Although
not significantly so, the interincisal angle increased from
a mean of 127.05 degrees at the end of treatment (T2) to a
mean of 129.38 degrees at the final observation (T3). This
change can possibly be ascribed to the recorded uprighting
of the lower incisor teeth. Although the lower incisors
showed slight uprighting following treatment, the mean
measured values for these incisor positions were slightly
more proclined than the mean for the norms described in the
literature. The uPPer incisor positions remained within the
norms throughout the Period studied. The slightly more
proclined lower incisors could play a role in the stability
of the overbite which is in contradiction to many other
studies. Clinically, OJB and OBB, remained reasonably
stable (Table XXVIII). No significant correlation could be
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shown between these two variables and
irregularity (Table XXXII).
234
lower incisor
Twenty subjects (22.8') initially presented with anterior
openbite problems. Of these fourteen subjects ~70.0') were
corrected to normal overbite and overjet relationships. Six
subjects (30.0') relapsed (Table XXX). No overt habits were
present at the end of the post-orthodontic phase (T3), r"lt
it is possible that some abnormal muscle function or habit,
which caused the openbite r could stil~ have been present in
the immediate post-retention period before the final records
were taken (mean post-retention time interval 5 years; mean
post-orthodontic time interval 7 years). Oral habits are
seldom conducive to normal occlusion (Hughes, 1949;
Swinehart, 1950; Baker, 1954; proffit, 1986; Moyers, 1988).
The mean occlusal plane to anterior cranial base angle
(OCC-SN) was slightly more obtuse at the end of treatment
(Table XXVIII), possibly as a result of Class II mechanics.
This non-significant change from Tl to T2 was followed by a
significant change (p = 0.C001) from T2 to T3. This change
could be attributed to the closing rotation of the lower jaw
during the post-pubertal phase and may have influenced the
slight relapse in lower incisor alignment. Bjork and
Skie .ler (1972) noted similar findings. The mean occlusal
plane angle became more acute and as a result ~f this
occurance became closer to the Steiner (1953) norm of
fourteen degrees (T3 = mean 15.33 degrees). During anchorage
preparation, as wa~ advocated by Tweed (1966), it was
suggested that the preparation of the occlusal plane (up
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235
forward and down posterior) in order to withstand CIa•• II
elastic intermaxillary traction during the latter pha~e. of
treatment and to eventually change back to its normal
position after active treatment. This increase of aCC-SM
during treatment and the return to a value below the
original observed value could thus possibly be ascribed to
similar changes. Clinicians should endeavour not to change
the original occlusal plane angle with their treatment
(Tweed, 1966). Although relatively small, this OCC-SM
change, however, was significant (Table XXVIII) and although
relatively small, showed a tendency to return to the
original mean value. This change could not be held
responsible for contributing to lower incisor irregularity,
as no significant statistical correlation could be shown
between these two variables (Table XXXII).
The mean anterior crossbite at the pre-treatment observation
was totally corrected (100%) (Table XXX). Only 5.7\ of
subjects showe~ a return of anterior crossbite at the final
observation (T3). Of the 94.3% sUbjects in whom posterior
crosshites were completely corrected during treatment, 3.4%
relapsed. There was originally thirty subjects (34.1\) with
~osterior crossbites (T1), five subjects were not corrected
during treatment for some unknown reason and eight subjects
presented with posterior crossbites at the final observation
(T3). A variety of causes may be responsible for the relapse
of a crossbite. These include, amongst others: impaired
upper airway, failing to overcorrect the problem during
treatment, not achieving correct axial inclination of the
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236
corrected teeth or too short a retention time. Wo
significant relationship could be shown between lower
incisor irregularity and crossbites (Table XXXIII).
The occlusal traits were assessed and expressed as total
malocclusion scores (TMSCORE). These scores did not change
significantly from Ti to T3 and it is immediately assumed
that the there was no benefit from the orthodontic
treatment. This is not true because the change is reflected
by the treated occlusion (T3) tending to return to the
original malocclusion (Ti). However, a significant change
was shown during the active treatment (Ti-T2) and during
the post-orthodontic period (T2-T3) (Table XXVIII), but the
post-orthodontic change did not equal the treatment change
thus showing a nett correction (Table XXVIII). The change
following active treatment could be partly ascribed to
growth changes and/or partly to rebound of treated variables
post-treatment. It was not possible to show significant
correlations between the malocclusion scores and lower
ificisor ir.regularity (Table XXXII).
It can only be a matter of speculation whether third molars
cause lower incisor crOWding following treatment. According
to Table XXXI there was 80.71 of the sample who had no
third molars present, being either congenitally ~sent or
having been removed following the active orthodontic
treatment. This high incidence of missing third molars may
have helped to keep the Little Irregularity Index within
acceptable clinical norms. There is no definite
confirmation that the third molars cause or do not cause
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237
lower incisor crowding following treatment. There are
results reporting in favour of the third molars a. an
aetiological factor of late lower incisor crowding
(Bergstrom and Jensen, 1960. 1961; Sheneman, 1968; Sch~artz,
1975; Schulhof, 1976; Richardson, 1977, 1979, 1980;
Ricketts et al., 1979; Lindqvist and Thilander, 1982) and
there are reports in the literature that ascribe no
significance to the third" molars as factors in
post-treatment lower incisor relapse (stemm, 1961; Shanley,
1962; Lundstrom, 1969; Kaplan, 1973, 1974; Rocke at al.,
1980; Ades et al., 1990). No significant relationship could
be shown between the absence or presence of third molars and
late lower incisor crowding (Little Irregularity Index) at
the final observation (T3) (Table XXXIII).
A ganeral overview of the dental changes noted in this
study, leads to the conclusion that a major contributing
factor leading to the clinically acceptable lower incisor
crOWding following active trea~ent, was the ability of the
operators to keep arch dimensions within the described norms
during treatment. Arch width dimensions should thus be
maintained in order to assist with the achievement of
successful post-orthodontic results. A post-treatment
occlusion with a flat curve of Spee and no rotations could
be stable following orthodontic treatment. Correctly
maintained arch dimensions as well as accurately positioned
teeth on basal bone calls for superb orthodontic technique.
Growth changes outside the scope of the treatment period
and thus not within the control of the orthodontists, may
have played a role in causing the slight lower incisor
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shown
dental
238
crowding recorded at the final observation. The variable.
showing the worst chang~B following removal of the
appliances were changes of a matcrational nature that
included decreasing arch lengths and mesial molar migration
(p < 0.0001; Table XXVIII). The clinically acceptable level
of stability achieved at the end of the post-orthodontic
period (T3), underwrites good overall orthodontic
technique. This includes correct diagnosis, setting a
meticulous treatment plan and the support of an excellent
mechanical technique.
7.13 Conclusions
1. A continual decrease in arch length post-treatment may
contribute to lower incisor crowding.
2. The ideal cephalometric norms for incisor position should
be adhered to as they tend to remain stable if kept witain
clinical norms.
3. Arch width dimensions should be maintained or if changed,
rather be slightly reduced as this dimension decreases in
the long-term.
4. Mesial movement of the dentition was the only variable
which correlated significantly, but weakly with lower
incisor irregularity at the final observation (T3).
5. No strong significant correlations could be
between lower incisor crowding and the other
var~ables measured in this study.
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239
6. Lower incisor position was slightly more proclinad in
respect to the mean normal values, but was atill within
clinically acceptable limits and especially so when it was
assessed in comparison to the change in the post-orthodontic
Little Irregularity Index.
7. Overbite remained unchanged during the post-retention
interval which is in contrast to other studies.
8. Better long-term stability of the Little Irregularity
Index was shown when compared to other well-known studies.
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A LONGITUDINAL srl'UDY OF '1UE STABILITY OF THE
DENll'nON FOlLOWING ORmODONTIC TREATMENT
VOLUME 2
PAUL EMILE ROSSOUW
Thesis submitted to the Faculty of Dentistry,
University of Stellenbosch
in fulfilment or the '·equ. ements
for the degree of Doctor of Philosophy
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VOLUME 1
VOLUME L
CHAPTER 1
CHAPTER 2
CHAPTER 3
CONTENtS
Chapters 1 - 7
Chapters 8 13
Referenl:es
INTRODUCTION •••••.••••••..•.•••••.••.•.
1.1 General overview of longitudinal
orthodontic changes ••••••.••••••••
1.2 Objectives of the present study •••
1.3 Presentation of the thesis .•••••••
TERMS USED TO DESCRIBE POST-ORTHODONTIC
TREATMENT CHANGES IN THE DENTITION ••••.
2.1 Relapse .
2.2 Physiologic recovery ••.•.••..•••••
2.3 Developmental changes .•.•.•..•••.•
2 •4 Rebound ....•...... ~ .
2.5 Post-retention settling ••.••••••••
2.6 "Recidief'· ~ .
2.7 Crowding or recrowding •••...•..•.•
2.8 Imbrication ., .
2.9 Stability .
2.10 Retention 1. •••••••., •
MATERIALS AND METHODS •..•.•..••••••••••
3.1 Sample description •....••.••••••••
3.2 Orthodontic study model analysis
3.2.1 Molar and canine
relationships .••••..•..•
3.2.2 Incisor overjet •••..•...
1
1
5
7
9
10
11
11
11
12
12
13
13
13
1.
15
15
19
22
26
i
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ii
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
Incisor overbite .•.•••.•
Anterior openbite •••••.•
Anterior cro.sbite ••••••
Posterior crossbite •••••
Maxillary and mandibular
26
26
30
30
crowding •••.•.•.•••••••• 30
3.2.8 Mandibular intercanine
width 33
3.2.9 Maxillary intercanine
3.2.10
3.2.11
3.2.12
width .
Rotations ••.•....••••••.
Curve of Spee ..•.••••...
Total malocclusion
37
37
37
score ................... 41
3.2.13
3.2.14
3.2.15
3.2.16
3.2.17
3.2.18
Bolton tooth-size
discrepancy .•.•..•••••.•
Arch length ...•.••••.•.•
Extraction .•.••.•••••.•.
Teeth present •••••••.•.•
Classification ...•••••.•
Little Irregularity
41
42
42
45
45
49
64
3.3.2
i.ndex ••••••••••••••••••• -47
3.3 Cephalometric measurements •••••••• 48
3.3.1 Definitions of radio-
graphic landmarks used
as seen on a lateral
cephalometric radiograph.
Definitions of the
variables measured ••••••
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3.3.3
3.3.3.1
Radiographic technique ••
The cephalometric
iii
64
64
65
67
67
68
74­
75
75
66
radiograph •••••.••.•.•.•
3.3.3.2
3.3.3.3
The enlargement error
Calculation of the
enlargement factor ••...•
Third molars present post-
retention .
Retention appliances .....•..•••..•
Intra-observer error ....•.••••••.•
3.4
3.5
3.6
3.7 statistical analysis of data •.•..•
3.7.1 Descriptive statistics
3.7.2 Inferential statistics
LONGITUDINAL CHANGES IN THE NASOMAXILLARY
COMPLEX AND ITS RELATIONSHIP TO LOWER
CHAPTER 4
INCISOR ........................•...•.•. 77
4.1 Introduction. . . . • . . . . . . . . . • • • • • . . . 77
4.2 The nasomaxillary complex and
related anatomy................... 79
4.3 Theories of nasomaxillary complex
growth 83
4.3.1 Sicher and Brodie's
4.3.2
theory .... '!'t •••••••••••••
The nasal septum growth
83
theory 84
4.3.3
4.3.4
The septa-premaxillary
ligament theory •..•.....
Moss's functional matrix
86
theory .. ................ 87
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iv
88
89
88
...
4.3.5
4.3.6
Theory of genetic
influence •••••••••••••••
A modern composite
(Ranly, 1980) •••••••••••
Dimensional changes of the Naso­
maxillary complex during growth
Treatment effects on the Naso-
4.4
4.5
Materials and methods •.•••••••••••
Objectives .4.6
4.7
maxillary complex ................. 89
93
94
4.7.1 Criticisms of SNA and
CHAPTER 5
ANS-PNS •••...••.••••••.•
4 •8 Results .
4.9 Discussion .
4.10 Conclusions ......•••••••••••••••••
LONGITUDINAL CHANGES IN THE MANDIBLE AND
ITS RELATIONSHIP TO THE STABILITY OF
ORTHODONTICALLY TREATED DENTITIONS •••..
5.1 Introduction .•.••••••••.••.•••••••
5.2 The mandible and related anatomy ••
5.3 Dimensional changes of the mandible
95
96
99
101
103
103
105
CHAPTER 6
during growth ••••••••••••••••••.••
5.4 Objectives .
5.5 Materials and methods •••••••••••••
5.6 Results .
5.7 Discussion .
5.8 Conclusions .
A LONGITUDINAL EVALUATION OF THE
ANTEROPOSTERIOR RELATIONSHIP OF THE
109
114
114
116
121
125
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MAXILLA TO THE MANDIBLE IN
ORTHODONTICALLY TREATED SUBJECTS ••••••• 127
6.1 Introduction •••••••••.•••••••••••• 127
6.2 Dimensional changes of variables
v
CHAPTER 7
during normal growth ••••••••••••••
6.3 Objectives .
6.4 Materials and methods •••...•••••••
6. 5 Resu!ts .
6.6 Discussion ••....•.••••.••.•.••••••
6.7 Conclusions ••••••.••••••••••••••••
A LONGITUDINAL EVALUATION OF POST­
ORTHODONTIC TREATMENT OCCLUSAL CHANGES
AND THEIR RELATIONSHIPS TO LOWER
133
133
135
137
143
150
INCISOR CROWDING ••••••••••.•••.•..•..•• 151
7 .1 Introduction. • • • • • • • • • • • • • • • • • • • • • 151
7.1.1 Development of the
occlusion ...•.••••••••.• 151
7.1.2
7.1.3
7.1.4
Characteristics of a
static occlusion •.•••.•.
Functional occlusiol~ ••••
Concepts of functional
155
156
7.1.5
occlusion •••...••••.••.• 158
Requisites for an ideal
functional occlusion at
the end of orthodontic
treatment •••••••.••••••• 159
Normal growth of the dental
arches .
7.2
7.2.1 Arch width .
163
163
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7.2.2
7.2.3
Arch length or depth ••••
Arch circumference or
vi
167
perimeter •••••••••••..•• 169
7.2.4
7.2.5
Incisor crowding/
irregularity ..•.•••...•.
Dimensional changes
during orthodontic
170
treatment ...•••••••••••• 173
7.2.5.1 Comparison of untreated
to treated subjects ..•.• 174
7.2.6 Overbite and overjet .... 174
7.3 Correlation of untreated normal
occlusion with other dentofacial
and skeletal dimensional variables
(Predictability) ...•••••...•••.••. 175
7.4 Dentofacial growth and tooth
position changes .........••..•.•.• 178
7.4.1 Incisor positions •.....• 178
7.4.2 Molar positions ..•••.... 179
7.5 Longitudinal occlusal stability 180
7.5.1 Lower incisor relapse 181
7.5.2 Growth cessation and
relapse .....••......•••• 183
7.5.3 Spacing of teeth and
relapse ...•.•.•••....... 184
7.5.4 Maxillary crossbite
correction and relapse 184
7.5.5 Mandibular arch
expansion and relapse 187
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7.5.6
7.5.7
7.5.8
The relapse of overbite
and overjet correction ••
The effect of third
molars on relapse •••••••
Oxytalan fibers and
vii
188
192
7.5.9
7.5.10
relapse •••.••••••••••••• 195
Oral habits and
relapse ••••••••••••••••• 196
The influence of muscle
function on relapse ..••• 196
7.6 Aetiology of relapse of ortho-
dontically treated occlusions •.••• 197
7.7 Tooth-size discrepancies in
relation to stability (Bolton
discrepancy) .
7.12 Discussion .
7 • 13 Cancius ions .
A LONGITUDINAL EVALUATION OF THE
7.8 Anterior component of force ••.••••
7.9 Objectives .
7.10 Materials and methods •••••••••••••
7.10.1 Maxillary teeth •••••••••
7.10.2 Mandibular teeth •..•••••
7.10.3 Maxillary and mandibular
teeth in occlusion ••.•••
CHAPTER 8
7.11 Results
7.11.1
7.11.2
7.11.3
...........................
Maxillary teeth ••.••••••
Mandibular teeth ••••••••
Occlusion •••.•••••••••.•
197
199
200
200
201
201
202
205
205
208
211
215
238
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CHAPTER 9
CHAPTER 10
ANTERIOR BORDER OF THE DENTITION AND
ITS RELATIONSHIP TO LOWER INCISOR
IRREGULAR ITY .•••••••••••••••••.••••••••
8.1 Introduction •••.•••••••••••.••••••
8.2 Objectives .
8.3 Materials and methods •••••••••••••
8.4 Resul ts .
8. 5 Discuss ion .•••••.••••••••.••••••••
8.6 Conclusions ••••• - ••••.•.•••.•.••••
A LONGITUDINAL EVALUATION OF THE
VERTICAL DIMENSION OF THE CRANIOFACIAL
SKELETON IN ORTHODONTICALLY TREATED
SUBJECTS AND ITS RELATIONSHIP TO POST­
ORTHODONTIC LOWER INCISOR CROWDING •.•••
9.1 Introduction •.•.•.•••••••••••••••.
9.2 Objectives .
9.3 Materials and methods •.••••.•••••.
9.4 Results .
9.5 Discussion .
9.6 Conclusions •.•..•••..••••.••.•••••
LONGITUDINAL EVALUATION OF EXTRACTION
VERSUS NONEXTRACTION TREATMENT WITH
SPECIAL REFERENCE TO POST-TREATMENT
IRREGULARITY OF THE LOWER INCISORS •••••
10.1 Introduction •••••.••••.•••••••••••
10.2 Objectives oj ••••
10.3 Materials and methods •.•••••••••••
10.4- Results .
10.5 Discussion .
viii
240
240
244
244
246
252
255
257
257
263
263
266
269
274
275
275
287
287
288
310
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CHAPTER 11
10.6 Conclusions •••.•••••••••••••••••••
SOFT TISSUE PROFILE CHANGES RESULTING
FROM ORTHODONTIC TREATMENT AND THEIR
RELATIONSHIP TO LOWER INCISOR
IRREGULARITY ••••••••••.•.•••••••••.••••
11.1 Introduction •..•...•••.••••.•.•.••
ix
310
312
312
11.1.1
11.1.2
11.1.3
Longitudinal changes in
the soft tissue profile ••
Changes in the components
of the soft tissue
profile .
11.1.2.1 Glabella •.••••
11.1.2.2 Nose •••••••••.
11.1.2.3 Lips •.•..•••••
11.1.2.4 Chin •.......••
Soft tissue changes
influencing the
317
318
318
318
319
320
11.1.4
dentition ....•.•••••.••• 322
The effect of ortho­
dontic treatment on soft
tissue 323
11.1.4.1 Vertical
changes ••••••• 323
11.1.4.2 Lip thickness
and strain •••. 324
11.1.4.3 Thickness of
soft tissue of
lips •••••••••• 324
11.1.4.4 Nasolabial
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326
328
11.1.4.5
11.1.4.6
11.1.4.7
angle ••••••••• 325
Hard tissue and
soft tissue •••
Lip changes
Orthognathic
surgery....... 329
x
11.2 Objectives .••••••••••..•••..••.•••
11.3 Materials and methods ••••••••••.••
11 . 4 Results .
11.5 Discussion .
11.6 Conclusions ••.•••••••..•.••••.•.•.
A LONGITUDINAL ASSESSMENT OF SEXUAL
DIMORPHISM IN ORTHODONT:CALLY TREATED
CHAPTER 12
11.1.5
11.1.6
11.1.7
11.1.4.8 Cephalometric
standard •••..•
Lip strength and its
effects on the
dentition ••••••...••••..
Soft tissue analysis ••••
Ethnic differences in
soft tissue profile •..••
329
330
331
334
335
336
338
340
348
CHAPTER 13
SUBJECTS •••••••••••••••••••••••••••••••
12.1 Introduction •••••••••••.•.••.••••.
12.2 Objectives .
12.3 Materials and methods ••••••••.••••
12 .4 Results .
12.5 Discussion .
12.6 Conclusions .
GENERAL SUMMARY AND CONCLUSIONS •••.••••
350
350
362
363
364
375
391
393
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13.1 Introduction ••.••.••••••••••••••••
13.2 Discussion ••••••••••••••••••••••••
xi
393
399
13.2.1
13.2.2
Changes in maxilla,
mandible and supporting
structures ••••••••.•.••. 401
Anteroposterior maxillary
versus mandibular
REFERENCES ••••••••.•••••••••••.••••••••
13.3 Conclusions ......••••..•••••••••.•
13.2.3
13.2.4
13.2.!J
13.2.6
13.2.7
relationship ••••••••••••
Occlusal changes •.••••••
Vertical changes •••.••••
Extraction versus non­
extraction treatment ••••
Soft tissue changes .••••
Sexual dimorphism •.••..•
403
404
409
411
412
413
415
421
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xii
TABLE 0
LIST OF TABLES
A Comparison of the Angle Dental
ana ANB skeletal classification
23-24
20
21
parameters .
Description of the sample ••....•.••
Data sheet for recording measure-
ments derived from dental casts ...•
Descriptive statistics of intra-
observer error calculation •••••••• 70
TABLE I
TABLE II
TABLE III
TABLE IV Level of significance (p) of
Wilcoxon signed ranks to indicate
differences between measurements
repeated three time to test for
intra-observer error •....••••••••• 71-73
TABLE V Age related mean values of certain
maxillary dimensions for males and
females 90
TABLE VI Age related mean values of the
palatal plane angle for males and
females. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
TABLE VII
TABLE VIII
TABLE IX
Age related mean values of certain
cranial base dimensions for males
and females .
Descriptive statistics for metrical
data in respect to the
nasomaxillary complex .•••••••••••••
Spearman correlation coefficients
comparing the relationship of the
92
97
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TABLE X
nasomaxillary and cranial base
dimensions to the lower incisor
irregularity index at T3 •••••••••••
Age related mean values of certain
mandibular anteroposterior spatial
positional changes for males and
98
xiii
TABLE XI
females 110
Age related changes in mandibular
growth direction - angular and
linear values for males and
females 111
TABLE XII
TABLE XIII
TABLE XIV
Age related mean values of
mandibular gonial angle growth
changes for males and females ....••
Age related mean values of
mandibular corpus length growth
changes for males and females .•••••
Age related mean values of
mandibular rant" 3 height changes for
112
112
TABLE XV
males and females •.•...•••••••.•••• 113
Age related mean values of
mandibular chin button/taper
change 113
TABLE XVI
TABLE XVII
Descriptive statistics for metrical
data in respect to the mandible ••••
Spearman correlation coefficients
comparing the relationship of the
mandibular dimensions to the lower
117-118
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TABLE XVIII
incisor irregularity (L-Irreg) •••••
Age related mean values of changes
of the ANB angle for males and
119
xiv
females............................. 134
TABLE XIX
TABLE XX
Descriptive statistics for metrical
data in respect to the antero­
posterior relationship of the
maxilla to the mandible •••••.••••••
Frequency of the severity of molar
and canine anteroposterior cusp
relationships recorded pre­
treatment, post-treatment and
138
140
141
TABT.JE XXI
TABLE XXII
TABLE XXIII
post-retention. . • • • • • • • • • • • • • • • • • • • • 139
Spearman correlation coefficients
comparing the relationship of the
irregularity of the mandibular
incisors at T3 to the variables
depicting anteroposterior dimension
at T1, T2 and T3 •.•.•••••.••.••••••
Kruskal-Wallis test indicating
whether significant relationships
existed between molar and canine
anteroposterior relationships at T1,
T2 and T3 and the irregularity of
the lower incisors at T3 ••••.••••••
Age related mean values of
mandibular intercanine dimension
(mm) for males and females •••••••.. 168
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TABLE XXIV
TABLE XXV
Age related mean values of maxillary
bimolar dimension (mm) for males and
fem;'~les ••••••••••••••••••••••••••••
Age related mean values of
mandibular arch length change (mm)
measurea mesial of the first
168
xv
molars 168
TABLE XXVI
TABLE XXVII
TABLE XXVIII
TABLE XXIX
Age related mean values of overbite
change (mm) for males and females ••
Age related mean values of overjet
change (mm) for males and females ••
Descriptive statistics of metrical
data in respect to the occlusion ••••
Frequency distribution (prevalence)
of Angle classification (molar
relationships) and Bolton tooth-
176
176
216-217
size discrepancy................... 218
TABLE XXX
TABLE XXXI
Frequency distribution of crowding
and occlusal parameters •••..•..•.••
Frequency of maxillary and
mandibular third molars present at
219-220
T3 221
TABLE XXXII
TABLE XXXIII
Spearman correlation coefficients
comparing the relationship of the
measured occlusal variables at T1,
T2 and T3 to the irregularity of the
mandibular incisors at T3 ••••••••••
Kruskal-Wallis test comparing
222
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TABLE XXXIV
TABLE XXXV
TABLE XXXVI
TABLE XXXVII
significant relationships of
occlusal variables at T1, T2 and T3
to thd irregularity of the lower
incisors at T3 •••••••••••••••••••••
Descriptive statistic~ for metrical
data in respect to the anterior
border of the dentition ••.•••.•••.•
Spearman correlation coefficients
(r) comparing similar measurements
depicting the anterior border of
the dentition for the three phases
of evaluation .
Spearman correlation coefficients
comparing the relationship of the
irregularity of the mandibular
incisors at T3 to archwidth, arch­
length and incisor position at T1,
T2 and T3 . . ......••.•......•....••
Longitudinal comparison of the
Spearman correlation coefficients
for the Little Irregularity Index
(Little, 1975) .•••••...•.•••••••••.
223
247
248
249
250
xvi
TABLE XXXVIII Descriptive statistics for metrical
data in respect to the vertical
dimens ion 267
TABLE XXXIX Spearman correlation coefficients
comparing the relationship of the
irregularity of the mandibular
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TABLE XL
TABLE XLI
TABLE XLII
TABLE XLIII
TABLE XLIV
TABLE XLV
incisors at T3 to the variables
depicting the vertical dimension at
Tl, T2 and T3 .
Differences between extraction and
nonextraction groups for a number
of variables .
Differences between extraction and
nonextraction groups for maxillary
variables .
Differences between extraction and
nonextraction groups for maxillary
to mandibular variables ...••••••.••
Differences between extraction and
nonextraction groups for soft tissue
variables .
Differences between extraction and
nonextraction groups : descriptive
statistics for the Little
Irregularity Index (Little, 1975) .•
Age related changes of cephalometric
parameters describing soft tissue
xvii
268
289-291
292-293
296-297
298
change 321
TABLE XLVI
TABLE XLVII
Descriptive statistics for metrical
data in respect to the soft tissue •
Spearman correlation coefficients
comparing the relationship of the
lower incisor irregularity at T3
against the measured variables at
341
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TABLE XLVIII
Tl, T2 and T3 ••••••••••••••••••••••
Sexual dimorphism in craniofacial
342
xviii
patterns ••••••••••••••••••••••••••• 361
TABLE XLIX
TABLE L
TABLE LI
TABLE LII
Differences between male and female
groups for age variable •••••••••••.
Differences between male and female
groups for a number of mandibular
variables .
Differences between male and female
groups for a number of maxillary
variables .
Differences between male and female
groups maxillary to mandibular
variables .
366
367-369
371-372
373-374
378
376-377
TABLE LIII
TABLE LIV
TABLE LV
Differences between male and female
groups for soft tissue variables •••
Differences between male and female
groups for initial Angle
classification and for extraction
and nonextraction treatment .•••••••
Differences between male and female
groups : descriptive statistics for
the Little Irregularity Index
(Little, 1975) .•••••••••••••••••••• 379
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FIGURE 1
FIGURE 2
FIGURE 3
FIGURE 4
FIGURE 5
FIGURE 6
FIGURE 7
FIGURE 8
FIGURE 9
FIGURE 10
FIGURE 11
FIGURE 12
FIGURE 13
FIGURE 14
FIGURE 15
FIGURE 16
FIGURE 17
FIGURE 18
FIGURE 19
LIST QF ILLUSTRATIOUS
Ideal intercuspation in buccal
view .
Overjet in sagittal view ••••••••••••
Overbite in sagittal view •••••.•••••
Anterior open bite •••••••.••.•••••••
Anterior cross bite ••••••••.•••••...
Posterior crossbit~ •••••••••••••••.•
Assessment of crowding/space
!!11()~t:2l~E! ••••••••••••••••••••••••••••
Little Irregularity Index •••••••••••
Mandibular intercanine width ••••••••
Maxillary intermolar width •••••••••.
Mensuration of rotation;
Deviation from mid-fossa occlusal
1ine (degrees) .
MP :1.dibular arch; Curve of Spee ••••••
Conventional arch length •••.•••••••.
Little arch length •••••••••.••••••••
Basic Cephalometric analysis •.•.••••
Ricketts analysis ••..•.•••••••••••••
Bjork/Jarabak analysis •.•..•••••.••.
Holdaway and more •••••••.•••••••••••
Landmark location necessary for use
of Oliceph Cephalometric
25
27
28
29
31
32
34
35
36
38
39
40
43
44
50
51
52
53
xix
analysis 54
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240
CHAPTER 8
A LONGITUDINAL EVALUATION OF THE ANTERIOR BORDER OF THI
DENTITION AND ITS RELATIQNSHIP TO LOWER INCISOR IRREGULARIty
8.1 Introduction
Orthodontists in clinical practice have directed specific
at-tention to the mandibular arch as being greatly limiting,
and therefore of primary consideration, in diagnosis
(Schulhof, Lestrel, Walters and Schuler, 1978).
The question as to whether it is possible for the mandibular
cuspids to remain stable after orthodontic movement is often
raised in discussions regarding the stability of
post-treatment results. A study of orthodontic patients
approximately 7 years following active treatment shed some
light on this question (Gardner and Chaconas, 1976).
Accordingly it was shown that mandibular molars may be
expanded in the order of 2mm with little relapse, while the
majority of cuspids(60%) showed relapse when expanded as
little as 1 mm. Extraction and nonextraction cases were
subject to similar incidences of relapse which is in
agreement with the findings of Riedel (1960) who believed
that lower cuspids can not be permanently expanded. Although
the literature provides few indications for predicting which
cases will tolerate expansion, there appears to be a
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241
tendency for the Class II division 2 cases to show a greater
potential for remaining stable following some incr.a.. in
lower arch width (Riedel, 1960; Shapiro, 1974).
Schulhof and associates (1978) derived a formula which
indicates that patients with brachyfacial patterns have
wider dental arches than those with dolichofacial patterns.
strang (1949) stated that the intercanine width of the
mandibular arch is an infallible guide to balance of the
muscles which dictate the limit of denture expansion in this
area. Others have also reported that intercanine width has a
tendency to remain the same or return to the original
dimensions after treatment (Dona, 1952; Arnold, 1963;
Welch, 1965).
A method for predetermining the ideal dental arch width has
become known as "Pont's Index" (Pont, 1909) and was used to
study 91 Navajo children with ideal occlusions (Worms ~
Al., 1969). At a confidence level of 1%, there was a
significant difference between observed and calculated
premolar and molar widths. Worms et ale (1969) and others
concluded that the reliability of Pont's index as a
diagnostic tool in orthodontics is highly questionable
(Greve, 1933; Hotz, 1961; Smyth and Young, 1932; Korkhaus,
1939; Joondeph, Riedel and Moore, 1970). The use of the
index was brought into focus by practitioners who depend
almost entirely on it for determining proper arch width and
who as a result may thus be expanding the mandibular teeth
beyond their stable limits.
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The determination of ideal arch form is greatly dependent on
the position of the cuspids which represent the cornerston••
of the dental arches (Andria and Dias, 1978). In general
orthodontists should not lose sight of the fact that our
biggest problem seems to be arch width (Howes, 1957) and it
may be pertinent to note some other observations on this
controversial issue.
Walter (1953, 1962) studied the stability of the dental
arches after expansion, taking measurements before, at the
end of treatment, and several years after retention was
discontinued. He reported that some extraction and
nonextraction cases, expanded during treatment, continued to
expand during and after retention. steadman (1961), somewhat
surprisingly, also found that intercanine width changes
were unpredictable in their post-treatment stability.
The anterior limits of the lower dental arch is described,
not only by the intercuspid width, but also by the incisor
position in the sagittal plane. Since the introduction of
cephalometries this position has become a valuable tool when
assessing a malocclusion (Broadbent, 1931; Williams, 1969).
The mandibular incisor is believed to be the crux of case
analysis (Williams, 1969). Various norms in respect of the
position of the lower incisors have been proposed (Steiner,
1953; Tweed, 1954, 1966; Ricketts et al., 1979) and used to
predict the stability of treatment results (Williams, 1985).
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It is suggested that the lower incisor can only be moved
within a small range if stability is to be achieved (Mill.,
1966, 1967).
In the maxilla the incisors play an important role a. they
provide the anterior guiding slope for protrusive excursions
of the mandible. The position of the upper incisors should
be in harmony with the morphology of the articular eminence
in order to protect the temporomandibular joint (Celenza and
Nasedkin, 1978; Ash and Ramfjord, 1982). The upper inci.or
position may be measured relative to the facial axis
(Ricketts et al., 1979) or to the Frankfurt horizontal line
(Riolo et al., 1974). It's relationship to the lower
incisors is described by the interincisal angle (Downs,
1948; Steiner, 1953) as well as by measurement of the
overbite and overjet (Moyers et al., 1976; Little, 1975).
Although these norms were described for North American
Caucasians, they are universally accepted. SPecific
population studies must be kept in mind when assessing the
norms for different ethnic groups (Ricketts et al., 1979;
Platou and zachrisson, 1983).
A~ a note of caution, however, it should be stated that the
abovementioned measurements may be influenced by changes in
arch length (Platou and Zachrisson, 1983; Sinclair and
Little, 1983). According to Sinclair and Little (1983)
dental arch lengths change in untreated normal subjects and
recently the same phenomenon was described in
orthodontically treated individuals (Little, 1990; Simons
and Joondeph, 1973).
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Various authors (Gardner and Chaconas, 1976; El-Mangoury,
1979; Udhe, Sadowsky and BeGele, 1983; Little, Wallen and
Riedel, 1981) have tried, with little success, to predict
whether orthodontically treated dentitions will remain
stable (Amott, 1962; Shields, Little and Chapko, 1985;
Kaplan, 1988).
8.2 Objectives
The objectives of this part of ~he present study were:
i) to assess the long-term changes in the parameters
defining the anterior limits of the dentition after
active orthodontic treatment.
ii) to discuss their possible relationships to lower
incisor crowding.
These objectives are encompassed in those of Chapter 7, but
the anterior border of the dentition, being such an
important area in function and aesthetics, merits a more
extensive evaluation and discussion than that presented in
Chapter 7.
8.3 Materials and methods
A general description of the materials used and methods
employed to analyse the duta are set out in Chapter 3.
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Orthodontic study casts and lateral cephalograms were
analysed for all three stages studied. Intra-obs.rver error
was found to be less than 1.0t and it was concluded that
this error had no effect on the outcome of the results.
The study casts were measured with digital calipers capable
of measuring to O.Olmm. Measurements of the following
metrical characters were obtained:
1. The lower intercanine width was measured between the
cusp tips (L3-3I) of the clinical crown (Moyers at al.,
1976) as well as the most prominent buccal aspect in the
mid-longaxis (L3-3B).
2. The arch length measured as the distance from the
midpoint between the mandibular central incisors
perpendicular to a line joining the mesial aspects of the
mandibular lower first molars (ARCHL) (Moyers et al., 1976)
as well as the measurement used by Little (LITTLE-A)
(Little, Riedel and Engst, 1990).
3. The ov~rjet was measured as the horizontal difference
between the buccal surfaces of the mandibular and maxillary
central incisors (OJB) (Ricketts et al., 1979).
4. The overbite was measured as the vertical difference
between the incisal edges of abovementioned teeth (OBB)
(Ricketts et al., 1979).
5. The Little irregularity index (Little, 1975) gave an
indication of lower incisor change during the period
following active orthodontic treatment.
Cephalometric measurements obtained with the use of the
Oliceph compuLe~ programme included the following:
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246
1. The mandibular incisor position as described by:
i) steiner (1953) (I-NB-MM and I-RB-DEG).
ii) Ricketts et 01. (1979) (I-APO-MM and I-APO-DEG).
iii) Tweed (1966) (IMPA).
2. The interincisal angle (I-I) (steiner, 1953).
3. The maxillary central incisor position as described by:
i) Steiner (1953) (I-NA-MM and I-NA-DEG).
ii) Ricketts et 01. (1979) (I-FACAX).
iii) Downs (1948) (I/APO-MM).
iv) Riolo et ale (1914) (I-FH).
The changes in these variables were determined
longitudinally with a mean post-treatment follow-up 7 years.
~rhey were chosen for their proximity to the anterior limits
of the dentition.
The data were subjected to descriptive statistics such as
the mean (X) and standard deviation (S.D.) for each of the
three evaluations. The Friedman test was used to test for
signi.ficant longitudinal changes and pairwise comparisons
"ere made if the overall test was significant. Associations
between measurements made at the same or different points in
::.:i.me were assessed by Spearman correlation coefficients (r)
(Zar, 1984). The significance level of this part of the
:3t.llcy was taken to be p = 0.05.
':';.4, Results
:'he findings are set out in Tables XXXIV, XX1..rv, XXXVI and
<XXVI I.
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jABLE XXXIV
DESCRIPTIVE STATISTICS FOR METRICAL DATA IN RESPECT TO THE ANTERIOR
BORDER OF THE DENTITION
(Friedman test inclUded)
Tl T2 T3 Tl-T2 Tl-T3 '12-'13
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D. p-value Pairwise Differences
L3-3I 26.19 1.72 25.99 1.69 25.77 1.88 0.08 x x x
L3-3B 30.52 1.90 31.07 3.14 30.16 2.11 0.10 x x x
LITTLE-A 61.06 4.31 56.69 6.83 54.99 7.05 0.0001 x + +
AReHL 23.50 2.37 20.75 3.19 20.01 3.52 0.0001 + + +
I-NB-MM 3.89 2.11 4.32 1.'.63 4.04 1.65 0.15 x x x
I-APO-MM 0.42 2.86 1.29 1.90 0.85 1.93 0.03 - x x
IMPA 96. 7~' 10.67 98.54 6.64 97.79 6.68 0.05 - x x
I-APO-DEG 23.75 5.17 27.71 4.68 27.38 4.65 0.0001 - - x
I-NB-DEG 27.22 6.41 28.43 5.08 26.71 4.72 0.03 x x +
I-I 126.40 11.05 127.05 9.34 129.38 7.79 0.03 x - x
OJB 6.21 3.29 2.85 0.85 3.17 1.23 0.0001 + + x
OBB 4.22 1.48 2.82 0.97 2.81 1.09 0.0001 + + x
I-NA-MM 4.14 2.86 2.84 2.61 3.49 2.60 0.002 + x
I/-APO-MM 7.29 3.13 4.31 1.73 4.42 1.93 0.0001 + + x
I-NA-DEG 22.99 9.09 22.60 8.44 22.35 7.48 0.83 x x x
I/-FH 114.41 8.76 112.55 8.11 112.65 7.09 0.14 x x x
I/-FACAX 4.02 8.65 5.57 7.29 6.19 6.08 0.19 x x x
L-IRREG 4.21 3.57 0.43 0.66 1.71 1.64 0.0001 + +
S.D. =
+ =
=
x =
Standard deviation
Significant, p ( 0.05 (TI > '12, '13)
Significant, p ( 0.05 ('11 < '12, T3)
Not significant, p > 0.C'5)
N
~
~
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TABLE xxxv
SPEAIUWf CORRELATION COEFFICIENTS (r) COMPARING SIMILAR
MEASUREMENTS DEPICTING THE ANTERIOR BORDER OF THE DENtITION
FOR THE TUREE PHASES QF EVALUATION
T1 T2 T3
VARIABLES r r r
L3-3I and L3-3B 0.79 0.72 0.69
LITTLE-A and ARCHL
·
0.87 0.94 0.91
·I-BB-MM and I-APO-MM: 0.74 0.67 0.50
I-BB-MM and IMPA
·
0.59 0.42 0.37
·I/-FH and I/-FACAX
·
-0.87 -0.85 -0.77
·I-I and I/-FACAX 0.82 0.80 0.79
p < 0.0001 for a11 va1ues.
248
I
I
i
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TABLE XXXVI
SPEARMAN CORRELATION COEFFICIENTS CQKPARING THE
RELATIOINSHIP OF THE IRREGULARITY OF THE MANDIBULAR INCISORS
AT T3 TO ABCHWITH. ABCHLEBGTH AND INCISOR POSITIQN AT Tl. T2
AND %3
L-IRREG
T1 T2 T3
VARIABLE r r r
L3-3I 0.05 0.64 -0.01 0.91 0.16 0.14
L3-3B -0.01 0.91 -0.06 0.58 0.06 0.58
LITTLE-A -0.11 0.32 0.06 0.55 -0.01 0.93
ARCHL -0.12 0.27 0.04 0.72 0.01 0.89
I-NB-MM -0.07 0.50 0.13 0.23 0.03 0.75
I-APO-MM -0.19 0.06 -0.03 0.80 -0.07 0.52
IMPA -0.07 0.49 0.01 0.91 0.05 0.65
I-APO-DEG -0.20 0.06 -0.04 0.69 -0.05 0.63
I-NB-DEG -0.16 0.14 -0.08 0.43 -0.06 0.59
I-I 0.06 0.61 -0.02 0.85 -0.09 0.39
OJB 0.20 0.06 0.09 0.43 0.04 0.75
DBB 0.11 0.31 0.13 0.23 0.11 0.29
I-NA-MM 0.04 0.74 0.08 0.45 0.08 0.46
I/-APO-MM 0.08 0.48 0.10 0.34 0.11 0.32
I-NA-DEG -0.01 0.96 0.07 0.53 0.09 0.42
I/-FH -0.03 0.79 -0.04 0.71 -0.03 0.79
I/-FACAX -0.03 0.81 -0.04 0.69 -0.09 0.39
r = Spearman correlation coefficient
Probability values in parentheses, p > C.05.
249
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TABLE XXXVI I
LONGITUDINAL CQMPARISOlf or THE SPIWUWf CORRELATION
COEFFICIENTS FOR TUB LITtLE IRREGULARITY IBDBX(Little, 1975)
250
I,
L-IRl
L-IR2
L-IR2
r
0.09 (0.43)
L-IR3
r
0.03 (0.78)
0.37 (0.0004)
r = Spearman correlation coefficient
Probability values (p) in parentheses.
L-IR = Little Irregularity at Tl, T2, T3.
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251
The majority of the measurements (Table XXXIV) r ...inad
clinically reasonably stable during the post-orthodontic
period (T2-T3). The lower incisor to NB-line meaaured in
degrees (I-NB-DEG), the upper incisor to NA-line measured in
millimetres (I-HA-MM) and the Little Irregularity Index
changes, although significant, all stayed within acceptable
norms (Steiner, 1953; Little, 1975). The only real
except:ion was the arch length change (LITTLE-A and ARCHL)
which significantly decreased monotonically from the initial
to the final observation (Tl-T3).
Some of the groups of variables were correlated with each
other in order to assess whether there was a significant
agreement between measurements measuring the same parameter.
Table XXXV indicates that very strong correlations were
indeed achieved. One could thus substitute Little-A for
ARCHL or I-NB-MM for I-APO-MM as an example and still make
valid conclusions.
None of the correlations in Table XXXVI were of any
significance when correlated with the Little Irregularity
Index. Regression models were formulated for the dependent
variable Little Irregularity (L-IRREG), but this was not
succesful. No measured variables could be combined to form a
prediction model for the Little Irregularity Index (R-square
= 0.01-0.15; C(P) = -0.58-5.69).
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The Little Irregularity Index measured at the po.t-tr••taent
observation (T2) and at the final observation (T3)
correlated significantly (r • 0.37; p. 0.0004) and thus
supported the acceptable clinical stability of the treated
results (Table XXXIV and XXXVII).
8.5 DiscussioD
The literature on the stability of the lower arch after
orthodontic treatment shows that there is a tendency for the
intercanine width to lose the expansion gained during
treatment as a result of the canines relapsing toward their
initial positions (Pont, 1909; Haas, 1961; Arnold, 1963;
Bishara, Chadha and Potter, 1973; Shapiro, 1974; Gardner
and Chaconas, 1976). The intercanine width in this sample
remained practically unchanged from T1 to T2 (was actually
slightly reduced during treatment) (p > 0.05) and although
it was stable from a clinical point of view when measured
at the final observation (T3), there was a tendency to
decrease to a value less than the original (T1) dimension
(Table XXXIV).
Clinical observation has given some indication of the
possibility of achieving a stable expansion of the lower
arch subsequent to expansion of the midpalatal suture (Haas,
1965, 1980; Wertz and Dreskin, 1977; Moyers, 1988). It would
appear from the data of this stUdy that the lower
intercanine dimension ought not to be changed during
treatment. The acceptable Little Irregularity Index (Table
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253
XXXIV) probably resulc8 !~(;rn the constant intercanine
dimension. The work of e;hields, Little and Chapko (1985)
would not entirely support tnis contention.
The lower and upper incisor positions and the interincisal
angle which were mensurated cephalometrically, as well as
the overbite, the overjet and the Little Irregularity Index
recorded on the orthodontic stUdy casts, all changed during
the study period (T1 to T3) to within ideal norms (Table
XXXIV). Significant changes measured during the
post-orthodontic period (T2-T3) were indicated in Table
XXXIV. The lower incisor (I-NB-DEG) uprighted 1.72 degrees
during this period. Although not highly significant (p =
0.03), it can be assumed that its contribution to
irregularity took place either as anterior movement beyond
stable limits during T1 to T2 or due to the anterior
component of force following debanding. This phenomenon
could have taken place because the upper incisors and the
orbicularis oris and related muscles prevented the lower
incisors from staying in a proclined position. The upper
incisor (I-NA-MM) proclined 0.65 mm (p = 0.002) during T2
to T3. This clinically negligible change could be ascribed
to physiological rebound or as part of the changes centering
around the lower incisor movement previously noted.
The only significant dimensional change (p = 0.0001) which
could have influenced the similarly significant change in
the Little Irregularity Index (p = 0.0001) following active
treatment was arch length (LITTLE-A and AReHL). Arch length
continually decreased between Tl and T3. It must be
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254
emphasized that although changes took place during T2 to T3
("relapse") all the end valuea measured were within
acceptable norms. The anterior component of force aa well a.
the mesial drifting tendency of teeth when in occlusion have
been cited as reasons for the above phenomenon (Van seek,
1978). The act of chewing produces a force with a ..aial
resultant expressed through the contact point. of the teeth.
The tendency for the teeth to move forward as a re.ult of
mastication and swallowing varies greatly according to the
angulations of the teeth with each other and is especially
affected by the steepness of the occlusal plane (Enlow,
1968; Van Beek, 1978; Behrents, 1984)
Groups of variables measuring practically the same parameter
as portayed in Table XXXV showed moderate to strong
correlations (p < 0.0001).
No significant correlation could be shown in this study for
the incisor position, arch length and arch width variables
compared with the Little Irregularity Index at T3 (Table
XXXVI). This is in accordance with the findings Shields At
Al. (1985).
It may thus be SPeculated that for this sample the anterior
border of the dentition remained stable following treatment
and that the constant reduction in arch length caused the
Little Irregularity Index to change from a mean value of
0.43 (T2) to 1.71 (T3). This value of discrepancy is in
accordance with a minimum irregularity, 1-3 as described by
Little (1975). The lower incisor irregularity at the end of
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255
treatment (T2) and the irregularity measured at the final
observation (T3) thus remained within clinically acceptable
stable limits (r. 0.37; p. 0.0004) (Table XXXVII). The
small change occurring in the Little Irregularity Index
could be ascribed to natural changes as was also reported in
the literature (Simons and Joondeph, 1973; Sinclair and
Little, 1983, 1985).
Sound orthodontic technique will help to attain the ideal
treatment goals noted previously and which are imperative to
achieve reasonable dental stability. Irrespective of all the
meticulous efforts taken by t"he orthodontists to secure a
functional and stable occlusion, certain changes do occur.
Some may call it relapse, others settling or physiological
rebound. The crux of the matter is that orthodontists have
to accept that natural changes will occur following
treatment and as long as there is a sound periodontium this
will be the order of the day. Patients must be made aware of
this fact and that, with slight irregularity, enaael
approximation may be required to help solve the probl..
(Sheridan, 1987; Radlanski and Jager, 1988; Sheridan and
Ledoux, 1989; Joseph and Rossouw, 1991). The orthodontist
cannot be held responsible for natural changes which aight
influence an ideal treatment result. Patient education or
informed consent relating to these changes cannot be
overemphasized.
8.6 Conclusions
1. Ideal treatment goals are essential if acceptable
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256
stability of orthodontic treatment i. to be achieved.
2. Variables de.cribing similar dimension. or positions
impart similar information and all or only one can be used
to evaluate the relevant recordings.
3. Expansion of the mandibular arch beyond the original
intercanine dimension is likely to lead to failure as this
dimension tends to decrease to below the original
measurement in the long-term.
4. change in arch length appears to be a major cause of
mandibular incisor irregularity.
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257
CHAnER 9
A LONGITUDINAL EVALUATION OF THE VERTICAL DIMElSIQR or THB
CRANIOFACIAL SKELETON IN SUBJECTS FOLLOWING QRTHQDQltIC
TREATMENT AND ITS RELATIONSHIP TO PQST-ORTHODQITIC LOIIB
INCISOR CROWDING
9.1 Introduction
The vertical relationship of the craniofacial skeleton of
orthodontic subjects can be assessed using cephalometric
analyses and photographic analyses. Originally the focus of
cephalometric analysis was on anteroposterior dimensions as
these measurements could be related to the Angle
classification of malocclusion (Angle, 1899, 1907). A
committee of the British Orthodontic Society suggested that
although the Angle system was an adequate classification of
anteroposterior jaw relationships, it did not include
information about the transverse and vertical planes of the
face and should be extended to do so (Bennett, 1912). It is
important to distinguish between dental and skeletal
components when measurements in the vertical plane are
evaluated.
The overbite or bite depth is determined by the contact
relationships of the teeth. This causes an inherent
contradiction in terms such as Itsk~letal oPen bite lt and
"skeletal deep bite lt • The work of Sassouni (1970; defined
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258
these terms OR indicating skeletal proportions that cau.. a
bu.i.lt.-in tendency toward deep bite or open bite
relationships. As the mandible rotates downwards, there i.
an increasing tendency towards an anterior open bite.
conversely, a closing or upward rotation of the mandible
results in a tendency towards a deep bite. The chin is also
influenced by the mandibular rotations. A closing or forward
rotation results in a prominent chin button and a backward
or open rotation leads to a relatively weaker or more
distally positioned chi~ (Graber ~nd Swain, 1985).
Various methods may be used to assess the vertical
relationships of the facial skeleton (Downs, 1948; Steiner,
1953; 1weed, 1954; Coben, 1955; Moorrees and Lebret, 1962;
Bell, Proffit and White, 1980; Ricketts, 1981; McNamara,
1983; Moyers, 1988). The Bjork facial polygons emphasize the
interaction between facial and cranial base factors and
demonstrate how variations in, for example the cranial Dase
flexure angle, can influence the mandibular plane angle or
anterior vertical facial dimensions (Jarabak and fizzell,
1972).
Vertical dental ploblems are normally associated with the
type of skeletal pattern which is present. The amount and
direction of mandibular rotation strongly influences
posterior dental eruption, which tends to be deficient in
skeletal deep bite facial patterns and excessive in skeletal
open bit& facial types. Dental compensation for the skeletal
jaw relationships can occur in the amount and direction of
eruption of the anterior teeth (Graber and Swain, 1985).
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259
Norms for infra-eruption and supra-eruption were publiahed
as linear measurements from the base of the alveolar proce••
(Riolo at 01., 1974). A critical distinction, however, au.t
be made in diagnosis of vertical problems. A skeletal
problem is not necessarily accompanied by a dental problem,
suggesting that for example, a skeletal open bite mayor .ay
not be accompanied by a dental oPen bite (Graber and Swain,
1985). It is obvious that the treatment prescribed for a
Class II deep bite dental relationship would be different
from that prescribed for a Class II skeletal deep bite
pattern.
The aetiological factors which may cause vertical problems
have been well documented ranging from simple thumb sucking
habits, ankylosis, upper airway obstruction to genetic
inheritance (Proffit, 1986; Moyers, 1988).
treatment)
measured
The success of non-surgical (only
correction of vertical
by the stability of
employing orthodontic
problems is normally
the overbite-overjet
relationship.
Overbite c.:>rrection and stabiliti' have been subjects of a
great deal of controversy (Fogel and Magill, 1970).
Concern:i.ng these subjects Schudy (1963) stC".tes that, "when
molars are moved occlusally during treatment, overbite
correction is nearly always successful". The intrusion of
incisors, he claims, will result in re-extrusion, causing a
return of the overbite, and he advises against the intrusion
of mandibular incisors. This concept is in di~ect contrast
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260
to the advised use of the utility arch (Rickett. ~ ~:.,
1979). They stated that when molars were extruded or .cved
occlusally, the masticatory muscles in reverting to their
previous origin and insertion lengths will re-establish
overbite and facial height. They further believe that
incisor intrusion al~o provides a greater likelihood of
stability in overbite reduction than does molar extrus!on.
This is due to the fact that the freeway space is preserved
when vertical problems are treated by incisor movements.
The modality and effectiveness of bite plate therapy has
also been a subject of debate. Mershon (1937) stated that
"elongation of the posterior teeth throws a constant strain
on the muscles of mastication, and destroys the interrelated
harmony of parts". He observed that the only permanent
change resulting from bite plate therapy was the depression
of anterior teeth in the alveoli. In contrast it was
reported that the correction of a deep overbite through the
use of ~ bite plate was permanent, and encouraged further
eruption of the posterior teeth (Hemley, 1953). The
latter author claimed that there was no depression of
mandibular incisors as the result of the use of a bite
plane.
The Begg orthodontic treatment philosophy encourages that
bite opening shou1d be accomp1ished by intrusion of upper
and lower incisor teeth, and that molar height should be
relatively undisturbed (8egg, 1971, 1977). Dr. Begg felt
that extrusion of molar teeth invited overbite relapse.
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261
In a study regarding intrusion of teeth Swain and Ackerman
(1969) found that anterior overbite correction va.
accomplished mainly through an increased eruption of the
mandibular molars, and not by an intrusion of the mandibular
incisors; and that in almost all cases examined, mandibular
molars continued to erupt after appliance removal. During
treatment, maxillary molars and incisors did not exhibit the
same degree of eruption as did their mandibular
counterparts. They pointed out that this observation may
be due to the fact that the palatal plane is not as reliable
as the mandibular plane for superimposition when assessing
total vertical growth.
There is some evidence to show that mandibular molars do not
intrude during retention, but actually continue to erupt as
do the mandibular incisors. During the retention period,
the maxillary molars and incisors remain at the same
vertical level, or tend to erupt to a lesser degree than do
their mandibular counterparts (Fogel and Magill, 1970).
Dental extractions perfomed as part of orthodontic treatment
should not cause an increase in the overbite if adequate
care is taken by the operator. Deep overbite per se,
before treatment, is thus not necessarily a contraindication
for extraction therapy (Magill, 1960). Orthodontists,
should in such patients refrain from using any force, which
would tip the occlusal plane upward in the incisor area.
Continued use of Class II elastics is advocated in these
instances (Schudy, 1964).
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262
The measurement of the interincisal angle forms an import~nt
part of many cephalometric analyses. The interiacisal angle
is concerned with the stability of the overbite. Norms
for the interincisal angle were proposed, arM:wgf1t others,
by Steiner (1953). He favours a labial axial i"~;;lination
of the maxillary and mandibular incisors with an ideal
interincisal angle of about 131 degrees. Schudy (1963)
prefprs a more obtuse interincisal angle of 135 degrees.
Ricketts et ale (1979) on the other hand advocate a more
acute interincisal angle, suggesting a value of 125 degrees
as an acceptable norm.
The greater the closing rotational growth within the
mandible, the greater will be the compensatory proclination
necessary to keep the incisors within the area of balance
(Perera, 1987). On the one hand downwardly-directed
mandibular growth and/or treatment change and on the other
hand forward mandibular rotations are among the factors
which may contribute to late crowding of the anterior part
of the lower arch (Bjork and Skieller, 1972; Richardson,
1986). Orthodontists should refrain from creating an open
rotation of the average mandibular plane angle during
treatment as this angle tends to become more acute during
maturation of the face (Tweed, 1954, 1966). This
phenomenon will cause lower incisor irregularity in a
similar way as that caused by the normal forward closing
rotation of ~he mandible during post-treatment growth (Bjork
and Skieller, 1972)~ Apart from the above two growth
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263
patterns no correlation could, however, be shown between
lower incisor relapse and other skeletal and dental
parameters (Shields, Little and Chapko, 1985; Little, 1990).
9.2 Objectives
There was no longitudinal data available for this sample
(Table I) in respect to growth or orthodontic treatment
changes. It was thus important to study the vertical
dimension, which was not previously defined in this manner,
with the purpose to add new data to the literature, and to
enable one to compare the changes occurring in this sample
to the studies noted previously.
Hence, the objectives of this part of the stUdy were:
i) to assess the longitudinal changes in the vertical
dimensions of subjects following orthodontic treatment.
ii) to determine if any correlation existed between the
vertical changes observed and post-orthodontic lower
incisor crOWding.
9.3 Materials and methods
Eighty-eight Caucasian SUbjects were longitudinally assessed
in respect of relapse of their dentitions following
orthodontic treatment. The malocclusions were treated using
conventional edgewise mechanics. A general description of
the materials used and the methods employed to assess the
data is given in Chapter 3. A description of the sample is
set out in Table I.
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calipers capable
variables were
Orthodontic study casts and lateral cephalograms were
analysed for all three of the stayes studied. Intra-observer
error for this part of the study was found to be less than
1.0% and it was concluded that this error had no significant
effp.ct on the outcome of the results.
The study casts were measured with digital
of measuring to O.Olmm. The following
measured:
1. The Little Irregularity Index (L-IRREG) as described
by Little (1975).
2. Overbite (OBB) (Ricketts et al., 1979; Moyers, 1988).
The cephalometric measurements selected to depict the
vertical facial development were the following:
1. The mandibular plane angle GOGN-SN (Steiner, 1953) and
FHA (Tweed, 1954; Ricketts, 1981).
2. The facial axis angle (FAC-AXIS), mandibular arc
(MANn-ARC) and lower facial height (L-FACH) as described by
Ricketts (1981). These variables together with the FHA
determine the chin position relative to the rest of the
face.
3. The Bjork/Jarabak cephalometric analysis (Jarabak and
Fizzell, 1972) describes the rotational pattern of the face.
Amongst other variables it also describes an anterior deep
bite tendency as contributing to a closing rotation of the
mandible. Mensuration of vertical dimensions by
Bjork/Jarabak (Jarabak and Fizzell, 1972) were:
i) Anterior facial height measured from Nasion to
Menton (ARTFACH-MM) .
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4.
(1953).
265
ii) Posterior facial height measured from Sella to
Gonion (POSTFACH-MM).
iii) The posterior to anterior facial height ratio
expressed as a percentage (SGO-NME). Open
rotation (smaller than 62\) or closing rotation
(larger than 65') could be predicted.
iv) The articular angle measured from Sella to
Articulare to GOnion (ARTANGLE).
v) The Gonial angle measured from Articulare to
Gonion to Menton (GONANGLE).
vi) The sum angle (SUMANGLE) is a summation of (iv),
(v) and the cranial base angle measured from
Nasion to Sella to Articulare (SADANGLE). The sum
angle gives an indication of a clockwise (the
value of the summation of the three angles is
larger than 396 degrees) or counterclockwise
(the value of the summation of the three angles
is less than 396 degrees) rotational facial
pattern.
vii) The ramus height measured as the distance between
Articulare and Gonion (RAMH-MM). Counterclockwise
or closing rotation of the mandible indicates a
more rapidly increasing posterior face height.
The ramus height dimension assisted in this
regard.
The interincisal angle (I-I) as described by Steiner
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266
The data were subjected to descriptive statistics .uch.s
mean and standard deviation for each of the three ••t. of
records studied. The Friedman test was used to test for
significant differences between the groups at the three time
intervals. Spearman correlation coefficients were used to
study the relationships of the different variables to the
post-orthodontic lower incisor irregularity (T3) (Little,
1975) (Zar, 1984). The accepted significance level of this
part of the study was taken to be p = 0.05.
9.4 Results
The findings of this study are set out in Tables XXXVIII and
XXXIX.
The purpose of the measurements in this part of the study
was to assess the longitudinal changes which took place in
the vertical relationship between the maxilla and the
mandible (Table XXXVIII). These changes were subsequently
correlated with the post-orthodontic Little Irregularity
Index (Little, 1975) (Table XXXIX).
Significant mean changes of variables (p < 0.05) that were
measured during active treatment (T1-T2) were: an open
rotation (increase of the angle) of the PAC-AXIS by an
average of 0.58 degrees, a mean increase in the L-FACH of
1.06 degrees, mean increases in the ANTFACH-MM of 6.74 mm
and POSFACH-KM of 4.45 mm, a mean increase in the RAMH-KM
of 3.18 mm and a mean decrease in the L-IRREG of 3.81 mm and
in OBB of 1.40 mm (Table XXXVIII).
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TABLE XXXVIII
DESCRIPTIVE STATISTICS FOR METRICAL DATA IN RESPECT TO THE VERTICAL DIMENSION
(fX1edmon test includeg)
Tl T2 T3 Tl-T2 Tl-T3 T2-T3
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D. p-value Pairwise Differences
GOGN-SN 33.44 4.93 34.05 5.76 32.19 6.24 0.0001 x + +
FHA 23.09 4.69 23.39 5.52 21.46 7.11 0.0001 x + +
FAC-AXIS 88.94 4.11 88.36 4.46 89.43 5.13 0.0001 + x
MAND-ARC 29.91 5.47 30.76 5.95 33.90 5.91 0.0001 x
L-FACH 43.56 4.44 44.62 4.83 44.03 5.01 0.0001 - x +
,~l~TFACH-MM 115.91 5.94 122.65 7.34 126.49 7.90 0.0001
tJOSTFACH-MM 74.44 4.89 78.89 6.27 85.01 7.98 0.0001
SGO-NME 64.32 4.39 64.50 4.93 67.25 5.17 0.0001 x
ARTANGLE 146.11 7.11 146.08 7.43 146.10 7.62 0.58 x x x
GONANGLE 124.31 6.34 124.44 6.54 121.83 6.81 0.0001 x + +
SUMANGLE 393.89 5.38 394.46 5.98 391.78 6.36 0.0001 x + +
RAMH-MM 42.94 4.16 46.12 5.25 51.49 6.82 0.0001
L-IRREG 4.21 3.57 0.43 0.66 1.71 1.64 0.0001 + +
OBB 4.22 1.48 2.82 0.97 2.81 1.09 0.0001 + + x
I-I 126.40 11.05 127.05 9.34 129.38 7.79 0.03 x - x
S.D. = Standard deviation
+ = Significant, p < 0.05 (Tl > T2, T3)
= significant, p < 0.05 (TI < T2, T3)
x = Not significant, p ) 0.05
N
0\
...,J
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TABLE XXXIX
SPEARMAN CQRRELATIOH CQEFFICIEHTS COMPARING THE BELATIOl8HIP
QF THE IRREGULARITY Qr THE MAHDIBULAR INCISORS AT T3 TO THE
VARIABLES DEPICTING THE VERTICAL DIMENSION AT Tl. T2 AID T3
L-IRREG
Tl T2 T3
VARIABLE r p r p r p
GOGH-SH 0.04 0.73 0.04 0.74 0.008 0.94
FHA 0.01 0.89 0.08 0.46 0.02 0.89
FAC-AXIS -0.09 0.39 -0.07 0.50 -0.10 0.35
MANn-ARC -0.05 0.66 -0.16 0.14 0.05 0.63
L-FACH 0.13 0.23 0.06 0.59 0.10 0.34
ANTFACH-MM 0.001 0.99 -0.02 0.84 0.17 0.12
POSTFACH-MM -0.03 0.81 -0.01 0.53 0.02 0.87
SGQ-NME -0.04 0.74 -0.05 0.62 -0.06 0.60
ARTANGLE -0.02 0.82 -0.04 0.69 0.01 0.91
GONANGLE 0.04 0.73 0.08 0.46 0.04 0.71
SUMAHGLE 0.06 0.61 0.05 0.63 0.06 0.59
RAMH-Ml(
-0.07 0.54 -0.18 0.09 -0.01 0.89QBB 0.11 0.31 0.13 0.23 0.11 0.29
I-I 0.05 0.61 -0.02 0.85 -0.09 0.39
r = Spearman Correlation Coefficient
p = Significance level, p < 0.05
268
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(r < 0.18, P > 0.05) were
studied in this part of the
lower incisor irregularity
269
significant mean changes (p < 0.05) which occurred during
the post-orthodontic assess.ent period (T2-T3) were
decreases in the GOGM-SM (1.86 degrees), FHA (1.93
degrees), L-FACH (0.59 degrees), GOMANGLE (2.61 d~gr••• )
and SUMANGLE (2.68 degrees), and increases in the FAC-AXIS
(1.07 degrees), HAND-ARC (3.14 degrees), ANTFACH-MM (3.84
mm), POSFACH-MM (6.12 mm), RAMH-MM (5.37 mm) and L-IRREG
(1.28 mm) (Table XXXVIII).
The anterior and posterior facial and ramus heights were
the only metrical variables which showed significant
changes (p = 0.0001) at all three of the intervals assessed
being pre-treatment to end of active treatment (Tl-T2),
pre-treatment to the final observation at the end of the
study (Tl-T3) and post-treatment to the end of the stUdy
(T2-T3) (Table XXXVIII).
No significant correlations
observed between the variables
project and post-orthodontic
(Table XXXIX).
9.5 Discussion
The subject of post-orthodontic treatment failure is as wide
as the field of orthodontics itself (King, 1974).
The general morphology
largely determines the
Orthodontists are well
of the face and its various parts
direction of growth of these parts.
aware that growth can account for
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270
the success or failure of a treated malocclusion (Brodie/
1941, 1953), Bjork (1947), Lande (1952), (Richardson (1986)
and Perera (1987).
Growth may also cancel out some of the unfavourable side
effects resulting from orthodontic appliances. For
example, in any type of malocclusion the simple placement
of an orthodontic appliance causes the teeth to extrude
sligthly frcm the alveolar processes. Leveling teeth in
most types of Class II treatment tends to cause further
dental extrusion. In nongrowing patients the nett effect
of the dental extrusion is to cause the mandible to tip
downwards and for Pogonion to move posteriorly. With active
growth, however, the unfavourable side effects of the
orthodontic appliances apparently did more or less what
growth would have done and the mandible usually recovered
its original position (King, 1960, 1974). When this
phenomenon of downward tipping of the mandible occurred in
the absence of growth, the subsequent recovery after
treatment contributed to some of the unfavourable sequelae
of orthodontic treatment.
The mandibular plane relationehip to the cranial base
(GOGN-SN and FHA) did not change significantly during
treatment. An opening rotation of the mandible was,
however: observed during tnis time (T1-T2), borne out by
sig~ificant mean changes in the variables GOGN-SN, FHA and
FAC-AXIS. The slight jaw opening could have been due to
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the treatment mechanics. HAND-ARC,
showed favourable counterclockwise
mandible.
SGO-NME and
rotation
271
RAMH-MM
of the
The general nicture of the facial changes observed (Tl-T3),
is in accordance with the changes expected in normal
patients without treatment (Riolo et al., 1974; Moyers At
Al., 1976; Ricketts, 1981; Sinclair and Little, 1983, 1985).
The general increase in facial dimensions, as a reeult of
growth, was also manifested in the anterior and posterior
facial heights.
Following on orthodontic treatment mean vertical dental
corrections were achieved as a result of the overbite
being significantly (p = 0.0001) reduced from 4.22 mm­
2.82 mm during active treatment (T1-T2). The interincisal
angle was slightly increased but remained within
acceptable means for normal individuals and this change was
not significant (p > 0.05) from Tl to T2. The achievement
of a low mean value of 0.42 mm for the Little Irregularity
Index (1975) at T2 indicated successful alignment of the
lower incisors (Table XXXVIII).
The forward closing rotation (counterclockwise) of the
mandible continued in the post-orthodontic period (T2-T3).
This was observed in all the variables describing this
phenomenum (Table XXXVIII). Only the ARTAHGLE showed no
significant change during this period. The average changes
occurring during this period were mainly due to growth.
Following the removal of appliances some rebound of areas,
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272
containing elastic tissues, could also have taken place,
especially if those areas were changed during treatment
and should have been kept unaltered. When assessing the
changes during the period T1 to T2 it may be noted that
clinically acceptable norms were maintained and that many
of the changes could be ascribed to normal growth changes.
Overbite changes recorded in this study were not consistent
with others reported in the literature which reported that
overbite decreased during treatment and had a tendency to
increase sligthly after treatment (Dona, 1952; Walter, 1953;
stackler, 1958; Magill, 1960; Rose, 1967; Hernandez, 1969;
Bishara, Chada and Potter, 1973; Simons and Joondeph, 1973;
EI-Mangoury, 1979; Uhde, Sadowsky and BeGele, 1983). It
has been suggested by some authors that deep overbite
situations should be overtreated in anticipation of relapse
which tends to occur during the post-treatment period
(Riedel, 1960, 1969; Ludwig, 1966; Smith, 1969). Bresonis
and Grewe (1974) reported that post-treatment overbite
increased the least in Class I and Class III cases, and the
most in Class II division 1 cases. In constrast Hechter
(1975) maintained that Class 11 division 2 and not Class
II division 1 malocclusions experienced the greatest
overbite increase after treatment. The mean post-orthodontic
follow-up period for the present study was 7 years (mean
post-retention period 5 years). The overbite remained
practically unchanged during this period (T2-T3). The mean
interincisal angle (Table XXXVIII) responsible for
maintaining the overbite was less than 130 degrees and the
incisor positions on their apical bases were also within
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273
norms (Table XXXIV, Chapter 8). Excellent orthodontic
technique or too short a post-orthodontic follow-up period
could be the reason that there was so little change in the
incisor region (T2-T3) in the present sample. Another
possible cause for this result could be the fact that all
the Angle dental malocclusions were studied as a mixed
group. Some of the other samples previously cited included
only one of Angle's classifications. There exists, however,
variability between the dental classification (Angle, 1899)
and the skeletal classification (Steiner, 1953) which makes
this observation doubtful (Table 0). The discrepancy between
the dental and skeletal classification lead to the decision
to study the malocclusions as a group.
Irregularity of the lower incisors was experienced at T3,
but never to the same extent as the recorded pre-treatment
crOWding. This is in agreement with the results of Uhde,
Sadowsky and BeGole (1983). The mean changes in the Little
Irregularity Index (Little, 1975) from T2 to T3, however,
were within clinical acceptable limits. The changes which
occurred appeared to be associated with a mandibular forward
rotation, although no significant correlation could be
found to support this observation (Table XXXIX). The
literatur~ reports similar findings (Richardson, 1986;
Perera, 1987). The application of sound treatment principles
could assist in preventing severe relapse in the incisor
region. Patients and parents, however, should be informed
that changes in the vertical dimension of the dentofacial
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environment may take place in the post-treatment
that these could influence the alignment
detrimentally.
period and
of teeth
9.6 Conclusions
the
noted
to
rotation was
corresponds
1. A mean mandibular forward
throughout the study (T1-T3) which
changes occurring during normal growth.
z. Growth appeared to be responsible for most of the
post-treatment changes.
3. Overbite tended to remain stable following orthodontic
treatment which is in contrast to overbite changes occurring
during normal growth and to that recorded in some studies
noted.
4. A slight increase in lower
have been caused as a result of
incisor irregularity could
mandibular growth changes.
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275
CHAPTER 10
LONGITUDINAL EVALUATION OF EXTRACTION VERSUS NONBXTRACTIQI
TREATMENT WITH SPECIAL REFERENCE TO THE POST-TREATMIKT
IRREGULARITY OF THE LOWER INCISORS
10.1 Introduction
It is much easier to extract teeth than to determine with
certainty whether it is absolutely necessary to do so. The
extraction of a tooth requires nothing more on the part of
the practitioner than some skill in the use of the
instruments which are usually employed in this operation:
whilst the knowledge nescessary to appreciate the long-term
consequences of dental extractions can only be acquired by
time and stUdy (Delabarre, 1815).
Extraction of teeth as an aid in the treatment of
malocclusion is one of the oldest and most controversial
subjects in the history of orthodontics. During the early
1900's the controversy reached its peak with Edward H.
Angle and Calvin S. Case representing opposite viewpoints in
this matter (Cole, 1948).
Angle's dictum of a full complement of teeth was: that the
loss of two, four or even eight premolars arrested facial
development and expression and was far more damaging to the
patient's future than were crowded anterior teeth. According
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276
to Angle, extraction procedures never overcame faulty
muscular function (Weinberger, 1950) and accordingly
orthodontic treatment should set out to remove th~ causes of
malocclusion while retaining a full compliment of teeth
(Angle, 1907). Angle's influence dominated the discipline
of orthodontics for many years. With the development of
gnathostatic evaluation of dental occlusions, as well as
the simultaneous introduction of cephalometrics by
Broadbent (1931) and Hofrath (1931), the limitations of a
dominant nonextraction philosophy could be assessed.
The extraction controversy gained momentum with Case in the
1920's (Case, 1964) promoting extractions in or~hodontic
treatment. Many others also played a significant role in
resisting Angle's demand that the teeth should be kept in
place despite the type of malocclusion being treated
(Tweed, 1946; Nance, 1947; Dewel, 1959). Tweed (1946)
maintained that the dentition remained relatively stable
once it reached that state in the development of a
malocclusion in which the forces, originally responsible for
initiating the malocclusion, became neutralized. An
irregular dentition which is in balance may therefore
present a far more stable condition than does that same
dentition after orthodontic treatment. This is
parLicularly so if the treatment forces the the teeth into a
protrusive relationship to the supporting portion of the
bony base. This form of orthodontic treatment tends to be
fclloWE!d by the "collapse" of the dental arches which in a
normal occlusion is in harmony with its skeletal apical
bases. A large Percentage of malocclusions, which
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277
orthodontists are called upon to treat, have deficient
and/or deformed apical bases (Howes, 1947). Begg (1954)
supported extractions in orthodontic treatment after
having studied stone-age man's dentition. As a result of
his studies he' attributed good alignment of teeth to
interproximal attrition as a result of coarse diets and
sUbsequently advocated extractions as a means of
compensating for the lack of attrition in most modern
dentitions. Tweed (1944), one of Angle's most ardent
supporters, was so discouraged by post-retention relapse
that he seriously considered giving up his profession as an
orthodontist. He examined 70 percent of the patients whom
he had treated during six and a half years of orthodontic
practice during which he followed Angle's philosophy which
demanded a full complement of teeth. To his amazement he
found that only 20 percent of the cases which he reviewed
still met his original orthodontic objectives, which were:
i) A stable end result teeth that remain in their
corrected positions.
ii) Healthy investing tissues to insure longevity of
the denture.
iii) A dental apparatus which works efficiently.
iv) The best facial aesthetics.
Following this humbling experience, Tweed displayed great
courage when he subsequently treated similar bimaxillary
protrusion cases, half by "conventional" nonextraction
treatment and half by the removal of four first premolars.
In the first group he reported a labial displacement of the
mandibular incisors from their normal positions and a
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278
resultant collapse of these incisors. In the second group,
where four premolars had been extracted and the mandibular
incisors correctly positioned in relation to their
supporting basal bone, the subjects remained free from
serious relapse following one year of retention.
Retreatment of those patients, who ended up in bimaxillary
protrusion, by removal of four premolars resulted in greater
stability several years post-retention. A study which
included 100 extraction, and 100 nonextraction subjects, was
examined 25 years post-retention (Tweed, 1968). While not
based on scientific facts, Tweed concluded that the
extraction cases were more stable than were the
non-extraction cases. Glenn, Sinclair and Alexander (1987)
studied 28 nonextraction cases which were an average of
eight years out of retention. In these patients, which
were treated by the same orthodontist, they found that
slight incisor irregularity occurred post-retention.
Relapse patterns were similar to but more severe than,
those seen in a study conducted in an untreated normal
population (Sinclair and Little, 1983). The changes in the
normal population were only one half as severe as those
observed in studies performed by Little et ale (1981, 1988).
According to Little et al. lower incisors, when measured
to the APo line, were proclined an average of 1.4 mm during
treatment, tended to remain stable post-retention. Sandusky
(1983) reported on the post-retention stability of 83
extraction cases treated by Tweed and Tweed foundation
members. Using Little's Irregularity Index (Little, 1975)
to grade the results he found less than ten percent relapse
of the lower incisors. Similar results showing that lower
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279
incisors maintained better alignment following orthodontic
treatment were reported by Davies (1971) and Kuft1nec
(1975). In a sample consisting of 45 nonextraction and 27
extraction cases Uhde, Sadowsky and BeGole (1983) showed a
greater degree of crowding at the beginning of treatment,
and less relapse 20 year~ post-retention in the extraction
group than did the non-extldction group of patients.
The presence of mandibular incisor crowding indicates that
there is a space shortage somewhere in the dental arches.
The incisor position (Downs, 1948; Steiner, 1953; Tweed,
1954; Ricketts, 1981) and facial profile (Holdaway, 1983),
in combination with a tooth-arch size analysis, provide
clues which can help to make a decision whether an
extraction or nonextraction treatment regime must be
followed. Mandibular incisors should, as is found in
normal individuals, always be positioned upright over the
medullary bone of the jaw (Tweed, 1946). Relapse of
dentitions following orthodontic treatment may be
influenced by apical base differences, the subject's age,
the period of retention, incisor positions relative to
basal bone, post-treatment growth, third molar
development, periodontal fibres, habits, occlusal
functioning, Bolton discrepancies, continued decrease in
arch length and other unknown factors (Little, Wallen
and Riedel, 1981). Richardson (1980, 1981) summarised a
number of possible aetiologic factors which cause
mandibular arch crowding.
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280
Following a nonextraction philosophy in the belief that a
particular orthodontic appliance will enhance bone growth
could lead to a great deal of disappointment. It is probably
impossible to induce meaningful growth in tooth-bearing
bones by means of orthodontic appliances (Brodie, 1940a).
Brocie (1940b) also demonstrated that once the growth
pattern of the facial bones is established, whether normal
or abnormal, it is virtually constant and resistant to
change. Natural expansion does, however, occur as a result
of normal growth and development (Friel, 1927). It would be
incorrect to assume that those appliances used during this
growth period were the cause of the expansion. The area of
the alveolar arch correlates closely with the area of the
dental arch (Richardson and Brodie, 1964). A cephalometric
study which evaluated relapse in Class II division 1
subjects who where treated without extraction of teeth,
with either the Andresen activator or the Bionator, showed
cn~siderable individual variation in relapse of overjet
(" age and Hunt, 1990). Using the results of a number of
cephalometric studies dealing with the treatment effects of
functional appliances on Class II division 1 malocclusions,
it was concluded that overjet reduction occurred
predominantly as a result of dento-alveolar changes (Mills,
1983). Dento-alveolar changes also appear to be largely
responsible for overjet relapse especially when incisors
are proclined during treatment (Wieslander and Lagerstrom,
1979; Clavert, 1982; Hunt and Ellisdon, 1985).
Antero-POsterior and/or lateral increase in the mandibular
arch form usually fails with the dental arch typically
returning to the pre-treatment size and shape (Little,
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281
1990). Malocclusions treated by means of rapid maxillary
expansion, however, have been shown to stay stable 8 years
post-treatment (Haas, 1980). Haas maintains that his
success can be ascribed to a combination of his method of
treatment (rapid maxillary expansion) and to the duration
of the retention which he uses.
Subjects treated without extraction by means of Bimler
appliances showed a greater degree of upper lip flattening
as a result of a stretching of the lips. This stretching
apparently results from an increase which occurs in
anterior facial height. Patients in whom extractions were
performed seemed to maintain more aesthetic lip morphology
(Stromboni, 1979). The health of the temporomandibular joint
as well as the convexity of the facial profile have been
used to justify both extraction and nonextraction
philosophies. Conlin (1989) recalled 1000 subjects and
evaluated their long-term dental stability and facial
aesthetics. He found that there is no real need for
extraction cases to apPear flat or for nonextraction cases
to appear full.
One of the greatest challenges in orthodontics is the need
to make a sound diagnosis. No cookbook reciPe is available
in respect of extraction or nonextraction treatment.
Various strategies are used to aid orthodontists in their
extraction decisions including the use of visual treatment
objectives (Ricketts et al., 1979; Holdaway, 1984).
Clinical experience gradually allows each orthodontist to
develop an own philosophy (De Castro, 1974).
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282
The frequency of extractions vary greatly a-ong
orthodontists. A study in the northwestern USA revealed that
the average prevalence is about 42.1' (peck and Peck, 1979).
Another study found the range to vary between 5 and 87' with
the average being 39' (Weintaub et al., 1989).
Ethnic and socio-economic differences will obviously
influence the prevalency of the extractions performed by
orthodontists. Japanese and Chinese orthodontists treat many
birnaxillary protrusions in conjunction with extractions,
whereas government clinics in eastern Europe favour
nonextration treatment. The National Health scheme in
England also appears to have tilted the scale in favour of
extractions in orthodontics (Peck and Peck, 1979).
Extraction, as an only option, regulary complicates a
treatment regime. Problems which dictate one or other form
of extraction, which is not within the control of the
orthodontist, include: caries, periodontitis, endodontic
problems or even some development defect. Extraction
treatment on average was found to consume more time to
complete than does nonextraction treatment (Vig et al.,
1990).
The ultimate decision as to whether extractions should be
performed as part of the orthodontic treatment may depend on
how well the patient co-operates. Anchorage control plays
an important part in allowing the clinician to achieve the
~lanned-for goals. Anchorage, a term used
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loosely in orthodontics,
283
may be derived from variou.
sources, including root aurfaces, cortical bone or even
extra-oral appliances (headgear) (Ricketts et al., 1979;
Moyers, 1988). Dental implants used to augment anchorage ~re
a recent development (Roberts, Marshall and Mozsary, 1990).
The conventional Begg technique uses differential anchorage
(Storey and Smith, 1952) and not extra-oral traction to
preserve anchorage when retracting the anterior segment of
teeth (~illiams and Hosila, 1976). Williams and H08ila
(1976) noted additional advantages to performing
extractions. Extractions tend to reduce the mandibular plane
angle (FHA) between 1.2 to 1.8 degrees during treatment and
the chances of the third molars erupting, improve from 52.5'
(first premolar extractions) to 90' (first molars
extractions). The latter Observation, however, cannot be
taken fo~ granted as it was shown that the impaction of
third molars need not necessarily be avoided by extracting
premolar teeth (Faubian, 1968; Richardson, 1989). Molar
extraction, however, will in most instances eliminate third
molar impaction (Richardson, 1974). Late lower arch crowding
may on occassion be prevented by relieving the eruptive
pressure from third molars by extracting the
molars (Richardson and Mills, 1990).
lower second
In orthodontics a variety of teeth may be extracted. These
include: mandibular incisors (Bahreman, 1977; Kokich and
Shapiro, 1984) , maxillary canines (Jacoby, 1983),
premolars (Hotz, 1970; Graber, 1971; Gianelly and
Valentini, 1973; Dewel, 1976; Joondeph and Riedel, 1976;
Ingram, 1976; Ketterhagen, 1979) , first molars
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284
(Daugaard-Jensen, 1973; Williams, 1979), second molars
(Liddle, 1977; Richardson and Mills, 1990) and third molars
(Chipman, 1961; Ricketts et al., 1979; Richardson, 1987).
Dental changes, including the common occurance of lower
incisor crowding, many years after successful orthodontic
treatment, may signify failure in orthodontics. Hence the
need to distinguish between operator error and normal
growth changes (Hellman, 1944). The extraction of four
premolar teeth has been recommended to limit incisor
crowding following orthodontic treatment (Hellman, 1943;
Proffit, 1986). Proffit (1986) believes that an additional
benefit of extraction therapy lies in the better lip
contours which are usually obtained. There is no complete
agreement in respect of the latter observations. It has
been reported that irrespective of whether individuals
were treated with or without extractions, relapse of
overbite (Simons and Joondeph, 1973) as well as relapse or
lower incisor alignment still occurs following the removal
of the appliances (Little, Wallen and Riedel, 1981). Only
about 30% of occlusions treated with first premolar
extraction therapy retain good anterior mandibular alignment
while two thirds of the sample relapse (Little, Wallen and
Riedel, 1981). In comparing the results of a sample showing
minimal incisor relapse (Sandusky, 1983) with a sample
showing about two thirds relapse (Little, Wallen and
Riedel, 1981) it was concluded that the orthodontic
technique utilised plays an important role in achieving
stabilit~· the post-treatment orthodontic result (Gorman,
1990).
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285
In an attempt to search for associations between long-term
skeletal and dental change, a cephalometric appraisal was
performed on first-premolar-extraction subjects (Shields,
Little and Chapko, 1985). The post-treatment and
post-retention incisor positions as well as amount or
direction of facial growth, were found to be poor predictors
of long-term mandibular incisor irregularity. Other studies
also failed to demonstrate any correlation between
pre-treatment and post-treatment lower incisor alignment in
first, (Little, Wallen and Riedel, 1981) and second
premolar extractions (McReynolds and Little, 1991).
Statistically significant differences in their cephalometric
measurements existed between minimally, and moderately to
severe crowding groups in the post-retention period of
subjects treated with second premolar extractions
(McR~inolds and Little, 1991). Nonextraction treatment
regimes have also provided information in respect of
post-orthodontic stability (Shapiro, 1974; Gallerano, 1976;
Glenn, Sinclair and Alexander, 1987). The lesser degree of
initial crowding in the nonextraction groups tend to bias
such studies and a direct comparison of extraction, and
nonextraction samples must therefore be made with caution
(McReynolds and Little, 1991).
Teeth which are moved together orthodontically following
extraction of an adjacent tooth do not move through the
gingival tissue, but appear to push the gingivae in front
of it into a fold of epithelial and connective tissue. This
excess tissue can result in the opening of the extraction
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286
space which constitutes a common form of relapse of
orthodontically treated occlusions. By surgically removing
this tissue, relapse could be alleviated (Edwards, 1971).
Enlow (1980) defined relapse as "a histogenetic and
morphogenic response to some anatomical and functional
violation of an existing state of anatomic and functional
balance." Relapse is usually thought of as a "rebound"
movement in which teeth recoil back somewhere close to
their original positions once the retentive forces are
removed. Enlow does not accept the idea that the relapse
process is merely a passive mechanical recoil reaction of
the periodontal membrane to stresses placed on it's fibres.
He stated that periodontal fibres have a great capacity for
remodeling and can accomodate to virtually any tooth
position if a regional state of anatomic and physiologic
balance exists. Early writings stressed the importance of
placing the teeth in excellent occlusion and holding them
there until the perioral musculature adapts to the new
position' (Barnes, 1956). Lower incisor crowding which
develops pest-retention has been attributed to a failure of
the muscles to adapt.
Mershon (1936) stated that the final position of the teeth
was like "an argument with Mother Nature" who always won.
Post-retention stability, one of the major problems facing
orthodontists, was well defined by Hawley (1919) when he
said that he would gladly give half his fee to anyone who
would be responsible for the retention of his results after
the active appliances are removed. Parker (1989) stated in
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287
his article entitled, "Retention Retainer. may be
forever", that "Experience does not give wisdom but it may
and should grant perspective." With over 28 year. of
orthodontic experience, Gorman (1990) explained that his
perspective on retention has changed from an expectation of
universal stability following bicuspid extraction and two
years of retention, to the realization that individual
retention plans must be developed for each patient whether
an extraction or nonextraction treatment regime was used.
10.2 Objectives
controversy exists in respect to the stability of the
dentition following extraction and nonextraction treatment.
Only long-term evaluation of orthodontic treatment results
can possibly provide answers to this dilemma.
Hence, the objectives of this part of the study were:
i) to assess whether significant differences exist
between the post-t~eatment changes experienced in
extraction and nonextraction orthodontic treatments.
ii) to determine the relationship between these groups
and lower incisor ir.regularity.
10.3 Materials and methods
The basic materials used and methods employed in order to be
able to assess the longitudinal changes experienced in the
sample of eighty-eight Caucasian SUbjects were described in
Chapter 3. The extraction group consisted mainly of
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288
premolar extractions, but the odd molar was alao removed a.
part of a treatment regime. The sample, con.i8ting of
extraction (56') and nonextraction (441) treated subjects,
is set out in Table I.
Orthodontic study casts and lateral cephalograms were
analysed for all three stages studied as was previously
described. Intra-o~server error was found to be lesa than
1.0% and it was concluded that this error had no effect on
the outcome of the results.
The study casts were measured with digital calipers capable
of measuring to O.Olmm. Measurements of sagittal, transverse
and vertical dimensions were included.
Cephalometric measurements were obtained with the use of the
Oliceph computer program and included measurements of the
popular analyses of Steiner, Tweed, Ricketts, Bjork/Jarabak
and Holdaway with additions such as the Wits appraisal.
The data (extraction and nonextraction) were subjected to
descriptive statistics, the Wilcoxon and the Chi-square
statistical tests for each of the three treatment stages
studied (T1, T2 and T3) (Zar, 1984). The significance level
of this part of the study was Bet at 0.05.
10.4 Results
The findinga are set out in Tables XL, XLI, XLII, XLIII and
XLIV.
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TABLE XL
DIFFERENCES BETWEEN EXTRACTION AND NQNEXTRACTION GROUPS
FOR A NUMBER OF VARIABLES
VARIABLE NONEXTRACTION EXTRACTION
Mm.
MEAN S.D. MEAN S.D. P
AGE Tl 11.73 1.09 12.06 1.10 0.14
T2 14.45 2.02 14.97 1.54 0.03*
T3 21.88 3.82 20.92 3.04 0.31
MANDIBULAR VARIABLES
MANDIBLE - DIMENSIONS:
SNB Tl 76.77 3.32 76.73 3.46 0.93
T2 76.42 2.89 76.49 3.92 0.99
T3 77.36 3.27 77.19 4.05 0.90
SND Tl 74.03 3.19 73.45 3.28 0.56
T2 74.05 2.79 73.93 3.86 0.79
T3 75.46 3.13 75.07 4.05 0.87
GOGN-MM Tl 73.74 4.22 72.22 4.64 0.17
T2 76.54 4.55 75.62 4.94 0.39
T3 80.10 6.01 77.73 4.73 0.08
GOGC-MM Tl 56.58 3.42 56.13 4.31 0.62
T2 61.48 4.54 58.56 4.30 0.004*
T3 66.42 6.57 61.43 9.73 0.01*
GOGN-GOCO Tl 123.31 4.23 126.63 4.94 0.001*
T2 123.37 4.83 126.92 5.48 0.001*
T3 121.33 5.30 125.77 5.67 0.001*
RAMH-MM Tl 44.15 3.78 41.99 4.29 0.02*
T2 47.75 4.75 44.72 5.30 0.01*
T3 54.01 6.17 49.63 6.63 0.002*
CORL-MM Tl 71.53 4.25 70.64 4.42 0.28
T2 74.39 4.56 73.86 4.43 0.67
T3 78.26 6.32 75.76 5.20 0.08
CORLCRAN Tl 0.99 0.08 1.01 0.17 0.59
T2 0.99 0.06 1.01 0.56 0.39
T3 1.02 0.07 1.01 0.63 0.75
289
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IWfI)IBLE - TEETH:
MDCROWD Tl 0.99 •• 67 -2.36 •. 94 0.06
T2 1.33 1.88 2.32 0 ••6 0.11
T3 -2.93 4.11 -2.90 5.44 0.85
SPEE Tl 2.13 1.08 2.24 0.82 0.54
T2 2.65 5.36 1.75 0.87 0.45
T3 1.92 0.73 2.39 0.82 0.04*
L3-3I Tl 25.93 2.02 26.42 1.41 0.16
T2 26.18 1.80 25.78 1.64 0.43
T3 26.15 1.88 25.56 1.85 0.14
L3-3B Tl 29.97 2.05 30.95 1.56 0.02*
T2 31.29 4.55 30.77 1.27 0.91
T3 30.41 2.40 30.00 1.91 0.69
AReHL Tl 23.76 2.17 23.12 2.41 0.29
T2 23.31 1.87 18.92 2.36 0.0001*
T3 22.88 2.44 17.93 2.35 0.0001*
L-IRREG Tl 2.71 2.12 5.11 3.97 0.002*
T2 0.33 0.51 0.49 0.74 0.29
T3 1.67 1.52 1.74 1.78 0.83
LITTLE-A Tl 62.36 3.66 59.86 4.55 0.02*
T2 62.34 3.94 52.20 5.27 0.0001*
T3 60.91 3.98 50.25 5.31 0.0001*
I-HB-DEG Tl 25.10 4.83 28.63 7.03 0.01*
T2 29.12 5.39 28.06 4.77 0.41
T3 27.41 4.38 26.55 4.75 0.31
I-NB-MM Tl 2.92 1.61 4.50 2.12 0.0003*
T2 4.41 1.66 4.22 1.53 0.57
T3 4.14 1.57 4.04 1.69 0.42
I-APO-MM Tl -1.14 2.29 1.43 2.55 0.0001*
T2 1.14 2.29 1.34 1.56 0.94
T3 0.66 2.27 1.04 1.65 0.79
I-APO-DEG Tl 22.56 4.45 24.58 5.55 0.09
T2 29.38 5.28 26.64 3.65 0.008*
T3 29.11 4.24 26 ••9 •• 18 0.01*
IMPA Tl 9"1.86 5.6. 95.94 13.63 0.82
T2 101.77 6.28 96.52 5.61 0.0003*
T3 101.34 5.28 95.79 5.83 0.0001*
FMIA T1 62.63 4.88 59.00 7.68 0.01*
T2 58.70 5.51 59.49 5.83 0.48
T3 59.34 11.29 61.84 6.29 0.45
2S0
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MANDIBLE - GROWTH DIRECTION:
GOGN-SN T1 31.13 3.45 35.08 5.25 0.0004*
T2 31.59 4.06 35.71 6.24 0.002*
T3 29.36 4.34 34.23 6.79 0.0003*
FMA Tl 20.65 3.74 24.68 4.45 0.0001*
T2 20.68 4.19 25.13 5.37 0.0003*
T3 18.03 7.27 23.71 5.73 0.0001*
FAC-AXIS Tl 90.16 3.18 87.91 4.59 0.02*
T2 89.55 3.47 87.38 5.06 0.03*
T3 90.83 3.77 88.26 5.86 0.05*
FAC-TAPE Tl 70.92 3.27 66.99 3.69 0.0001*
T2 70.07 3.51 66.28 3.90 0.0001*
T3 71.59 3.81 67.54 4.37 0.0001*
MANn-ARC Tl 32.48 4.42 28.40 5.16 0.0004*
T2 33.16 5.21 29.33 5.65 0.001*
T3 35.99 5.46 32.69 5.55 0.03*
FAC-ANGL Tl 89.05 2.74 87.94 3.16 0.09
T2 89.53 3.11 88.54 3.62 0.22
T3 90.72 3.27 89.55 3.80 0.20
L-FACH Tl 41.08 3.32 45.34 4.21 0.0001*
T2 42.69 3.95 45.99 5.04 0.002*
T3 42.20 4.26 45.40 5.19 0.002*
ARTANGLE Tl 145.53 7.29 147.15 6.69 0.33
T2 144.87 6.76 147.46 7.72 0.16
T3 145.14 8.01 147.18 7.19 0.33
GONANGLE Tl 121.40 4.89 125.82 5.98 0.0001*
T2 122.06 5.85 125.69 6.24 O.Cl*
T3 118.77 6.25 123.58 6.08 0.001*
SUMANGLE T1 391.00 3.69 395.94 5.55 0.0001*
~2 391.81 4.16 396.25 6.47 0.001*
T3 388.87 4.45 393.93 6.94 0.0003*
GONSLING Tl 51.73 4.08 51.81 4.17 0.85
T2 51.03 4.19 50.76 4.83 0.88
T3 49.26 4.46 49.67 4.16 0.51
eORSLING T1 69.64 3.06 51.81 4.17 0.0001*
T2 71.03 3.53 74.93 4.76 0.0001*
T3 69.52 3.55 73.92 5.49 0.0001*
P = Significance level, p <0.05 (WILCOXON 2-Sample Test)
* = Significant differences, p < 0.05
291
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TABLE XLI
DIFFERENCS BETWEEN EXTRACTION AND NQNAXTRACTION GROUPS
FOR MAXILLARY VARIABLES
VARIABLES NONEXTRACTION EXTRACTION
MEAN S.D. MEAN S.D. P
MAXILLA - DIMENSIONS:
8N-FH Tl 10.40 2.92 10.48 1.95 0.62
T2 10.91 2.40 10.58 2.76 0.70
T3 10.68 2.47 10.52 2.67 0.93
SNA Tl 81.06 3.37 81.44 3.88 0.57
T2 79.39 3.16 79.62 3.86 0.97
T3 79.98 3.39 79.97 3.49 0.85
ANSPNS-SN Tl 7.86 2.87 7.29 2.96 0.37
T2 8.28 2.85 8.08 3.58 0.72
T3 7.81 2.89 7.90 3.34 0.92
A-CONVEX Tl 4.08 2.54 3.45 3.07 0.49
T2 1.40 2.47 2.33 2.75 0.17
T3 0.50 2.89 1.61 3.04 0.14
SADANGLE Tl 122.99 4.19 124.04 5.14 0.24
T2 124.88 4.83 123.11 4.74 0.10
T3 124.90 5.17 123.17 4.72 0.15
SN-MM Tl 71.61 3.21 72.02 3.32 0.23
T2 74.57 3.24 73.29 3.37 0.05*
T3 77.06 4.21 75.03 4.01 0.01*
SAR-MM Tl 34.35 2.86 35.63 4.07 0.12
T2 37.25 4.06 35.98 2.83 0.13
T3 38.06 4.67 36.81 3.15 0.17
292
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MAXILLA - TEETH:
293
MXCROWD T1
T2
T3
U6-61 T1
T2
T3
U6-6B T1
T2
T3
1-NA-DEG T1
T2
T3
I-NA-MM T1
T2
T3
I/-FH-DEG T1
T2
T3
I/-FACAX-DEG T1
T2
T3
I/-APO-MM Tl
T2
T3
UM-PTV-MM Tl
T2
T3
UM-CCV-MM Tl
T2
T3
1.92
-0.78
50.81
52.96
50.97
54.33
57.16
54.36
23.64
23.33
23.02
3.92
3.16
3.76
115.34
113.41
113.46
4.52
6.11
6.84
6.74
4.24
4.18
16.65
17.69
21.97
15.55
16.41
20.46
5.48
4.13
4.15
3.13
3.05
4.02
6.52
2.99
10.45
9.18
8.03
3.25
3.04
3.01
10.46
8.63
7.76
9.93
7.79
6.38
3.32
1.99
2.14
3.54
4.16
3.42
3.45
4.27
3.66
-1.78
-1.46
-1.97
48.59
48.08
48.63
52.13
52.02
5: .21
22.19
21.85
21.72
4.14
2.57
3.37
113.45
~11.83
111.99
4.01
5.31
5.85
7.43
4.31
4.59
17.36
22.05
23.45
16.24
20.63
21.89
6.16
0.74
5.57
2.95
2.84
2.91
2.96
3.01
2.72
7.96
7.49
6.42
2.53
2.17
2.12
7.21
7.55
6.20
7.64
6.89
5.72
2.81
1.49
1.76
4.01
4.47
4.94
4.03
4.:55
5.09
0.09
0.38
0.01*
0.0001*
0.001*
0.01*
0.0001*
0.001*
0.32
0.39
0.40
0.83
0.44
0.71
0.16
0.35
0.31
0.94
0.77
0.54
0.58
0.97
0.53
0.21
0.0001*
0.10
0.24
0.0001*
0.11
p = Significance level, p < 0.05 (WILCOXON 2-Sample Test)
* = Significant differencs, p < 0.05
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TABLE XLII
DIFFERENCES BETWEEN EXTRACTION AND NOHEXTRACTION GROUPS
FOR MAXILLARY TO MAlfDIBULAR VARIABLES
VARIABLE NONEXTRACTION EXTRACTION
MEAN S.D. MEAN S.D. P
MAXILLA TO MANDIBLE:
ANB T1 4.67 2.74 4.33 2.12 0.44
T2 2.96 2.13 3.13 1.86 0.92
T3 2.62 2.31 2.78 2.15 0.96
POSFACH-MM Tl 76.06 4.81 73.14 4.73 0.01*
T2 80.75 6.72 77.32 5.49 0.01*
T3 87.75 8.32 82.56 7.09 0.003*
ANTFACH-MM Tl 114.39 5.78 116.84 5.75 0.07
T2 121.74 8.25 122.89 6.22 0.55
T3 126.39 9.36 126.22 6.59 0.64
SGQ-NME Tl 66.54 3.41 62.70 4.45 0.0001*
T2 66.55 3.86 63.05 5.16 0.001*
T3 69.44 4.17 65.49 5.42 0.001*
WI TS-MM Tl 2.41 3.82 0.29 3.85 0.004*
T2 0.63 3.45 0.29 2.79 0.38
T3 1.58 3.89 0.19 3.41 0.09
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OCCLUSIOlf:
OJB Tl 6.93 3.63 5.59 2.86 0.04*
T2 3.01 0.93 2.74 0.78 0.24
T3 3.18 1.25 3.21 1.23 0.73
OBB Tl 4.64 1.38 3.87 1.46 0.03*
T2 3.00 1.02 2.61 0.86 0.14
T3 2.75 0.89 2.86 1.30 0.99
BOLTON A Tl 78.69 1.53 78.12 2.57 0.56
T2 -----
T3 77.98 2.55 77.10 8.47 0.67
BOLTON P Tl 92.06 1.75 91.13 2.03 0.33
T2 -~----
T3 91.29 2.54 89.11 8.74 0.89
I-I Tl 127.71 11.28 125.98 10.97 0.58
T2 125.73 10.73 128.09 7.69 0.18
T3 130.09 6.72 128.09 8.40 0.16
OCC-SN Tl 15.91 5.60 17.71 4.97 0.09
T2 16.98 3.59 18.18 4.60 0.32
T3 16.59 5.52 14.03 3.67 0.06
MOLAR L Tl 0.003* x
T2 0.33 x
T3 0.73 x
MOLAR R Tl 0.01* X
T2 0.43 X
T3 0.69 X
CANINE L Tl 0.03* X
T2 0.31 X
T3 0.95 X
~~INE R Tl 0.02* X
T2 0.26 X
T3 0.17 x
OPENBIT Tl 0.94 X
T2 0.79 x
T3 0.54 X
ANTXBIT Tl 0.06 x
T2
T3 0.83 X
POSTXBIT Tl 0.19 x
T2 0.47 X
T3 0.23 X
ROTATE Tl 0.49 x
T2 0.09 X
T3 0.13 X
P = Significance level, p < 0.05 (WILCOXON 2-Sample Test)
* = Significant difference, p < 0.05
x = CHI-SQUARE Test
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TABLE XLIII
DIFFERENCES BETWEEN EXTRACTIQN AND NQREXTRACTIQN GROUPS
lOR SOFT TISSUE VARIABLES
VARIABLES NONEXTRACTION EXTRACTION
MEAN S.D. MEAN S.D. P
U-LIPE-MM T1 -1.35 2.15 -0.79 2.49 0.01*
T2 -4.19 1.94 -4.19 1.89 0.88
T3 -6.00 2.76 -5.72 2.07 0.14
Z-ANGLE T1 71.61 6.27 68.58 7.83 0.06
T2 75.49 5.22 74.65 6.55 0.49
T3 77.04 14.31 76.78 6.80 0.16
L-LIPE-MM T1 -0.69 2.67 1.14 2.92 0.01*
T2 -2.32 1.96 -2.14 2.12 0.88
T3 -4.17 2.34 -3.37 2.84 0.18
STFAC T1 89.84 2.99 88.64 3.48 0.08
T2 90.31 3.20 89.34 :3.96 0.19
T3 91.89 3.21 90.33 3.82 0.07
NOSE-MM T1 13.04 1.59 13.30 2.22 0.74
T2 15.78 2.21 15.99 1.97 0.88
T3 18.15 2.50 17.91 2.22 0.69
SUPSULD Tl -9.59 3.21 -9.78 2.78 0.68
T2 -8.76 3.09 -8.98 2.59 0.69
T3 -8.19 3.20 -8.29 3.22 0.49
SAHLlNE T1 6.08 2.06 7.14 2.16 0.03*
T2 4.72 2.06 4.86 1.38 0.95
T3 4.53 1.92 4.89 1.55 0.26
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ULIPTH-MM Tl 15.04 1.75 14.43 1.26 0.11
T2 16.28 2.14 15.60 1.97 0.09
T3 16.82 2.23 16.18 2.11 0.14
ULIPTAP-MM Tl 11.61 2.50 11.37 1.89 0.71
T2 13.66 1.82 13.22 2.06 0.22
T3 13.99 2.30 13.15 2.72 0.09
ULIPSTR-MM Tl 3.43 2.14 3.06 1.89 0.33
T2 2.62 1.79 2.38 1.52 0.37
T3 2.83 1.81 3.03 2.19 0.65
HANGLE Tl 16.79 3.98 16.90 3.79 0.89
T2 13.76 3.66 13.36 2.74 0.65
T3 12.34 4.08 12.37 3.30 0.93
LIPH-MM Tl 0.21 1.91 1.67 2.06 0.003*
T2 0.49 1.29 0.75 1.57 0.42
T3 0.03 1.35 0.49 1.88 0.10
ISULH-MM Tl 6.09 2.08 4.30 2.21 0.0002*
T2 5.42 1.85 4.45 1.89 0.03*
T3 6.08 2.07 5.03 2.43 0.02*
STCHIN-MM Tl 10.04 2.15 10.14 2.08 0.95
T2 10.37 1.80 10.50 2.24 0.96
T3 11.18 2.27 11.26 2.46 0.91
P = Significance level, p < 0.05 (WILCOXON 2-Sample Test)
* = significant differences, p < 0.05
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TABLE XLIV
DIFFERENCES BETWEEH EXTRACTION AID BQNEXTRACTION GROUPS;
DESCRIPTIVE STATISTICS FOR THE LITTLE IRREGULARITY IBDEX
(Little, 1975)
298
EXTRACTION:
T1
VARIABLE MEAN S.D.
L-IRREG 5.11* 3.97
NQNEXTRACTION:
T1
VARIABLE MEAN S.D.
L-IRREG 2.71* 2.12
T2
MEAN S.D.
0.49 0.74
T2
MEAN S.D.
0.33 0.51
T3
MEAN S.D.
1.74 1.78
T3
MEAN S.D.
1.67 1.52
S.D = Standard deviation
* = Statistically significant difference, p < 0.05
(WILCOXON 2-Sample Test)
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Significant age differences were only experienced at the end
of appliance therapy (T2), possibly due to the treatment
periods not all being of similar duration for the extraction
and nonextracLion groups.
The mandibular dimensions (GOGC-MM at T2 and T3; GOGN-GOCO
at T1, T2 and T3; RAMH-MM at T1, T2 and T3), as well as
mandibular growth direction (GONANGLE, SUMANGLE, CORSLING,
GOGN-SN, FMA, FAC-AXIS, FAC-TAPE, MANn-ARC and L-FACH at Tl,
T2 and T3) showed significant differences between the
extraction and the nonextraction groups. The mandibular
dental arch differences were limited to arch length (ARCHL
at T2 and T3 and LITTLE-A at Tl, T2 and T3), lower incisor
axial inclination (I-NB-MM and I-APO-MM at T1; I-APO-DEG and
IMPA at T2 and T3; FMIA at Tl) (Table XXXVII). Mandibular
intercanine width (L3-3B) showed significant differences at
the start of treatment (Tl) only and the Curve of Spee
(SPEE) at the post-retention phase only (T3) (Table XL).
The Little Irregularity !ndex (Little, 1975) showed
significant differences at the pre-treatment observation
(T1) only. No significant differences were measured at the
end of the active orthodontic treatment (T2) and at the
final observation (T3) between the two groups (Table XL and
XLIV) •
The only upper facial dimension which displayed a
statistical difference was the anterior cranial base length
(SN-MM at T2 and T3). Dental arch width measured as the
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maxillary bimolar dimension showed difference. between the
groups throughout the study (Ti-T3). The upper fir.t molar
position (UM-PTV-MM and UM-CCV-MM) showed difference. only
at the end of treatment (T2) (Table XLI).
Assessment of the maxillary-mandibular relationships showed
a statistical significant difference between the extraction
and nonextraction groups and that occurred in the posterior
facial height (POSFACH-MM) at all three obsrevations
(Tl-T3). Differences in the posterior facial height also
affected the percentage ratio between the anterior and
posterior facial heights (SGO-NME) which showed significant
differences at all three the stages studied. The WITS-MM
showed statistically significant differences only at the
commencement of the treatment (Ti) (Table XLI).
The occlusal variables which showed significant differences
(OJB, OBB, MOLAR L, MOLAR R, CANINE L, CANINE R) did so
only at the start of the treatment (Tl) (Table XLII).
The soft tissue parameters showed differences only at the
'.
beginning of treatment (U-LIPE-MM, L-LIPE-MM, SAHLINE,
LIPH-MM, ISULH-MM at Tl). Following treatment only the
inferior lip sulcus depth to the H-line (ISULH-MM at T2
and T3) displayed statistically significant differences and
then only at the end of treatment and at the end of the
post-orthodontic phase (Table XL).
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The differences in the descriptive statistics of the Little
Irregularity Index between the two groups are .et out in
Table XLIV. The pre-treatment (Tl) lower inci.or
irregularity showed a significant difference between the
groups, but no significant differences were measured at the
other observations (T2 and T3).
10.5 Discussion
Spectacular results achieved as a result of orthodontic
treatment are very impressive and greatly admired. The
problem lies in the fact that failures, too, occur often.
Treatment reliability, therefore, depends upon proof that
the proportion of success is greater than that of failures.
Hellman (1943) mentioned that to ascertain the relationship
between the successes and the failures in orthodontics
requires long stretches of time. Although a number of
long-term studies (Sadowsky and Sakols, 1982; Little, 1990;
McReynolds and Little, 1991) discuss the stability and
relapse of post-treatment orthodontic results, there are
still numerous debates as to whether extraction or
nonextraction therapy produces more stable results.
Does extraction solve all our problems? A very positive no!
Without meticulous planning, extraction therapy will result
in unwarranted and unjustifiable failures (Nance, 1947).
The assessment of the data of this study indicated certain
significant differences between extraction and nonextraction
groups.
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The significant difference in age at the end of treatment
(T2) is probably not of any clinical significance a. it is
expected that treatment time will differ for individual
subjects and more so when comparing males and females with
their different growth curves (Table XL).
The mandibular dimensions (GOGN-GOCO and RAMH-MM), the lower
intercenine width (L3-3B), the lower incisor position
(I-NB-MM, I-APO-MM and FMIA), the incisor irregularity
(L-IRREG), the arch length (LITTLE-A) and mandibular growth
pattern (GOGN-SN, FHA, FAC-AXIS, FAC-TAPE, MAND-ARC, L-FACH,
GONANGLE, SUMANGLE and CORSLING) all showed significant
differences between the two groups at the start of treatment
(Tl) (Table XL). Upper bimolar width (U6-6I and U6-6B)
showed similar differences (Table XLI). The mensuration of
the group differences of the maxillary to mandibular data at
the start of treatment (TI) also revealed significant
differences. They were the antero-posterior discrepancy (~TB
and WITS-MM), the anterior to posterior facial height ratios
(ANTFACH-MM, POSFACH-MM and SGO-NME), overbite and overjet
(OBB and OJB) as well as molar and canine relationships
(MOLAR L, R and CANINE L, R) (Table XLII). Soft tissue
variable differences at the start of treatment included the
lower and upper lip to the E-line (U-LIPE-MM and L-LIPE-MM),
the lower lip to H-line (LIPH-MM), the upper lip curl
(SAHLINE) and the inferior lip sulcus (ISULH-MM) (Table
XLIII). All of these significant differences could be
expected. They not only justify the reasons for the
differences in treatment regimes, but also ackowledge the
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fact that
regarding
treatment.
303
orthodontists possibly made the correct decisions
the extraction, or nonextraction approach•• to
The end of active orthodontic treatment (T2) normally
signifies the achievement of ideal occlusal and soft tissue
parameters. Functional and aesthetic results which please
both the orthodontist and the patient symbolises ultimate
success.
The variables measured at the end of mechanical therapy
(T2) again showed significant differences between the
extraction, and nonextraction subjects. Mandibular
differences still included those which indicate the
morphological differences which were preserved. The only
addition to these measurements was the change in posterior
mandibular growth that took place during the treatment
period (Tl-T2). This finding is exemplified by the
measurement from Gonion to Condylion (GOCO-MM) (Table XLI).
The mandibular dental dimensio~s including the intercanine
dimension, the curve of Spee and the irregularity of the
lower incisors showed no significant differences which can
be ascribed to good orthodontic technique. This is expected
irrespective of the treatment regime. The lower incisor
position showed angular differences between the two groups
(I-APO-DEG and IMPA). Although it appears as if the lower
incisor goals for both groups were attained, the two
angular differences mentioned above could be ascribed to
the cephalometric landmarks used. The measurments recorded
in relation to the Point A-Pogonion lin~ can be influenced
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by the chin button shape (FAC-TAPE). It i. known that
brachycephalic and dolichocephalic facial pattern.,
mensurated by GOGH-SH, FHA, PAC-AXIS, PAC-TAPE, HARD-ARC
and L-FACH, do differ in this respect and that the
extraction philosophy is also different for the two types
of facial patterns (Tweed, 1966; Ricketts et al., 1979).
The IMPA (Tweed, 1954) could also be influenced by growth
changes in the lower mandibular border as were shown by
Bjork and Skieller (1983). Mandibular dimensions ~re
different for vertical and horizontal growers. Horizontal
growers show a flatter mandibular plane when compared to the
more acute mandibular plane of the vertical grower which is
characterized by strong antegonial notching (Ricketts ~
41., 1979; Lambrechts, 1991). Differences in the arch length
(ARCHL and LITTLE-A) between extraction and nonextraction
sUbjects were expected. The arch length does not only
decrease because of the natural phenomenon of mesial
migration or drifting (Moyers et al., 1976; Moyers, 1988),
but also due to extractions which caused tremendous
differences in this dimension. This finding supported
studies showing a decrease in arch length (Shapiro, 1974;
Gallerano, 1976; Little, Wallen and Riedel, 1981; Little
and Riedel, 1989; Little, Riedel and Engst, 1990). Similar
changes occur in untreated individuals (Sinclair and
Little, 1983).
Maxillary variables also showed some expected significant
differences between the extraction and nonextraction groups
(Table XLI). The anterior cranial base measurement,
Sella-Nasion (SN-MM), was significantly different between
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305
the groups at the e~d of treatment (T2). This finding can be
ascribed to a possible enlarge.ent of the frontal sinus with
an accompanying forward bulging of the frontal bone. Due to
these growth changes Nasion could have been displaced
forwards. Jacobson (1975) used the Wits appraisal of jaw
disharmony to show how different positions of Hasion could
influence the basic grouping of a malocclusion. It was
shown in a cross-sectional study that mandibular growth
correlates with incr~ases in frontal sinus size (Ros.ouw,
Lombard and Harris, 1991). As was previously noted,
extraction or nonextraction treatment will to some extent
he dependent on the mandibular morphology. The maxillary
himolar width (U6-61 and U6-6B) was significantly different
between the groups at all the observation periods (Tl-T3),
hut the position of the maxillary first molar to the
pterygoid root vertical (PTV) (UM-PTV-MM) and centre of the
cranium (CCV) (UM-CCV-MM) showed significant differences
only at the end of treatment (T2). As the molars move
forwards due to extractions, loss of leeway or noraal
growth, it may be expected that these dimensions (T1, T2
and T3) will change. Extraction of premolars results in a
forward movement of the molars into a narrowe~ part of the
alveolar trough which results in narrowing of the bimolar
width. The opposite is of course also true when the first
molars are distalized using extra-oral traction. Decreases
in arch width have also been reported in a second premolar
extraction study (McReynolds and Little, 1991).
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Antero-posterior maxilla-mandibular discrepancies may also
be influenced by facial patterns (brachifacial or
dolichofacial) or treatment regimes. Extractions for example
may cause the mandibular plane angle to rotate in a for~ard
closing direction. With headgear and Class II
intermaxillary elastic wear the lower facial height may be
increased. Natural mandibular growth rotation (Bjork and
Skieller, 1983) in the various growth patterns will also
account for differences in extraction and nonextraction
groups. Due to these rotations the ratio of anterior and
posterior facial heights (SGO-NME) as well as the posterior
fal:ial height (POSF1~CH-MM) were significantly different for
the groups (Table XLI).
Interestingly enough, the diff~rent occlusions appeared to
have been treated to similar occlusal goals for both groups
(Tabl@. XLII and XLIV). The ultimate aim was, probably to
achieve the six keys of occlusion in all the treated
subjects (Andrews, 1972, 1976). Good orthodontic technique
in order to achieve these goals is imperative and played a
major role in producing occlusions with no significant
differences at the end of treatment (T2) and at the e~d of
the post-orthodontic phase (T3). Tooth-size discrepancies
(Bolton, 1958) could be an aetiologic factor in causing
malocclusions as w~:ll as leading to an extraction treatment
regime (Bahreman, 1977; Kokich and Shapiro, 1984), but
fortunately it can be corrected by a process of
interproximal enamel stripping (Joseph, Rossouw and Basson,
1991). No significant differences were, however, detected
in the Bolton relationships between the groups (Table XLII).
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Soft tissue profile assessment is an important aid in total
orthodontic evaluation. SOft ti••ue can be grossly
influenced if extractions are performed in a nonextraction
facial profile. Holdaway (1983, 1984) emphasised this fact
with his soft tissue analysis and visual treatment
objective. Initial significant differences in soft tissue
variables w~re expected. Sound diagnosis and subsequent
correctly treated orthodontic subjects should not
necessarily produce major differences in soft tissue profile
whether treated extraction or nonextraction. This is borne
out by the non-significant differences which was observed
between the groups at the end of treatment (T2) and at the
final observation (T3) (Table XLIII). The only soft tissue
variable showing a significant difference at the end of
treatment and the post retention phase was the inferior lip
sulcus (ISULH-MM). This difference can be accounted for by
the fact that the morphology of the chin button, a slight
proclination or retroclination of the lower incisors and an
enlarged overbite or overjet may affect this dimension.
The mean lower incisor axial incli~ation was slightly
proclined in this study during the orthodontic treatment
(Table XXXIV, Chapter 8), although the millimetre distance
of the incisor tip to the various lines (NS and APO) was
within norms.
An analogy suggesting that teeth move as long as we live,
just as surely as our hair colour changes throughout our
lives, possibly explains some of the post-treatment changes
measured (Parker, 1989). Changes in the parameters of this
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308
study between the end of t~eatment (T2) and the end of the
post-orthodontic phase (T3) indicated the rebound or relapse
50 often referred to in the literature (Little, Wallen and
Riedel, 1981; Sadowsky aud Sakols, 1982; Shields, Little
ar:d Chap. " 1985; Little and Riedel, 1989; McReynolds and
Little, 1991).
Similar differences which occurred in the mesial positions
of the first maxillary molars at end of treatment (T2) were
also significant when measured at the final observation (T3)
for the two groups. The only variables which became
non-significant were depended on the movement of the first
molars (UM-PTV-MM and UM-CCV-MM) (Table XLI). Some settling
or rebound movement obviously took place and in so doing
eliminated the previous differences (end of treatement)
between the two groups. An analysis of variance showed that
the molar positions from the end of treatment to the final
observation (T2-T3), however, remained reasonably stable.
No significant changes occurred after the achievement of the
post-treatment molar and canine relationships. Behrents ~
gl. (1989) reported similar findings.
Ext~actionists and nonextractionists can show excellent
results and offer persuasive arguments for their
philosophies. Extractionists will usually rely on the
lower incisor position as their key cephalometric
measurement (Williams, 1969, 1985). The nonextractionist
again will likely focus on an articulation where all the
teeth are made to fit. These orthodontists will sometime~
"develop" the arches by starting the treatment with
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309
functional appliances in the aarly mixed dentition. If the
teeth are, irrespective of the type of treatment,
correctly placed for the individual, good aesthetics will
follow, the finished dentition will be stable and facial
harmony will be achieved.
The aesthetic rewards of straight teeth and a gorgeous smile
following orthodontic treatment are sought by both
orthodontist an1. patient. Boley (1991, 1992) pI'eS(;I:.ted data
in respect to soft tissue features which wele objp.ctively
recorded by leading orthodontists in the USA f0110wing
orthodontic treatment. No significant differences (p < 0.05)
could be shown between the facial profiles of subjects who
had extraction or nonextraction treatment. Orthodontists,
however, have the added responsibility of achieving
functional occlusions. If this harmony is achieved, one may
well be on the way to achieving long-term stability
(Conlin, 1989),
Early intervention for the correction of orthodontic
problems has been a neclected phase of orthodontic treatment
for too long a time (Barnes, 1955). Being able to clinically
assess young orthodontic subjects and realising the use of
natural spaces available, including the primate and the
leeway spaces (Moorrees and Chadha, 1962), will certainly
enable many occlusions to be treated nonextraction. The
responsibilty in educating new dentists and orthodontists
to this philosophy cannot be overemphasized.
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The indicator used in this study to determine lower inci.or
alignment, the Little Irregularity Inde~ (Little, 1975),
indicated a more severe situation for the extraction group
at T1. The mandibular crowding, as was clinically mea.ured
(MDCROWD), supported this lower incisor irregularity at T1
although the statistically significant level was
fr' .ctionally exceeded (p = 0.06). This indicated that the
correct diagnosis was made in treating with extractions. A
V~,l_,.~ of practically zero was achieved for the Little
Irreg.i:arity Index at the end of active treatment (T2). A
slight relapse occurred in both groups, but no significant
difference was shown in the lower incisor irregularity at T2
and T3 (Table XLIV). The relapse or rebound as indicated
from T2 to T3 was well within clinically acceptable
standards (Little, 1975). Both groups showed similar
~hanges. Moreover, it can be concluded that when competent
or1:hodontists select an extraction, or nonextraction
orthodontic treatment regime for the correction of
malocclusions, there need not be any significant
differences between the post-treatment results of the
groups. Patients must however be informed of the benefits
and disadvantages of both treatment regimes.
10.6 Conclusions
1. The extraction of teeth does not necessarily assure
long-term stability of the lower incisors.
2. The differences experienced between extraction and
nonextraction groups:Tere mainly maxillary and mandibular
dimensional as well as growth pattern differences.
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3. The Little Irregularity Index (Little, 1975) .howed no
significant (p > 0.05) difference. between the extraction
and nonextration groups at T2 and T3.
4. Meticulous orthodontic care, including proper diagno8i.
in order to distinguish between extraction and nonextraction
malocclusions, is imperative.
5. The extraction versus nonextraction controversy ••ems to
be here to stay.
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CHAPTER 11
SOFT TISSUE CHANGES RESULTING FROM ORTHODONTIC TREATMEIT AID
~HEJR RELATIONSHIP TO LOWER INCISOR IRREGULARITY
11.1 Introduction
In the orthodontic literature various authors have expressed
opinions about faces and profiles. Edward Angle, considered
to be the father of modern orthodontics, was one of the
first to write about facial harmony and the importance of
the soft tissues. He referred to the mouth as being the
facial feature most able to make or mar the beauty and
character of the face. He added that "orthodontics is
indissolubly connected with studies of art as related to the
human face" (Angle, 1907). Angle's concept of facial
harmony was further expanded by Wuerpel (1931), who stated
that "a variety of faces can be considered to be beautiful
provided that their proportions are in balance". Wuerpel in
describing facial balance noted that one part of the face
should not be overemphasized at the expense of another.
A review of art taken from Egyptian times, the height of
the Greek and Roman Empires and the periods influenced by
the modern French, Italians, and Germans shows constantly
changing concepts as to what constitutes a beautiful
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profile. In modern times, straight profiles
selected by newspapers, magazines, movies, and
being the most popular (Hambleton, 1964).
313
have baen
theatre. a.
The disciplines of psychology and sociology help to identify
aesthetic preferences in different ethnic groups. Such
studies have, however, shown that there is a nurprising
degree of agreement among different population groups
regarding facial preferences (Peck and Peck 1970). In a
study to determine whether the dentofacial appearance
contributes to the attractiveness of a young adult, it was
concluded that faces displaying normal incisor
relationships gained the most favourable ratings. Of the
differrent facial characteristics examined, good incisor
appearance was rated highest as indicating friendliness,
social class, popularity, and intelligence. Unilateral
palatal clefts were consistently, in the public eye,
associated with negative character traits (Shaw, Rees, Dave
and Charles, 1985). Lay persons are more likely to rate an
individual's profile as being normal than would
orthodontists and oral surgeons. Individuals perceive
their own profiles differently, than do others, who are
asked to do so (Bell, Kiyak, Joondeph, McNeill and
Wallen, 1985).
Judgments of facial aesthetics tend to be subjective. An
appropriate goal for orthodontic treatment is to improve
facial harmony by correcting facial disproportions (proffit
1986; Bishara, Hession and Peterson 1985).
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Soft tissue and skeletal measurements made on lateral head
films show that males and females with poor facial
balance have more convex faces (Bishara, H.88ion and
Petersen, 1985). Furthermore, males with poor facial
harmony show more protrusive incisors. A number of faces
with good facial harmony were found in association with
malocclusions. This raises the question as to whether
cephalometric standards have been set too rigidly and with
too little freedom for variation (Cox and Van der Linden,
1971). It should be kept in mind that all profile
evaluations should be made with care (Barrer and Ghafari,
1985).
With time, orthodontists have become increasingly aware that
facial aesthetics, and not only the occlusion, should be
considered when planning orthodontic treatment (Rakosi
1982). Usually when orthodontists correct malJcclusions
they improve the appearances of their patients. Most
experienced orthodontists, however, have made the unpleasant
discovery that some patients looked "better" prior to
orthodontic intervention. Practitioners should determine
beforehand what orthodontic treatment will accomplisr
in terms of facial apprearance (Holdaway 1983).
In trying to provide good facial aesthetics vertical
profile characteristics are as important, as are
anteroposterior features and a lengthening of soft tissue
profiles is rarely desirable (De Smit and Dermaut, 1984).
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315
Common aesthetic standards for lip posture were determined
by Foster (1973) who believed that younger individuals bave
"fuller" lips. He also proposed that in general normal adult
males tend to have less prominent lips than have femal.s
of the same ages. This observation holds true for mature
faces which with age get more concave in the lip region.
The latter finding is particularly true for females
(Mauchamp and Sassouni, 1973).
Radiographic cephalometric studies of craniofacial growth
should take account of the facial soft tissues as well as
of th& underlying hard tissues (Bishara,
Peterson, 1985).
Hession and
The above studies demonstrate that there is a definite need
to establish harmonious relationships between the dental
and facial features. Some attempts have been made to
quantify facial growth and maturational changes. Simon
(1924) attempted to divide the head into planes and to
relate profile contours to the Frankfurt horizontal and
orbital planes. He used photographs to measure soft tissue
growth and other facial changes.
in 1922 Case made facial casts of patients prior to and
following orthodontic treatment. As a result of this work
he stated that, in the correction of malocclusions, the
facial outlines should be regarded as being important in
developing a proper treatment plan. He did emphasize the
complexity of the problem by showing three different
profiles, each with a similar Class I malocclusion.
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316
Tweed (1944) gave special attention to aesthetics and stated
that a thorough knowledge of the normal growth pattern of
the face is as important to orthodontists, if not more so,
as is a complete mastery of the science of occlusion. Using
cephalometric standards, in a cross-sectional study of 95
patients \,!ith "good facial esthetics", he emphasized the
importance of the Frankfurt-mandibular incisor angle (FMIA)
and the use of the diagnostic triangle in the treatment
planning and prognosis.
It is important to note that, up to 1950, most Cephalometric
studies were concerned with bony tissues as it was assumed
that the soft tissue profile was dependant on the underlying
skeletal configuration.
Not all parts of the soft tissue profile follow changes in
the underlying skeletal structures in a strictly linear
fashion (Subtelny, 1959). This finding may be due to the
variation in the thickness of the soft tissue covering the
skeletal face (Burstone, 1967).
Computerized cephalometric analyses and stereophotogrammetry
have been used in studies of the facial profiles in an
attempt to quantify growth and treatment changes in the
overall profile, as well as in its various components
(Chaconas et al., 1990). Angular and planar measurements
provide essential information in respect of changes in
facial morphology. If two parts of a face grow in complete
harmony the angular relationships between these two parts
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317
will remain essentially the same. Linoar measurement., are
probably best used to quantify the amount ot growth
expressed by a particular component of a face (Broadbent,
Broadbent and Golden, 1975; Riolo et 01., 1974; Bishara,
Peterson and Bishara, 1984).
Soft tissue analyses have been proposed to evaluate
profiles and these point to the fact that cognizance must
be taken of ethnic differences in soft tissue profiles
(Peck and Peck, 1970; Thomas, 1979; Ricketts, 1982;
Holdaway, 1983; Proffit, 1986). Some analyses which appear
to have the most clinical value may have insufficient
dOCllmer ':ation in respect of longitudinal facial changes.
This fact could affect the applicability of such analyses in
patients of different ages.
11.1.1 Longitudinal changes in the soft tissue profile
The exact relationship between the bony skull and its facial
drape of soft tissue is not fully understood. Angle (1907)
claimed that a dentition which is arranged according to
given standards, will ensure that the facial soft tissues
are displayed in a harmonious manner. Fifty years later ~his
viewpoint still found some support (Riedel, 1957). The
existence of an absolute relationship between the hard and
soft tissues of the face was doubted by some (Burstone,
1958; Neger, 1959). Subtelny (1959, 1961) made the point
that the bony facial profile tends to become more concave
with age. This increase in the concavity of the total soft
tissue profile, partly as a result of the increase in the
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318
size of the nose, was also noted by other. (Chacona. and
Bartroff, 1975; Genacov, Sinclair and nechow, 1990). The
soft tissue profile, excluding the nose from the profile
analysis, shows a tendency to remain relatively .table in
its degree of convexity. This view is supported by
Bishara, Hession and Petersen (1985) following their
longitudinal study in respect of soft tissue changes not
analogous to those of hard tissue skeleton. At the same it
seems that all parts of the soft tissue profile did not
directly follow the underlying skeletal profile changes
(Subtelny, 1961; Genecov, Sinclair and Dechow, 1990).
11.1.2
profile
11.1.2.1
Changes in the components of the soft tissue
Glabella
Soft tissue Glabella becomes more prominent well into adult
life. Beside the presence of sexual dimorphism in size, it
is evident that the location of Glabella is higher in
females than in males. In both sexes Glabella tends to move
downwards with time as does soft tissue Nasion (Behrents,
1984).
11.1.2.2
In both sexes the most anterior point of the nose continues
to mova forwards and downwards with age (Subtelny, 1959,
1961; Ricketts, 1960). Although males have larger noses than
females there appears to be no sexual dimorphism in
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319
respect of the angular relationships of the nos. to the
cranial base. The angle formed by a continuation of the
bridge of the nose and the columella becomes more acute
during the later stages of development (Subtelny, 1961). It
was reported that subjects with straight profiles tend to
have straight ~:,Jses (Robison, Rinchuse and Zullo, 1989).
At the same time those with convex profiles tend to ha"'e
convex noses and thos~ with concave profiles tend to have
concave noses.
11.1.2.3 ~
The nasiolabial angle becomes more acute with age. Soft
tissue A point has a downwards and forwards direction of
movement during growth of the nasomaxillary complex and the
downward movement becomes more apparent as the lip
lengthens. Stomion follows the same direction during growth
as it moves away from the Anterior Nasal Spine. The lower
lip also follows this behaviour, as does soft tissue B
point. The angle formed by the lower lip, mental sulcus and
Pogonion becomes deeper for the female, perhaps as the
result of a relatively more prominent lower lip and a lesser
for«ard movement of soft tissue B point (Behrents, 1984).
Males, however, have larger and more prominent lower lips.
Both sexes show a tendency to a relatively less prominent
upper lip with the passage of time. The nose relates
continually to the movements of Stomion with age having
little or no effect. This suggests that the whole midface is
moving proportionately downwards and forwards through time.
As the skeletal profile straightens, or becomes more
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320
concave, so soft tissue pogonion becomes more prominent with
age and it may be expected that the upper lip will flatten
as it elongates (Behrents, 1984). The vermilion aspect of
the lips, especially of the lower lip, was concomitantly
observed to become more retruded in relation to the facial
profile (Subtelny 1959). Following the complete eruption of
the anterior teeth, the lip embrasure has been found to be
closely related to the incisal edges of the incisors.
After about nine years of age, the upper lip was found to
cover just more than sixty per cent of the maxillary central
incisor crown. The remainder of this tooth is of course,
usually covered by the vermilion aspect of the lower lip
(Subtelny, 1961). In the relaxed position a small vertical
space or interlabial gap is normally found between the upper
and lower lips. In malocclusions and facial disharmonies,
the interlabial gap may be larger than normal or completely
lacking (Burstone, 1967).
11.1.2.4
Both the skeletal and integumental chins become less
retrognathic with progressive growth and development. The
integumental chin tends to be closely related to the degree
of prognathism of the underlying skeletal framework
(Subtelny, 1959, 1961). A panel of jUdges rated the majority
of subjects with horizontal growing mandibles, and thus
"strong" chins, as being good looking (Lundstrom, Woodside
and Popovich, 1987).
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321
TABLE XLV
AGE RELATED CHANGES OF CEPHALOMETRIC PARAMETERS DESCRIBIRG
sorT TISSUE CHAHGE
S.D.
N.A.
(1981):lip to I-line Ricketts
(years) HEAR (mm)
-1.25
-2.50
-3.75
-5.00
AGE
8
13
18 m
23 m
Lower
HoldAWAY H-angle
AGE (years)
5 m
f
10 m
f
15 m
f
25 m
f
(Bisbara et aI" 19ail:
ME1u~ (deg) S.D.
15.0 3,9
14,5 5.0
13.6 3.8
13.8 5.1
13,2 4.8
10,5 5.6
8.1 5.5
9.1 6,0
S.D.
3.4
4.2
3.6
4.7
4.4
6.0
4.9
6.2
Soft tissue ~rofile (including nose) ­
Glabella-t1p of nose-soft-pogonion
(Dishara et al., 1984):
AGE (years) HEAR (deg)
5 m 147.4
f 148.0
10 m 144.3
f 143.2
15 m 139.2
f 139.8
25 m 140.2
f 138.9
Soft tissue profile (excluding the nose) -
Glabe+ip(;~;6;~~~~s:i~:s~I;4~goniOn
AGE (years) MEAN (deg) S.D.
J m 169.7 4.1
f 170.3 4,0
10 m 168.1 3.3
f 167.4 4.2
15 m 166.9 4.7
f 169.6 6.0
25 m 173.0 5.9
f 171.3 6,5
m = Male
f = Female
S.D. = Standard deviation
N.A. = Not available
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322
Normal, or average, soft tissue dimensions for the
parameters studied in the present investigation are not
freely available. Nevertheless, two sets of measurements
were found in the literature and have been presented for
comparative purposes (Table XLV).
11.1.3 Soft tissue changes influencing the dentition
The dentition is not permanently fixed in relaticn to its
skeletal base. Similarly the soft tissues overlying the
teeth are not stable relative to the skeletal base of the
denture. After approximately thirteen years of age they do,
however, maintain a relatively fixed horizontal and vertical
relationship to the denture itself. With these factors in
mind, it seems reasonable to assume that the uprighting
movements of the incisors, which are discussed in Chapter
8, result from functional relationships which exist between
the dentition and the surrounding muscular forces. These
functional relationships may become fully established before
skeletal growth has been completed. A continuing downwards
and forwards growth of the maxilla and mandible tends to
create somewhat more protrusive skeletal bases for the
teeth. Since the degree of growth expressed by the mandible
exceeds that which occurs in the maxilla (Subtelny, 1959),
this discrepancy in growth is evidenced by a decrease in
the convexity of the skeletal profile.
In terms of functional objectives,
position the teeth in such a position
activity is required to move the lips
it seems reasonable to
that minimal muscular
from a relaxed to a
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323
closed position. The ability to produce an adequate oral
seal then becomes a functional objective of orthodontic
therapy. The lower lip normally contributes more movement to
effect oral closure than does the upper lip, as both lips
simultaneously retrude and flatten against the incisors
(Burstone, 1967).
The effect of vertical growth of the lips
emphasized by Vig and Cohen (1979) who found
lower lip is elevated during growth between the
and eleven years and that there is a reduction
seperation.
was also
that the
ages of ten
in the lip
11.1.4
tissue
The effect of orthodontic treatment on the soft
It is most important to have a sound understanding of the
changes which occur in the soft tissue profile during
orthodontic treatment, concurrent with normal growth and
development (Attarzadeh and Adenwalla, 1990).
11.1.4.1 Vertical changes
A predictable closure of the interlabial gap
both horizontal and vertical movements of
incisors occur during retraction of the
(Jacobs, 1978).
occurs when
the maxillary
anterior teeth
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11.1.4.2 Lip thickness and strain
324
The placement of teeth according to accepted cephalometric
criteria does not necessarily ensure that their overlying
soft tissue will drape in a harmonious manner. Holdaway
(1983, 1984) illustrates this with his soft tissue analysis.
According to Holdaway's findings there is an upper lip to
up~er incisor ratio which has to be attained in order to
achieve soft tissue balance at the end of treatment. This
is true for growing subjects, but not so for adults and for
subjects with either thin or thick lips. On average,
however, there seems to be a significant correlation between
osseous, and soft tissue changes in both males (r = 0.83,
p < 0.01) and females (r = 0.85, P < 0.01) (Oliver, 1982).
11.1.4.3 Thickness of soft tissue oyer lips
Research done by of Holdaway (1983) indicates that for
adolescents the normal thickness of the soft tissue at point
A is 14 to 16 rom. When the position of point A is altered
by tooth movement, the soft tissue overlying this landmark
will follow the bone movement and remain at the same
relative thickness. When there is tension and thinning of
the upper lip, immediately anterior to the incisors, the
tissues will thicken if the i~lcisors are moved palatally.
This will occur until the tissues approach their normal
thickness over point A. When the lip tension has been
eliminated, further palatal movement of the incisor will
cause the lip to follow the incisors in a one to one ratio.
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325
In some patients with lip tension and in whom the tiaaue
thickness at point A is very thin, the lip may follow
incisor retraction immediately and so retain a reduced
thickness. If the tissue at point A is very thick the lip
may not follow incisor retraction at all. In the adult the
the lips will usually follow the teeth immediately even
though there may be lip tension present.
11.1.4.4 Nasolabial angle
athat
angle were
amount of
indicatestudythis
Changes in the nasolabial angle during orthodontic treatment
were studied by Lo and Hunter (1982). They found that:
i) The nasolabial angle did not change signifj~antly
with growth.
ii) Increases in the nasolabial
significantly correlated with the
maxillary incisor retraction.
iii) Increases in lower facial height and/or the
mandibular plane angle, during treatment, were
accompanied by increases in the nasolabial angle.
iV) The response of the nasolabial angle in an
extraction group was not significantly different
from that found in a similar nonextraction group.
v) The observed changes in the soft tissue profiles
were significantly correlated with changes in the
underlying hard tissue landmarks for the
period studied.
vi) No significant sexual dimorphism was noted in this
study.
vii) The results of
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significant portion
could be influenced by
326
of the soft tissue profile
orthodontic treatment.
11.1.4.5 Hard tissue to soft tissue
Different workers have tried to show a relationship between
hard and soft tissue alterations in the lip area. Some
observed that successful orthodontic treatment did not
consistently result in improved aesthetics (Brodie et 01.,
1938; Wylie, 1955). Others were of the opposite opinion
(Angle, 1907; Tweed, 1954; Stoner et 01., 1956).
Most authors agreed, however, that changes in the position
of the incisors, especially retraction, alter the contour of
the lips (Buchin, 1957; Ricketts, 1960; Bloom, 1961;
Subtelny, 1961; Rudee, 1964; Branoff, 1971; Hershey, 1972;
Anderson et al., 1973; Garner, 1974; Wisth, 1974; Huggins
and McBride,1975; Forsberg and Odenrick, 1981; Oliver, 1982;
Holdaway, 1984). Upper lip retraction was found to equal
about 40 percent of the distance of a maxillary incisor
retraction while the lower lip retraction equaled about 70
percent of the maxillary incisor retraction distance
(Yogasowa, 1990).
There are, however, different opinions as to whether there
is a definite correlation between treatment-induced
incisor changes and soft tissue responses (Finnoy, Wisth
and Boe, 1987). Some workers claim to have found such a
relationship (Bloom, 1961; Rudee, 1964; Anderson et al.,
1973; Huggins and McBride, 1975; Oliver, 1982; Holdaway,
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327
1984), whereas others reported great individual diff.r.nc••
(Branoff, 1971; Hershey, 1972; Wisth, 1974) and that the
response was dependent on many different factor.. The••
included the degree of incisor retraction, lip strain and
morphology, age, sex, and type of treatment. Lower lip
changes in response to orthodontic tooth movement were found
to be more predictable than those brought about in the
upper lip. The low degree of predictability which is
associated with upper lip responses to orthodontic tooth
movement may be caused by the complex anatomy and/or
dynamics of the upper lip (Talass, Talass and Baker, 1987).
When profile changes are compared to values representing
"normal" facial aesthetics, it is evident that, in
general, extraction of four first premolars does not result
in a concave profile (Drobocky and Smith, 1989).
There is general agreement that orthodontic treatment can
influence the soft tissue profile, but there is still
disagreement on the exact amount of response of the soft
tissues to changes in the positions of the teeth and/or
alveolar processes (Finnoy, Wisth and Boe, 1987).
Some workers report that a definite correlation exist
between incisor movement and soft tissue changes (Stoner ~
£1., 1956; Riedel, 1957; Bloom, 1961; Rudee, 1964; Anderson
et al., 1973; Garner, 1974; Roos, 1977; Koch et al., 1979;
Oliver, 1982). Others, in contrast, have found that observed
changes in the soft tissues do not follow changes in the
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328
dentition proportionately (Burstone, 1958; Neger and
Newmark, 1959; subtelny, 1961; Hershey, 1972; Angelle, 1973;
Wisth, 1974).
These different respo.u:&es in different individuals may be
attributed to variation in gender (Huggins and McBride,
1975), variation in lip morphology (Oliver,1982; Holdaway,
1983), the amount of incisor retraction (Wisth, 1974),
different treatment mechanics (Forsberg and Odenrick, 1981)
or to extraction or nonextraction treatment regimes
(Strombo~i, 1979).
11.1.4.6 Lip changes
During treatment, the lower lip tends to increase slightly
more in length with mesiocclusion (Class III) than it does
with distocclusion (Class II). The measured changes were
principally connected with growth and increased bite height.
Following retraction of the upper teeth during treatment of
Class II malocclusions, the lower lip "curls up" and moves
forwards. During treatment of Class III malocclusion, the
lower incisors tend to tip lingually and the lower lip
tends to move lingually. Sublabially, lip contours behave in
the same way as the roots of the lower incisors (Rakosi,
1982).
The upper lip became thicker during the treatment of Class
II malocclusions and thinner during treatment of Class III
malocclusions. The result was that differences in upper lip
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329
thickness, between the two types of malocclusion, cea••d to
be significant after treatment.
Lip tension needs to be considered
aesthetic prognosis and restoration of
1982; Holdaway, 1983, 1984).
when assessing the
lip closure (Rakesi,
11.1.4.7 Qrthognathic surgery
The reader is referred to the abundant descriptions of the
various orthognathic surgical analyses and techniques which
have a bearing on the soft tissue profile (Worms, Isaacson
and Spiedel, 1976; Suckiel and Kohn, 1978; Proffit, Turvey
and Moriaty, 1981; Kinnebrew, Hoffman and Carlton, 1983;
White and Proffit, 1985; Wolford, Hilliard and Dugan, 1985).
11.1.4.8 Cephalometric standard
Park and Burstone (1986) tested the efficacy of
cephalom~tric dentoskeletal standards, when used as
clinical tools, to predict desirable facial aesthetics. They
concluded that the chances of consistently producing
desirable profiles by treating according to such a
standards is questionable.
There are hundreds of measurements that may be used in
tracing cephalometric head films (Steiner, 1960). Steiner
cautioned, however, that orthodontists should not let the
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330
number of parameters which are measured become .0
complicated and unwieldy that they cea.e to be of practical
use.
11.1.5 Lip strength and its effects on the dentitign
Posen (1972) described a clinical method for measuring the
strength of the lips with a POmmeter. The rationale behind
his procedure was the belief that the teeth are in a .tate
of balance between forces which oct on them from the labial
and lingual sides. Although the importance of muscle forces,
which result from normal oral functions has at times been
questioned, it can not be denied that forces which originate
from lips, cheeks and tongue may be important. It was
Posen's belief that strong lips may indicate the presence
of a high lip muscle tone and which could result in
substantial labial forces acting on the front teet~. He
found that subjects with Angle Closs II division 2
malocclusion have an increased, and subjects with
bimaxillary protrusion a decreased lip strength, when
measured with his method. From a clinical point of view
these findings seemed logical and measurements of lip
strength could therefore be of importance in orthodontic
treatment planning.
The concept which proposes that the teeth are in a state of
equilibrium between all the muscle forces which oct upon the
dentition (Posen, 1972) has largely been rejected (Marx,
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331
1965; Proffit, 1986). It is now recognized that fore•• ,
other than those which result from the facial muscles, have
an effect on the positions of the teeth (Proffit 1986).
Marx (1965) found with his electromyographic study that the
postural activity of lips is reduced in subjects with Class
II division 2 malocclusions and concluded that the forces
generated by lip activity is generally secondary to incisor
position. The theory thus proposed by Posen (1972) that the
upper incisor inclination in, for example, Class II division
2 malocclusions are due to an increase in lip force was
already earlier disposed of by Marx (1965) with his
electromyographic findings.
Simpson (1977) observed changes in muscle activity of ~he
upper lip to be unrelated to the amount of upper incisor
orthodontic retraction.
Janson (1981)
have limited
value of lip
As a result of their studies Ingerval and
concluded that lip strength measurements
reproducibility and thus that the clinical
strength measurement is limited to some degree.
11.1.6 Soft tissue analyses
Profilometric
attained from
tissue profiles
Lines, 1978).
analyses, by means of a
photographs, were used
(Peck and Peck, 1970;
silhouette profile
to evaluate soft
Lines, Lines and
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532
Various cephalometric soft ti88ue analyses are de8cribed in
the literature (Rakosi, 1982). Included among th••• are
proportional analyses, angular analy8es, analy.i. of the
th~ckness of soft tissue profile and the profile analy.is
of Schwarz.
The Moorrees mesh diagram graphically displays variations
among facial components and thereby provides a description
of facial morphology in a single step. A modification of
the Moorrees mesh diagram takes advantage of linear and
angular measurements which were added to the original
analysis. This modification is particularly useful for
planning surgical corrections of facial dysmorphology
(Ghafari, 1987). A proportional assessment of both hard and
soft tissue craniofacial relationship furnishes a valuable
guide in orthodontic treatment planning (Carlotti and
George, 1987).
Radiographic cephalometric analyses which use profile lines
to evaluate the portion of the lips in relation to the face
include the popular cephalometric analyses of steiner
(1953), Merrifield (1966), Ricketts (1981) and Holdaway
(1983).
Lips lying behind the S-line of S'teiner (1953) are too flat,
while those lying anterior to it, are too prominent. The
Z-line of Merrifield (1966) is based on the Frankfurt
horizontal plane and gives a critical description of a
number of lower facial relationships. Merrifield
incorporated aspects of the Tweed (1966) triangle into his
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333
soft tissue analysis. In adults with normal Tweed triangle
and ANB measurements, the average Z-angle i. 80 d.gr••••
In patients eleven to fifteen years of age with normal Twe.d
and ANB measurements, the average z-angle is 78 degrees.
The soft tissue reference line used by Ricketts (1981)
e~tends from the tip of the nose to soft tissue pogonion. In
average individuals the upper lip is 2-3 rom and the lower
lip 1-2 rom behind this line.
The Holdaway soft tissue analysis (Holdaway, 1983),
reflecting the relatiollships of 11 soft tissue paramaters,
is clinically a very useful tool. It assists the
orthodontist in his evaluation of the soft tissue profile,
especially the important area of the lower face which is
easily affected by orthodontic treatment.
The Ricketts E-line, the steiner S-line and the soft t.:ssue
facial plane all seem to be equally acceptable as basis for
assessment of the soft tissues of the profile (Saxby and
Freer, 1985). A study of the reproducibility of these
profile lines found that the S- and E-lines were almost
equally reproducable and that they are less variable than
the Holdaway H-line (Hillesund, Fjeld and Zachrisson, 1978).
An additional finding of this study was that reproducibility
is not definitely dependent upon whether or not the
cephalograms were made in patients with open or closed
lips.
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334
Lip protrusion can be evaluated by relating the lips to a
true vertical line Passing through the 80ft tissue point A
and through soft tissue point B. The lips should lie along
or only slightly in front of this line. This evaluation
should be carried out with the subject's lips relaxed. It is
also important to note the extent to which the lips are
separated when they are relaxed and whether the subject must
strain to bring the lips together (Proffit, 1986).
soft tissue parameters commonly used by orthodontists in
their diagnosis and treatment planning, as well as in the
evaluation of profile changes which occur as a result of
growth and/or orthodontic treatment, were reviewed. The
literature indicates that th~ various angles and lines used
to evaluate the soft tissue profiles as previously noted do
not all behave in a similar manner with age. Therefore,
the clinicians need to use a series of soft tissue
parameters in order to better evaluate soft tissue profiles
(Holdaway, 1983; Bishara, Peterson and Bishara, 1984;
Bishara. Hession and PeterEon 1985).
11.1.7 Ethnic differences in soft tissue profile
When examining facial aesthetics clinicians should be aware
of the implications of variation in ancestral heritage
(Thomas, 1979).
Although it appears that no single cephalometric dentofacial
or study cast parameter significantly correlates with
post-treatment lower incisor crowding (Little, Wallen and
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335
Riedel, 1981; sinclair and Little, 1983, 1985; Shield.,
Little and Chapko, 1985) it may be postulated that certain,
as yet not fully understood, aSPects of soft tissue chang••
are able to influence the stability of an orthodontically
treated dentition. A question also often asked i8 whether
the findings of other researchers are applicable to our
5~mples. It is thus imperative to encourage the comparison
of similar studies, but on different samples and on
different continents in order to enable researches to find
the elusive answers in respect to long-term changes
following orthodontic treatment.
11.2 Objectiyes
There exists no longitudinal data in respect to this or
another similar sample (Table I). Soft tissue can influence
the hard tissue and the opposite can also occur. stability
of the dentition following treatment can thuo be influenced
by the soft tissue changes occurring during and following
treatment. It is thus essential to assess the changes
occurring in one sample. The results should not be accepted
as dogma, but it must be compared to other studies in order
to establish whether direct comparison is valid and if
differences exist, to point them out or if none exist, to be
able to support the SPecific philosophy.
Hence, the objectives of this part of the stUdy were:
i) to assess some longitudinal soft tissue changes in the
orthodontically treated subjects of this sample.
ii) to correlate these changes with lower incisor
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336
irregularity in the same group.
11.3 Materials and methods
The basic description of the materials used and the methods
employed to assess the data of this study are documented in
Chapter 3 of this thesis.
Cephalometric measurements describing the soft tissue
variables were obtained using the Oliceph computer
programme. The Holdaway soft tissue analysis (Holdaway,
1983) requires the lips to be together. Hence, all the
cephalograms were taken with the lips together. In the
construction of a visual treatment objective, prediction of
the changes in lip morphology is of great importance. A
major factor is the vertical position of the lip embrasure
and its relation to the incisal edges of the upper incisors.
Lip mobility should thus be included in a clinical
evaluation of the subject, especially when a short upper lip
is present. The immobile upper lip can easily be assessed by
taking two lateral cephalograms, one with lips closed and
the other with relaxed lips as proposed by Steyn (1981). The
Holdaway soft tissue analysis and visual treatment objective
adapt for these situations (Holdaway, 1983, 1984). The
following cephalometric measurements wela used:
i) Nose prominence (Holdaway, 1983):
Nose prominence measured from the tip of the nose to a
line perPendicular to Frankfurt horizontal and
running tangential to the vermilion border of the
upper lip (NOSE-MM).
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337
ii) Sulcus depth (Holdaway, 1983):
a) Superior sulcus depth measured from the deepe.t
aspect of the concavity of the su:cu. to a
perpendicular to Frankfurt horizontal and
tangential to the vermilion border of the upper
lip (SUPSULD-MM).
b) Inferior sulcus depth measured from the deepest
aspect of the concavity of the sulcus to the
H-line (I-SULH-MM).
iii) Upper lip curl (Holdaway, 1983):
Measurement of soft tissue subnasale to the H-line
(SAHLlNE-MM).
iv) Lips to profile lines as described by:
a) Ricketts (1981). Lower lip to the E-plane
(L-LIPE-MM).
b) Ricketts (1960). Upper lip to the E-plane
(U-LIPE-MM).
c) Merrifield (1966). Angular measurement of the
Z-line intersection with Frankfurt horizontal
(Z-ANGLE-DEG). The Z-line is a line tangential
to the most prominent lip which can be either
upper or lower lip (the H-line in comparison is
tangential to only the upper lip).
d) Holdaway (1983). Angular measurement of the
H-line to the soft tissue Nasion-pogonion line
or soft tissue facial plane (H-ANGLE-DEG).
e) Holdaway (1983). Lower lip to the H-line
(LLIPH-MM).
v) Lipstrain (Holdaway, 19B?):
a) Basic upper lip thickness near the base of the
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338
alveolar process about 3mm below point A
(ULIPTH-MM).
b) Upper lip thickness at the vermilion border with
closed lips (ULIPTAP-MM).
c) upper lip strain measurement produced as the
difference between ULIPTH-MM and ULIPTAP-MM
(ULIPSTR-MM).
vi) Soft tissue chin (Holdaway, 1983):
a) Soft tissue facial angle measured at the
intersection of Frankfurt horizontal and the soft
tissue facial plane (STFAC-DEG).
b) Soft tissue chin thickness (STCHIN-MM).
Only one metrical variable was assessed on the orthodontic
study cast by means of digital calipers capable of measuring
to 0.01 mm. Pre-treatment (T1), post-treatment (T2) and
post-orthodontic (T3), lower incisor crowding were assessed
according to the Little Irregularity Index (Little, 1975).
The data were subjected to descriptive statistics (mean and
standard deviation), pairwise differences assessment
(Friedman test) and Spearman correlation coefficient tests
for each of the three time intervals (T1, T2 and T3) (zar,
1984). The significance level of this part of the study was
set at 0.05.
11.4 Results
The =esults are set out in Tables XLVI and XLVII.
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339
The purpose of the measurement. in this part of the .tudy
was to assess possible longitudinal soft ti••u. chang••
as a result of the orthodontic treatment. Correlations of
the changes in the soft tissue parameters studied with the
post-orthodontic (T3) Little Irregularity Index (Little,
1975) indicated the occurence of a relationship between the
recorded soft tissue changes and the stability of the
orthodontically treated dentitions.
The variables which were not significantly (p > 0.05)
changed during treatment (Tl-T2) were the inferior sulcus
depth (I-SULH-MM), lower lip to H-line (LLIPH-MM), soft
tissue facial angle (STFAC-DEG) and soft tissue chin
thickness (STCHIN-MM) (Table XLVI).
Variables which changed significantly (p < 0.05) during the
post-orthodontic interval (T2-T3) were nose prominence
(NOSE-MM), inferior sulcus depth (I-SULH-MM), upper lip to
E-line (U-LIPE-MM), lower lip to E-line (L-LIPE-MM),
Merrifield Z-angle (Z-ANGLE-DEG), lower lip to H-line
(LLIPH-MM), upper lip strain (ULIPSTR-MM), soft tissue
facial angle (STFAC-DEG), soft tissue chin thickness
(STCHIN-MM) and the Little Irregularity Index (L-IRREG)
(Table XLVI).
Some of the variables ·showed a significant change when
assessment was done for the total evaluation period (Tl-T3),
but not during the post-orthodontic interval. They
included the superior sulcus depth (SUPSULD-MM), upper lip
curl (SAHLIRE-MM), Holdaway H-angle (H-ANGLE-DEG), upper lip
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thickness near the base of the
and upper lip thickne.s
(ULIPTAP-MMj (Table XLVI).
3.0
alveolar proce.s (ULIPTH-MM)
at the vermilion border
The Spearman Correlation Coefficients, set out in Table
XLVII, showed only a few weak, significant relation.hips
between the variables measured and the post-orthodontic
(T3) lower incisor irregularity. The infer sulcus depth
(I-SULH-MM) (r = -0.42. P • 0.0001) and lower lip to H-line
(LLIPH-MM) (r = 0.31, P • 0.003) correlated significantly at
the pre-treatment period (Tl) and the Z-angle (Z-ANGLE-DEG)
(r = -0.24, P = 0.02) and soft tissue facial angle
(STFAC-DEG) (r = -0.27, P = 0.01) showed similar results at
the final observation (T3).
11.5 Discussion
Soft tissue changes occur not only as part of a normal
physiologic process, but also during and following
orthodontic treatment. These changes are important when the
stability of the occlusion following orthodontic treatment
is at stake.
Numerous attempts have been made to assess the influence of
muscle function on the dentition (Marx, 1965; Posen, 1972;
Simpson, 1977; Ingerval and Janson, 1981). The clinical
value of these results appear to be limited (Ingerval and
Janson, 1981). The influence of the soft tissues surrounding
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TABLE XLVI
DESCRIPTIVE STATISTICS FOR METRICAL DATA IN RESPECT OF THE SOFT TISSUE
(Friedman test included)
Tl T2 T3 Tl-T2 Tl-T3 T2-T3
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D. p-value Pairwise Differences
NOSE-MM 13.14 1.96 15.93 2.11 18.04 2.35 0.0001
SUPSULD-MM -9.79 2.98 -8.96 2.80 -8.27 3.19 0.0001 - - x
I-SULH-MM 5.02 2.35 4.84 1.91 5.45 2.30 0.02 x x
SAHLINE-MM 6.74 2.21 4.82 1.70 4.73 1.72 0.0001 + + x
U-LIPE-MM -0.93 2.39 -4.14 1.91 -5.86 2.36 0.0001 + + +
L-LIPE-MM 0 ••9 3.07 -2.13 2.09 -3.69 2.61 0.0001 + + +
Z-ANGLE-DZG 69.55 7.49 74.80 5.99 76.85 10.57 0.0001
H-ANGLE-DEG 16.98 3.85 13.59 3.14 12.35 3.65 0.0001 + + x
LLIPH-MM 1.13 2.19 0.69 1.46 0.34 1.67 0.0002 x + +
ULIPTH-MM 14.73 1.52 15.95 2.06 16.48 2.16 0.0001 - - x
ULIPTAP-MM 11 ••8 2.14 13.49 1.99 13.56 2.53 0.0001 - - x
ULIPSTR-MM 3.25 1.98 2.46 1.65 2.92 2.01 0.0002 + x
STFAC-DEG 89.09 3.28 89.71 3.62 90.98 3.58 0.0001 x
STCHIN-~ 10.13 2.13 10.47 2.05 11.29 2.43 0.002 x
L-IRREG 4.21 3.57 0.43 0.66 1.71 1.64 0.0001 + +
S.D. = Stondard deviation
+ = Significant, p < 0.05 (Tl > T2, T3)
== Significant, p < 0.05 (Tl < T2, T3)
x = Mot significant, p > 0.05
w
..
...
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TABLE XLVII
SPEARMAN CORRELATIQN COEFFICIENTS COMPARING THE RELATIQlSHIP
OF THE LOWER INCISOR IRREGULARITY AT T3 AGAINST THE MEASURED
VARIABLES AT Tl. T2 AND T3
L-IRREG
342
VARIABLE
NOSE-MM
SUPSULD-MM
I-SUIIH-MM
SAHLIHE-MM
U-LIPE-MM
L-LIPE-MM
Z-ANGLE-DEG
H-ANGLE-DEG
LLIPH-MM
ULIPTH-MM
ULIPTAP-MM
ULIPSTR-MM
STFAC-DEG
STCHIN-MM
Tl
r
-0.02
0.03
-0.42
-0.13
0.16
-0.1.0
-0.1.0
-0.16
0.31
-0.05
-0.04
-0.01
-0.19
0.03
P
0.84
0.78
0.0001
0.24
0.14
0.34
0.35
0.15
0.003
0.64
0.74
0.94
0.07
0.78
T2
r
0.02
-0.12
-0.06
0.14
0.12
0.1.0
-0.15
0.18
0.10
-0.01
0.11
-0.16
-0.06
-0.02
P
0.82
0.26
0.60
0.19
0.27
0.38
0.15
0.10
0.44
0.91
0.33
0.14
0.56
0.86
T3
r
-0.09
-0.12
0.12
0.11
0.20
0.12
-0.24
0.17
-0.01
0.13
0.10
0.10
-0.27
-0.12
P
0.39
0.27
0.26
0.32
0.06
0.25
0.02
0.12
0.92
0.24
0.34
0.43
0.01
0.29
r = Spearman Correlation Coefficient
p = Probability value, significance level 0.05
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343
the dentition, however, can not be underestiaated.
Significant changes were measured in the soft tissue during
the post-orthodontic period (T2-T3) and cognizance must be
taken of the significant correlations shown with late lower
incisor irregularity (Table XLVII).
The concept of continued growth following puberty was
reported by Behrents (1984). This continued growth as
recorded during the post-orthodontic period (T2-T3) (Table
XLVI) plays its part in influencing tooth position. Behrents
(1984) noted similar findings during adulthood and stated
that growth changes take place in the environment created
by the normal function of facial muscles.
In the present study cephalometric soft tissue analyses
were used to assess the longitudinal changes which occur
during and following orthodontic treatment (Merrifield,
1966; Ricketts, 1981; Holdaway, 1983). The observed
changes were subsequently correlated ~o lower incisor
irregularity (Little, 1975).
All the variables measured, except the inferior sulcus depth
(I-~ULH-MM), lower lip to H-1ine (LLIPTH-MM), soft tissue
facial angle (STFAC-DEG) and soft tissue chin thickness
(STCHIN-MM) showed significant changes from the
pre-treatment to end of treatment observations (T1-T2)
(Table XLVI). The changes were expected as the lips change
as a result of the better tooth positions attained at the
end of active treatment (T2). A similar finding was also,
amongst others, reported by Finnoy, Wisth and Bee (1987).
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344
The mean increase in nose prominence (NOSE-MM), which wa.
significant at all three observations (p • 0.0001), was
2.79 mm (T1-T2) and 2.81 mm (T2-T3). The mean anterior
positioning of the chin (STFAC-DEG) was 0.62 degrees
(T1-T2) (p > 0.05) and 2.27 degrees (T2-T3) (p. 0.0001).
The increase in soft tissue chin thickness was 0.34 mm
(T1-T2) (p > 0.05) and 0.82 mm (T2-T3) (p • 0.002) (Table
XLVI). These three parameters measured mainly growth related
changes and thus not within the control of the clinician.
The values of the variables at the end of treatment (T2)
(Table XLVI) are within the clinically accepted norms
described by Merrifield (1966), Little (1975), Ricketts
(1981) and Holdaway (1983), except for upper lip strain
which should have been closer to 1.00 mm (Holdaway, 1983)
than the 2.46 mm mean value recorded and the upper lip being
further retruded from the E-line (4.14 to 0.7 mm). The lips
become more retrusive with age (Table XLV), but the upper
lip strain, which was not entirely eliminated during
treatment, possibly contributed to the upper lip being
flatter in relation to the E-line. The mean value for lower
incisor inclination (Chapter 7), was at the maximum end of
the described norms (proclined) at the end of treatment
(T2). If the lower incisor is not SUfficiently uprighted
(Tweed, 1962), the upper incisors cannot be entirely
retracted into their ideal position. This phenomenon could
also explain why the upper lip strain was not entirely
reduced during the treatment (Tl-T2).
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345
When evaluating the overview of changes which took place
from the pre-treatment to the final observation (Tl-T3) it
will be observed that there were only two which .howed
non-significant changes. The non-significant (p > 0.05)
changes are inferior sulcus depth (I-SULH-MM) which
increased by a mean value of 0.43 rom and upper lip strain
(ULIPSTR-MM) which decreased by a mean value of 0.33 mm
(Table XLVI). The upper lip strain, however, significantly
increased during the post-orthodontic period (T2-T3) (p.
0.0002). This slight increase could indicate clinically
significant anterior movement of the dentition (Moyers,
1988). Previously reported changes such as the lips becoming
less protrusive in respect to the tip of the nose and soft
tissue chin (lower soft tissue profile), as well as the
total soft tissue profile increasing in convexity (Table
XLV) were all observed during this longitudinal study (Table
XLVI). The total soft tissue profile is especially
influenced by the elongation of the nose during growth.
The most important phase of the study was the evaluation of
changes which occurred from the end of treatment to the
final observation (T2-T3). Such changes could have a major
influence on the stability of a treated dentition. The
Little Irregularity Index (Little, 1975) was significantly
improved from T1 to T2 (4.21 mm to 0.43 mm) (Table XLVI). It
did, however, significantly (p = 0.0001) increase again
during the post-orthodontic phase (T2-T3) (0.43 mm to 1.71
rom). Although these mean values indicate an increase in
lower incisor irregul~~ity, the mean final crowding was well
within clinically accepted norms (Little, 1975) or in other
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346
words, not clinically significant. The significant .oft
tissue changes which occurred during this period of
evaluation were, a continued increase in nose prominence, a
deepening of the lower lip sulcus, the lips becoming more
retrusive to the profile lines, the upper lip strain
increased, the soft tissue pogonion moved forward and the
soft tissue chin thickness increased slightly. All of these
changes could be ascribed to those normal maturational
c:langes which are a part of ageing (Behrents, 1984). The
measured variables even though changing, remained within the
accepted norms as described in the literature (Merrifield,
1966; Little, 1975; Ricketts, 1981; Holdaway, 1983). The
inferior lip sulcus depth (I-SULH-MM) which did not show any
significant change during the treatment (T1-T2) and in
general from T1 to T3, did increase significantly (p =
0.02) by a mean value of 0.61 mm during the post-orthodontic
phase (T2-T3) (Table XLVI). A slight, but significant
increase in incisor overjet (mean 2.85 mm to 3.17 mm)
(Chapter 8) could have contributed to this deePening of the
lower lip sulcus as a result of upper incisor pressure on
the lower lip. The observed uprighting of the lower
incisor (Chapter 8) could have complimented the increase in
the depth of the lower lip sulcus.
The visual treatment objective (V.T.O.) is a useful tool
when used as an adjunct to the other orthodontic study
records (Ricketts et al., 1979; Holdaway, 1984) . This is
true especially when assessing the predicted results at the
end of treatment (T2). Holdaway (1984) describes certain
goals which can be achieved if the soft tissue changes are
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347
planned according to his V.T.O. One of the guideline.
suggested by holdaway (1984) is to determine the future lip
position (lip profile) according to the H-angle and it's
relationship with the point A convexity (Chapter 4). The
H-angle should be 10 degrees plus the measured value of the
point A covexity (Holdaway, 1984). This goal was achieved
during the study. The noted value of this relationship was
within clinically acceptable norms achieved at the final
observation (T3) (H-angle = 12.35 +/- 3.65 degrees, Table
XLVIi Point A convexity = 1.12 +/- 2.99 mm, Table XIX).
Significant correlations of the measured soft tissue
variables with the post-orthodontic lower incisor
irregularity are portrayed in Table XLVII. These were the
inferior sulcus depth (I-SULH-MM) and lower lip to H-line
(LLIPH-MM) at the pre-treatment observation (T1) and the
Z-angle (Z-ANGLE-DEG) and soft tissue facial angle
(STFAC-DEG) at the final observation (T3) which showed
weak significant (p < 0.05) correlations with lower incisor
irregularity (r = -0.42, 0.31, -0.~4 and -0.27
respectively). It is, however, an indication that lip
profile (Z-ANGLE-DEG) and mandibular growth (STFAC-DEG)
change can influence incisor position following orthodontic
treatment.
Facial biologists appreciate that a relapse of the occlusion
following orthodontic treatment is a normal reaction of the
growth process itself, and that it serves to restore
morphology in a manner that protects against incursions
disturbing functional and morphologic balance, either during
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348
or subsequent to the childhood growth period. Behrent.
(198.) referred to these post-pubertal maturity chang•• a.
growth in the adult. Either a new composite balance i.
achieved or, likely, some degree of rebound occurs becau.e
of the aggregate influence exerted by the composite of all
regional growth fields (Enlow, 1986).
The soft tissue growth and maturational changes measured in
the present study, which the orthodontists have no control
over whatsoever, could have influenced the increase in the
lower incisor irregularity during the post-treatment
interval.
11.6 Conclusions
lower lip sulcus
correlations with
1. Mainly growth and maturational changes occur in the
soft tissue post-treatment. These changes could influence
the stability of the treated occlusion.
2. No strong significant correlations could be shown
between the observed soft tissue changes and lower incisor
irregularity. The Merrifield Z-angle and Holdaway soft
tissue facial angle (chin prominence) did, however, show
weak significant associations with post-treatment lower
incisor irregularity.
3. Protrusive lower lips influence the
depth. Both variables showed moderate
pre-treatment lower incisor irregularity.
4. The Holdaway H-angle and the point A convexity
relationship as used for the Holdaway soft tissue visual
treatment objective (Holdaway, 1984) is supported by the
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349
be taken 1n
orthodontic
of the present study and must
when prospectively planning
long-term d\.tta
consideration
treatment.
5. The mean lower incisor irregularity increase which
followed orthodontic treatment can be partly attributed to
soft tissue growth changes. The prerequisite when making
this assumption, however, is that clinical acceptable noras
be the order of the day at the end of active treatment.
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350
CHAPTER 12
SEXUAL DIMORPHISM AND ITS RELATIONSHIP WITH PQST-ORTHODQITIC
LOWER INCISOR IRREGULARITY
12.1 Introduction
Growth, which does not occur uniformly, results in increases
in size of the dento-facial complex. Growth also includes
differential and proportional changes (Hellman, 1927a,
1927b; Krogman, 1939). Sexual differences observed during
growth in orthodontic patients include the more prognathic
mandible of females when compared with male subjects of the
same age (Hellman, 1932). In terms of Hellman's dental age,
girls attain their pubescent growth about one dental age
ahead of boys (Krogman, 1951). Growth tends to continue in
boys after it has ceased in girls (Hellman, 1935; Krogman,
1951).
Studies on morphological changes of the craniofacial
skeleton and soft tissues are numerous (Behrents, 1984). For
most part these studies can be historically dated as before
or following the invention and utilization of the
cephalometric technique which was introduced by Broadbent
(1931) and Hofrath (1931).
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351
Prior to the development of the cephalometer, most studie.
were cross-sectional in nature dealing with mea.ure.ent. on
dry skulls or cadavers, casual observations or gro.s body
measurements on living individuals. After the advent of the
cephalometer, precisely controlled longitudinal
cephalometric studies became possible on living, growing
individuals (Behrents, 1984).
There are generally recognized structural and proportional
differences between young and mature faces and between male
and female faces (Baum, 1961).
During a comparison of the skeletal and dental patterns of a
group of children (7 to 9 years of age), with excellent
occlusions, with those of an older group (11 to 13 years of
age) various differences were noted. Boy's over-all facial
patterns are essentially the same except for increases in
size. The facial patterns of the girls are significantly
different between the younger and older age groups, with
older subjects showing less convex faces, more upright
incisors, increases in facial size and higher facial
angles. In both groups the mandibles appear to have larger
dimensions than the maxilla (Baird, 1952). Barnes (1954)
studied a group of children with excellent occlusions from
twelve to fifteen years of age. His findings show that
boys exhibit a significant increase in linear length of the
maxilla and mandible. Girls show no increase in maxillary
length, but the increase in mandibular length observed,
results in less convex faces in the female group. The
skeletal patterns ot both male and female faces also change
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352
in positional relationship, the mandibl.. becoming
increasingly more protrusive and the profiles less convex.
The boys in this age range develop leS8 protrusive
dentitions as a result of the maxillary incisors becoming
more upright. No such change occur in the dental pattern of
the girls.
Total facial height, as measured in a cross'-sectional study,
increases initially in males and females (Wunsche, 195J)'
Males show increases in the order of 1.1 mm from twenty to
approximately forty years of age and decreases amounting to
2.4 rom after sixty years of age. Females reach their
greatest facial height in the age group 26-30 years, and it
subsequently starts to decrease thereafter to the extent of
7.7 mm after 71 years (Wunsche, 1953). Significant increases
of head width and height is noted in females with a tendency
for increases in males in a cross-sectional study of two
Mexican adult populations (Lasker, 1953).
Males appear to be larger than females. Although this is
noted, sex differences become less significant as the age
level of the subjects increase. The maximal growth period of
girls appear to be between eight and thirteen years of age
and seem to start earlier and to be of a shorter duration
than that of be ~:l, whose maximal growth period is between
thirteen and eighteen years of age (Seal, 1957). A study
involving 100 males and 100 females (twenty to thirty years
of age) with Class I occlusions show that male dimensions
are larger than female dimensions except for the gonial
angle. The sexual dimorphism in size and relationships of
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353
the facial components tend to increase with age (Horowitz
and Thompson, 1964). The findings of an anthropo.etric
study, including 87 male and 77 female Swedes age.
twenty-five to forty-nine, of the head and the face (Lewin
and Hedegard, 1970), show that males are larger than
females.
Cross-sectional studies have some inherent limitations.
They often demonstrate those factors which are not true, but
can offer little in the way of clarifying or providing
information as to what is actually occurring. These studies
do, however, point out the features worth pursuing through
subsequent longitudinal assessment.
The introduction of roentgenographic cephalometries
(Broadbent, 1931), allowed for longitudinal studies to be
performed. This resulted in the development of a series of
diagrams (Broadbent, 1937) illustrating an orderly,
consistent growth pattern. The straight-line path of
landmark migration for ages one to eighteen years of age ia
available in published format as the Bolton standard. for
males and females (Broadbent, Broadbsnt and GOlden, 1975).
The results of a serial study of the human male head frca
the third month to eight years showed little change in the
development behaviour of the mean pattern, although
considerable individual variation was found. Enlargement of
the various anatomic areas occurs in a proportional aanner.
After an early age the nasal flo~r, occlusal plane, and the
lower border of the mandible all retain stable angular
relat.;_unships during growth and development. No change occ',U'
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354
in the gonial angle, and no growth spurts are evident in
these areas (Brodie, 19~1). Realising that individual
variations need to be pointed out, the era of cophalometric
analyses started (Wylie, 1944; Downs, 1948; steiner, 1953;
Tweed 1 1954; Ricketts, 1981; Holdaway, 1983).
A longitudinal cephalometric study performed on males and
females in their twenties at initial examination and then
re-examined at five years and ten years later, indicates a
siL~ difference between the sexes, but no sexual dimorphism
is observed in regard to the degree of prognathism and
in~lination of the incisors (Forsberg, 1979). For.sberg
(1979) finds no anteroposterior change in jaw relations for
men, but a more retrognathic mandibular position is shown
for the female group. Uprighting of the incisors is noted~
which Forsberg (1979) believes to be the result of posterior
mandibular rotation. This rotation of the mandible enlarges
the lower facial height (0.35 .urn in age group 24 to 29
years). No significant uprighting of the lower incisors is
observed in a longitudinal study of 243 Swedish males
(twelve to twenty years of age) (Bjork and Palling, 1955).
Earlier studies O~ the human head by Bjork (1947), males
after seven years, and Brodie (1941), ages prior to seven
years, show increases in mandibular prognathism. The
mandible shows greater prognathism tha~ the maxilla, but
both increase in prognathism which is characteristic of
profile changes with age (Bjork, 1947). Lande (1952) also
supports this findi.ng as shown in his study of a male
sample (four to seventeen years of age). Lande (1952) shows
the mandible becoming more prognathic in relation to both
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355
Nasion and the maxilla and in this way decreasing the
skeletal convexity. The skeletal patterns of a group
including boys (twelve to nineteen years of age) and girls
(twelve to eighteen years of age), with excellent
occlusions, echoes these results (Meinhold, 1957). These
changes occur faster in boys than girls (Schultz, 1955).
The mandible in its forward movement, which normally occurs
at a greater rate than in the maxilla, causes the facial
angle to increase from 82 degrees to 88 degrees and thus
decreases the angle of convexity from +10 degrees to 0
degrees. Vertical growth is also greater in the posterior
facial area (area of the ramus) than in the anterior facial
area (at the profile), thus decreasing the mandibular plane
angle from 28 degrees to 22 degrees. Accordingly, Gnathion
may move downward and forwards along the Y-axis as much as
1/2 inch and may thus change the Y-axis several degrees
(Downs, 1956) and at the same time cause an increase in the
facial angle (Lundell, 1955). Similar obsevations are
reported with Gnathion moving down the facial axis between
2.5 mm to 3 mm per year during growth of the mandible
(Ricketts, ~~., 1979; Holdaway, 1984). It is also noted
that the face lengthens in vertical height in the later
age groups (Bjork, 1947). A longitudinal study of a group
of nineteen boys betw~en the ages of eight years to
seventeen years and beyond, shows that the late stages of
growth are accompanied by a continuation of forwards and
downwards movement of the Anterior Nasal Spine and of
Pogonion, while the dental arch and its supporting bone
tend to move more slowly and thus to drop behind (Brodie,
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356
1953). The prominence of the ~entition subsequently
decreases (Schaeffer, 1949; Brodie, 1953). This fact that
the incisal edges and the lab1al surfaces of lower incisors
from typical mandibles, when superimposed with o~ientation
at Menton, became more retrusive in relation to the chin
point is also supported by other studies inclUding female
and male subjects (Davis, 1956).
Subtelny (1959) studied the profile characteristics of soft
tissue facial structures and their relationship to
underlying skeletal structures. The long-term cephalometric
parameters of thirty subjects with normal profiles, equally
divided as to sex, and recorded at intervals of from three
months to eighteen years of age show the following findings:
i) At eighteen years of age there are no striking
differences in soft tissues or skeletal mandibular
prognathism between boys and girls. At saven to
eight years of age the boys, however, show only
one-half the amount of prognathism that they would
achieve by eighteen years of age, while the girls
have already expressed tnree-fourths or more of the
amount that they will achieve by eighteen years of
age.
ii) In both sexes the skeletal profile tends to become
less convex with each increment in age.
iii) The prominence of the nose tends to increase in
comparison with the millimetre increments at the chin
and the frontal prominence. No sex differences are,
however, recorded. It is noted with reference to
this lack of sex differences that con-comitant
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357
sex-differential increments at chin point, which are
expected at this age, mask sex difference. in
forward growth at the tip of the nose, when asses.ed
by the angle of convexity.
iv) The pattern of nose growth and the location of the
tip of the nose, when studied by linear
measurements, vary between boys and girls at
certain ages. In twelve of fifteen boys a growth
spurt is described which seems to centre around the
thirteen and fourteen year old subjects. A similar
spurt is evident in only three of fifteen girls and
is observed to centre around twelve years of age.
v) Both mandibular and maxillary dentitions become less
protrusive with increasing age.
A decrease in the angle of the maxillary incisor is a common
change observed in females and males. In girls, however,
the interincisal angle increases significantly (Lundell,
1955). crowding of the incisors, loss of arch length, an
increase in the interincisal angle and "normally"
changing facial relationships occur in both sexes (Humerfelt
and Slagsvold, 1972).
A comparison of the facial and dental patterns of a group of
thirty-one boys and thirty-one girls (Baum, 1951) with those
of young adults appraised by Downs (1948) in an earlier
study shows that the face of the eleven to fourteen year old
child, with excellent occlusion, does not present the same
proportions as the face of the young adult. In general, the
younger person has a more convex face, less upright
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358
incisor.s, and a more protrusivG dentition. It i. thu.
obvious that the den~Jfacial pattern changes with
maturation. During this ~ge range the female facial
pattern becomes significantly l~ss convex (more similar to
the adult face) than the male facial pattern. The girl
between eleven and fourteen years of age is thus closer to
having achieved an adult dentofacial relationship than the
boy, and therefore she has less post-pubertal growth
potential (Baum, 1951). The facial and dental patterns of
12~year-old boys and girls when cOlnpared to those of adult
men and women show that the facial patterns of boys are
significantly different from those of men, but the facial
patterns of girls are not significantly different from
those of grown women except in size (petraitis, 1951).
Females show consistent minimum facial changes in size and
proportion after fourteen to fifteen years of age. Males,
on the other hand, consistently continue their growth
and development until twenty years of age (Downs, 1956;
Meinhold, 1957). Van Rensburg (1981) notes that male
mandibles can increase in dimension late into the twenties.
These findings are also observed in a stUdy of 100
Caucasian children between the ages of eleven and twenty
years, equally divided as to sex, showing strong
correlations between the incremental changes ~,t glabella
and at the mandibular SYmPhysis (Lavin, 1958). He shows
that these changes are common in boys during the entire
period of his stUdy, but are less pronounced in girls of
whom the majority show no change after the age of fifteen
years (Lavin, 1958).
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359
Females show facial growth changes which continue late into
the second decade and males exhibit similar change. into
their third decade of life (Hun~er, 1966). Concerning these
late growth changes, a study by Baer (1956) illustrates
changes in the facial dimensions of 5,600 men and 7,420
women during the third decade of life. Saer (1956)
demonstrates significant increases in facial height, nose
height, and bizygomatic width in the men, but no such
increases are shown in the women. A longitudinal study of
subjects originally included in the Bolton growth study and
later re-examined shows that growth changes of the
craniofacial skeleton continues into old age in an apparent
adaptive, but decelerating manner for both males and females
(Behrents, 1984). Females are smaller, grow less and show a
more vertical facial growth direction than males at all ages
(Behrents, 1984).
Several other long-term studies have been reported j.n which
the generalized normal growth of the craniofacial complex is
described for males and females. Of the most popular are the
Burlington growth study in Toronto (Popovich, 1955), the
Michigan studies at Ann Arbor, Michigan (Riolo et al., 197·1;
Moyers et al., 1976), the Bolton study in Cleveland, Ohio
(Broadbent et al., 1975) and the implant studies by Bjork
and Skieller (1983).
Age and sex are significant factors for orthodontists to
consider in formulating a treatment plan in which growth is
to play an important part. Orthodontists find themselves
able to alter facial conformation to some considerable
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360
extent (Herzberg, 1952; Tweed, 1954; Ricketts et 01., 1979;
Holdaway, 1981, 1984; Proffit, 1986; Moyer., 1988).
Appliance sys~ems have been devised by which the
orthodontist can control normal, progressive facial
alterations as a part of the routine treatment procedure in
correction of abnormal or unpleasant facial contours (Klein,
1957; Tweed, 1966; Graber, 1977; Frankel, 1980; Haas,
19BO; Graber and Swain, 1985; Teuscher, 1986; Woodside,
Metaxas and Altuna, 1987; Bass, 1990: McNamara, Howe and
Dischinger, 1990).
In summary, there is apparently a well-ordered and
predictable pattern in the dentofacial changes that
accompany growth and development. A period which might be
called the period of primary growth or growth in which sex
is not a variable is followed by a period during which the
adult pattern begins to assert itself. This second period
might be called the period of developmental growth, since it
involves both increase in size and progress toward
matnrity. The developmental growth period is sex and time
linked, beginnig and ending earlier in girls than in boys
and probably progressing further in boys. The progressive
development of the adult complex has certain general
characteristics which B~um (1961) describes as follows:
The adult dentofacial relationship differs from that of the
child in that the adult has a less convex face, a more
protrusive dentition with more upright incisors, and a
more prognathic mandible. In the male, these effects appear
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TABLE XLVIII
SEXUAL DIMORPHISM 1M CRANIOFACIAL PATTERNS
(AdApted from Broadbent et 01 .. 1975)
361
VARIABLE
GENERAL:
Circumpubertal
growth spurt
Mature size
PHYSICAL
CHARACTERISTICS:(differences develop
in middle to
late adolescence)
FEMALE
10-12 years
14-16 years
MALE
12-14 years
18 years
Supraorbital ridges
Frontal sinuses
Nose
Zygomatic prominences(cheekbones)
Mandibular symphysis(Pogonion)
External mandibular
angle (Gonion)
Occipital condyles
Mastoid processes
Occipital protuberance(Inion)
Virtually absent Well developed
Small Large
Moderate More massive
Small Large
Rounded Prominent
Rounded Prominent
lipping
Small Large
Small and delicate Large
Insignificant Prominent
* These dissimilarities were not significantly related to
skeletal balance or malocclusion.
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362
late, continue long~r, and produce more marked changes
resulting in a "three-L" postulate being formulated stating
that boys grow later, longer and larger (Baum, 1961).
A tabulated adaptation from Broadbent et ale (1975) clearly
illustrates the sexual dimorphism in craniofacial patterns
(Table XLVIII). These differences are not correlated with
skeletal balance or malocclusion (Sinclair and Little,
1983, 1985).
Sexual dimorphism is an important factor to evaluate in the
search for post-orthodontic stability, especially when the
active treatment is completed before facial growth and
proportional change have ceased.
12.2 Objectives
The literature presents the orthodontist with results from
pooled studies .·.nd from studies where the sexes are
separated. When comparing data of different studies or when
the presentation of new data is made, both types of
assessments must be kept in mind. The differences between
sexes can be ideally evaluated using longitudinal data.
There exists no such information in respect to the present
sample (Table I) or other equivalent samples.
Hence, the objectives of this part of the present study were
to:
i) assess the long-term changes between males and females
during and following active orthodontic treatment.
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363
ii) test whether a relationship exists between sexual
dimorphism and post-orthodontic lower incisor crowding.
12.3 Materials and methods
Eighty-eight Caucasian subjects (33 males and 55 females)
were longh:udinally assessed in respect of relapse of
their dentitions following orthodontic treatment. The
malocclusions were treated using conventional edgewise
mechanics. The sample is set out in Table I.
The basic materials used and methods employed in order to
assess the changes which occurred during the pre-treatment
(Tl), post-treatment (T2) and post-orthodontic (T3)
periods were described in Chapter 3 of this thesis.
Orthodontic study casts and lateral cephalograms were
analysed for all three stages studied. Intra-observer error
was tested analysing a random repetition of measurments
using the Wilcoxon test (Chapter 3).
The study casts were measured with digital calipers capable
of measuring to O.Olmm as was previously described.
Cephalometric measurements were obtained with the use of the
Oliceph computer program (Chapter 3).
The measurements of the various parameters have been
described in the preceeding chapters.
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364
The data (male versus female) were subjected to descriptive
statistics such as mean and standard deviation for each of
the three evaluations. The Wilcoxon and the Chi-square tests
tested for significant differences between the groups at the
three time intervals (Zar, 1984). The significance level of
this part of the study was set at 0.05.
12.4 Results
The findings are set out in Tables XLIX, L, LI, LII, LIII,
LIV and LV.
There was no significant (p > 0.05) difference in the~
between females and males at the three time intervals (Table
XLIX).
The mandibular variables showing significant (p < 0.05)
sexual dimorphism at the pre-treatment observation (Tl) were
the aggregate of the cranial base deflection, articular
angle and the gonial angle (SUMAHGLE: p = 0.03), the
vertical deviation of the corpus of the mandible (CORSLIHG:
p = 0.01), the arch length (ARCHL: p = 0.05 and LITTLE-A: p
= 0.0002), the lower incisal edge position relative to the
APo-line (I-~PO-MM: p = 0.04) and the mandibular growth
direction (GOGH-SM: p = 0.01 and FHA: p = 0.01) (Table L).
The significant differences between males and females at
the end of treatment (T2) were the mandibular length
(GOGN-MM: p = 0.02 and GOGC-MM: p = 0.004), the articular
angle (ARTANGLE: p = 0.01), the ramus height (RAMH-MM: p =
001), the arch lehgth (ARCHL: p = 0.001 and LITTLE-A: p =
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365
0.0001) and the mandibular growth direction (GOGH-SM; p •
0.03, FK': p • 0.04 and FAC-TAP~: p • 0.02). At the final
observation (T3) the following variable..' showed significant
differences, being the mandibular length (GOGN-MM: p.
0.0001 and GOGC-MM: p = 0.0001), the ratio between the
anterior and posterior mandibular lengths (GOGN-GOCO: p.
0.004), the articular angle (ARTANGLE: p = 0.03), the gonial
angle (GONANGLE: p = 0.04), the aggregate of the cranial
deflection, articular angle and the gonial angle (8UMANGLE:
p = 0.002), the vertical deviation of the corpus of the
mandible (CORSLIHG: p = 0.01), the ramus height (RAMH-MM: p
= 0.0001), the corpus length (CORL-MM: p = 0.0001), the
arch length (ARCHL: p = 0.01 and LITTLE-A: p = 0.0003), ~he
lower incisor irregularity (L-IRREG: p = 0.02), the lower
incisor position nii:asured to the HB-line (I-BB-DEG: p z
0.04) and the mandibular growth direction (GOGN-8N: p =
0.0004, FMA: p = 0.001, FAC-AXIS: p = 0.03 and FAC-TAPE: p =
0.001) (Tables L).
~.llary variables showing significant sexual dimorphism at
the pre-treatment observation (Tl) werA the posterior
cranial base length (SAR-MMj p = 0.02) and the upper first
bimolar width (U6-6I: p = 0.02 and U6-6B: p = 0.002); at the
end of treatment (T2) were the cranial base deflection
(SADAHGLE: p = 0.05), the anterior cranial base length
(SN-MMj p = 0.001), the posterior cranial base length
(SAR-MM p = 0.001) and the upper first bimolar width
(U6-6I: p = 0.0001 and U6-6B; p = 0.0001); at the
post-orthodontic observation (T3) were the point A
convexity (A-CONVEX: p = 0.01), the cranial base length
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TABLE XLIX
DIffERENCES BETWEEN MALE AND FEMALE GROUpa
FOR AGE VARIABLE
VARIABLE MALE FEMALE
MEAN S.D. MEAN S.D. P
AGE Tl 11.77 1.06 12.00 1.12 0.29
T2 15.15 2.42 14.49 1.15 0.17
T3 21.96 3.94 21.18 3.21 0.46
P = Significance level, p < 0.05 (WILCOXON 2-Sample Test)S.D. = Standarc deviation
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TABLE L
DIFFERENCES BETWEEN MALE AND FEMALE GROUPS
FOR A NUMBER QF MAHDIBULAB VARIABLES
VARIABLE MALE FEMALE
MEAN S.D. MEAN S.D. P
MANDIBLE-DIMENSIONS:
SNB Tl 76.82 2.96 76.80 3.58 0.35
T2 76.51 3.17 76.49 3.60 0.99
T3 77.71 3.20 77.16 3.96 0.48
SND Tl 73.70 2.52 73.73 3.54 0.93
T2 74.12 2.75 73.92 3.68 0.79
T3 75.91 2.87 74.96 3.99 0.36
GOGN-MM Tl 73.66 4.49 72.34 4.25 0.18
T2 77.88 5.31 74.94 3.96 0.02*
T3 81.99 5.75 76.69 4.06 0.0001*
GOGC-MM Tl 57.05 3.81 55.78 3.93 0.17
T2 61.86 4.62 58.61 4.13 0.004*
T3 70.17 5.39 '59.75 7.86 0.0001*
GOGN-GOeo T1 124.37 5.25 126.14 5.01 0.07
T2 124.45 5.28 126.42 5.87 0.07
T3 121.73 6.09 125.52 5.62 0.004*
ARTANGLE Tl 143.96 7.62 147.39 6.53 0.04
T2 143.42 6.79 147.68 7.39 0.01*
T3 143.70 7.81 147.55 7.20 0.03*
GONANGLE Tl 123.55 6.19 124.77 6.44 0.16
T2 124.14 6.73 124.61 6.48 O. 56
T3 119.96 6.79 122.95 6.63 0.04*
SUMANGLE Tl 392.19 3.81 394.92 5.93 0.03*
T2 392.82 4.57 395.44 6.53 0.06
T3 388.91 4.19 393.49 6.84 0.002*
GONSLING Tl 52.95 4.61 51.48 3.98 0.17
T2 51.89 4.51 50.50 4.49 0.19
T3 49.78 4.55 49.54 4.14 0.77
CORSLING T1 70.57 3.77 73.29 4.72 0.01*
T2 72.26 4.35 74.11 4.91 0.07
T3 70.18 4.69 73.42 5.31 0.01*
RAMH-MM Tl 43.47 3.43 42.62 4.54 0.18
T2 48.44 4.19 44.73 5.35 0.001*
T3 56.50 6.11 48.48 5.31 0.0001*
CORL-MM Tl 71.50 4.88 70.65 3.92 0.38
T2 75.39 4.95 73.30 4.01 0.08
T3 80.56 6.00 74.41 4.29 0.0001*
CORLCRAN Tl 1.02 0.20 0.99 0.05 0.41
T2 0.99 0.06 1.01 0.06 0.55
T3 1.02 0.06 1.01 0.06 0.48
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MANDIBLE-TEETH:
MDCROWD Tl -0.95 3.92 -0.39 5.68 0.75
T2 -0.55 2.79 -1.66 1.49 0.66 (N 3)
T3 -1.66 3.78 -3.84 5.34 0.17
SPEE Tl 2.16 1.05 2.16 0.89 0.97
T2 1.71 0.79 2.56 4.89 0.73
T3 2.04 0.70 2.25 0.86 0.46
L3-3I Tl 26.53 2.01 26.00 1.50 0.24
T2 26.42 1.73 25.73 1.64 0.19
T3 26.08 1.87 25.57 1.88 0.32
L3-3B Tl 30.77 2.08 30.37 1.79 0.42
T2 31.18 1.56 30.99 3.79 0.09
T3 30.59 2.33 29.89 1.95 0.21
ARCHL Tl 24.13 2.52 23.13 2.21 0.05*
T2 22.11 3.20 19.93 2.92 0.001*
T3 21.04 3.37 19.39 3.49 0.01*
L-IRREG T1 3.85 3.96 4.43 3.33 0.18
T2 0.44 0.57 0.42 0.71 0.52
T3 2.24 1.77 1.39 1.48 0.02*
LITTLE-A T1 63.06 3.91 59.87 4.12 0.0002*
T2 60.55 6.08 54.36 6.22 0.0001*
T3 58.36 6.89 52.97 6.39 0.0003*
I-NB-DEG T1 26.43 6.69 27.69 6.24 0.43
T2 27.58 5.36 28.95 4.87 0.36
T3 25.31 4.91 27.54 4.44 0.04*
I-NB-MM T1 3.65 2.15 4.05 2.08 0.40
T2 4.18 1.77 4.40 1.55 0.61
T3 3.68 1.59 4.26 1.66 0.13
I-APO-MM T1 -0.28 2.82 0.83 2.82 0.04*
T2 0.92 2.19 1.51 1.68 0.16
T3 0.46 2.05 1.09 1.84 0.16
I-APO-DEG Tl 23.13 5.48 24.12 4.99 0.59
T2 27.66 4.46 27.74 4.85 0.72
T3 27.46 4.75 27.34 4.6. 0.68
IMPA Tl 98.62 6.71 95.70 12.39 0.16
T2 99.56 6.89 97.92 6.47 0.16
T3 99.24 7.42 96.92 6.11 0.12
FMIA Tl 61.26 6.30 59.92 7.15 0.29
T2 59.99 4.84 58.69 6.19 0.32
T3 61.02 12.63 60.86 5.66 0.27
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MANDIBLE-GROWTH DIRECTIQN:
GOGN-SN T1 31.63 3.17 34.53 5.47 0.01*
T2 32.15 4.26 35.19 6.26 0.03*
T3 28.99 4.16 34.11 6.52 0.0004*
FMA Tl 21.24 3.79 24.19 4.85 0.01*
T2 21.56 4.26 24.51 5.91 0.04*
T3 18.03 7.64 23.52 5.94 0.001*
FAC-AXIS Tl 89.78 3.50 88.44 4.39 0.27
T2 89.38 3.8? 87.74 4.70 0.26
T3 91.26 4.06 88.34 5.42 0.03*
FAC-TAPE Tl 69.99 3.82 67.72 3.98 0.01
T2 69.07 4.14 67.01 4.18 0.02*
T3 71.25 4.40 67.93 4.29 0.001*
MANn-ARC Tl 29.98 4.82 29.87 5.87 0.52
T2 31.07 5.25 30.59 6.38 0.72
T3 35.19 5.44 33.13 6.09 0.10
FAC-ANGL Tl 88.70 2.42 88.17 3.31 0.40
T2 89.20 2.73 88.72 3.78 0.52
T3 90.55 2.95 89.67 3.89 0.41
P = Significance level, p < 0.05 (WILCOXON 2-Sample Test)
*
.. Significant differences, p < 0.05
S.D. = Standard deviation
N = Sample
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370
(SN-MM: p a 0.0001 and SAR-MM: p • 0.0001), the upper first
bimolar width (U6-6I: p. 0.04 and U6-6B: p • 0.04) and
the upper first molar position relative to Pterygoid root
vertical (UM-PTV-MM: p = 0.05) (Table LI).
The maxillary versus man1ibular variables (combination of
maxillo-mandibular variacles) showing significant
differences between males and females, including
ant~roposterior, vertical and occlusal measurements, were
the posterior facial height (POSFACH-MM: p = 0.03), the
anterior to posterior facial height ratio (SGQ-NNE: p.
0.03), the overbite (OBB: p = 0.003) and the total
malocclusion severity (TMSCORE: p = 0.0003) at the initial
observation (T1); the posterior facial height (POSFACH-MM: p
= 0.0001), the anterior to posterior facial height ratio
(SGO-NME: p = 0.02) and the total malocclusion severity
(TMSCORE: p = 0.001) at the end of treatment (T2)i the
posterior facial height (POSFACH-MM: p = 0.0001), the
anterior facial height (AHTFACH-MM: p = 0.0001), the ratio
between the latter two (SGO-HME: p = 0.001) and the occlusal
plane angle (OCC-SM: p = 0.0001) at the final observation
(T3) (Table LII).
Significant soft tissue differences between females and
males included the following variables, being the upper lip
to E-plane (U-LIPE-MM: p = 0.03), the anteroposterior
dimension of the nose (MOSE-MM: p = 0.02) and the inferior
sulcus depth (ISULH-MM: p = 0.03) at the initial
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TABLE LI
DIFFERENCS BETWEEN MALE AND FEMALE GROUPS
FOR A NUMBER OF MAXILLARY VARIABLES
VARIABLES MALE FEMALE
MEAN S.D. MEAN S.D. P
MAXILLA-DIMENSIONS:
SN-FH Tl 10.39 2.53 10.33 2.52 0.92
T2 10.59 2.68 10.68 2.58 0.75
T3 10.19 2.60 10.59 2.72 0.25
SNA Tl 81.68 3.75 81.09 3.46 0.35
T2 79.46 3.53 79.60 3.52 0.75
T3 79.84 3.31 80.21 3.68 0.88
ANSPNS-SN T1 7.05 2.69 7.82 2.99 0.31
T2 8.55 3.25 7.94 3.21 0.36
T3 8.05 3.39 7.75 3.13 0.41
A-CONVEX Tl 3.93 2.92 3.83 2.72 0.82
T2 1.48 2.42 2.23 2.78 0.29
T3 0.02 2.78 1.82 3.01 0.01*
SADANGLE Tl 124.65 4.84 122.77 4.46 0.10
T2 125.25 4.91 123.17 4.64 0.05*
T3 125.24 5.77 122.96 4.58 0.11
SN-MM Tl 72.48 3.44 71.46 3.02 0.15
T2 75.62 2.92 72.87 3.10 0.001*
T3 79.17 3.01 74.02 3:46 0.0001*
SAR-MM T1 36.39 4.08 34.19 2.79 0.02*
T2 38.29 3.92 35.57 2.77 0.001*
T3 39.76 3.73 36.13 3.41 0.0001*
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MAXILLA-TEETH:
MXCROWD Tl 0.14 5.45 0.56 6.28 0.89
T2
T3 -0.73 5.81 -2.29 4.58 0.91
U6-6I Tl 50.95 3.97 48.79 3.19 0.02*
T2 52.31 3.28 48.92 3.51 0.0001*
T3 50.49 3.41 48.91 3.14 0.04*
U6-6B Tl 54.77 3.84 52.16 3.03 0.002*
T2 56.27 3.29 53.05 6.09 0.0001*
T3 54.00 3.45 52.42 2.83 0.04*
I-NA-DEG Tl 22.19 10.02 23.48 8.56 0.22
T2 22.42 9.43 22.71 7.88 0.80
T3 23.36 8.07 21.74 7.10 0.45
I-NA-MM Tl 3.99 2.86 4.23 2.88 0.63
T2 3.07 2.90 2.69 2.43 0.67
T3 3.92 2.58 3.23 2.61 0.37
I/-FH-DEG Tl 114.01 9.58 114.65 8.31 0.52
T2 112.15 8.51 112.79 7.92 0.69
T3 113.13 6.96 112.37 7.21 0.79
I/-FACAX-DEG Tl 5.34 9.53 3.23 8.06 0.13
T2 7.01 7.83 4.70 6.87 0.15
T3 7.05 6.33 5.69 5.93 0.29
I/-APO-MM Tl 7.22 3.11 7.33 3.17 0.79
T2 4.18 1.94 4.39 1.61 0.57
T3 4.01 1.69 4.66 2.03 0.06
UM-PTV-MM Tl 16.98 4.06 17.17 3.58 0.79
T2 20.01 5.58 20.37 4.41 0.77
T3 24.29 4.87 22.25 4.12 0.05*
UM-CCV-MM Tl 15.93 4.17 15.98 3.46 0.69
T2 18.74 5.79 18.93 4.39 0.69
T3 22.91 5.08 20.59 4.17 0.06
P = Significance level, p < 0.05 (WILCOXON 2-Sample Test)
* = Significant differences, p < 0.05S.D. = Standard deviation
372
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TABLE LII
DIFFERENCES BETWEEN MALE AND FEMALE GROUPS FOR
MAXILLO-MANDIBULAR VARIABLES
VARIABLE MALE FEMALE
MEAN S.D. MEAN S.D. P
MAXILLA TO MANDIBLE:
ANB Tl 4.86 2.55 4.28 2.29 0.21
T2 2.95 2.05 3.12 1.~9 0.90
T3 2.13 2.29 3.05 2.22 0.11
L-FACH T1 42.99 4.19 43.90 4.59 0.23
T2 43.57 3.79 45.24 5.29 0.09
T3 42.90 4.46 44.71 5.23 0.07
POSFACH-MM T1 75.78 4.75 73.64 4.85 0.03*
T2 82.29 6.34 76.84 5.31 0.0001*
T3 91.47 6.90 81.13 5.79 0.0001*
ANTFACH-MM Tl 115.62 6.17 116.09 5.84 0.56
T2 124.84 8.04 121.33 6.62 0.09
T3 131.19 7.22 123.69 6.95 0.0001*
SGO-NME Tl 65.59 3.38 63.56 4.77 0.03*
T2 65.98 3.94 63.62 5.28 0.02*
T3 69.73 3.84 65.76 5.32 0.001*
WITS-MM T1 2.11 3.89 0.65 3.88 0.07
T2 0.89 3.19 0.19 2.96 0.18
T3 1.07 4.06 0.65 3.39 0.70
373
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OCCLUSION:
OJB Tl 6.67 3.61 5.94 3.09 0.28
T2 3.02 0.98 2.75 0.75 0.30
T3 3.19 1.<55 3.16 1.02 0.57
OBB Tl 4.84 1.29 3.86 1.47 0.003*
T2 3.02 1.02 2.70 0.93 0.23
T3 2.95 1.22 2.72 1.02 0.53
TMSCORE Tl 91.08 5.51 86.49 4.99 0.0003*
T2 88.99 5.28 84.89 4.51 0.001*
T3 91.02 5.95 88.85 5.69 0.09
BOLTON A Tl 79.23 2.10 78.15 2.10 0.18
T2 -----
T3 77.74 2.77 77.49 6.51 0.84
BOLTON P Tl 92.35 2.19 91.43 1.90 0.10
T2
T3 90.74 2.41 90.35 6.88 0.77
I-I Tl 127.64 12.15 125.66 10.39 0.23
T2 128.19 9.88 126.36 9.02 0.46
T3 130.34 8.48 128.80 7.37 0.44
OCC-8N Tl 16.55 3.45 17.10 6.06 0.92
T2 16.85 3.67 18.13 4.44 0.18
T3 12.53 3.58 17.00 4.87 0.0001*
MOLAR L Tl 0.28 x
T2 0.07 x
T3 0.30 x
MOLAR R T1 0.09 X
T2 0.81 X
T3 0.57 X
CANINE L T1 0.49 X
T2 0.12 x
T3 0.14 X
CANINE R Tl 0.16 X
T2 0.83 X
T3 0.19 X
OPENBIT T1 0.87 X
T2 0.13 X
T3 0.54 x
ANTXBIT Tl 0.32 x
T2 0.43 x
T3 0.91 x
POSTXBIT Tl 0.55 X
T2 0.65 x
T3 0.06 x
ROTATE Tl 0.74 X
T2 0.26 X
T3 0.33 X
374
p
*
x
S.D.
= Significance level, p < 0.05 (WILCOXON 2-Sample Test)
= Significant differences, p < 0.05
= CHI-SQUARE Test
= Standard deviation
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375
observation (T1); the upper lip to E-plane (U-LIPE-MM: p •
0.01), the upper lip curl to H-line (SAHLINE: p • 0.02),
the upper lip thickness (ULI::-TH-MM: p. 0.001), the upper
lip taper (ULIPTAP-MM: p = 0.0001), the H-angle (MANGLE: p
= O.Ol) and the inferior lip sulcus (ISULH-MM: p • 0.001)
at the end of t.reatment (T2); the lower lip to E-plane
(L-LIPE-MM: p = 0.001), the anteroposterior dimension of
the nose (NOS~-MM: p = 0.01), the upper lip thickness
(ULIPTH-MM: p = 0.0001), the upper lip strain (ULIPSTR-MM:
p = 0.0001), the lower lip to H-line (LIPH-MM: p • 0.001),
the inferior lip sulcus (ISULH-MM: p = 0.0001) and the soft
tissue chin thickness (STCHIN-MM: p = 0.01) at the final
observation (T3) (Table Llll).
Significant differences existed between the sexes in respect
to extraction and nonextraction treatment regimes. Males had
less extractions as part of their orthodontic treatment
in comparison to females (p = 0.02) (Table LlV). The Little
Irregularity Index (Little, 1975) recorded at the final
observation (T3) also differed between the sexes (p < 0.05)
(Table LV).
12.5 Discussion
When orthodontic treatment is completed before or during the
period of developmental growth a progressive change in
location of the dentition in relation to the rest of the
face can be expected. The dentition will become
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TABLE LIII
DIFFERENCES BETWEEN MALE AND FEMALE GROUPS
FOR SOFT TISSUE VARIABLES
VARIABLES MALE FEMALE
MEAN S.D. MEAN S.D. P
U-LIPE-MM Tl -0.19 2.29 -1.38 2.36 0.03*
T2 -3.51 1.59 -4.52 2.00 0.01*
T3 -6.23 2.89 -5.64 1.97 0.07
Z-ANGLE Tl 69.19 6.72 69.76 7.97 0.71
T2 74.19 4.39 75.17 6.79 0.46
T3 77.06 15.03 76.72 6.79 0.22
L-LIPE-MM Tl 0.67 2.97 0.39 3.16 0.70
T2 -1.94 1.99 -2.25 2.16 0.52
T3 -4.92 2.33 -2.95 2.51 0.001*
STFAC Tl 89.34 2.81 88.94 3.56 0.58
T2 90.02 2.86 89.52 4.02 0.52
T3 91.78 2.94 90.49 3.86 0.19
NOSE-MM Tl 12.52 1.65 13.52 2.06 0.02*
T2 15.93 1.84 15.93 2.28 0.97
T3 19.01 2.11 17.46 2.32 0.01*
SUPSULD Tl -10.13 2.93 -9.59 3.02 0.36
T2 -9.45 2.83 -8.66 2.77 0.18
T3 -7.92 3.34 -8.47 3.12 0.23
SAHLINE Tl 7.15 2.12 6.50 2.25 0.29
T2 5.39 1.50 4.48 1.73 0.02*
T3 4.78 1.82 4.69 1.67 0.92
ULIPTH-MM Tl 14.68 1.42 14.75 1.59 0.94
T2 16.87 2.14 15.41 1.81 0.001*
T3 17.99 1.74 15.57 1.87 0.0001*
ULIPTAP-MM Tl 11.54 2.08 11.45 2.19 0.59
T2 14.61 1.78 12.83 1.81 0.0001*
T3 15.28 2.13 12.53 2.17 0.0001*
ULIPSTR-MM Tl 3.15 1.57 3.31 2.21 0.37
T2 2.26 1.77 2.57 1.58 0.37
T3 2.71 1.93 3.04 2.07 0.44
BANGLE T1 17.93 3.97 16.40 3.69 0.08
T2 14.76 3.02 12.89 3.03 0.01*
T3 12.17 4.08 12.46 3.39 0.52
LIPH-MM Tl 0.81 2.16 1.33 2.19 0.28
T2 0.39 1.56 0.87 1.39 0.16
T3 -0.46 1.66 0.83 1.49 0.001*
ISULH-MM Tl -5.71 2.16 -4.60 2.38 0.03*
T2 -5.73 1.75 -4.31 1.81 0.001*
T3 -6.96 2.17 -4.54 1.87 0.0001*
376
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STCHIN-MM Tl
T2
T3
9.87
10.47
12.28
2.12
1.85
2.56
10.28
10.47
10.70
2.12
2.18
2.16
0.43
0.99
0.01*
377
p = Significance ~evel, p < 0.05 (WILCOXON 2-Sample Teat)
* = Significant differences, p < 0.05
S.D. = Standard deviation
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TABLE LIV
DIFFERENCES BETWEEN KALE AND FEMALE GROUPS
FOR INITIAL ANGLE CLASSIFICATION AND FOB
EXTRACTION AND NOHEXTRACTION TREATMENT
378
VARIABLE
ANGLE CLASSIFICATION
EXTRACTION VS NONEXTRACTION
P
0.32 x
0.02* x
p = Significance level, p < 0.05
* = Significant differences, p < 0.05
x = CHI-SQUARE test
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TABLE LV
DIFFERENCES BETWEEN MALE AND FEMALE GROUPS;
DESCRIPTIVE STATISTICS FOR THE LITTLE IRREGULARITY INDEX(Little. 1975)
KM&:
T1 T2 T3
VARIABLE MEAN S.D MEAN S.D. MEAN' S.D.
L-IRREG 3.85 3.96 0.44 0.57 2.24* 1.77
FEMALE:
Tl T2 T3
VARIABLE MEAN S.D. MEAN S.D. MEAN S.D.
L-IRREG 4.43 3.33 0.42 0.71 1.39* 1.48
379
S.D.
*
= Standard deviation
= Statistically significant difference, p < 0.05
(WILCOXON 2-Sample Test)
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380
progressively less protrusive as was noted in Chapter 7
with the post-orthodontic uprighting of the lower inci.or
teeth. The ideal location of the dentition for example in a
!.'-year-old boy, should be planned with the expectation
that in the succeeding months, the developmental growth
changes will carry the rest of the facial structures
forward relative to the dentition to a greater degree than
would be true in a girl of similar age (Baum, 1961).
Orthodontists must consider these changes when planning
orthodontic treatment. Visual treatment objectives have
already been a tremendous advance in this respect (Johnston,
1975; Ricketts et al., 1979; Jacobson and Sadowsky, 1980;
Holdaway, 1984). Earlier studies have also shown that it is
imperative to take note of growth and sex differences. It
was reported that mandibular growth increments closely
followed the statural growth pattern (Ludwick, 1958). The
standing height of a subject ~easured at four-monthly
intervals and plotted on a height velocity chart, can be
used to give an indication of the maximal pubertal growth
spurt. This occurs normally between twelve and sixteen years
for boys and between ten and fourteen years for girls
(Sullivan, 1983). It is suggested to have appliances in the
mouth a year preceeding:,L .aaximal growth spurt in order to
utilise this accelerated growth in order to attain the
clinician's set orthodontic goals. This prediction appeared
to be more accutate for boys (95') than for girls (Sullivan,
1983).
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381
An examination of physical anthropologic work in the field
of growth prediction might not be such a far fetched idea a.
it could provide orthodontists with the additional
information to establish more accurately the end of the
developmental growth level of an individual. This then,
might provide orthodontists with the means to disclose the
amount of dentofacial changes to be anticipated in the
post-orthodontic phase (Baum, 1961). Various skeletal
parameters and their relationship to the frontal sinus have
been studied in order to aid the orthodontist in predicting
mandibular growth (Rossouw, Lombard and Harris, 1990).
The mature size as well as the percentage of growth
completed can be predicted with fair accuracy from a child's
present size and from his skeletal age as determined by
Todd's method (Bayley, 1943a, 1943b). More recently,
studies using thE: ossification events of the hand-wrist
radiograph were used to assess the pubertal growth :'9urt
(Greulich and Pyle, 1976; Hagg and Taranger, 1982; Fishman,
1982, 1987). The;Je authors support this method as the most
enlightening in respect of maturity of a subject's
developmental status. This method must, however, be
supplemented by a clinical examination. Dental age appeared
not to be vey accu~ate in this regard (Suthpen, 1985). It
did, however, give a better indication, although still weak,
of the pubertal growth spurt in girls (Ragg and Taranger,
1984). The mean pubertal growth spurt was reported to be two
years later in boys. An individualized evaluation is the
best, as subjects were shown to deviate from this mean by
three to six years (Sinclair, 1978).
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382
A secular trend has been noticed in girls the past 300-400
years indicating an increase in size as well as an ealler
onset of menarche (Proffit, 1986).
Sexual dimorphism is widely reported, as was previously
noted, and various ways were mentioned to determine and
distinguish craniofacial patterns between males and females
(Broadbent et al., 1975 in Table XLVIII; Riolo et al., 1974,
1979). There was no significant age difference between the
sexes in this study (Table XLIX), which made it ideal to
assess differences amongst the variables studied.
Krogman (1955) discussed the findings of several authors
regarding the level of sexual development in relation to
growth expectation. He concluded that, in general, sex
maturation signals the end of significant growth increments.
Thus, children at a high level of sexual maturity for their
age, may be expected to have little growth potential and
little prospect of further dentofacial change. It was
reported that 99 per cent of adult stature was achieved at
16.4 and 14.6 years in }~erican boys and girls
respectively (Nicholson and Hanley, 1953). Recent studies,
however, in resp~ct of the continuum of growth in the aging
subject showed changes well into adulthood which is
supported by the post-pubertal changes experienced in the
present study (Behrents, 1984). "Growth" in the
post-orthodontic period may be responsible for the dental
changes experienced (Behrents, 1984) and also for the
changes reported as relapse of treated dentitions (Behrents
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383
et al., 1989; Little, 1990). It can, however, also happen
that this growth might enhance the excellence of a treated
occlusion (Behrents, 1984).
It is naive to expect the bones of the craniofacial skeleton
to remain stable after treatment. The practitioner that
mentally imparts stability of the dentition to the
well-treated subject after treatment is not being realistic.
On average, most dentitions fortunately remain reasonably
stable following orthodontic treatment, but this is due
mainly to the post-treatment growth characteristics of the
subject being in favour rather than against the treatment
itself. As was noted previously, it seems that those
changes which do occur in the dentition during the period
following treatment, are growth related. The statement made
by Parker (1989) that "retention may be forever", seems to
be validated by the findings of the present stUdy. Retention
should thus be continued consistent with the amount of
growth activity which is occurring and on the basis of
continued growth, retention should be continued into the
twenties and thirties if possible. Growth is important
during treatment and it must also be planned for, used, and
respected after treatment (Behrents et al., 1989). No
long-term studies have been conducted to show whether any
damage to the teeth or periodontium occurs when permanent
retention is employed. Should the orthodontist thus feel
conservative in this regard, stability can be maintained of
well aligned incisors, and perhaps more so for the lower
incisors, by interproximal reapproximation (Williams, 1985;
Joseph, Rossouw and Basson, 1991).
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384
Mensuration of mandibular variablep~t the end of treatment
(T2) and at the end of the post-orthodntic period (T3)
showed the significant differences between the sexes to be
mainly growth related (Table L). The mandibular dimensions
which changed significantly were the corpus length (GOGM-MM
and CORL-MM), posterior mandibular height (GOGC-MM and
~{-MM), rotation direction of the mandible (ARTAHGLE,
GONANGLE, SUMANGLE, CORSLING, GOGN-SN, P'MA and PAC-AXIS)
and the indicator of the chin morphology, facial taper
(FAC-TAPE). The mandibular dental measurements which
showed significant differences between T2 and T3, were
mainly those pertaining to the arch length measurements
(ACRHL and LITTLE-A). These are mainly growth related
(Moyers, 1988). The only mandibular incisor position
variable showing a significant difference was the I-NB-MM.
This could be ascribed to the facial pattern differences in
males and females. This incisor measurement showed that the
males had less protruding dentitions at the end of treatment
(T2) (males: mean 4.18 rom and females: mean 4.40 mm) and
that the males, possibly as a result of later mandibular
growth, showed more post-orthodontic (T3) uprighting of the
mandibular incisor measured to the NB-line (males: mean
3.68 rom and females: mean 4.26 rom). The mandibular lower
incisor irregularity measurements showed the same
correction in alignment with no significant difference
between males and females at the end of treatment (T2)
(males: mean 0.44 mm and females: mpan 0.42 mm). A
significant difference, however, was experienced at T3
(males: mean 2.24 mm and females: mean 1.39 rom) (Table L
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385
and LV). The difference in growth, as noted, may have
contributed to the significant differences measured, but it
could also be speculated that males were not as
conscientious about wearing their retention appliances
especially as later maturity is expected (Greulich and Pyle,
1976; Sullivan, 1983).
The maxillary variables showing significant differences also
reflected the difference in morphology between the sexes
(Table LI). The convexity at point A (A-CONVEX) was
significantly reduced during the post-orthodontic period
(T2-T3). Although no significant difference was experienced
at the end of treatment (T2) (males: mean 1.48 rom and
females: mean 2.23 rom), significant differences were,
however, noted post-orthodontically (T3) (males: mean 0.02
rom and females; mean 1.82 rom). This change was in harmony
with the larger increment of mandibular growth in the male
group (p < 0.05). The post-treatment (T2) cranial base
length (SN-MM and SAR-MM) measured significantly different
between males and females (mean SN-MM 75.62 rom - males and
72.87 rom - females; mean SAR-MM 38.29 rom - males and 35.57
rom - females) and also significantly different at the final
observation (T3) (mean SAR-MM 79.17 rom - males and 7•. 02 rom
females; mean SAR-MM 39.76 rom - males and 36.13 rom ­
females). This is in accord with the growth changes expected
and in harmony with the mandibular growth changes. The male
group showed a significant larger bimolar dimension
throughout the study (Tl-T3). The upper molar mesial
movement (UM-PTV-MM) showed that t~e male group had
significantly more mesial first molar movement or migration
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386
(males: mean 24.29 mm and females: mean 22.25 mm) which
supported the differences in the mandibular arch length as
well as the ultimate sign "of these changes, the Little
Irregularity Index (1975).
The significant difference in the extraction pattern (Table
LIV) might playa role in this occurrence. The male group
had less extractions as part of the treatment regime (males
38.71% and females 64.81%), which leads to the speculation
that the extractions in the female group could have created
enough space for ideal positioning of teeth and
subsequently less post-orthodontic lower incisor crowding.
It was previously reported that subjects who had extractions
as part of their treatment experienced less mandibular
incisor crowding and were more stable than nonextraction
cases (Davies, 1971). Little, Wallen and Riedel (1981)
noted, however, that no significant difference existed
between extraction and nonextraction groups which is in
contrast with the results shown in the present study with
the data pooled (Chapter 10). This finding by Little, Wallen
and Riedel (1981) reiterates why the data of the present
study was pooled and when comparative findings were shown
for certain parameters and not for others, it was separated.
In this search for excellence in treatment results, the
objective was to assess the males and females separately,
due the fact that similar differences in the treated samples
may also exist as were reported for untreated subjects by
Riolo et al. (1974). Psychological hindrances in the
female sample relating, for example, to reluctance in
headgear wearing as a reason for performing nonextraction
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387
treatment, could also have played a part. It must, however,
be added that the other factors described as po8sible
aetiologic factors of post-orthodontic crowding, could
contribute individually or as a group to lower incisor
crowding.
No significant differences could be shown for the
measurements normally used to describe the anteroposterior
skeletal (ARB and WITS-MM) and dental (according to the
Angle (1899, 1907) classification) variables from the
initial to the final observation (Tl-T3) (Table LII and
LIV). The male sample showed significantly larger vertical
dimensions (Table LII) from T1 to T3 (POSFACH-MM: mean
increase males 75.78 rom to 91.47 rom; females 73.64 mm to
81.13 mm; ANTFACH-MM: mean increase males 115.62 mm to
131.19 mm and females 116.09 mm to 123.69 mm). The males
experienced greater anti-clockwise mandibular rotation than
the females (SGO-NME at T1: males 65.59% and females 63.561;
at T3: males 69.75% and females 65.76'). This closing
rotation of the mandible could influence the lower incisor
alignment detrimentally (Bjork and Skieller, 1972, 1983)
and is borne out by the significant difference in the
Little Irregularity Index (1975) as was previously
demonstrated (Table L and LV). Only two of the occlusal
variables reported in Table LII changed significantly from
T2 to T3 (TMSCORE: mean increase males 88.99 to 91.02 and
females 84.88 to 88.85; OCC-SN: mean decrease males 16.85
degrees to 12.53 degrees and females 18.13 degrees to 17.00
degrees). The total malocclusion score difference was
greatly influenced by the maxillary bimolar width increase
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388
which was larger for the males than the females. There wa.,
however, a greater increase in the female group bringing it
closer to the male severity score. This resulted in no
significant (p = 0.09) difference at the final observation
T3.
The occlusal plane angle (DCC-SM) should ideally not be
changed during treatment as it was reported to remain stable
during growth and would return to the original value if
changed (Ricketts et al., 1979). The original aCC-SM
measurements (T1) were 16.55 degrees for the males and 17.10
degrees for the females. The measurement for the female
group remained reasonably stable from T1 to T3, but the
occlusal plane for the male group, although practically
unchanged during treatment (T1-T2), changed significantly
following treatment (T2-T3). Growth changes in the
mandible and the nasomaxillary complex could be responsible
for this occurrance in the males and thus also be partly to
blame for the larger incisor irregUlarity score. It
appeared that the other occlusal variables showed no
significant sexual dimorphism. This could possibly be due
to the fact that successful corrections attained aftlongst
these variables either stayed stable or equal changes in
both groups were measured.
Soft tissue findings were presented in Table LIII. The upper
(U-LIPE-MM) and lower lip (L-LIPE-MM) to the E-line
(Ricketts, 1981) showed significant differences at T2 and T3
respectively. The upper lip was significantly more
retrusive in the females at the end of treatment (T2)
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389
(males: mean -3.51 mm and females: mean -4.52 mm). The
lower lip, although not significantly different between the
males and the females, was also more retrusive in the
females (males: mean -1.94 mm and females: mean -2.25 mm).
The lower lip (LIPH-MM) to H-line (Holdaway, 1983) showed
similar significant differences at the final observation
(T3). This could be ascribed to the larger percentage of
extractions performed as part of the treatment regime in
the female group resulting in more retrusive dentitions at
this evaluation. The males, however, surpassed the female
values and showed significantly more retrusive lower lip
(L-LIPE-MM) measurements at the final observation (T3)
(males: mean -4.92 rom and females: mean -2.95 rom). This is
supported by the difference in the H-angle (HAHGLE)
measurement which showed a significant difference at the end
of treatment (T2) between the sexes. Although the upper lip
(U-LIPE-MM) also showed more retrusive values, it was not
significantly different between the two groups (males: mean
-6.23 rom and females: mean -5.64 mm). This could be
attributed to nose (HOSE-MM) and soft tissue chin
(STCHIH-MM) enlargement producing lips that appear
relatively retrusive. Caution must be expressed when
evaluating the lip values. Males showing later, larger and
longer growth (Baum, 1961) will become dentally more
retrusive as was shown earlier with regard to the lower
incisor position. There was a significant difference
measured at the end of the post-orthodontic period (T3) for
these variables with males showing the larger dimensions
(HOSE-MM: males mean 19.01 rom and females mean 17.46 mmi
STCHIN-MM: males mean 12.28 mm and females mean 10.70 mm).
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Significant differences were measured for upperlip
thickness (ULIPTH-MM) and upperlip taper (ULIPTAP-MM) at T2
and T3. The male group recorded larger dimensions. Changes
in parameters which may have contributed to the larger
inferior lip sulcus measured between T2 to T3, were the
combination of a larger soft tissue chin and more retrusive,
but proclined lower incisors. Support for these findings
were the measurements for lower incisor position to NB line,
to APo line and to the mandibular plane (IMPA). The lower
incisor incisal edge to HB (p < 0.05), APo line (p > 0.05)
and the IMPA (p > 0.05) indicated that the lower incisors
were slightly more proclined at the end and following
treatment (mean IMPA: males 99.24 degrees at T2 and 99.56
degrees at T3; females 96.92 degrees at T2 and 97.92 degrees
at T3). Lower incisor torque control or upright incisor
position on basal bone (Tweed, 1954, 1966) are parameters
that must be considered during treatment. The more proclined
lower incisor teeth of the males remained proclined, but
this position does not make it immune from the influence of
the mandibular forward growth. This could be a contributing
factor, with the others already noted, to more lower incisor
crowding in the male group.
There have been numerous reports in the literature on the
relationships between general body growth and development,
facial growth and development, and a measure of
predictability concerning the fate of the dentition after
treatment. The dentition of an immature subject must be
placed in an "immature" location, that is, more forward than
in a mature face. Placing an immature patient's dentition
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391
in an adult relationship can only result in a further
retrusian of the dentition as the inevitable facial
maturation changes take place. For most of our patients
orthodontic treatment is commonly finished during the very
years when these differences in dentofacial behaviour
operate. A distinction must be made in dentofacial
relationships and possibly in upper incisor to lower
incisor relations between boys and girls during these
years. Failure to do so may lead to the unpleasant
experience of watching helplessly while the face of a male
subject becomes more and more concave as his lips retreat
and his nose and chin achieve their adult proportions (Baum,
1961).
From the foregoing findings and discussion, a generalization
m~ght be permitted: The dentition of a pre-pubertal girl
should be placed further back in relation to the qarious
cephalometric planes than that of a boy in a similar age
group. Similarly, a pre-pubertal bvy can accept a fuller
dentition than a girl of the same age, since the girl
probably will experience little or no change in distance
from the central incisor plane to the nose and chin point
while the boy can expect a significant increase in these
distances after the age of thirteen years (Baum, 1961).
12.6 Conclusions
1. Significant mandibular and maxillary dimensional
differences were apparent between males and females.
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2. ~he males grew larger, longer and later than the
females.
3. Anti-clockwise mandibular rotation was more obvious in
males.
4. More extractions were done in the female sample.
5. More lower incisor irregularity was experienced with the
male sample.
6. Extractions could influence the stability of lower
incisor alignment.
7. The male group who had less extractions as part of their
orthodontic treatment attained more retrusive lips with age
in comparison to the female group who had more extractions
performed during their treatment.
8. Growth, which the orthodontist has no control over,
appeared to influence the lower incisor irregularity in the
post-orthodontic period.
9. Retention, although equally important for both sexes
should be more stringently prescribed and utilised in males.
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CHAPT~R 13
GENERAL SUMMARY AND CONCLUSIONS
13.1 Introduction
The various components and dimensions contributing to the
composition of the craniofacial region have been separately
described, discussed and certain conclusions were made
(Chapters 4-12). These elements, forming the core of the
thesis, were the nasomaxillary complex, the mandible, the
anteroposterior dimension of the maxilla versus the same
dimension of the mandible, the occlusion, the anterior
border of the dentition, the vertical dimension, extraction
versus nonextraction treatment, soft tissue changes and
sexual dimorphism. In this concluding chapter an attempt is
made to summarize the significant findings from which a few
broad conclusions emerged. No data in regard to the
abovementioned regions are available for this or a
comparable South African Caucasian sample. The results are
also presented in a format which has not previously been
recorded.
The volume of data presented in this thesis contributes
generously to the literature and will hold benefits not only
for the clinician, but als~ for the academician who must
continuously seek better. and more significant ways and
means of conducting research of this nature. The thesis is a
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394
milestone in this regard and as no such data exists for a
comparable sample and it's contribution to research locally
and internationally is important. Comparisons with data from
other studies are essential, and only by doing so can
certain trends for long-term changes in respect to
orthodontic treatment be established, confirmed or
supported. In this way new data is contributed to the
orthodontic literature. All these criteria were
satisfactorily met in the present thesis.
This study has direct relevance in respect of the
stability and relapse of an orthodontically treated
subject. Orthodontists have a concept that they are totally
responsible, borne out by post-orthodontic care and
treatment, for lasting perfection and stability. However,
orthodontists have little control over the biological
aspects of growth and development and should not in every
case have feelings of guilt when their perfect results show
signs of relapse in the long-term (Behrents, 1984).
Enlargement, as a result of growth, creates a constant
series of localized imbalances. In most instances growth
results in periods of transient balance and ultimately in
a state of total equilibrium. The latter state is rarely
achieved in a lifetime of biological flux. Facial biologists
should appreciate that orthodontic relapse, in most
instances, is a normal reaction of the growth process
itself (Enlow, 1986). stability will, certainly, be
undermined when one or more of the delicate physiological
relationships are overwhelmed by improper diagnosis, the
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395
use of inappropriate appliances and/or improper orthodontic
technique. Overexpansion of arch width, incomplete
correction of anteroposterior relationships and rotations,
poor uprighting of lower incisors and incorrect vertical
control are but a few examples of factors which could result
in relapse. Continued growth of the craniofacial complex
after the removal of appliances (Behrents, 1984) could
influence the post-orthodontic occlusion as was probably the
case in the present study. Because growth of the
craniofacial skeleton can not be switched on and off
according to the wishes of clinicians, it is naive to assume
that the craniofacial morphology is ever stable. A
thorough understanding of the principles of craniofacial
growth is imperative. If sophisticated therapy is used only
to correct malocclusions, and stability is automatically
assumed, ultimate failure is guaranteed (Behrents, 1984).
It is important, when assessing relapse, to segregate the
changes which result from the orthodontic treatment from
those which would have taken place if no orthodontic
treatment was instituted (Brown and Duagaard-Jensen, 1951;
Lundstrom, 1969; LaVelle and Foster, 1969; Hunter and Smith,
1972; Sinclair and Little, 1983). Riedel (1975) discussed
nine popular causes of relapse, supported by relevant
research, and Moyers (1988) added another. They were:
i) Teeth that have been orthodontically moved, tend to
return to their former positions. This is especially
true for rotations in the incisor regions. In the
posterior teeth intercuspation aids retention to
some extent.
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396
permanentrequire
ii) Elimination of the aetiology of malocclusion will
assist in the preventing of recurrence.
iii) Malocclusion should be overcorrected as a safety
precaution.
iv) Proper occlusion is a potent factor in holding teeth
in their corrected positions.
v) Bone and adjacent tissues must be allowed time to
reorganize around newly positioned teeth. If
occlusal disharmony still exists post-treatment, it
makes little difference as to what kind of retainer
is worn or for how long. In such instances when the
retainers are removed stability will return at the
expense of the dental correction.
vi) If the lower incisors are placed upright over basal
bone they are more likely to remain in good
alignment.
vii) Corrections carried out during periods of growth are
less likely to relapse.
viii) The further the teeth have been moved, the less is
the likelihood of relapse to the original position.
ix) Arch form, particularly in the mandibular arch,
cannot be altered permanently by appliance therapy.
Arch form changes occurring in response to
alterations in the muscular environment may be more
stable.
x) Many treated malocclusions
retenion devices.
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The mean findinqs of the present study supported the
abovementioned bt?~ements and also showed that the
cephalometric and clinical no~ms described in the literature
are still excellent guidelines in treatment planning.
Practically all the variables in the study were treated to
these norms and the relapses that occurred were minimal and
clinically acceptable. The contribution of the present study
in this regard cannot be overemphasized.
Malocclusions are in a stable condition before treatment.
The practitioner must endeavour to attain the same
situation following treatment. It has, however, been pointed
out in the present study that even with an almost zero lower
incisor irregularity and more than 90% stability of the
molar and canine relationships, changes still occurred
within clinically acceptable limits. Proper goals of
treatment, excellent appliance control, precise occlusal
equilibration and well-chosen retention procedures all
contribute to achieving occlusal stability (Moyers, 1988).
The ideal duration of retention has not yet been determined
(Reitan, 1967). No satisfactory comparisons have been made
between similar malocclusion groups which were similarly
treated, but which had greatly different retention times
(Joondeph and Riedel, 1985). The literature suggests
anything from no retention whatsoever (Englert, 1960;
Williams, 1985) to permanent retention (Little, Wallen,
Riedel, 1981; Moyers, 1988; Parker, 1989). It is advisable
to have some form of mandibular retention until evidence of
completion of growth is forthcoming. Retention in the
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398
present study was implemented mainly by lower intercu.pid
fixed retention and the use of maxillary Hawley retaining
appliances. Four prefinishers were used as retention
appliances and two subjects had no retention device fitted
at all. The retention of the maxillary arch was ceased
before the mandibular arch. The latter was retained until at
least the third molars had shown signs of erupting or were
removed as a result of impaction. Retention was implemented
for a mean 2 years following treatment (post-retention
intervalS years; post-orthodontic interval 7 years).
Statistically significant and clinically significant are not
always the same. The term statistically significant means
that an observed difference is unlikely to be merely the
effect of chance, not necessarily that the difference is
clinically important. Many variables such as radiographic
technique, the pencil thickness on a cephalometric tracing,
the difficulty of locating a cephalometric landmark or the
attrition of a plaster cast may have influenced the data.
Hence, all the chapters included significant as well as
non-significant data.
The findings of the present study may provide insight
in establishing a sense of perspective regarding the level
of responsibility that may be accepted by an orthodontist
when relapse, rebound or physiologic settling do occur.
Moreover, informed consent is a topic of general discussion
not only in orthodontic journals, but also at meetings of
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399
orthodontic societi.s. The results of the pre.ent .tudy will
provide tremendous assistance to the orthodontist in thi.
regard.
13.2 Discussion
From the early days of orthodontics to the present time,
orthodontists have been faced with the primary problem of
moving each dental unit to its proper position in the dental
arch. The secondary problem, though often SUbjugated to an
inferior role, has b~en to maintain these teeth in their new
positions with retaining devices (straub, 1949). Retainers
succeed in some mouths, but fail in others. This finding
encouraged many orthodontists to examine their treatment
modalities, as they suspected that the incorrect placement
of the teeth was responsible for relapse rather than the
failure of different types of retainers and retention
methods used (Straub, 1949). Tweed (1944), Strang (1943,
1954) and Nance (1947) realised that a full complement of
teeth could not be placed in their correct positions in all
cases of crowding without "ballooning" out the dental
arches, and without changing the apical base sizes. In such
instances relapse often occurred either while the retainars
were being worn or after their removal, and it is doubtful
whether any
1949) •
retention device could maintain them (Straub,
Nance (1947) convincingly showed that the stability of the
dentition was dePendent upon the correct positioning of the
teeth ovar skeletal (basal) bone. He added that the
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400
correctio~ of any and all malocclusions was not tbe re.ult
of stimulating bone growth, but depended rather upon an
accurate ap~raisal of the amount of bone available in which
to move the te~th into their proper arch relationships and
good occlusion. It is conceivable that there exists an
enveloPe in which tooth movement may be accomplished without
significant relapse and that extreme changes violating
these limits are more likely associated with long-term
relapse. This envelope has been described by the clinical
and cephalometric norms widely published in the literature.
The only way to ensure continued satisfactory post-treatment
alignment is probably by the use of permanent fixed or
removable retention (Little, Riedel and Artun, 1988;
Parker, 1989). The number of hours during which the
removable retention appliances are worn is, however, out of
the control of the orthodontist.
The purpose of the present longitudinal study was not to
study the effects of prolonged retention, but to asses.
and describe changes which occur in occlusions following
orthodontic treatment.
The craniofacial complex is made-up of very intricate hard
and soft tissue structures. Changes occurring in even the
smallest of these stru ';.ures could contribute to relapse of
an ideally treated occlusion. The different parts of this
"puzzle" must thus, either by normal growth or perhaps
orthodontic treatment, be placed in their correct positions.
Moreover, patients undergoing orthodontic treatment
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401
should be informed beforehand of the ~••ibility of
post-treatment change. They must under.tand the
limitations of orthodontics and their own roles in the
maintenance of the treated results. Orthodontists should
assume that stability will not follow treatment, and in 80
doing can plan against, and prevent undesirable
post-treatment changes (Little, Riedel and Artun, 1988).
13.2.1 Changes in the maxilla, mandible and sugport\ng
structures
A knOWledge of basic anatomy (Longmore and McRae, 1985;
DuBrul, 1988) and how normal growth influences it (Enlow,
1968), is important in orthodontics. In this study growth
changes were cited according to norms reported in the
literature (Riolo et a1., 1974; Moyers et al., 1976;
Ricketts, 1981). It was deemed important to take cognizance
of these norms as pre-treatment, treatment and
post-treatment growth played its part in the present study.
A variety of treatment modalities are able to influence the
dimensions of the craniofacial skeleton (Ricketts at al.,
1979; Proffit, 1986; Moyers, 1988).
In the present sample the mean position of point A was
changed to a more retrusive position during treatment. This
could have been due to a variety of reasons including, for
example, upper incisor rEtraction, upp~r incisor palatal
root torque and extraoral tracti~n to ths maxilla. This
posterior movement of point A was reflected by the mean SNA
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402
and A-CONVEX measuements (Chapter 4; Table VIII). The
mandible on the other hand di~ not significantly change its
spat.ial anteroposterior position dUI'ing treatment (Chapter
5, Table XVI). Treatment mechanics were meticulously
excecuted in respect of the palatal plane position and
mandibular clockwise (opening) rotation. The palatal plane
was kept unchanged and the mandible was not significantly
r~tated open (Table VIII and XVI).
Normal increases as expected, were observed in the overall
mean maxillary and mandibular dimensions. The Bjork/Ja~abak
facial rotation pattern determination (Jarabak and Fizzell,
1972) indicated a counterclockwise pattern for the pooled
sample of the present study. The cranial base angle remained
unchanged throughout the study (Table VIII and XVI). The
post-treatment forward growth ~isplacement and closing
rotation of the mandible in combination with the more
retrusive stable maxillary position correlated
significantly, but weakly with the post-treatment lower
i.~l~lsor irregula~:'ity (Table IX and XVII). caution should
-us be excercised ~yhen planning to distalize the maxilla.
The retrudad position of the maxilla may restrict the late
forward growth of the mandible and the SUbsequent uprighting
of the lower incisor teeth as a result of this movemant is a
possible aetiologic factor of lewer incisor crowding.
Reports supporting these findings have been pUblished by
ojork ani Skieller, 1972, 1983; Richardson, 1986 and
Behrents et al., 1989.
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13.2.2 Anteroposterior
relationship
mAXillary versus
403
mandibular
The anteroposterior dimensions of the maxilla and mandible
are frequently used to classify and to determine the
severity of a skeletal disharmony between the two jawbones
(Steiner, 1953; Jacobson, 1975; Ricketts, 1981). Occlusal
relationships in the anteroposterior reference plane have
also served as a popular method of classifying
malocclusions (Angle, 1899, 1907). Many authors disagree
with the Angle classificati_fi system, but its usefulness
has outlasted most critics (Ackerman and proffit, 1969;
Mangazini, 1974). Concepts of the ideal occlusion have been
described inclUding the molar relationship in various
planes (Andrews, 1972, 1976). Irrespective of the
shortcomings of the Angle classification system, it
correlated very favourably with the ANB classification when
the number of subjects in each classification was assessed
(Table 0 and I). Both of these anteroposterior
classifications produced similar' information in regard to
the "relative" severity of the malocclusions, however at
closer scrutiny i. t was shown that discrepancies do exist and
that an Angle malocclusion is not necessarily analogous with
its skeletal counterparL (Table 0).
The mean ARB angle significantly decreased throughout the
period of observation, but true to the reports in the
literature, the mean Wits appraisal (Jacobson, 1975) did
not follow the ARB decrease and remained stab~e. It appears
that most of the ANa reduction during treatment was the
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404
result of relative posterior movement of point A rather
than mandibular forward growth. Th~ mandible shuwed forward
growth only during the post-treatment period and
contributed to the ARB reduction during this period (Table
XIX). Similar findings were reported by Holdaway (1956). No
significant correlation could be shown between these
variables and post-treatment mandibular incisor irregularity
(Table XXI).
13.2.3 Occlusal changes
The establishment of occlusal relationships were described
by Baume (1950) and Friel (1954). Ideal occlusion, although
rarely achieved in nature (Proffit, 1986), has been
described in the literature by various authors (Ricketts,
1969; Ricketts et al., 1979; Andrews, 1972, 1976; Roth,
1981) .
Normal dimensionsal changes have been shown during this
present study to serve as guidelines when pla.nning
orthodontic treatment. It was shown that dimensions such as
mean mandibular intercanine width (Table XX) remained
stable during normal growth and a dimension such as the mean
arch length decreased with age (Table XXV) . These and other
norms were described by Moyers et ale (1976) in Chapter 7 of
this thesis. Similar changes were measured during ~he
orthodontic treatment period (TI-T2) of this study (Table
XXVIII). As noted above, similar findings have also been
recorded in other studies.
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post-orthodonticall'i while the upper incisor
slight mean mesial movement as a consequence
maxillary and mandibular changes (Table XXVIII).
406
showed a
of these
The mean overjet values, although reduced to acceptable
norms (Moyers et al., 1976; Ricketts flt al., 1979; Moyers,
1988) tended to return to their original mean values, but
this was not a statistically significant change (Table
XXVIII). The mean overbite remained stable after
orthodontic correction (Table XXVIII), possibly as a
result of the ide~l mean interincisal relationships which
were obtained. Schudy (1963) reported similar findings in
respect of the interincisal angle and overbite. Mean
openbite values showed signs of returning to the original
malocclusion state possibly due to the presence of
uneliminated aetiological factors during the immediate
post-treatment period. No overt habits were, however, noted
at the final observation (T3) of the present study.
Crossbites seemed to remain reasonably stable once
corrected (Table XXX). The mean measurements for rotations
showed that an increase in the frequency extent of rotations
post-treatment, was possibly in part due; to the mean
increase of the post-treatment lower incisor irregularity
as well as rebound of previously rotated teeth (Table YJCK).
The reappearance of rotations seems to be a universal
problem. Even with the use of surgical fiberotomies,
corrected rotations still show small percentages of
relapses. This procedure does appear, however, to be
beneficial (Edwards, 1970; Boese, 1980). It is a
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recommended policy to
variable showed signs of
XXX) •
overcorrect
~'.n.c:ceasing
407
rotations as this
post-treatment (Table
Although the mean occlusal plane angle was not significantly
changed during treatment, it was slightly enlarged, possibly
as result of the Class II mechanics during treatment (Tweed,
1966). This parameter appeared to become more acute
relative to the anterior cranial base (Sella-Nasion plane)
during the post-orthodontic period of this study (Table
XXVIII). This post-orthodontic change was, however, in a
direction back towards the original mean value of the
recorded parameter, it ~~tually reduced to a mean value
smaller than the pre-treatment one and it can be referred to
as par.t of the rebound effect of orthodontic treatment or
relapse. The mean mandibular occlusal curve or Curve of Spee
(VO!! Spee, 1890) tended to return to its pre-treatment
value following orthodontic trea.tment (Table XXX) •
Orthodontists should thus strive towards a post-treatment
flat Curve of Spee (overtreatment) to accommodate for this
change. Space will be created when this phenomenon occurs
and possibly lead to less lower incisor crowding (Sandusky,
1983) .
The mean Bolton tooth-size discrepancy for the sample was
within the norm (Table XXIX). The mean anterior measurement,
however, did appear slightly larger than the norm described
by Bolton (1958, 1962) and it is suggested that even this
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small increase in the mandibular
mesio-distal dimensions coul~ influence
post-treatment crowding.
anterior
the lower
408
tooth
incisor
Third molars, irrespective whether they were removed before
the final observation (T3) or were congenitally absent,
were only noted as being present or not present in the
mouth. It was then only ~ecorded as a yes or no and no
metrical measurements were recorded. Third molars were
absent in 80.7% of the jaws (quadrants) studied (Table
xy.xI). It may be speculated that the relatively small mean
post-orthodontic increase (within clinical norms) in lower
incisor irregularity can partly be ascribed to the absence
of the wisdom teeth. The study did, however, not include a
SUfficiently sensitive assess..lent method to support this
speculation.
A total m~locclusion score was developed to give an
indication of the severity of malocclusions (Sadowsky and
Sakols, 1982). The mean total severity score, similar to the
abovementioned, did not significantly change during the
study which indicates a tendency for the post-treatment
occlusion to return to the original situation. The mean
differences measured during treatment included treatment
changes. The mean post-treatment changes echoed changes due
to the accompanying growth (Table XXVIII). A large number of
the post-orthodontic changes in the present study appeared
to be growth-related.
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409
Lower incisor irregularity is an acceptable clinical
indicator of post-treatment relapse (Little, 1975). Only the
mesial movement of the upper molar correlated
significantly, but weakly, with this parameter. The molar
movement which normally occurs as part of the mesial
migration of the dentition forms part of the
post-orthodontic growth variables. All the other occlusal
variables showed no correlation with the post-orthodontic
Little Irregularity Index (Table XXXII). The post-treatment
and post-orthodontic Little Irregularity Index of the
present study were lower than for other studies (Little ~
gl., 1988).
13.2.4 Vertical changes
The vertical dimensions of orthodontic subjects can be
assessed by means of cephalograms. The mandibular plane
angle is normally used in this respect (Downs, 1948;
Steiner, 1953; Tweed, 1954). Ricketts (1981) besides using
the Frankfurt mandibular plane angle to assess the vertical
relationship of the mandible, also suggests the use of the
facial axis angle, facial angle and lower facial height to
record the vertical dimension or mandibular growth
direction. The Bjork/Jarabak analysis (Jarabak and Fizzell,
1972), as used in the present study, emphasized the
mandibular rotation patterns of the subjects. The mean
changes of these parameters appeared to be towards a
closing rotation of the mandible (Table XXXVIII). Vertical
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410
dental problems normally follow the skeletal pattern, but a
vertical skeletal problem does not necessarily accompany a
vertical dental problem (Graber and Swain, 1985).
Overbite stability is often used to determine vertical
stability. Overbite correction and stability have been
reported with great controversy (Fogel and Magill, 1970).
described in the literature (Schudy, 1963;
Various ways of correcting this dimension have been
Ricketts .e.t
gl., 1979). Schudy suggested molar extrusion while Ricketts
et ale advocated incisor intrusion to correct overbite. The
interincisal angle also plays an important part in overbite
stability (Schudy, 1963) . The mean overbite correcti~n in
the present stUdy remaino.d stable (Table XXXVIII) possibly
due to vertical control during t"':eatment and to the
achievement of interincisal goals as described by Schudy
(1963). Extraction therapy and the counterclockwise rotation
of the mandible did not seem to influence the overbite
stability negatively.
Although no significant correlations were shown be"tween the
vertical variables and the post-orthodontic lower incisor
irregularity (Table XXXIX), various measurements changed
significantly in the post-treatment period (Table XXXVIII).
The vertical dimension was maintained rather than increased
during the active orthodontic treatment. This probably
contributed in keeping the mean post-orthodontic lower
incisor irregularity to a minimum. Tweed (1966) noted that
when the mandibular plane angle is increased during
treatment, it always tends to return to its pre-treatment
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value. If this change, as well as the normal closing
rotation tendency of the mandible (Bjork and Skieller, 1972,
1983; Riolo et al., 1974, 1979), are taken into
consideration then the importance of these contributing
factors to lower incisor crowding is realised. ~he
counterclockwise rotation of the mandible causes the lower
incisors to become more upright with a sUbsequent decrease
in dental arch space for these teeth, resulting in lower
incisor crowding (Table XXXVIII). Similar findings were
reported in the literature (Richardson, 1986; Perera, 1987).
13.2.5 ExtractiQn.versus nQnextractiQn treatment
ExtractiQn of teeth in the treatment Qf malocclusions is one
of the oldest and most controversial sUbjects in
Qrthodontics (Cole, 1948). It is much easier to extract
teeth than to establish the absolute necessity to follow
this philosophy (Delabbarre, 1815).
Successfully treated malocclusions can be achieved with
either extraction or nonextraction therapy. The frequency
of extractiQns vary greatly amQng orthodontists. Peck and
Peck (1979) reported an average prevalence of 42.1%, while
others found a range between 5% and 87% (Weintraub et al.,
1989). The present study was divided into 56% extraction,
and 44% nonextraction cases (Table I).
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412
It has been shown that extractions per se do not necessarily
produced stable result~, but that meticulous diagnosis and
planning of orthodontic treatment possibly could contribute
in this regard (Nance, 1947).
All the significant differences between the extraction and
nonextraction groups were set out in Chapter 10. The general
picture of this evaluation showed no significant differences
between the extraction and nonextraction groups at the
post-treatment stage (T2) and post-orthodontic (T3) stage
for the lower incisor irregularity of the pooled male and
female groups (Table XLIV). This suggested that irrespective
of treatment regime post-treatment crowding of mandibular
incisors occurred in a sample where no distinction is made
between males and females. It must, however, be mentioned
that the post-orthodontic lower incisor irregularity was
within clinically accepted limits (Little, 1975). Other
studies reported similar findings (Shields, Little and
Chapko, 1985; McReynolds and Little, 1991).
13.2.6 soft tissue changes
One of the first orthodontists to write about facial harmony
and the importance of the facial soft tissues was Angle
(1907). An important goal for orthodontic treatment is to
improve the facial harmony by correcting disproportions
(Rakosi, 1982; Holdaway, 1984; Proffit, 1986; Bishara,
Hession and Peterson, 1985).
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413
It was reported that young sUbjects have fuller lip. as
compared to the more retrusive lips found in adult. (Foster,
1973; Ricketts, 1981). Males have more retrusive lips than
their female counterparts when assessed according to the B­
and H-lines. Female profiles are also described as being
straighter than are mature male profiles (Mauchamp and
Sassouni, 1973). Similar mean findings were recorded in the
present study (Table XLVI). These findings are in accordance
with normal soft tissue growth changes (Table XLV). The
lips became significantly more retrusive throughout the
duration of the present study possibly due to a combination
of treatment procedures and normal growth processes. This
finding was borne out by a reduction in the overjet (Table
XXXIV) , a lower incisor position which was not
significantly retruded (Table XXXIV), and a significant
increase in nose prominence, soft tissue chin thickness and
a larger soft tissue facial angle (Table XLVI).
Significant, but weak correlations of the lower incisor
irregularity were shown for both the Merrifield Z-angle
(Merrifield, 1966) and Holdaway soft tissue facial angle
(Holdaway, 1983) (Table XLVII) . No other significant
correlations were shown for the soft tissue variables.
13.2.7 Sexual dimorphism
Differences between craniofacial parameters in males and
females have been widely published (Hellman, 1932; Baird,
1952; Barnes, 1954; Horowitz and Thompson, 1964; Lewin and
Hedegard, 1970; Broadbent et al., 1975; Greulich and Pyle,
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414
1976; Forsberg, 1979; Behrents, 1984). Boys attain their
pUbescent growth about two years later than do girl.
(Krogman, 1955). The absence of any significant age
differences, at the various time inter'ra!s studied, between
the male and female groups of the present study made for
ideal correlation of variables (Table XLIX).
The facial dimensions of males were reported to be larger
than those of females (Forsberg, 1979). It was also reported
that males grew later, longer and larger (Baum, 1961).
Similar findings were noted in the present study and
significant differences between the sexes were reported in
Chapter 12.
Mandibular and maxillary mean differences in the present
study were mostly growth-related. The males showed greater
counterclockwise rotation. Males appeared to be dentally
more retrusive than females. This obviously also influenced
the soft tissue profile as was previously noted. Moreover,
males showed more mean upper first molar mesial migration,
altbough they had less extractions as part of the
orthodontic treatment than did females.
The female group who had more extractions as part of their
treatment regimes, also showed a significantly smaller value
of the post-orthodontic lower incisor irregularity (Table
LII). This significant finding is in contrast to the results
o~ the pooled male and female sample of the present study
and also contradicts the results of other studies with such
pooled data (Shields, Little and Chapko, 1985; McReynolds
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415
and Little, 1991). According to the Little Irregularity
Index (Little, 1975), it appears as if the extraction.
could have benefitted the stability of the treated
dentitions. It must, however, be remembered that other
variables such as motivation during treatment and retainer
wear, which was subjectively assessed, could have played a
part in the result.
13.3 Conclusions
1. Ideal treatment goals are essential if acceptable
stability of orthodontic treatment is to be achieved.
2. Sound orthodontic technique could help to attain these
goals.
3. Distalization of point A, creates the possibility of a
more retrusive anteroposterior maxillary post-treatment
position. This may contribute to lower incisor crowding in
the post-orthodontic period.
4. Growth of the mandible occurred in keeping with the norms
quoted in the literature.
5. Orthodontic treatment complimented facial growth. Ho
adverse effects such as mechanical opening of the bite,
which could lead to relapse of treated dentitions, took
place.
6. A forwards and closing rotation of the mandibular growth
arc occurred monotonically throughout the present study.
The continual forward growth of the mandible, which was
accentuated by the dis,talization of point A, could have
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416
added to the mean post-treatment crowding of the mandibular
incisors. Anti-clockwise (opening rotation) mandibular
rotation was more obvious in males.
7. The mean anteroposterior dimensions SMA, ABB and
A-CONVEX decreased throughollt the study. This occurred
mainly because of treatment (Tl-T2), but was growth related
during the post-orthodontic period.
8. The mean overjet, although significantly corrected during
treatment, showed a mean post-orthodoni:.ic increase.
9. Significant, but weak correlations were shown between the
anteroposterior maxillary and mandibular positions and the
post-orthodontic Little Irregularity Index.
10. The mean post-pubertal growth changes which were
measured in the mandible, contributed to the continued
decrease in the point A-point B dimension, and although no
significant correlations were shown between the
post-orthodontic lower incisor irregularity and the
variables ANB, A-CONVEX and WITS-MM, it ma7 possibly have a
contributing influence on t.he late lower incisor
crowding.
11. Molar and canine relationships once established in
Class I, remained extremely stable and no significant
relationship could be shown between these and the late lower
incisor crowding.
12. Similar numbers of subjects were grouped according to
Class I, II or III when the skeletal classification
according to angle ARB and the dental classification
according to the Angle molar classification was used.
However, discrepancies existed between the two
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417
classification systems which r~sulted in some sUbjects being
grouped in one class when using the angle ANB and grouped
in another class when using the molar relationship.
13. Expansion of the mandibular arch beyond the original
intercanine dimension is likely to lead to failure, as this
dimension tends to decrease below the original measurement
in the long-term.
14. The mean anteroposterior measurement of the arch length
significantly decreased throughout the study. Although
related to treatment during the initial phase, growth and
occlusal forces were mainly responsible for the
post-treatment changes.
15. Change in arch length appears to be a major cause of
mandibular incisor irregularity.
16. Normal interincisal angular relationships contribute to
post-orthodontic overbite stability. Overbite remained
stable in this stUdy in contrast to other studies which
reported relapses in this dimension.
17. The ideal cephalometric norms for incisor position
should be adhered to, as once attained, they tend to
remain stable within clinical norms.
18. No strong, significant correlations could be shown
between lower incisor crowding and the various other dental
variables measured in this stUdy.
19. A post-treatment occlusion with a flat curve of Spee
and with all rotations eliminated could contribute to
stab1lity of the orthodontically treated dentition.
20. Correct diagnosis to distinguish between extraction
and nonextraction treatment of malocclusions, is imperative.
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418
21. The extraction of teeth does not necessarily a••ure
long-term stability of the lower incisors.
22. More extractions were carried out in the female sample
which showed a smaller value for the Little Irregularity
Index.
23. Greater lower incisor irregularity was recorded for
the male sample, in whom a larger number of nonextraction
treatments were performed. The male soft tissue profile
showed, irrespective of the type of treatment, les.
protrusive lips in comparison to the female sample.
24. From the conclusions 22 and 23, it appears that
extractions could influence the stability of the lower
incisor alignment.
25. The differences experienced between extraction and
nonextraction groups were mainly found in the maxillary and
mandibular dimensions.
26. No strong, significant correlations could be shown
between the relationship of the general soft tissue changes
and the post-orthodontic lower incisor irregularity.
27. The male group attained more retrusive lips with age
than did the female group.
28. Growth appeared to be responsible for most of the
post-treatment changes.
29. Significant differences were shown between the
dentofacial dimensions of males and females.
30. The lower incisor irregularity increases following
orthodontic treatment could be attributed mainly to growth
changes. The prerequisite when making this assumption is
that clinically acceptable norms should be the or~er of the
day at the end of active treatment.
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31. Orthodontists have little control over post-orthodontic
growth changes and cannot be held responsible for natural
changes which might influence an ideally treated dentition.
32. Pati.ents and parents should be informed that chang••
brought about mainly by growth, will take place during the
post-orthodontic period and could influence the alignment of
teeth detrimentally.
33. Retention, although equally important for both sexe.,
should be more stringently prescribed and utilised in males
as they showed more post-orthodontic lower incisor
irregularity.
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420
ORTHODONTISTS SHOULD BE AWARE THAT THE PERFECT RESULT HAS
NOT BEEN, AND PERHAPS WILL NEVER BE, OBTAI~~D. THERE WILL
FORTUNATELY ALWAYS BE MORE TO LEARN WHICH COULD BRING THE
CLINICIAN CLOSER TO PERFECTION.
THE END
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421
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