Mandibular morphological variation : implications for fracture repair

McKay, Cyrilleen (2019-12)

Thesis (MSc)--Stellenbosch University, 2019.

Thesis

ENGLISH SUMMARY : Achieving a predictable clinical outcome during mandibular fracture repair necessitates thorough knowledge of variations of the neurovascular bundle, the location of tooth roots and bone quantity in the region of interest. In South Africa, the prevalence of mandibular body fractures due to alcohol-related interpersonal violence is increasing and is largely stratified socio-economically. Approximately 80% of people presenting with mandibular fractures rely on the resource-limited public health care system. In addition, South African population groups have a high prevalence of structures resembling accessory mental foramina (AMF) which may impede fracture fixation and outcomes. These considerations form the basis of this study which aimed to define population specific information on interforaminal variations and assess their applicability in clinical decision-making prior to fracture repair, using dry mandibles. Hemi-mandibles (N = 213) with known age and varying tooth loss patterns were obtained from four ancestry and sex subgroups, namely South African Coloured (SAC) females, SAC males, Black (SAB) males and White (SAW) males. The location of the mental foramen (MF) and AMF was determined in relation to mandibular topographical landmarks. Buccal cortical plate (BCP) and buccal bone thickness was assessed at 12 points – four points on transverse planes through, superior, and inferior to the MF midpoint. Transverse planes correspond with possible locations for mini-plate fracture fixation and the four points on each plane corresponds with locations for mono-cortical screw insertion. The MF was most commonly located between the first and second premolar teeth and the distance from the symphysis menti to the anterior border of the MF was smaller in SAC males when compared to SAC females. However, this parameter had a greater reading on right hemi-mandibles of SAB males when compared to SAC males. Tooth loss was associated with a decreased height of the mandible superior to the MF and age was associated with an increased MF diameter. Accessory mental foramina were observed in 6.54% of hemi-mandibles and was most commonly located mesial and superior to the MF. The BCP differed between subgroups and showed negative associations with tooth loss and age at selected assessment points. The buccal bone was thickest at the foraminal transverse plane when compared to superior and inferior transverse planes. It was thicker in SAC females when compared to SAC males on the inferior transverse plane of left hemi-mandibles. Overall, the influence of tooth loss and age on mandibular morphology did not vary between sex and ancestral subgroups. Results show that in comparison to superior and inferior transverse planes, the foraminal transverse plane had the lowest risks for inadvertent injuries to vital structures. Risks on this plane increased from 1.9 to below 8% for screw lengths 4 – 8 mm bilaterally. These findings expand population-specific knowledge of anatomical variations which could aid clinical and preoperative decision-making in the repair of mandibular fractures in South Africa.

AFRIKAANSE OPSOMMING : Dit is noodsaaklik om ‘n deeglike kennis te hê van variasies in die neurovaskulêre bondel, tandwortel apekse sowel as die hoeveelheid been teenwoordig, tydens die herstel van mandibulêre frakture. Die voorkoms van frakture in die mandibulêre liggaam as gevolg van alkohol-verwante interpersoonlike geweld, is aan die toeneem in Suid Afrika en is hoofsaaklik as gevolg van sosio-ekonomiese omstandighede. Ongeveer 80% van mense met mandibulêre frakture is afhanklik van die hulpbron-beperkte publieke gesondheidsstelsel. Bykomend, het Suid Afrikaanse populasiegroepe ‘n hoë voorkoms van structure wat lyk soos aksessoriese mentale foramina (AMF) wat moontlik fraktuur fiksering en fraktuur uitkomstes kan belemmer. Hierdie oorwegings vorm die basis van die huidige studie wat poog om populasie-spesifieke informasie op interforaminale variasies te definieer, asook hul toepaslikheid in kliniese en preoperatiewe besluitneming aangaande die herstel van frakture, deur die gebruik van droeë mandibula. Hemi-mandibulae (N = 213) met bekende ouderdomme en met verskeie tandverlies patrone, is verkry vanaf vier geslags en populasie subgroepe naamlik Suid-Afrikaanse Kleurling vroue, Kleurling mans, Swart mans en Wit mans. Die posisie van mentale foramina (MF) en AMFs is bepaal in verhouding tot mandibulêre topografiese landmerke. Bukkale kortikale plaat (BKP) en bukkale been dikte is op 12 punte bepaal - vier punte op dwarsvlakke, superior, inferior en deur die midpunt van die MF. Dwarsvlakke stem ooreen met moontlike posisies vir mini-plaat fraktuur fiksering en die vier punte op elke vlak stem ooreen met inplantingspunte vir mono-kortikale skroewe. Die MF was mees algemeen geleë tussen tand wortel apekse van die eerste en tweede premolaar tande. Die MF was nader aan die simfise geleë in linker en regter hemi-mandibulae van Kleurling vroue, maar was verder vanaf die simfise geleë in regter hemi-mandibulae van Swart mans in verglyking met Kleurling mans. Tandverlies is geassosieer met ‘n afname in die mandibulêre hoogte superior tot die MF, en ouderdom is geassossieer met ‘n toename in die MF se deursnit. Aksessoriese mentale foramina het in 6.54% hemi-mandibulae voorgekom en is mees algemeen mesiaal en superior tot die MF geleë. Die BKP het verskille tussen subgroepe getoon by bepaalde assesseringspunte. Die BKP het ook negatiewe assosiasies met tandverlies en ouderdom getoon by bepaalde assesseringspunte. Bukkale been was dikker op die foraminale dwarsvlak in vergelyking met dwarsvlakke superior en inferior tot die foraminale dwarsvlak. Bukkale been was dikker in Kleurling vroue in vergelyking met Kleurling mans op die inferior dwarsvlak. Oor die algemeen het die invloed van tandverlies en ouderdom op mandibulêre morfologie, nie tussen geslag en populasiegroepe verskil nie. Hierdie resultate dui daarop aan dat die foraminale dwarsvelak die laagste risiko vir onopsetlike beserings aan noodsaaklike structure in hou. Die risiko op hierdie vlak styg vanaf 1.9% tot onder 8% vir skroewe van 4 tot 8 mm in lengte. Hierdie bevindinge brei uit op reedsbestaande kennis van populasie-spesifieke anatomiese variasies wat die kliniese en preoperatiewe besluitnemingsproses vir die beplanning van interforminale fraktuur behandeling mag ondersteun in Suid-Afrika.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107196
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