Morphological integration in inferior alveolar canal and mandibular shapes

Objective: During embryogenesis of mandible, the initial ossification centre begins at the bifurcation of the inferior alveolar (IA) and the mental nerves. Additionally, in congenital anomalies like craniofacial microsomia (CFM), the IA canal is completely absent on the microsomic side. These observations led us to hypothesise that there may be a morphological integration between these structures - the IA nerve and the mandibular shapes. Therefore, the primary objective of this study was to test for morphological integration between these structures and the secondary objective was to determine if there were shape variations in these structures among skeletal Classes I, II and III subjects.Setting and sample population: The sample size of the study is 80 full head cone beam computed tomography (CBCT) scans (age 16- 56 years).Methods: We retrieved CBCT scans from our archived database using specific inclusion/exclusion criteria. In the de-identified CBCT scans, traditional coordinate landmarks and sliding semi-landmarks were placed on the mandible and the IA canal (proxy for IA nerve). Using geometric morphometric analyses, we tested integration between the IA canal and the mandibular shapes. We used Procrustes ANOVA to test for overall shape variations among the three skeletal classes (Classes I, II and III).Results: The IA canal and posterior/inferior border of mandible showed strong integration (r- PLS = .845, P = .001). Similar strong integration was also observed between the IA canal and the overall shape of the mandible (r- PLS = .866, P = .001). Additionally, there was a statistically significant variation in overall shape between skeletal Class I and Class II (P = .008) and Class II and Class III (P = .001).Conclusions: The strong integration between two structures suggests that the IA nerve may play a role in establishing mandibular shape early in development. We posit this may be important in driving mandibular defects seen in CFM, which warrants further investigation.