Do mandibular functional units exhibit inherent asymmetry in adults with a normal degree of chin deviation? A cone-beam computed tomography study

This study aimed to investigate the inherent asymmetry of mandibular functional units and to compare the degree of asymmetry between adults with different sagittal skeletal patterns. Ninety CBCTs scans of normodivergent adults with a normal degree of chin deviation, representing different sagittal skeletal patterns (Classes I, II, and III) were included; 30 each. Three-dimensional mandibular models were generated, and volumetric and linear bilateral measurements were obtained for the hemimandible and the condylar, coronoid, ramus, angular, alveolar, body, and chin units. The degree of asymmetry was presented using the asymmetry index (AI) and between groups measurements were compared using ANOVA test and GEE model. The mean AI values were significantly higher than 0% across all measurements for all sagittal skeletal patterns. Volumetric measurements yielded higher overall AI values than linear measurements (3.55 ± 3.6 vs 1.83 ± 1.74, P < 0.001). Negative and positive correlation values were found between mandibular units, thus supporting the theory of compensatory mechanism of the mandible. In all groups, the coronoid process volume and angular unit length exhibited the highest degree of asymmetry, whereas the total body length and hemimandibular volume showed the lowest. No significant differences were found in the AI of volumetric or linear measurements between sagittal skeletal patterns (P > 0.05). Mandibular functional units exhibited a degree of asymmetry in adults from different sagittal skeletal patterns. Clinical Relevance: This study quantifies the inherent asymmetry and compensatory mechanisms in mandibular functional units of adults with normal chin deviation.