Three-Dimensional Mandibular Asymmetry Assessment in Unilateral Type IIA Craniofacial Microsomia Using Functional Unit Analysis: A Retrospective Case-Control Study

Objective: While the Pruzansky-Kaban classification categorizes mandibular deformity in craniofacial microsomia (CFM), significant morphologic variability exists within each subtype. This study aimed to characterize mandibular morphology in type IIA CFM using functional unit analysis. Methods: This retrospective case-control study included 55 unilateral type IIA CFM patients (6–17 years) and 55 matched controls. Three-dimensional CT scans were used to measure ramus height, body length, and 5 mandibular functional units (condylar, coronoid, angular, body, and chin). Asymmetry index (AI) and absolute asymmetry index (AAI) were calculated, and nonparametric tests assessed group differences and correlations. Results: Mandibular asymmetry was pronounced in CFM patients versus controls, particularly in the condylar unit (median AI: 13.9%–17.5%, P <0.001), followed by the coronoid and angular units. While angular unit AI showed no intergroup differences in adolescents, its AAI was significantly elevated ( P <0.001), indicating age-related interindividual variability. In children (6–11 years), ramus height and body length asymmetry strongly correlated with condylar unit AI ( P =0.007 and 0.003, respectively), whereas adolescents (12–17 years) showed a shift to angular unit dominance ( P <0.001 and P =0.001, respectively). Conclusions: Type IIA CFM primarily involves the condylar unit, with the angular unit demonstrating significant growth variability. The developmental transition in asymmetry correlations from condylar to angular units suggests distinct growth patterns in CFM. These findings enhanced our understanding of mandibular morphology in CFM and suggested potential directions for future therapeutic research.