Orthognathic surgery effects on temporomandibular joint compressive stresses

Introduction: This study tested orthognathic surgery effects on temporomandibular joint (TMJ) compressive stresses. Methods: Pre- (T1) and post-surgery (T2) cone-beam computed tomography images were collected from consenting subjects aged ≥15 years. Anatomical data were used to measure surgical changes in anteroposterior mandibular position and occlusal plane angle (FH-OP), estimate condylar loading areas (mm²) and calculate T1 and T2 TMJ and jaw muscle forces (N) during canine biting via numerical modelling. Analysis of covariance tested for sex and biting angle differences in T2 − T1 TMJ compressive stresses (TMJ force/loading area, MPa). Principal component analyses identified jaw muscle forces that accounted for changes in T2 − T1 TMJ loads. Regression analyses tested the correlations between surgical changes in mandibular position, FH-OP, TMJ loads and muscle forces. Results: Of 148 cases screened, 28 females and 16 males provided complete records. Condylar loading areas were significantly smaller (P =.024) for females vs males (124 ± 5 vs 144 ± 7 mm²). T2 − T1 differences in TMJ compressive stresses varied by surgical change, biting angle and sex. Overall, the largest increases in TMJ compressive stresses post-surgery were for females with mandibular setbacks where FH-OP angle decreased. T2 − T1 changes in jaw muscle forces had moderate (ipsilateral, λ = 4.59; η² = 0.071) to large (contralateral, λ = 1.49; η² = 0.31) effects on TMJ loads. Conclusions: T2 − T1 differences in TMJ compressive stresses during canine biting were affected by surgical changes in mandibular position and occlusal plane angle, biting angle and sex. Surgical changes altered jaw muscle forces for the same biting conditions and, thus, affected TMJ loads and compressive stresses.