The influence of bilateral sagittal split ramus osteotomy on the stress distributions in the temporomandibular joints of the patients with facial asymmetry under symmetric occlusions

The aim of this study is to compare the differences in the stress distributions in the temporomandibular joints (TMJs) of the patients with facial asymmetry before and after bilateral sagittal split ramus osteotomy (BSSRO) under the symmetric occlusions using the three-dimensional (3D) finite element method. Ten facial asymmetry patients (Preoperative group, age 24.6 +/- 4.8 years) and 10 asymptomatic subjects (Control group, age 26.8 +/- 4.9 years) were recruited. After the patients underwent BSSRO, they were further assigned as the Postoperative group. 3D geometries of the finite element models of the mandible, disc, maxilla, and teeth were reconstructed according to cone-beam computed tomography (CBCT) image data. Contact elements were used to simulate the interaction of the disc-condyle, disctemporal bone, and upper-lower dentition. The muscle forces and boundary conditions corresponding to the central and anterior occlusions were applied on the models of the 3 groups. The finite element models were validated with experimental data showing the accuracy of the simulation results. The simulation predicted preoperative significant differences of stresses between non-deviated sides and deviated sides were disappeared after the surgery under the central and anterior occlusions (P<.05). Almost all stresses in the patientmodels had significantly decreased after BSSRO, leveling it to the stress values of the normal subjects. Moreover, the simulation results coincided with the clinical cases which showed that BSSRO had helped to release or remove the signs and symptoms of temporomandibular disorders (TMD). In conclusion, BSSRO could correct the asymmetric stress distributions of TMJs and decrease the magnitude of the stresses for the patients with facial asymmetry. Those decreases also associated with the recovery of TMD.