Effect of sagittal split ramus osteotomy on stress distribution of temporomandibular joints in patients with mandibular prognathism under symmetric occlusions.

Sagittal split ramus osteotomy (SSRO) is the representative orthognathic surgery for the patients with mandibular prognathism. It is essential to understand the biomechanical environment of temporomandibular joint (TMJ) to analyse the effects of SSRO. This study aimed to investigate the influence of SSRO on the stress distributions in the TMJs of the patients with mandibular prognathism under symmetric occlusions. Thirteen patients with mandibular prognathism and ten asymptomatic volunteers were recruited. Finite element models of the asymptomatic, preoperative, and postoperative subjects were established, based on the CT of the asymptomatic volunteers and preoperative and postoperative scans of patients with mandibular prognathism. Contact was used to simulate the interactions between discs and articular surfaces, and between the upper and lower dentition. Muscle forces and boundary conditions corresponding to the centric and anterior occlusions were applied on the models. Under both occlusions, the maximum and minimum principal stresses of the articular disc and condyle in the preoperative group were significantly greater than those in the control group. After SSRO, the maximum and minimum principal stresses of the articular disc and condyle of the patients under both occlusions were greatly reduced, but the principal stresses of the articular disc were not significantly higher than those in the control group. Mandibular prognathism led to excessive stress on the TMJ. Severe asymmetric compression between the TMJs on both sides might cause temporomandibular disorder (TMD) symptoms. SSRO could improve the stress distribution of the TMJ and partially relieve the symptoms of TMD.