Abstract: Objective To explore the change of the TMJ after bilateral sagittal split ramus osteotomy （BSSRO）- postoperative orthodontics therapy by radiographic measurement in mandibular prognathism （MP） patients. Methods From 2012 to 2014, 24 patients （8 male and 16 female） diagnosed with MP with and without asymmetry were included in this study. They were divided into 2 groups （12 symmetric patients and 12 asymmetric patients） and all received SSRO - postoperative orthodontics therapy. TMJ space, condylar and ramus angle were assessed by computed tomography （CT） pre- and post- operatively. Results There was no significant difference on the deviation side between the asymmetry and symmetry groups. Coronal ramus angle on the non - deviation side in the symmetry group was significantly larger than that in the asymmetry group （P=0.016 1）. Horizontal Condylar angle on the deviation side in the symmetry group was significantly smaller than that in the asymmetry group while no significant difference was found on the non - deviation side between the asymmetry and symmetry groups postoperatively （P=0.017 9）. The postoperative coronal condylar angle and anterior joint space were significantly larger than the preoperative value on non - deviation side in symmetry group （P=-0.035 5 and 0.041 2, respectively）. The oostoperative coronal ramus angle and saggital ramus angle were larger while the sunerior Joint soace was smaller than the preoperative value on non - deviation side in asymmetry group （P=0.017 5, 0.039 8 and 0.031 9, respectively）. The preoperative condylar position was not changed on deviation side in either group. Conclusion Significant expansion of coronal condylar angle and anterior joint space could occur on the non - deviation side in symmetry group. In asymmetry group, the coronal ramus angle and saggital ramus angle.can be enlarged and the superior joint space can be reduced.

Key words: Mandibular prognathism, Sagittal split ramus osteotomy, Temporomandibular joint space, Asymmetry