Abstract: Objective: Changes of the position and shape of the condyle of TMJ before and after orthodontic-orthognathic treatment were measured to evaluate its influence on TMJ and to provide reference for the prediction of preoperative comprehensive therapeutic schedule.Methods:20 patients with severe skeletal Class III malocclusion were selected. CBCT of these patients were collected before orthodontic treatment, after decompensation and after orthodontic-orthognathic treatment. The diameter, gap and angle of TMJ were measured through CBCT and compared the changes before and after treatment. Results: There was no statistical difference in the measurement items of TMJ between the left and right sides (P > 0.05) before and after treatment. There was a significant difference (P < 0.05) in the horizontal angle of the left condyle before and after decompensation of orthodontic treatment, while there was no significant difference (P > 0.05) in the other three-dimensional measurement items of TMJ. The horizontal angle of the left and right condyles, the supra articular space and the anterior articular space increased significantly before and after treatment (P < 0.05). Conclusions: The preoperative orthodontic treatment had no significant effect on the temporomandibular joint. But after orthodontic-orthognathic surgery, the condyle position changed backward and downward.

Key words: Class Ⅲ malocclusion, temporomandibular joint, combined orthodontic and orthognathic treatment