Abstract: Abstract: Objective To analyze the changes in different stages of bimaxillary orthognathic surgery in patients with severe Skeletal Class Ⅲ malocclusion, and compare their postoperative stability. Methods 30 patients with severe skeletal Angel Class Ⅲ malocclusion were selected and treated with bimaxillary orthognathic surgeries. SPSS20.0 software package was used to analyze the changes of the hard tissues at the following stages: before treatment(T0); before surgery(T1); 6 weeks after surgery(T2); after treatment(T3). Results Comparing T1 with T0, significant changes occurred in the corresponding measurements of both upper and lower incisors (P<0.05). Comparing T2 with T1, the maxilla moved forward and downward, while the mandible moved backward and upward (P<0.05). The SNA angel, the SNB angel, the ANB angel and Wits appraisal varied significantly(P<0.05). OP-SN increased significantly(P<0.05).The occlusal plane had a counterclockwise rotation(P<0.05). The upper and lower facial height changed significantly(P<0.05) and the vertical facial proportions became more harmonious. All the patients had established good occlusion relationship. Comparing T3 with T2, the landmarks of the maxilla and mandibular had slightly relapsed, but the changes were not statistically significant(P<0.05). Conclusion Bimaxillary surgery can correct maxilla deformity, improve vertical facial proportions, change occlusal plane inclinations, improve the occlusion relationship significantly, and have a good postoperative stability.

Key words: skeletal class III malocclusion, bimaxillary surgery, X-ray cephalometry, changes of hard tissues