Abstract: Objective To explore the stability of operation-first sagittal split ramus osteotomy（SSRO）-postoperative orthodontics therapy for the correction of mandibular prognathism（MP） by cephalometric radiographs. Methods Eighteen patients diagnosed with MP with and without asymmetry were treated. BSSRO-postoperative rapid orthodontics therapy was performed without preoperative orthodontics therapy and lateral cephalometric radiographs were taken before operation（T0）,five days after operation（T1） and one year after operation（T2）. The landmarks were measured by the software. Results The mean surgical setback was 7.5 mm at B point and 6.6 mm at pogonion. The mean long-term horizontal relapse was 2.1 mm（28.0%） at B point and 2.9 mm（43.9%） at pogonion. The mean vertical surgical changes showed downward displacement of B point（1.3 mm） and pogonion（1.0 mm）. The mean long-term vertical relapse was 0.1 mm at B point and 0.3 mm at pogonion.The mean increase was 4.3 ° at ramus angle and the long-term relapse was 1.1 °（25.6%）. The magnitude of the surgical movement of B point and pogonion（T1-T0） didn ＇t correlate with long-term changed distance（T2-T1） horizontally and vertically（P0.05）. The magnitude of the surgical movement of Go, Condylion point and ramus angle（T1-T0） didn ＇t correlate with long-term changed distance of Pog point（T2-T1） horizontally（P 0.05）. Conclusion The skeletal relapse do exist in the BSSRO-postoperative rapid orthodontics therapy for MP and there is no linear correlation between the surgical movement of B point, pogonion and skeletal relapse.

Key words: Mandibular prognathism, Sagittal split ramus osteotomy, Relapse