Mandibular advancement surgery in high-angle and low-angle Class II patients: Different longterm skeletal responses

The objective of this cephalometric study was to compare skeletal stability and the time course of postoperative changes in high-angle and low-angle C lass II patients after mandibular advancement surgery. The subjects were 61 consecutive mandibular retrognathism patients whose treatment included bil ateral sagittal split osteotomy and rigid fixation. The patients were divid ed according to the preoperative mandibular plane angle; the 20 patients wi th the lowest mandibular plane angle (20.8 degrees +/- 4.9 degrees) constit uted the low-angle group. while the 20 cases with the highest mandibular pl ane angle (43.0 degrees +/- 4.0 degrees) represented the high-angle group. Lateral cephalograms were taken on 6 occasions: immediately before surgery, immediately after surgery. 2 and 6 months after surgery, and 1 and 3 years after surgery. Results demonstrated that the high-angle and low-angle grou ps had different patterns of surgical and postoperative changes. High-angle patients were associated with both a higher frequency and a greater magnit ude of horizontal relapse. While 95% of the total relapse took place during the first 2 months after surgery in the low-angle group, high-angle patien ts demonstrated a more continuous relapse pattern, with a significant propo rtion (38%) occurring late in the follow-up period. Possible reasons for th e different postsurgical response are discussed.