Transverse and sagittal angulations of proximal segment after sagittal split and vertical ramus osteotomies and their influence on the stability of distal segment

This study aimed at comparing the transverse and sagittal angulations of proximal segment after sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO), and examining their influences on the stability of distal segment. Methods: Patients who received SSRO (n = 21) or IVRO (n = 11) for mandibular setback were included. Lateral and posteroanterior cephalograms taken within 1 month before surgery (T1), within 1 week after surgery (T2), and at least 6 months after surgery (T3) were analyzed. The angulation of each proximal segment relative to the upper orbital margin line was measured on posteroanterior cephalogram and the sum of both angles (total ramus angle, TRA) was obtained. On lateral radiograph, ramus inclination angle (RIA) relative to a horizontal reference line 7° to the sella–nasion was assessed and B-point position was measured. Results: From T1 to T2, more increases in TRA and RIA were noted after IVRO than after SSRO. From T2 to T3, TRA and RIA significantly decreased in IVRO group but remained relatively stable in SSRO group. ΔTRAT1–T2 positively related to upward rotation of distal segment for SSRO and downward rotation for IVRO from T2 to T3. For SSRO only, ΔRIAT1–T2 significantly related to forward movement of distal segment during remodeling. Conclusion: TRA and RIA increase significantly after IVRO and then regress, whereas they increase mildly after SSRO and remain stable. Increase in TRA significantly relates to distal segment rotation during remodeling for both surgeries, but increase in RIA relates to forward relapse of the distal segment only for SSRO. The reasons underlying the correlations are not certain and deserve future investigations