The osteotomy line in sagittal split ramus osteotomy (SSRO) has a wide variation among surgeons. Recently, short lingual osteotomy (SL), in which the lingual split is limited up to the area near the mandibular foramen, is performed in many facilities. The reason for this is that SL can reduce the amount of interference between the proximal and distal segments, and shorten the operation time compared with Obwegeser osteotomy (Ob). However, since medial pterygoid muscles (MPM) are included in the proximal segments, SL is prone to induce backward rotation and distal positioning of the mandibular ramus due to the interference between MPM and distal segments when mandibular setback is performed.
The purpose of this study was to compare the postoperative outcome of SL and Ob for mandibular prognathism. Twenty-two skeletal Class III cases without lateral deviation treated by SSRO in Meikai University Hospital, were examined. Among the 22 cases, 15 and 7 cases underwent SL and Ob, respectively. The postoperative changes of the proximal and distal segments were evaluated in lateral and postero-anterior cephalograms taken immediately before the surgery (T1), immediately after the surgery (T2), and one year after the surgery (T3). At T1, there was no significant difference in SNB, FMA, or gonial angle between the SL and Ob groups. No significant difference in the amount of mandibular setback was found between the two groups. Comparing values at T1 and T2, the proximal segments tended to rotate backward in the SL group, but there was no significant difference in the anterio-posterior position of proximal segments between the two groups. Comparing values at T2 and T3, counter-clockwise rotation of proximal segments was seen in the SL group but not in the Ob group. It is likely that this rotation of proximal segments in the SL group was caused by the muscular strength of MPM attached mainly to the proximal segments. Moreover, a significant negative correlation in the amount of rotation of proximal segments was detected between T1-T2 and T2-T3 in the Ob group, but not in the SL group.
These findings indicate that special attention to the rotation in SL cases is important since a wider variation in the rotation of proximal segments may occur compared with the Obwegeser method.
