Postoperative Evaluation of SSRO with Short Lingual or Obwegeser Osteotomies for Mandibular Prognathism
Yuichiro OtsukaMasaki FujitaHiroto EgawaKeisuke SanjoMai FujimotoTSUNEYASU TATSUTAShigeyuki MatsuiJun ShimadaNaoto Suda
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Abstract:
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.Keywords:
Mandibular prognathism
Gonial angle
Mandible (arthropod mouthpart)
Prognathism
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.
Mandibular prognathism
Gonial angle
Mandible (arthropod mouthpart)
Prognathism
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Postoperative skeletal stability is associated with osteotomy design of orthognathic surgery. The purpose of this study was to investigate osteotomy site-related factors of intraoral vertical ramus osteotomy (IVRO) related to skeletal relapse in a 2-year postoperative follow-up. Twenty-seven patients with mandibular prognathism underwent surgical mandibular setback with IVRO. Cephalometric radiographs of the patients were collected after completing preoperative orthodontic treatment (T1), at the stage immediately after surgery (T2), and in the 2-year postoperative follow-up (T3). Pir was located at the posterior most and inferior most ramus point. Io was the inferior most osteotomy point of the mandible. Relapse was defined as forward movement of menton (Me) in the 2-year follow-up. Hierarchical modeling analyses were used to assess changes in the variables, including the amount of postoperative relapse (MeT32), the quantity of surgical setback (MeT21), the available setback horizontal distance (Pir–Io), and the available setback ratio (MeT21/Pir–Io). The mean setback of Me was 12.6 mm, and the mean relapse was 0.9 mm (7.1% = 0.9/12.6). In the 1-by-1 and 1-by-2 models, there were no significant differences between the relapse and other variables. However, we found a significant difference in the 1-by-3 model. The MeT21 and MeT21/Pir–Io were significant factors in postoperative relapse. We found that multiple factors contributed to postoperative relapse of IVRO. Our study also confirmed the 2-year stability of IVRO in treating mandibular prognathism.
Mandibular prognathism
Setback
Prognathism
Mandible (arthropod mouthpart)
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The hypoplastic mandible results in facial convergence and pseudo-prognathism. We present a patient with significant maxillary hypoplasia in both the vertical and sagittal dimensions resulting in a reverse occlusal plane. Given the significant maxillary movements required, particularly clockwise rotation, more traditional mandibular osteotomies resulted in an unsatisfactory result. A modified version to the classic “C” osteotomy with the use of surgical planning and cutting guides was performed. A review of the literature on this rarely discussed ramus osteotomy is also presented.
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