Stability of pre-orthodontic orthognathic surgery depending on mandibular surgical techniques: SSRO vs IVRO

The aim of this retrospective cohort study was to evaluate the postoperative stability of sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO) in pre-orthodontic orthognathic surgery (POGS) for skeletal Class III malocclusion. Thirty-seven patients (SSRO, n = 18; IVRO, n = 19) who underwent bimaxillary surgery were divided into two groups according to the type of surgery. During the postoperative period, there were no significant differences in anterior and superior movements of the mandible at point B between the two groups, but occlusal plane angle of the SSRO group significantly decreased more than that of the IVRO group (P = 0.003). Only the SSRO group showed a linear relationship between the amount of postoperative horizontal and vertical movements of the mandible (R(2) = 0.254; P = 0.033), indicating that the amount of postoperative upward movement of the mandible increased as the amount of postoperative forward movement increased (r = -0.504; P = 0.033). The mandible after SSRO in POGS rotated counterclockwise due to rigid fixation between two segments, whereas the mandible after IVRO without rigid fixation in POGS moved mainly in a superior direction. These differences must be considered before surgery to ensure postsurgical stability for patients with mandibular prognathism.