하악 후퇴술 후 근·원심 골편의 위치 변화

Abstract

I. Introduction Most of the relapse of mandibular setback surgery occurs as a rotational relapse. To predict this relapse, positional changes of proximal and distal segments of the mandible during postsurgical orthodontics treatment are needed. The purpose of this study was to evaluate changes in the proximal and distal bony segments following bilateral sagittal split ramus osteotomy (BSSRO) setback orthognathic surgery.

II. Methods Thirty patients (mean age 21.9 ± 4.3 years) who were diagnosed with skeletal Class III and mandibular prognathism and underwent BSSRO setback surgery were included. Cone-beam computed tomography (CBCT) scans were taken before treatment (T0), immediately after surgery (T1), and after orthodontic treatment (T2). Skull models from CBCTs were superimposed to assess condylar displacement and to measure the position of the center of rotation (CRot) for proximal and distal segments and the amount of rotation. Positional changes of landmarks that can affect mandibular rotation were also evaluated.

III. Results During T0-T1, the condyle was displaced lateroinferiorly and rotated mesially. During T1-T2, it was moved mediosuperiorly and rotated distally but did not reach its pretreatment (T0) position. The development of the vertical bony step (VBS) during surgery was correlated with the anterior relapse of the pogonion (r = -0.623). During T1-T2, all proximal segments rotated counterclockwise, with the center of rotation near the condyle. However, the CRot of the distal segment was distributed along a posterosuperior oblique line passing near the condyle. Also, the vertical and anteroposterior positions of the CRot of the distal segment were correlated with the VBS developed during surgery (r = -0.465 and r = -0.433, respectively), indicating that the larger VBS, the higher and posterior the position of CRot. The ratio of the anterior movement of the pogonion to the superior movement of the menton during T1-T2 was 1.7 ± 1.3 (mean ± standard deviation).

IV. Conclusions Mandibular setback surgery displaced the condyle, which does return but not entirely to its pretreatment position. As VBS developed more during surgery, anterior relapse increased and the CRot of distal segment for postsurgical counterclockwise rotation moved posterosuperiorly. Reducing VBS during BSSRO setback may reduce postsurgical relapse. The CRot of distal segment may be predicted through the developed VBS, and predictive treatment can be performed with STO using the CRot.