The Relation Between Mandibular Relapse and the Postoperative Mandibular Ramus Rotation Following BSSO Setback.

Objectives: This retrospective study aimed to determine the angulation changes of the proximal segment following bilateral sagittal split osteotomy (BSSO) setback and its correlation with the amount of immediate postoperative surgical movement. The correlation between postoperative relapse of the distal and proximal segment at six months postoperatively was also evaluated.

Materials and methods: The CBCT-generated lateral cephalometric images of 39 patients who underwent BSSO setback with or without Le Fort I osteotomy were evaluated preoperatively (T0), immediately postoperative (T1), and six months postoperatively (T2).

Results: The mean surgical setback was 7.28 ± 4.45 mm at B point. The proximal segment's immediate postoperative mean posterior rotation was 2.13 ± 3.59 degrees. Six months after the operation, the mean distal segment relapse was 0.89 ± 3.03 mm at B point. The proximal segment relapse was 0.81 ± 1.63 degrees. A significant moderate correlation was found (P < 0.05) between the surgical movement and the immediate postoperative proximal segment rotation and between the surgical movement and the distal segment relapse. A significant correlation was found between the distal segment relapse and the average and left proximal segment relapse. There was no significant correlation between immediate postoperative proximal segment rotation and distal segment relapse.

Conclusion: The immediate postoperative posterior rotation of the proximal segment had a negligible effect on mandibular relapse. The amount of surgical movement, on the other hand, was more related to distal segment relapse. The intraoperative proximal segment rotation should thus be minimized in cases with a significant surgical setback.