3D analysis of condylar remodelling and skeletal relapse following bilateral sagittal split advancement osteotomies

A major concern in mandibular advancement surgery using bilateral sagittal split osteotomies (BSSO) is potential postoperative relapse. Although the role of postoperative changes in condylar morphology on skeletal relapse was reported in previous studies, no study so far has objectified the precise changes of the condylar volume. The aim of the present study was to quantify the postoperative volume changes of condyles and its role on skeletal stability following BSSO mandibular advancement surgery. A total of 56 patients with mandibular hypoplasia who underwent BSSO advancement surgery were prospectively enrolled into the study. A cone beam computed tomography (CBCT) scan was acquired preoperatively, at 1 week postoperatively and at 1 year postoperatively. After the segmentation of the facial skeleton and condyles, three-dimensional cephalometry and condylar volume analysis were performed. The mean mandibular advancement was 4.6 mm, and the mean postoperative relapse was 0.71 mm. Of 112 condyles, 55% showed a postoperative decrease in condylar volume, with a mean reduction of 105 mm(3) (6.1% of the original condylar volume). The magnitude of condylar remodelling (CR) was significantly correlated with skeletal relapse (p = 0.003). Patients with a CR greater than 17% of the original condylar volume exhibited relapse as seen in progressive condylar resorption. Female patients with a high mandibular angle who exhibited postoperative CR were particularly at risk for postoperative relapse. Gender, preoperative condylar volume, and downward displacement of pogonion at surgery were prognostic factors for CR (r(2) = 21%). It could be concluded that the condylar volume can be applied as a useful 3D radiographic parameter for the diagnosis and follow-up of postoperative skeletal relapse and progressive condylar resorption.