Objectives: The objective of the current study is to quantify the postoperative 3D morphologic changes of condyles using cone beam computed tomography (CBCT) and evaluate the subsequent effects on skeletal stability following a BSSO advancement of the mandible.

Methods: 56 consecutive patients with mandibular hypoplasia were treated with a BSSO. The preoperative, one week and one year postoperative CBCT scans were acquired and superimposed using voxel based registration. 3D cephalometric analysis was performed to assess the perioperative skeletal displacements and postoperative skeletal relapse. The condyles in the preoperative and one year postoperative CBCT scans were rendered accurately in 3D and matched using a voxel based regional superimposition protocol. The condylar volumes were calculated.

Results: A mean mandibular advancement of 5.0 mm and 3.1°, and postoperative relapse of 0.7 mm and 0.5° were found at point-B and SNB angle respectively. The mean postoperative flaring at gonion was 4.3 mm. The mean condylar volume decreased during the follow-up period by 24.5 mm ³ (1.4 vol%). This decrease was significantly correlated to the skeletal relapse ( P < 0.01) but not to flaring ( P = 0.66).

Conclusions: A postoperative decrease in condylar volume appears to be associated with skeletal relapse. Key words: condylar remodeling; BSSO; 3D; CBCT