Change in condylar position in posterior bending osteotomy minimizing condylar torque in BSSRO for facial asymmetry.

During the correction of an asymmetric mandible with sagittal split ramus osteotomy (SSRO), bony interference between the proximal and distal segments inevitably occurs. This results in positional change of the condyle. In order to avoid this, a posterior bending osteotomy (PBO) has been introduced. This is an additional vertical osteotomy posterior to the second molar after SSRO. To investigate the change in condylar position after SSRO with PBO, 22 patients with facial asymmetry were enrolled and divided into two groups based on the surgical method used to remove the bony interference after SSRO: PBO (n = 13) and the grinding method (n = 9). Each group was subdivided into large and small bony interference groups by estimating the volume of bony interference with simulation surgery. Condylar displacement was evaluated by three-dimensional superimposition and the amount of condylar displacement was calculated. The positional changes of the condyles were variable in each patient. When comparing patients with large bony interference in the PBO and grinding groups, the condyles were significantly inwardly rotated in the grinding group (p < 0.05). The grinding method can be used to remove small bony interferences with tolerable condylar torque. However, PBO would be beneficial in correcting large bony interferences while minimizing condylar torque.