Postoperative changes in mandibular position after mandibular setback surgery via the surgery-first approach in relation to the increase of vertical dimension and the amount of mandibular setback

Objectives. This study aimed to compare preoperatively predicted rotational relapse with actual post-treatment mandibular position after mandibular setback surgery via the surgery-first approach and to evaluate the effect of the increase of vertical dimension (VD) on surgical occlusion and the amount of mandibular setback on postoperative mandibular positional changes. Study Design. Twenty-nine patients who underwent bilateral sagittal split ramus osteotomy for mandibular prognathism were evaluated by using lateral cephalograms, which had been obtained preoperatively, immediately postoperatively, and immediately after debonding. Increase of VD on surgical occlusion was measured preoperatively. We estimated the mandibular forward movement resulting from the postoperative mandibular anticlockwise rotation during postoperative orthodontic treatment and compared it with the actual post-treatment mandibular position. Results. The actual postoperative mandibular forward movement (2.1 mm) was significantly greater compared with the forward movement (1 mm) predicted preoperatively (P <.01). The postoperative mandibular forward movement was greater in the groups with greater VD increase (> 1.5 mm) or greater mandibular setback (> 10 mm), even though there was no statistically significant difference. Conclusions. These results suggest that additional postoperative relapse may occur with mandibular rotational relapse, and VD increase and the amount of mandibular setback may affect post-treatment mandibular position in surgery-first orthodontic treatment.