Linear and rotational changes in large mandibular advancements using three or four fixation screws.

Forty-one patients who underwent bilateral sagittal ramus osteotomy for large mandibular advancements were evaluated by retrospective cephalometric analysis for rotational and linear stability of the proximal and distal segments of the mandible. The patients were grouped by the number of screws used in fixation (three versus four 2-mm bicortical screws) and matched for the amount of advancement measured from changes in mandibular body length. The group with four fixation screws did receive significantly larger advancements relative to the cranial base than did the group with three screws. However, the pattern of postoperative change was similar for the two groups. There was no higher rate of relapse seen in those patients with high mandibular plane angles, genioplasties, mandibular constriction with a symphyseal osteotomy, or open bites preoperatively, nor did the number of screws used in fixation affect changes seen in those patients. Factors associated with both relapse and continued postoperative movement in the direction of advancement independent of the screw fixation group were identified.