Factors contributing to relapse in rigidly fixed mandibular setbacks.

The incidence of, and factors accounting for, relapse in 25 subjects who underwent mandibular setbacks via a bilateral sagittal split osteotomy with rigid fixation were studied. Fourteen had single-jaw operations, and the remaining 11 had concomitant maxillary procedures. Cephalometric radiographs were reviewed preoperatively, immediately postoperatively, and 6 months to 3 years after surgery. Relapse was defined as forward movement of pogonion during the postoperative period. No difference in the movement of the mandible in one- or two-jaw cases was noted. Even with excellent occlusal results, there was a tendency for the mandible (chin point) to rotate forward. In the one-jaw cases 43.7% relapse was noted, whereas 53.4% was seen in the two-jaw cases. A regression analysis showed that the magnitude of setback was the single factor that significantly predicted relapse in one-jaw cases, whereas alteration of the proximal segment accounted for relapse in two-jaw procedures. These results seem interrelated when considering alterations in the spatial arrangement of the muscular tissues and their attachments.