Skeletal change at surgery as a predictor of long-term soft tissue profile change after mandibular advancement

This study examined the time course of hard and soft tissue changes after mandibular advancement surgery and the association between skeletal changes as a result of surgery and subsequent soft tissue changes.

Subjects were enrolled in a randomized clinical trial of rigid versus wire fixation after sagittal split ramus osteotomy, with cephalometric data obtained before orthodontics, immediately before surgery and at 8 weeks, 6 months, 1 year, and 2 years postsurgery. This early report describes changes in 20 Caucasian female subjects who had completed all phases of the study; these were not segregated by fixation method. Cephalometric changes were referenced to a cranial base coordinate system. Differences in soft and hard tissue changes among time intervals were examined using analysis of variance; the associations between immediate surgical change in chin landmarks and subsequent short- and long-term soft and hard tissue changes were examined using linear regression analysis.

Soft and hard tissue mandibular structures were positioned anteriorly and inferiorly during surgery; the horizontal and vertical hard tissue mandibular changes were stable for 2 years after surgery (P > .30), as were the vertical soft tissue changes (P > .08). There was horizontal relapse of the lower lip and the inferior sulcus (P < .03) by 8 weeks; no horizontal relapse was detected in soft tissue chin points for up to 2 years after surgery. The time course of changes in osseous pogonion was more strongly predicted by the amount of surgical osseous chin change than were changes in soft tissue chin projection.

Prediction of changes in soft tissue chin projection after mandibular advancement surgery is less certain as time from surgery increases and less certain than the prediction of changes in bony chin projection.