Three-Dimensional Soft Tissue Assessment Following Mandibular Bilateral Sagittal Split Osteotomy.

Purpose: The purpose of the study is to quantify anteroposterior and transverse facial soft tissue changes with respect to underlying skeletal movements after bilateral sagittal split osteotomy by using cone beam computed tomography (CBCT).

Patients And Methods: The study was conducted on 6 patients who required bilateral sagittal split osteotomy for correction of mandibular retrognathism. The patients were scanned using CBCT 1 week preoperatively, and 6 months postoperatively. The differences between pre- and postoperative images were measured and the ratios of different hard to soft tissue movements were calculated.

Results: There was a statistically significant difference in the mean measurements postoperatively. The ratio of the mean hard to soft tissue movement after mandibular advancement was 1:0.97 in the chin region and 1:0.80 in the lower lip area. The mean decrease in the mentolabial fold (MLF) depth was 1.4  mm and the mean increase in the mentolabial angle (MLA) was (27.7).

Conclusions: The soft tissue changes related to mandibular advancement would appear to be fairly predictable and follow their underlying skeletal structures in 1:0.97 ratio in the chin area. Also, increase in facial convexity has an important influence on changes in the position of the lower lip as well as on changes in MLF depth and MLA.