Orthognathic Surgery for Correction of Patients With Mandibular Excess: Don’t Forget to Assess the Gonial Angle

Abstract

To evaluate the gonial angle (GA) and associated factors that can contribute to stability after bilateral sagittal split ramus osteotomy setback and Le Fort I advancement osteotomy for the treatment of patients with mandibular excess. This retrospective study included 42 randomly selected, adult patients. Lateral cephalometric radiographs were obtained before and 1 week and 1 year after surgery. Patients in group 1 (n= 18) had a GA smaller than 125° and those in group 2 (n= 24) had a GA larger than 125°. Data were analyzed by analysis of variance and Pearson correlations. Multivariate linear regression analysis was used to identify factors that influenced postsurgical stability. Mean surgical changes were similar in the 2 groups. The mandible was set back an average of 5.4mm in group 1 and 6.4 mm in group 2, whereas the maxilla was advanced 2.5 mm in group 1 and 1.7mm in group 2. Statistically significant postoperative changes were noted for group 1 only. Relapse was found at the innermost point of the contour of the mandible between the incisor tooth and bony chin and the pogonion for the horizontal landmarks; the innermost point of the contour of the maxilla between the anterior nasal spine and incisor tooth and the menton for the vertical landmarks; and the GA, the angle between the sella-nasion line and the innermost point of the contour of the mandible between the incisor tooth and bony chin, and the esthetic plane to the upper lip for the dimensional landmarks. No statistically significant changes were noted for group 2 (GA >125°). Patients with a preoperative GA smaller than 125° have a greater risk of relapse after receiving bilateral sagittal split ramus osteotomy setback and Le Fort I advancement for the treatment of mandibular excess. Patients with a preoperative GA larger than 125° appear to have a more predictable procedure.