Risk Factors for the Development of Lower Border Defects After Bilateral Sagittal Split Osteotomy

PurposeDefects at the lower border of the mandible may persist after bilateral sagittal split osteotomy (BSSO). The purpose of this study was to estimate the frequency of lower border defects after BSSO and to identify factors associated with the development of these defects.Materials and MethodsThis retrospective study included patients who underwent BSSO at St John's Hospital from January 2010 through December 2011. The predictor variables were length of advancement and inclusion of the full thickness of the lower border in the split. The outcome variable was the presence or absence of a lower border defect. Other variables were age and the side of the mouth. All analyses were performed using SAS 9.22.ResultsThe analysis included 400 operation sites in 200 patients (124 female, 76 male; median age, 24.5 yr; range, 14 to 57 yr). A defect at the mandibular border presented in more than one third of operation sites. Inclusion of the full thickness of the lower border in the split, length of advancement, side of the jaw, and age (P < .0001) were risk factors for a permanent defect at the lower border of the osteotomy gap after BSSO.ConclusionsInclusion of the full thickness of the lower mandibular border, the age of the patient, and the magnitude of advancement during BSSO are important predictors of whether a postoperative mandibular defect will remain after surgery. Surgeons should ensure that the lingual cortex of the lower border is not included in the split in large mandibular advancements.