What are the Effects of Age and Presence of Third Molars on the Occurrence of Unfavorable Splits during Sagittal Split Osteotomy

Abstract Purpose Several studies have investigated risk factors of unfavorable splits associated with sagittal split osteotomies but yielded conflicting information. The purpose of this study is to estimate the frequency of and identify factors associated with unfavorable splits during sagittal split osteotomies (SSOs). Material and Methods A retrospective cohort study was conducted on patients who underwent orthognathic surgery including SSOs at our institution from January 2010 to October 2016. The independent variables were mandibular third molar (M3) status, age, gender and preoperative dentofacial diagnosis. The outcome variable was the effectiveness of the sagittal split resulting in either favorable or unfavorable split. Data analyses were performed using logistic regression models except in the case of small sample sizes of preoperative dentofacial diagnoses for which the Fisher’s exact test was used. Results A total of 888 patients with an average age of 24.97 ± 5.09 years underwent 1776 SSOs. Sixteen (0.90%) unilateral unfavorable splits occurred. Unfavorable splits were less common in patients with an M3 present than in patients with the M3 absent. Having an M3 present reduced the chance of an unfavorable split by 69%, adjusted for age and gender; OR (95% CI) = 0.308 (0.103, 0.919); p = 0.035. The odds of having an unfavorable split were increased by 8.8% for every year of age increase; adjusted OR (95% CI) =1.088 (1.004, 1.178); p = 0.038. Based on this estimation, a 45-year-old is 2.3 times more likely to have an unfavorable split compared to a 35-year-old (95% CI:1.041, 5.146), and is 5.4 times more likely to have an unfavorable split compared to a 25-year-old (95% CI:1.083, 26.48). Conclusion The presence of a mandibular third molar (M3) was associated with a decreased risk of unfavorable split, independent of age and gender. There was a significant association between increased age and the i ncidence of unfavorable split.