Do patients with different mandibular plane angles have different time-to-relapse following bilateral sagittal osteotomy with mandibular advancement?

Abstract Purpose To answer the question: Do patients with different mandibular plane angles(MPA) have different time-to-relapse following mandibular advancement with bilateral sagittal split osteotomy(BSSO)? Methods A retrospective cohort study was performed on patients who underwent BSSO advancement at Massachusetts General Hospital between 2005-2017. The primary predictor variable was MPA, categorized as low( 35°). The outcome variable was time-to-relapse(≥ 2 mm posterior change at B-point). Other covariates included gender, age, temporomandibular joint(TMJ) symptoms, bimaxillary surgery, the direction of mandibular rotation, the magnitude of advancement, genioplasty, and fixation method. Time-to-relapse was estimated using the Kaplan-Meier method. Cox and parametric regressions for interval-censored data were performed. P-value was set at .05. Results The sample was composed of 58 patients(40 females) with a mean age of 26.1±4.9 years, grouped as follows: low-MPA(n=15); medium-MPA(n=26); and high-MPA(n=17). Clinically significant relapse was found in 18(31%) patients. Age, TMJ symptoms, counterclockwise rotation and magnitude of advancement were statistically different among the 3 groups. When assessing time-to-relapse, Kaplan-Meier method showed that high-MPA patients had longer mean time at risk and higher estimated probabilities of relapse at different time points compared to low and medium MPA patients(p Conclusion Our results suggest that clinically significant relapse was found during the first postoperative year in low-MPA patients and from 2-5 years postoperatively in high-MPA patients. Multivariate regression analyses did not demonstrate a significant association between MPA and time-to-relapse, suggesting that other covariates may play a role in the observed time-to-relapse.