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Published on: January 28, 2020
Do Patients With Different Mandibular Plane Angles Have Different Time to Relapse After Bilateral Sagittal Osteotomy
Youbai Chen1, Jie Zhang2, Naman Rao3
1Resident, Department of Plastic and Reconstructive Surgery, First Medical Center, Chinese PLA General Hospital, Beijing, China; Fellow, Center for Applied Clinical Investigation, Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, Boston, MA; and MS Candidate in Clinical Investigation, Harvard Medical School, Boston, MA.
Purpose:
This study sought to answer the following question: Do patients with different mandibular plane angles (MPAs) have a different time to relapse after mandibular advancement with bilateral sagittal split osteotomy?
Materials And Methods:
We performed a retrospective cohort study of patients who underwent bilateral sagittal split osteotomy advancement at Massachusetts General Hospital between 2005 and 2017. The primary predictor variable was MPA, categorized as low (<25°), medium (between 25° and 35°), or high (>35°). The outcome variable was time to relapse (≥2-mm posterior change at the B point). Other covariates included gender, age, temporomandibular joint symptoms, bimaxillary surgery, direction of mandibular rotation, 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 < .05 was considered statistically significant.
Results:
The sample was composed of 58 patients (40 female patients), 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 patients (31%). Age, temporomandibular joint symptoms, counterclockwise rotation, and magnitude of advancement were statistically significantly different among the 3 groups. When we assessed time to relapse, the Kaplan-Meier method showed that high-MPA patients had a longer mean time at risk and higher estimated probabilities of relapse at different time points compared with low- and medium-MPA patients (P < .05). However, this association was not significant in Cox and parametric regressions.
Conclusions:
Our results suggest that clinically significant relapse was found during the first postoperative year in low-MPA patients and from 2 to 5 years postoperatively in high-MPA patients. Multivariate regression analyses did not show a significant association between MPA and time to relapse, suggesting that other covariates may play a role in the observed time to relapse.
