Evaluation of the mandibular split patterns in sagittal split ramus osteotomy.

Purpose: To evaluate the split patterns of the mandibular ramus in sagittal split ramus osteotomy (SSRO) using cone-beam computed tomography (CBCT) and examine the related anatomic features that may be associated with these split patterns.

Patients And Methods: The authors designed and implemented a retrospective cohort study and enrolled a sample composed of consecutive patients with different maxillofacial deformities who underwent an SSRO from July 2011 through October 2012 at the Department of Orthognathic Surgery at the Tianjin Stomatological Hospital of Nankai University. The split patterns, which were selected at random at 1 side per patient, were evaluated by CBCT as the outcome variable 1 month after the operation. The predictor variable was composed of a set of heterogeneous anatomic variables that could be associated with the split patterns. Type I split was defined as a split at the lingual side near the mylohyoid sulcus. Type II split was defined as a split at the posterior border of the mandibular ramus. Appropriate bivariate and regression statistics were computed, and the level of statistical significance was set at a P value less than .05.

Results: One hundred thirty patients with different maxillofacial deformities (62 male and 68 female; mean age, 23 yr) underwent an SSRO. Two types of split patterns of the mandibular ramus were observed in SSRO: a split at the lingual side near the mylohyoid sulcus, which occurred in 75.38% of patients, and split at the posterior border region of the mandibular ramus, which occurred in 24.62% of patients. No fracture lines were observed through the mandibular canal. The thickness of the lingual cortical bone between the mandibular canal and the posterior border of the ramus was significantly associated with the split patterns (P < .05). The thickness of the cortical bone in the posterior border of the ramus, the degree of the mandibular angle, and the shapes of the mandibular ramus in the axial plane also were found to influence these split patterns. There was no meaningful association between the split patterns and a patient's age and gender.

Conclusion: The split patterns of the mandibular ramus during SSRO were influenced by some anatomic features of the mandibular ramus. Therefore, examining the anatomy of the mandible with CBCT before surgery may play an important role in predicting the split patterns of the mandibular ramus during SSRO.