The Impact of Mandibular Anatomy on the Incidence of Bad Splits in Sagittal Split Ramus Osteotomy: A Retrospective Study

Background The objective of this study was to conduct three-dimensional cone beam computed tomography (CBCT) analysis of posterior mandibular anatomy in order to investigate its potential correlation with the occurrence of bad splits during sagittal split ramus osteotomy (SSO). Materials and Methods A retrospective review was conducted on 56 patients (112 hemimandibles) who underwent bilateral SSO between 2016 and 2022. Distances between the mandibular canal and the borders of the mandible, along with anatomical landmarks, were measured. Sites with and without bad splits were compared using chi-square and Mann–Whitney U tests (p = 0.05). Intra- and inter-observer reliability were assessed via intraclass correlation coefficients. Results The overall incidence of bad split was 8.9% per site (10/112) and 14.3% per patient (8/56). Patient-related variables, including age, sex, skeletal deformity type (Class II vs. Class III), and the presence of impacted third molars, were not significantly associated with bad split (all P > 0.05). Among the morphometric parameters, the distance from the mandibular canal to the inferior cortical border at the mesial of the second molar (M2-inferior) was significantly greater in the bad-split group (P = 0.045). Other measurements, including ramal thickness, anteroposterior length, and canal position relative to buccal and inferior cortices, were not significantly different. Reliability analysis demonstrated good to excellent agreement for all the measurements. Conclusions A greater inferior mandibular border thickness at the mesial of the second molar appears to increase the risk of bad split during SSO. Routine preoperative CBCT evaluation and careful attention to inferior border osteotomy in this region may help reduce complications. Further prospective, standardized studies are needed to confirm these findings.