Anatomical Predictors of Lingual Fracture Sites in Bilateral Sagittal Split Osteotomy: A 3D Morphological Study

Bilateral sagittal split osteotomy (BSSO) is widely used in orthognathic surgery; however, unpredictable lingual fractures can complicate outcomes and surgical planning. This study aims to determine why lingual fractures consistently occur at specific anatomical locations and not at adjacent sites by analyzing the relationship between cortical thickness and cancellous bone content. Preoperative and postoperative cone-beam computed tomography (CBCT) scans of 21 patients (42 hemimandibles) were retrospectively evaluated. Bone morphology was assessed across multiple planes and points to measure buccal cortex, lingual cortex, and cancellous bone thickness at the fracture site and neighboring regions. LSS type 3 fractures were the most common pattern (71.4%). Lingual fractures consistently occurred at sites where the lingual cortex was significantly thinner than the anterior neighbor and where cancellous bone volume decreased. The fracture point was located just anterior to a region where the cortical bone content increased markedly, particularly on the lingual side, especially in the ramus and mandibular angle. Lingual fractures during BSSO occur at transition zones of increased cortical resistance and reduced cancellous content. These anatomical characteristics can guide surgeons in anticipating fracture behavior and improving osteotomy planning.