Population-Based 3D Mapping of Inferior Alveolar Nerve Clearance in Bilateral Sagittal Split Osteotomy

Background/Objectives: Inferior alveolar nerve injury is a common complication of Bilateral Sagittal Split Osteotomy. Preoperative three-dimensional tracing of the mandibular nerve canal using Cone-beam CT may help reduce this risk. We reconstructed the nerve course in 428 consecutively planned BSSO cases and developed a statistical model that quantifies population-level canal position to guide safe, evidence-based osteotomy planning. Methods: Traceable mandibular nerve canal CBCTs from 440 BSSO candidates (2023-2025) were retained. The mandibles and 2.5 mm diameter canals were segmented in Mimics and fused with intraoral scans. Next, the meshes were aligned non-rigidly to a template. A k-nearest-neighbour analysis mapped the outer mandibular surface to canal distances of all the patients on the template mandible model. Results: After excluding 12 scans because the nerve could not be traced, 428 mandibles were studied. The canal's position varied, with regions near the vertical ramus and premolar regions frequently showing fewer than 3 mm of buccal bone covering the mandibular nerve. In contrast, a preferred safe zone was identified in the second molar region, where more than 97.8% of patients had greater than 5 mm of buccal bone clearance. A population-based colour map was generated to visualise the risk areas and confidence intervals for outer cortex-to-canal distances. Conclusions: This study provides the first high-resolution, population-based 3D map of nerve clearance in BSSO patients. Routine use of CBCT with patient-specific nerve tracing is recommended to reduce the risk of nerve injury.