Analysis of Mandibular Incisive Canals with Critical Clinical and Anatomic Landmarks in a Chinese Population: A...

Despite being deemed a surgical safe zone for various surgical procedures, the anterior mandible carries significant risk of neurovascular injury to the mandibular incisive canal (MIC). The variable intraosseous path of MIC makes preoperative assessment challenging. Current safety guidelines, based on bone landmarks alone, are insufficient to prevent nerve damage. This study defines the three-dimensional (3D) trajectory of the MIC using cone beam computed tomography (CBCT), correlating it with critical landmarks such as the cementoenamel junction (CEJ), root apices (RA), cortical plates, mandibular margin, and median lingual canal (MLC). We aim to provide a quantitative framework that specifically alerts clinicians to neurovascular injury risks that persist even when general guidelines are followed.

264 human mandibles were evaluated using CBCT to measure the distances of MIC to CEJ, RA of adjacent teeth, labial cortex plate (LaC), lingual cortex plate (LC), and the inferior margin of mandible (IM), and MLC by CBCT in a Chinese population. The effect of age, gender, and sides was analyzed.

MIC was visible up to the central and lateral incisors in 57.0% and 39.4% of cases, respectively. Vertically, 91.6% of the MIC-CEJ distance is 16 mm or more while 83.9% and 9.4% of MIC located within 10 mm distance to root apices and inferior margin of mandible, respectively. From the incisors to canines, the MIC run gradually closer to RA, IM, LaC, and LC. Horizontally, MIC runs slightly buccal, with 27.3% located <3 mm from the labial cortical plate. Males exhibited greater distances than females across all measurements. Distances from MIC to CEJ, RA, and IM increased with age. In the mandibular symphysis, 31.1% MIC coexists with MLC, of which 95.5% were ≥ 1 mm.

A safety depth of 16 mm below the CEJ of adjacent teeth may avoid 91.6% neurovascular injuries in implant placements. The facts that 83.9% and 9.4% of MIC located within 10 mm to root apices and the inferior margin of mandible, and 27.3% of MIC located less than 3 mm deep to the labial cortical plate in the anterior mandible, pose neurovascular injury risk in chin bone harvesting. The 95.5% of MLC with a diameter of more than 1 mm alert us to limit lingual flap elevation to avoid injuring vessels in the MLC and prevent postoperative bleeding. To avoid nerve injury and postoperative hematoma, a meticulous evaluation of the course of MIC is recommended rather than relying on a fixed marginal safety value.