Background/Purpose: The purpose of this study was to determine the position of the mandibular canal in relation to the buccal cortical bone in Chinese patients with three dentofacial relationships: normal dentition, retrognathism, and prognathism. Methods: Cone-beam computed tomography and lateral cephalograms of patients with normal dentation, retrognathism, and prognathism (n = 32 each group) were reviewed. Measurements of the shortest distance from the outer/buccal edge of the mandibular canal to the inner surface of the buccal cortex, and the distance from the lingula of the ramus to the dorsal root of the first molar were recorded. Results: No significant difference was observed between the three groups in the distribution of contact or fusion of the mandibular canal, or in the course of the mandibular canal on the right or left side. When the shortest distance at the lingula on the left side was >2.1 mm, no instances of contact or fusion were observed. On the right side, 100% of the patients had no contact or fusion when the shortest distance was >2.7 mm at the lingula. Conclusion: The shortest distance from the outer/buccal edge of the mandibular canal to the inner surface of the buccal cortex measured at the lingula can predict contact or fusion. During sagittal split ramus osteotomy, great care should be observed at the point halfway between the lingula and the anterior ramus border where the inferior alveolar nerve is the closest to the cortical bone.
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