Relationship of the mandibular canal to the lateral cortex of the mandibular ramus as a factor in the development of neurosensory disturbance after bilateral sagittal split osteotomy

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Purpose: This study evaluated the location of the mandibular canal in the ramus of the mandible before bilateral sagittal split ramus osteotomy and examined its relationship with postoperative neurosensory disturbance. Patients and Methods: The subjects consisted of 20 patients undergoing bilateral sagittal split ramus osteotomy. Before surgery, the region from a plane containing the lowest point of the mandibular foramen to 22 mm below it was observed on transaxial computed tomograms acquired with a slice thickness of 2 mm and a slice interval of 2 mm. The relationship between the distance from the mandibular canal to the external cortical bone and neurosensory disturbance in the lower lip or mentum more than 1 year after surgery was evaluated. Results: The mandibular canal came into contact with the external cortical bone on 10 sides (25%); neurosensory disturbance occurred on all these sides, an incidence significantly greater than that (20%) on the 30 sides (75%) without contact between the canal and the external cortical bone (P <.05). In patients with mandibular canal/external cortical bone contact, the vertical extent of contact ranged from 2 to 18 mm (mean, 10.6 ± 4.9 mm). Neurosensory disturbance was significantly more likely to be present 1 year after surgery, when the width of the marrow space between the mandibular canal and the external cortical bone was 0.8 mm or less (P <.002). Conclusions: The increased risk of neurosensory disturbance associated when there is contact between the mandibular canal and the external cortical bone should be considered when sagittal split ramus osteotomy is performed. © 2002 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 60:490-495, 2002