Background: In the literature the incidence of permanent nerve lesions ranges from 3 to 39%. Therefore, we think that it is necessary to discuss the procedure of individual risk assessment and management. Standard imaging techniques for the preoperative planning and preparation of a sagittal split osteotomy usually include a panoramic radiograph and lateral cephalometric radiograph. If an assessment of the transversal thickness of the lower jaw and cortical substance is required, or the position of the inferior alveolar nerve needs to be determined for preoperative planning, computed tomography of the viscerocranium has to be performed. By employing the conventional computed tomographic X-ray imaging system CommCAT, we are able to determine preoperatively both the transversal thickness of the lower jaw including the cortical substance and the diameter of the ascending ramus of the mandible at the proximal osteotomy site.
Patients and method: We examined prospectively the value of these additional investigations and compared them with the intraoperative findings in 29 patients. With these tomograms, the relation between the position of the inferior alveolar nerve and the vestibular cortical bone was metrically evaluated. In 17 of 58 jaw sides we detected the nerve at a distance from the outer cortical bone of 2 mm or less. The situation for the upper osteotomy was critical in eight cases where the thickness of the mandibular ramus was only 3 mm.
Results: By using of the conventional computed tomography system CommCAT, we have the preoperative opportunity to determine the transversal thickness of the mandibular ramus as well as the exact position of the inferior alveolar nerve and its distance from the cortical bone of the mandibular corpus. By predicting the nerve's position and its relation to the osteotomy site, we are able to individualize the operation procedure so that a high standard of safety can be achieved.