This study was undertaken to quantify the path of the inferior alveolar nerve in the normal human mandible and in the mandibles of patients presenting for cosmetic reduction of the mandibular angles. The goals were: (1) to provide normative information that would assist the surgeon in avoiding injury to the nerve during surgery; (2) to characterize gender differences in the normal population; and (3) to compare the course of the nerve in the normal population to its course in a group of patients who presented with a complaint of “square face.”
The study was based upon the computerized tomographic scans of 10 normal patients (six men, four women) and 8 patients (all women) complaining of “square face.” Using AnalyzePC 2.5 imaging software, the mandibles were segmented and the position of the nerve was recorded within its osseous canal in the mandibular ramus on each axial slice in which it was identifiable. Distances were calculated between the nerve and the anterior, posterior, lateral, and medial cortices. The positions of the lateral ramus prominence and the lowest point on the sigmoid notch were also recorded. The position of the mental foramen was recorded in relation to the nearest tooth, and the three-dimensional surface distances from the foramen to the alveolar bone, the inferior border of the mandible, and the mandibular symphysis were determined. The distances from the entrance of the nerve into the mandible to the lateral ramus prominence and the lowest point on the sigmoid notch were calculated. Summary statistics were obtained, comparing differences in gender.
The nerve was identifiable in each ramus over a mean distance of 12.7 mm. On average, the lateral ramus prominence was 0.3 mm higher on the caudad-cephalad axis than the point at which the nerve entered the bone, whereas the location of the lowest point on the sigmoid notch was 16.6 mm above the nerve. The average distances from the nerve to the anterior, posterior, medial, and lateral cortices were 11.6, 12.1, 1.8, and 4.7 mm, respectively. Gender differences were significant for all of these except the medial cortex to nerve distance. On average, the mental foramen exited the body of the mandible immediately below the second premolar and the average surface distances from the foramen to the symphysis, the most cephalad alveolar bone, and the inferior border of the body were 30.9, 14.2, and 19.3 mm, respectively. With regard to the patients presenting for mandibular angle reduction, there were a few statistically significant but small scalar differences from normal controls.
From the Department of Plastic and Reconstructive Surgery and the Department of Health Care Management, Chang Gung Memorial Hospital.
Received for publication May 7, 1999;
revised January 6, 2000.
Lun-Jou Lo, M.D. Department of Plastic and Reconstructive Surgery Chang Gung Memorial Hospital 199 Tun Hwa North Road Taipei, Taiwan 105 email@example.com