The location of the inferior alveolar nerve is generally constant in a fully-grown mandible. If we know its average distance from the lower border of the mandible, available bone length from the crest of the edentulous ridge can be estimated by physical measurement of the whole length of the mandible in that area. Purpose: This study aimed to measure the superior-inferior distance of the inferior alveolar nerve (SIDIAN) from the base of the mandible in posterior regions on the right and left sides based on cone beam computed tomography (CBCT) scans and to evaluate gender- and ethnicity-related variations in the Malaysian population. Material and methods: A total of 100 CBCT Digital Imaging and Communications in Medicine (DICOM) files of patients of three ethnic populations (namely Malay, Chinese and Indian) between the age of 18-80 years were selected for the study. The files were imported onto the iCAT software. The SIDIAN measurements to the lower border of the mandible in molar regions were done on both sides. The data were analysed with 't' test, one-way analysis of variance (ANOVA) test, and correlation coefficient test using the software SPSS. Results: Statistically significant positive correlations were identified between the SIDIAN from the lower border of the mandible in the first and second molar regions within same side as well as between both sides of the mandible (r≈.8). There were no statistically significant differences between genders. However, there were statistically significant differences in both molar regions and on both sides in all three ethnic groups (P.05). In general, the SIDIAN from the lower border of the mandible was greatest amongst Chinese and smallest amongst Indians. Conclusions: The strong positive correlations on both sides of the mandible indicate the presence of symmetry. Only ethnicity-related variations were identified. Additional variables may aid in the development of a robust algorithm that can be used to determine the safe zone for implant osteotomy in the posterior mandible. Keywords: Keywords. Dental Implants; Implant osteotomy; Inferior alveolar nerve; Mandibular landmarks; Nerve injury