The purpose of this study was to evaluate the relationships between different facial types, and both the buccolingual molar inclination and cortical bone thickness of the mandible. The material consisted of 31 dry skulls of modern Japanese males from the Museum of the University of Tokyo. They all demonstrated normal occlusion with minimal dental discrepancy, and without crossbite or facial asymmetry. The buccolingual inclination of the second molar (M2) in the long-faced subjects was significantly smaller than the same dimension in the average- and short-faced subjects. It was found that the teeth of long-faced subjects were more lingually inclined than those of the short-faced subjects. The cortical bone thickness of the first molar (M1) and M2 sections was thicker in short-faced subjects than in average- and long-faced subjects. The results of this study provide evidence that a significant, but complex relationship exists between structures of the mandibular body and facial types. The morphological features that relate to masticatory function and facial types are associated with the cortical bone thickness of the mandibular body, and the buccolingual inclination of the first and second molars.