This study investigated biomechanical aspects of the action of the biting force during mastication upon the mandibular bone in the lower first molar area. A three-dimensional (3D) finite element model (FEM) consisting of the tooth, periodontal ligament (PDL), alveolar bone, and cortical bone corresponding to the lower first molar area based on computed tomogram (CT) images was constructed. The model was then analyzed while applying a biting force during mastication, which was transmitted from the tooth to the cortical bone, through the PDL and cancellous bone. A compressive stress of 0.3-7.9 MPa acted on the cortical bone during mastication. In the model, the stress in the cortical bone was distributed from the linguo-superior margin to the basal area, and was also observed in the bucco-medial area. These areas completely agreed with the areas that were significantly thicker in the morphological study described by Masumoto et al. (10). It is suggested that there may be a relationship between masticatory force and cortical bone hypertrophy. Further study of the effects of various factors is required.