Making a mandibular CAD model was difficult because of the limit of computer performance. But recently the progress of computer performance is remarkable. In this study, entire mandibular CAD model was made using two softwares. First, the mandibular STL (Standard Triangulated Language) model was made using the three-dimensional image analysis software. It was extracted from CT image. Second, Mandibular CAD model was made using reverse engineering software. The dental implant model was made on the basis of products made in Japan. It was placed in first premolar and second premolar. The vertical load (100N) was applied on the dental implant and the stress distribution was calculated using FEM. The heterogeneity stress was generated in the surface of the cortical bone around the body of the implant. Uneven surfaces were made in process of making mandibular STL model. The stress distribution was affected by the place of dental implants and the surface forms of the cortical bone.