The aim of the present work is to investigate the effects of cementum-dentine junction (CDJ) and cementum on the stress distribution in the periodontal ligament (PDL) and alveolar bone.Based on the anatomical profiles and the recently reported theories about the tooth attachment mechanism, the finite element (FE) model of a mandibular second premolar along with its detailed supporting structures was developed. The effect of CDJ and cementum was evaluated by comparing the resulting stresses of FE models of the second mandibular premolar with and without CDJ and cementum in tooth supporting structure.The stress levels are higher in the structure without CDJ and cementum than that with CDJ and cementum. The function of CDJ and cementum is as a cushion pad decreasing the stress in the PDL and alveolar bone under loading.As a major result of this study, it can be concluded that the CDJ and cementum significantly influence the stress distribution within the tooth supporting structure. However, most of the reported FE analysis did not take CDJ and cementum into account, which possibly resulted in overestimated stress values in the PDL and alveolar bone. From a bio-engineering perspective, the results of this study provide guidance for the design of dental implants and the application of orthodontic force system as well.