The evaluation of the stress distribution on implant-natural tooth supported overdenture prostheses by finite elemet stress analysis

The rigidity of the connection of the implants with the alveolar bone and the flexibility of the natural teeth due to the periodontal membrane may cause biomechanical problems in implant-natural tooth supported overdenture prostheses. The aim of this study was to determine the stresses caused by the forces acting on the prosthesis on the cortical and cancellous bone in natural teeth and implant supported overdenture prostheses, in which different numbers of implants were used by finite element stress analysis method. In this study, 9 different overdenture prostheses were designed by placing natural teeth and implants in 9 different combinations on the 3D mandibular model created in the computer environment. A load of 150 N was carried out on the overdenture prosthesis in 3 different ways by distributing it to the posterior teeth in the vertical direction. The first loading was applied to the right side of the lower jaw, the second loading was performed to the left side of the lower jaw and the third loading was enforced to both sides of the lower jaw. As a result of these loadings, Von Mises stresses were investigated on cortical and cancellous bone around natural teeth and implants. The highest stresses which observed in the cortical bone around the natural tooth or implant in all loads were determined in consequence of the study. The design with one natural tooth and one dental implant with a bar (Model 3) produced higher stress values on the cortical bone at all loadings than all other models (except Model 1). The stress rates in the models with ball atachment holders were detected to be lower than the stress amounts in the models with bar holders when they copmpared to each other with the models with bar holder and ball atachment holder in the cortical bone with the same support number. While the increase in the number of implants in bar-retained designs reduces the stresses on the cortical bone, this procedure did not provide the same benefit in all loadings in ball-head-retained designs. According to the results obtained from this study; in the meanwhile placing at least one dental implant on the opposite side of the jaw in the presence of a single tooth in the mandible ensures significant biomechanical benefits, designs with ball-head attachments that cause less stress on the cortical bone than designs with bar retainers may be more biomechanically advantageous.