Investigation of the effects of different implant planning and different prosthesis designs on stress distribution in rehabilitation of atrophic posterior maxilla by finite element analysis

Purpose: The aim of this study is to evaluate the significance of the difference between the models by examining the effects of retention type (cemented / screwed) and splinting on implant structures and bone stresses in implant placements of different designs in the atrophic posterior maxillary region (in cases where sinus elevation cannot be performed) by using the three-dimensional finite element stress analysis method. Materials and Methods: Using computer-aided design software, 10 study models consisting of three-unit implant-supported restorations in atrophic posterior maxilla were designed. The implant model selected on the 3D model was integrated and stress analysis was performed by applying 100 N static oblique occlusal forces to the palatinal tubercles of each crown. Von Misses stress, tensile stress and compressive stress values were analyzed by modeling fixed prosthetic designs with two implants supporting prosthesis with distal cantilever, two implants supporting prosthesis with mesial cantilever, 2 or 3 implant supported conventional splinted prosthesis and three implants supporting non splinted crowns with a screwed prosthesis and cemented prosthesis. Results: The highest von Misses stress values were determined in the cervical region of the implants. Regardless of the retention type, the highest Von Misses stress values were seen in implants adjacent to the cantilever extension, and more stress values were found in implants adjacent to the distal cantilever extension than those with mesial cantilever extension. Implants in models with three implants generally showed lower von Misses stress values than other models. Lower von Misses stress values were observed in implants with splinted models compared to non-splinted ones. In the cement-retained models, slightly lower tensile stress values were found in the cortical bone in the cervical circumference of the implants compared to the screw-retained models. While standard implants with splinted models have lower tensile and compression stress values in cortical bone compared to non-splinted ones, tensile and compression stress values in short molar implants increased slightly in splinted models. Lower Von Misses stress values were found in implants in screw-retained models compared to cement-retained model. Conclusion: Significantly lower values of tensile stress were noted in cortical bone with shorter implant placement configurations compared with the cantilever prosthesis. As the number of implants increases, von Misses stresses generally decrease. Implants in screw-retained models showed lower Von Misses stress values than implants in cement-retained models. Cemented systems generally showed slightly lower stress values in periimplant tissues. Splinted prostheses exhibited better stress distribution for the implants. Lower tensile and compression stress values were measured in cortical and trabecular bone in the cervical circumference region of the standard implants in models with splints compared to those without splinting. Splinting resulted a slight increase in the stress and compression stress values in the cortical bone around the short implants.