Evaluation of traditional total prosthesis, implant supported overdenture and "all-on-four" system applied to atrophic mandible wi̇th bilateral temporomandibular joint prosthesis using finite element analysis method

Aim: The aim of our study is to evaluate the effects of conventional total prostheses and implant-supported prosthetic restorations on the surrounding bone tissue, the joint prosthesis, and its components under chewing forces in patients who have undergone alloplastic total joint replacement for temporomandibular joint dysfunction and have atrophic mandibles. This evaluation will be conducted using finite element analysis. Material and Method: In this study, a three-dimensional (3D) model of a total temporomandibular joint (TMJ) prosthesis was created in a digital environment using a standard total TMJ prosthesis. This model was integrated into a 3D edentulous atrophic mandible model, which was reconstructed from CT scans of patients using computer-aided design, in a manner simulating an actual TMJ replacement. Three different models were generated by applying a conventional complete denture, a two-implant-supported overdenture, and an All-on-Four implant-supported prosthetic system to the TMJ prosthesis-integrated atrophic mandible model. Based on values used in previous studies, a total of 450 N of vertical chewing force was applied—150 N to the right and left first molars posteriorly and to the incisors anteriorly. Additionally, a total of 300 N of oblique chewing force was applied—100 N to the right and left first molars posteriorly and to the incisors anteriorly. The loads transmitted to the TMJ prosthesis and surrounding bone tissue as a result of these chewing forces were calculated using the finite element analysis method. Result: Under vertically applied 450 N masticatory forces, the maximum principal stress values in the cortical bone around the titanium screws of the ramus component were measured as 317 MPa in Model 1, 308 MPa in Model 2, and 252 MPa in Model 3. Regarding Von Mises stress values in the ramus component, the lowest stress was observed in Model 3 (849.9 MPa), while Models 1 and 2 showed higher values of 888.8 MPa and 888.6 MPa, respectively. The fossa component exhibited the highest Von Mises stress in Model 3 (101.6 MPa), whereas Models 1 and 2 showed equal values of 98.8 MPa. For the screws in the ramus component, the highest Von Mises stress was recorded on the uppermost (1st) screw in Model 3 at 288.1 MPa, compared to 280.9 MPa in Model 1 and 283.6 MPa in Model 2. In the fossa component screws, the highest stress value was observed on the 2nd screw in Model 1 (116.8 MPa), while Models 2 and 3 had similar values of 110.2 MPa and 110.5 MPa, respectively. Under oblique 300 N masticatory forces, the maximum principal stress in the cortical bone around the ramus screws was 186 MPa in Model 1, 180.7 MPa in Model 2, and 150.5 MPa in Model 3. The lowest Von Mises stress in the ramus component was recorded in Model 3 (802.7 MPa), whereas Models 1 and 2 showed values of 846.1 MPa and 845.7 MPa, respectively. The Von Mises stress values in the fossa component were relatively similar across all models: 54.9 MPa in Model 1, 52.1 MPa in Model 2, and 52.3 MPa in Model 3. For the ramus component screws, the highest stress in Model 3 was found on the uppermost screw (234.8 MPa), followed by 227.8 MPa in Model 1 and 229.5 MPa in Model 2. For the fossa component screws, the highest stress was observed on the 3rd screw in Model 1 (54.9 MPa), with Models 2 and 3 showing similar stress values of 52.1 MPa and 52.3 MPa, respectively. Conclusion: Our study demonstrates the potential of finite element analysis to provide guidance for clinical applications, but it should be kept in mind that simulations need to be supported by clinical trials. The findings provide insights for significant improvements in the design of temporomandibular joint prostheses and implant systems. In particular, the all-on-four system has been shown to have the potential to provide a more stable and long-lasting treatment in atrophic mandible cases with temporomandibular joint prostheses. Future studies will examine the effects of different chewing forces, compare different materials and implant systems, and integrate biomechanical tests with clinical observations in more detail, thereby increasing the knowledge in this field. This will lead to more successful outcomes in prosthesis design and improve the quality of life for patients.