Evaluation of stress distributions of subperiosteal implants of different designs and materials in atrophic mandible by finite element analysis

Objective: Today, with the prolongation of human life span, there is a significant increase in the number of completely edentulous individuals. This situation brings both functional and aesthetic problems. In addition, when other factors related to the prolonged period of edentulism and the general health status of the person are combined, advanced alveolar bone loss (resorption) may occur. As a result, it is often not possible to perform fixed prosthesis treatment without surgical intervention with conventional methods. Patients who require fixed prostheses or who cannot tolerate removable prostheses therefore undergo various surgical procedures. However, such surgeries also carry a serious risk of complications. This situation has led researchers to develop alternative methods. Thanks to modern technology, personalised subperiosteal implants and fixed prosthetic superstructures can be produced by using computerised tomography instead of advanced surgical procedures. The aim of this study is to evaluate the stresses on the implant, metal substructure, screws and bone caused by the use or non-use of screws in the lingual while fixing subperiosteal implants produced in different designs to the jawbone by SESA method. Material and Method: In this thesis, subperiosteal implants of 3 different designs and different materials were placed in the atrophic mandible models. While fixing the implants, we used screws on the lingual in the first model with lingual extension, we did not use screws on the lingual in the second model with lingual extension, and there was no lingual extension in the third model. Vertical and oblique forces were applied to all models. The results were evaluated by finite element analysis. Results: Considering all principle values, the highest stress was found in the model 3 design without lingual extension in all values except the trabecular max principle value against vertical and oblique forces. The lowest values were found in model 1, which is the standard design with lingual extension and fixed with screws from the lingual. Trabecular max principle value was highest in model 2(Grade 4:0.942, Grade 5:0.941) and lowest in model 3(Grade 4:0.818, Grade 5:0.813) under vertical force, and highest in model 1(Grade 4:0.885, Grade 5:0.883) and lowest in model 3(Grade 4:0.842, Grade 5:0.838) under oblique force. When the von Mises stress values were analysed, the highest values were seen in model 1 and the lowest values were seen in model 3 for subperiosteal implants and metal substructures under vertical and oblique forces. When the values found in the screws were analysed, the highest values were seen in model 3. However, all values were very close to each other. Conclusion: When all the results were evaluated, the values were found to be very close to each other in all models with lingual extension and lingual fixation, with lingual extension but not lingual fixation and without lingual extension, which were designed from different materials under different forces. Based on the results of this study, we concluded that fixation of subperiosteal implants for the treatment of atrophic mandible may not need to be fixed with screws from the lingual side. Thus, complications that may occur due to flap removal in the lingual region are avoided and the operation time is shortened.