Evaluation of implant-supported overdenture prostheses with different attachment types and substructures, and the stresses created in prosthetic structures, implants, and surrounding tissues by finite element analysis in the case of completely edentulous mandible

Aim: This study aims to investigate the effects of variations in implant number, attachment type, and substructure material on the stress distribution in cortical and trabecular bone, as well as in implant and prosthetic components, in mandibular overdenture prostheses for completely edentulous cases, using the Finite Element Stress Analysis (FESA) method. Materials and Methods: In this study, Straumann implants with a diameter of 4.1 mm and a length of 12 mm were placed in two different configurations in the completely edentulous mandible. In the two-implant models, the implants were axially positioned in the lateral incisor and canine regions, whereas in the three-implant models, they were placed axially in the right and left canine regions and the midline. A total of 12 overdenture models were designed using ball and locator attachments in combination with different substructure materials: base-free (polymethyl methacrylate [PMMA]), Chromium- Cobalt (Cr-Co), and Polyether Ether Ketone (PEEK). To simulate masticatory function, a rigid foodstuff in the shape of a 1 cm radius circle was positioned on the central fossa of the first molar and the incisal edge of the canine. Bilateral vertical forces were applied perpendicularly at the midpoint, with magnitudes of 100 N at the molar region and 65 N at the canine region. The models were analyzed using the finite element stress analysis method to evaluate tensile and compressive stresses in cortical and trabecular bone, as well as von Mises stresses in the implant, abutment, and prosthetic components. Results: According to the results of the finite element stress analysis, it was determined that the stress in the cortical bone was higher than that in the trabecular bone in all models. It was determined that a more balanced stress distribution occurred in the three-implant supported overdenture models than in the two-implant models, especially in the midline region. When attachment types were compared, von Mises stress levels increased in implant and prosthetic components in models using locator attachments, while stress accumulation in the surrounding cortical and trabecular bone tissues did not show a significant difference between ball and locator systems. When evaluated in terms of substructure material, PEEK substructured models were found to generate more stress than Cr-Co substructured models. Conclusions: An increase in the number of implants in overdenture prostheses improved load distribution; however, it also resulted in a shift in localized stress areas. Moreover, higher rigidity of the substructure material contributed to a lower and more uniform stress distribution in both bone and implant components.