Gökçen Akgün
Angled abutments and cantilever extensions in bar-supported full-arch implant prostheses may generate bending moments and localized stress concentrations within prosthetic components and peri-implant bone. Implant-supported rehabilitation becomes biomechanically more demanding in completely edentulous patients with posterior bone resorption. Therefore, understanding how connection geometry, cantilever length, and framework material influence prosthetic design is important. In this study, a three-dimensional mandibular model generated from CT data was used to compare conventional and spherical abutment-bar connection designs in All-on-Four prostheses with 30° angled posterior abutments. Cantilever lengths of 8, 10, and 12 mm were evaluated, and Ti6Al4V Grade 5 and PEEK were assigned as alternative bar prosthesis materials. Finite element analyses were performed in ANSYS Workbench, and von Mises stress distributions were evaluated in the bar prosthesis, prosthetic screws, abutments, implants, and surrounding cortical and trabecular bone. The results showed that increasing cantilever length increased stress levels in prosthetic components and bone tissues. The spherical connection design generally reduced stresses in the most critical distal components compared with the conventional design; however, this reduction was not uniform for all components, particularly in the PEEK models. The highest stress value was observed in the posterior angled abutment of the PC-12 model with a PEEK bar prosthesis (1592.2 MPa). Among the implant components, the lowest stress was observed in the anterior implant of the TS-8 model (27.99 MPa). In contrast, the lowest bone stress was recorded in the anterior trabecular bone capsule of the PC-8 model. These findings indicate that cantilever length and connection geometry are critical parameters in designing full-arch implant prostheses. At the same time, the use of PEEK as a bar material should be interpreted with caution under extended-cantilever conditions.