Biomechanical Evaluation of Framework Materials in All‐on‐Four Versus All‐on‐Six Prostheses: A Finite Element Study

PURPOSE: The objective of this study was to biomechanically compare the All-on-Four and All-on-Six implant configurations combined with various framework materials by assessing stress distribution in peri-implant bone, implants, and prosthetic structures using finite element analysis (FEA). MATERIALS AND METHODS: This study investigated the biomechanical behavior of six different framework materials titanium, zirconia, PEEK, PEKK, Trilor and Trinia in full-arch, implant-supported fixed prostheses using the All-on-Four and All-on-Six concepts in a total edentulous mandible. A three dimensional finite element model of the mandible, incorporating cortical and trabecular bone as well as mucosal tissue, was developed based on CBCT data. In the All-on-Four configuration, two anterior implants were placed axially and two posterior implants were tilted distally at 30°. The All-on-Six model featured axially placed anterior implants, with posterior implants angled at 15° in the premolar and 30° in the molar regions. Multi-unit abutments were used for all implants. Frameworks were digitally designed in a Toronto prosthesis configuration using each material, and a monolithic zirconia superstructure was applied as the veneering material. All models were subjected to a simulated vertical masticatory load of 150 N. Maximum principal stress values were assessed in the peri-implant bone, while von Mises stress distributions were analyzed in the framework, implants, and fixation screws. RESULTS: The highest stress accumulation was observed in the All-on-Four configuration, particularly around the cantilever region and distal implants. Materials with low elastic modulus (PEEK and PEKK) caused higher stress transmission to peri-implant bone and connection components. In contrast, rigid materials (titanium and zirconia) provided a more balanced load distribution and resulted in lower stress concentrations. Glass fiber-reinforced composite frameworks (Trilor and Trinia) remained within clinically acceptable biomechanical limits. CONCLUSION: The findings of this study indicated that both implant configuration and framework material properties play a critical role in the biomechanical performance and long-term success of the prosthesis.