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

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).

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.

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.

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.