Impact of Different Substructure and Superstructure Materials on Bone Stress Distribution in All-on-4 Prosthetic Restorations

Aim: This study aimed to examine whether different framework and superstructure materials in All-on-4 prosthetic restorations affect load distribution in peri-implant bone. Materials and Methods: Four implants were placed according to the All-on-4 concept, with distal implants angled at 30 degrees. Framework materials (cobalt-chromium alloy, titanium, PEEK, zirconia) and superstructure materials (composite, zirconia) created eight combinations. 3D models were designed using Rhinoceros 4.0 and VRMesh, then imported into Algor Fempro for finite element analysis. A 150N force was applied perpendicular to the occlusal surfaces of the left first molar and premolar. Results: The PEEK framework group showed the highest maximum principal stress values in the cortical bone near the applied force. The zirconia superstructure group exhibited lower maximum principal stress values than the composite group. Minimum principal stress was lower in the composite superstructure compared to the zirconia superstructure. For the cantilever section, the peak minimum principal stress values in the cortical bone were inversely proportional to the elastic modulus of the frameworks: PEEK > titanium > Cr-Co > zirconia. Conclusions: The PEEK framework and composite superstructure groups generated higher tensile forces in the cortical bone surrounding the implants. The highest compression values were observed in the PEEK framework, followed by titanium, Cr-Co, and zirconia. Greater stress accumulation was found in the cortical bone with the composite superstructure compared to the zirconia superstructure.