Effect of framework material and gyroid lattice design on the biomechanics of all-on-four full-arch prostheses

BACKGROUND: This finite element analysis (FEA) aimed to evaluate the biomechanical behavior of all-on-four implant-supported full-arch prostheses fabricated from different framework materials and internal designs. METHODS: Three-dimensional FEA models were constructed to simulate bar- and Toronto-type frameworks made of cobalt-chromium (Co-Cr), titanium (Ti), and polyetheretherketone (PEEK) materials. Each framework was modeled as a conventional solid structure, and metallic frameworks were also modeled with a gyroid lattice design. Vertical and oblique (30°, 150 N) loading conditions were applied to replicate masticatory forces. von Mises and principal stresses were analyzed for the framework, implant, abutment, and surrounding bone. RESULTS: Gyroid lattice frameworks exhibited 10-25% lower internal framework stresses but transmitted 12-22% higher stresses to the implant body, abutment, and abutment screw compared with solid designs. Cortical and trabecular bone stresses remained within physiological limits. PEEK frameworks demonstrated the lowest internal stresses yet exhibited the highest deformation due to their lower elastic modulus. Metallic frameworks, particularly Ti, showed higher rigidity and more balanced stress transfer. Toronto-type designs displayed more homogeneous stress distribution and lower peak stress values than bar-type frameworks. Under vertical loading, the smallest framework-bone deformation difference was observed in the Toronto-gyroid Co-Cr framework (2.73 μm), and the highest in the bar-gyroid PEEK framework (12.63 μm). Under oblique loading, the Toronto-gyroid Co-Cr model again exhibited the lowest deformation difference (6.67 μm), while the bar-gyroid PEEK framework showed the highest (16.87 μm). CONCLUSIONS: The Toronto-gyroid Co-Cr and Ti frameworks showed a more balanced load distribution and smaller framework-bone deformation differences under the tested conditions, whereas the PEEK frameworks demonstrated greater flexibility.