Influence of Framework Material on Stress, Fatigue, and Stability of “All-on-Four” System Components—Biomechanical Evaluation with Finite Element Analysis

The “all-on-four” concept is a prominent solution for rehabilitating edentulous patients with fixed full-arch restorations. This study aimed to examine the stress distribution pattern, material fatigue, and restoration displacement using different framework materials under static (SL) and dynamic (DL) loading conditions. Six three-dimensional finite element analysis models of an atrophic maxilla rehabilitated via the all-on-four concept were analyzed. Models utilized three different framework materials: Cobalt–Chromium Alloy (CoCr), Zirconia (Zr), and Polyetheretherketone (PEEK). The models were subjected to three types of SL (90, 150, and 200 N) and two cases of DL (150 N) simulating mastication. DL generated higher stress intensities compared to SL. PEEK models showed the highest stress concentrations in the cortical bone (up to 70.44 MPa) and implants across SL models. The PEEK frameworks showed a risk of fatigue-related fracture of the cortical bone around terminal implants. Models utilizing PEEK frameworks exhibited significantly greater structural displacement (up to −0.681 mm horizontally) under DL compared to their rigid counterparts. CoCr and Zr provide better resistance to cyclic loading and reduced displacement, ensuring a higher safety factor. PEEK frameworks demonstrated inferior mechanical resistance under fatigue.