Effects of restorative material on the mechanical performance of three-unit implant-supported fixed dental prostheses with bilateral cantilevers: an in vitro study.

This study aimed to evaluate and compare the fracture load and fracture mode of three-unit implant-supported fixed dental prostheses (ISFDPs) fabricated from polyetheretherketone (PEEK), composite, and zirconia, using two prosthetic designs: a bilateral cantilever supported by a single central implant (T-bridge) and a conventional two-implant-supported configuration (C-bridge). In this preclinical in vitro study, Straumann tissue-level regular implant analogs were embedded in Paladur resin and fitted with SN Variobase® abutments. Five restorative materials, PMMA-based polymer, resin composite, PEEK, 5 mol% yttria-stabilized zirconia (5Y-TZP), and 3 mol% yttria-stabilized zirconia (3Y-TZP), were used to fabricate standardized ISFDPs. Specimens were luted and subjected to vertical loading until failure using a universal testing machine. Fracture load, fracture mode, and abutment deformation were recorded and analyzed. 3Y-TZP exhibited the highest median fracture load (T-bridge: 5108 N [IQR: 1415]; C-bridge: 6572 N [IQR: 2438]). C-bridges consistently showed significantly higher fracture resistance than T-bridges. PEEK demonstrated no visible fractures and minimal deformation, indicating a distinct mechanical behavior. Significant differences in fracture patterns were found across materials, with zirconia and PEEK performing most favorably. 3Y-TZP zirconia provides the highest fracture resistance. While C-bridges provided superior mechanical performance, T-bridges with appropriate materials such as PEEK or 3Y-TZP show clinically acceptable strength. Absence of fatigue and long-term aging limits direct clinical extrapolation. T-bridge configurations may offer a less invasive alternative when C-bridges are not feasible, provided that high-performance materials are selected. Further validation through long-term and clinical studies is recommended.