Effect of material, prosthesis height, and aging on the fracture strength of additively and subtractively manufactured implant-supported cantilevered prostheses

Purpose: This study aimed to evaluate the inherent and after cyclic loading fracture strength of implant-supported cantilevered fixed prostheses fabricated from recently introduced additively manufactured (AM) and subtractively manufactured (SM) materials, considering variations in prosthesis height. Materials and Methods: Three cylinder-shaped master files (20 mm long and 11 mm wide) with varying heights (7, 11, and 15 mm) and a titanium-base (Ti-base) abutment space were designed. These designs were used to fabricate a total of 144 specimens with two AM resins indicated for definitive use (Crowntec; AM-CT and Flexcera Smile Ultra+; AM-FS), one high-impact polymer composite (breCAM.HIPC; SM-CR), and one SM strength gradient zirconia (IPS e.max ZirCAD Prime; SM-ZR) (N = 12). Following fabrication, all specimens and Ti-base abutments were prepared according to their respective manufacturers' recommendations prior to adhesive cementation using an autopolymerizing luting composite resin. Each set of specimens was then divided into two subgroups: control and cyclically loaded (n = 6). The specimens in the control groups were subjected to a load-to-fracture test, while the specimens in the cyclically loaded groups underwent 1.2 million loading cycles at 50 N and 1.7 Hz. The surviving specimens from cyclically loaded groups were then tested for load-to-fracture in the same manner. Data were analyzed with generalized linear model analysis and Bonferroni-corrected post hoc tests after logarithmic conversion (α = 0.05). Results: The fracture strength of tested specimens was affected by the interaction between the material type and aging condition, material type, and prosthesis height (p ≤ 0.020). SM-ZR specimens had the highest and AM-CT specimens had the lowest fracture strength values (p < 0.001), when aged or non-aged. The fracture resistance values of the specimens significantly increased as the prosthesis height increased (p ≤ 0.001). One AM-CT specimen and two AM-FS specimens, all 7 mm in height, failed during cyclic loading. Conclusions: AM-FS and AM-CT resins may resist masticatory forces in the molar region when the prosthetic height is not smaller than 11 and 15 mm, respectively, despite the use of a molar-size cantilever in the tested thickness.