3D-printing for zirconia abutment manufacturing and screw access hole effect: fatigue behavior of milled zirconia simplified restorations

The aim of this study is to evaluate the effect of the abutment manufacturing method (CAD/CAM milling or 3D-printing) and the presence of a screw access hole on the fatigue behavior of adhesively cemented zirconia restorations. Zirconia (3YSZ) discs, representing prosthetic abutments (Ø= 10 mm, 3 mm in thickness) were fabricated by simulated CAD/CAM milling (M) or lithography-based 3D-printing (3D), either with a screw access hole (Ø=2.5 mm, filled with resin composite) or without (Rigid) and allocated into four groups: M-Screw, M-Rigid, 3D-Screw and 3D-Rigid. Restorative zirconia discs (4YSZ; Ø=10 mm, 1 mm thickness) were adhesively cemented to the abutments using a dual-cure resin cemented. Cyclic fatigue test was performed (n = 15). Data were analyzed using Kaplan-Meier, Log-rank (Mantel-Cox) and Two-way ANOVA supplemented by fractography and finite element analysis. No significant effect of the manufacturing method was observed on fatigue behavior (p ≥ 0.05). Rigid groups exhibited no failures during testing. Conversely, the presence of a screw access hole significantly reduced fatigue behavior (p < 0.05), with similar mean fatigue failure loads for 3D-Screw (2,286 N) and M-Screw (2,273 N) groups. The manufacturing method of the zirconia abutments (3D-printing or milling) did not influence the fatigue behavior of the restorations. However, the presence of a screw access hole in the abutments significantly reduced the fatigue behavior of the specimen.