A comprehensive study on MDP effects: Microshear bond strength and fatigue resistance in 4YSZ ceramics

The aim of this study is to assess the presence of MDP at various stages of the bonding procedure, enhance the adhesive and mechanical behavior of cemented zirconia ceramics. Fifty ceramic slices (15 × 15 × 2 mm) and 48 discs (Ø= 10 mm, 1 mm thickness) were prepared, sintered, air-abraded with aluminum oxide, and allocated considering: 1) microshear bond strength (µSBS) between ceramic slices and luting agent cylinders (height= 1 mm, Ø= 1.2 mm); 2) fatigue behavior, ceramic discs paired and bonded onto fiber-epoxy resin discs (Ø= 10 mm, 2.5 mm thickness), and then mechanically tested (cyclic loading, starting at 400N, with increments of 100N, until failure). Four experimental groups were defined: Universal Primer (MDP primer+non-MDP resin cement - RC), Universal Adhesive (MDP adhesive+non-MDP RC), Cement (no primer+MDP RC), and Primer+Cement (MDP primer + MDP RC). For both outcomes, half of the specimens were tested after 24 hours, and half after aging. Bond strength data was analyzed via two-way ANOVA and Tukey post-hoc tests, while fatigue data went through Kaplan-Meier and Mantel-Cox post hoc tests. Regarding µSBS, aging impaired adhesion only for the Primer+Cement group (p<0.001). Universal Primer and Universal Adhesive showed the highest bond strength (p<0.05). Despite that, fatigue data indicates no significant differences (p>0.05). In conclusion, systems with MDP-containing components associated with non-MDP resin cement demonstrated enhanced adhesive capability for zirconia restorations. Nevertheless, no differences in terms of mechanical reinforcement were observed.