Different Strategies to Bond bis-GMA-based resin cement to zirconia

Purpose: To evaluate the effect of different bonding strategies on short- and long-term bis-GMA-based resin cement bond strengths to zirconia. Materials and Methods: One hundred twenty samples of fully-sintered zirconia (Prettau Zirconia) were sandblasted and randomly distributed into 5 groups (n = 24): UA: Scotchbond Universal Adhesive; SZP: Signum Zirconia Bond I + II; ZPP: Z-Prime Plus; EXP: MZ experimental primer; CO: No primer application (control). After performing these surface treatments, translucent tubes (0.8 mm diameter and 1.0 mm height) were placed on the zirconia specimens, and bis-GMA-based cement (Duo-Link) was injected into them and light cured. Specimens were tested for microshear bond strength either 24 h or 6 months (m) after water storage (37°C) and surfaces were characterized by SEM and EDX. Two-way ANOVA and Tukey's post-hoc test (p < 0.05) were used to evaluate bond strength results. Results: The mean bond strengths (MPa ± SD) were: UA=14.6 ± 4.7^a (24 h); 16.0 ± 4.8^a (6 m); SZP = 14.0 ± 5.4^ab (24 h); 11.9 ± 2.6^ab (6 m); ZPP=8.0 ± 1.8^b (24 h); 8.6 ± 3.3^b (6 m); EXP = 1.2 ± 0.5^c (24 h); 0.6 ± 0.7^c (6 m); CO=1.0 ± 1.2^c (24 h); 1.3 ± 1.2^c (6 m). Bonding strategy significantly influenced bond strength (p = 0.0001), but storage time did not (p = 0.841). Groups UA and SZP showed a homogeneous layer covering the zirconia surface. In these groups, EDX demonstrated the presence of phosphorus. Group ZPP resulted in a nonhomogeneous layer, exposing the zirconia substrate underneath. EXP application resulted in an undetectable layer. Conclusion: Water storage did not affect resin cement bond strengths to zirconia irrespective of the surface treatment. Bis-GMA-based resin cement bond strengths to zirconia are affected by specific bonding strategies.