Effect of surface treatments on the bond strength of veneering ceramic to zirconia

Aim: The purpose of this study was to evaluate the effect of different surface treatments on the bond strength of veneering ceramic to zirconia. Methods: Square (15 mm x 10 mm x 2 mm) zirconia specimens (n= 18) received one of the following surface treatments: Group 1, sandblasting; Group 2, Clearfil ceramic primer application; Group 3, grinding; Group 4, alloy primer application; and Group 5, RelyX ceramic primer application. The zirconia core specimens were layered with a veneering porcelain (5 mm x 3 mm x 3 mm). Mean shear bond strength values (MPa) were calculated. Data were analyzed with one-way ANOVA and Tukey's post hoc pairwise comparisons (alpha = 0.05). Fractured surfaces of the specimens were examined with scanning electron microscope (SEM). Results: This study showed that bond strengths of the metal primer-treated zirconia specimens (Group 4) were significantly higher than those of the other paired groups. The application of metal primer affected the specimens' failure mode. SEM analysis demonstrated that Group 4 had mainly cohesive fractures, while the other groups showed approximately equal levels of adhesive and mixed fracture types. The mean and SD values for shear bond strengths ranged from 8.90 +/- 3.42 MPa (Group 2) to 19.74 +/- 4.96 MPa (Group 4). Conclusions: In conclusion, the application of a metal primer to a zirconia core increased the bond strength of veneering ceramics. The use of chemical agents to improve the strength of the zirconia core's bond to veneering ceramic may have more benefits than the use of mechanical pretreatments.