Effect of silane and MDP-based primers on physico-chemical properties of zirconia and its bond strength to resin cement

Objective: To evaluate the effect of surface treatments on yttria-tetragonal zirconia polycrystal (Y-TZP) characteristics and on resin-mediated zirconia bond. Methods: Y-TZP slabs were grit blasted with 45 μm alumina or with 30 μm silica-coated alumina particles. The chemical treatments were: no-chemical treatment (NC), silane-containing primer (SP), MDP (10-Methacryloyloxydecyl dihydrogen phosphate) and silane-containing primer (MPS), MDP-containing primer (MP) and MDP and silane-containing adhesive (MPA). Contact angle as a function of surface roughness (θ_m) and surface roughness parameter (Sdr) were measured using Fringe Projection Phase Shifting (FPPS). Surface free energy (γ_s ^TOT) was calculated with a goniometer. Chemical interaction between primers/adhesive and zirconia was analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Resin cement microshear bond strength (μSBS) was analyzed at either 24-h or 8-months water storage (37 °C). θ_m values, Sdr values, γ_s ^TOT and μSBS values were analyzed using Analysis of variance (ANOVA) and post hoc Tukey test (α = 0.05). Results: Chemical treatment had an effect (p < 0.001) on all surface parameters analyzed: θ_m, γ_s ^TOT and Sdr. MP-treated group showed higher incidence of P–O–Zr bonds than the other groups, indicating more chemical linkages. Grit blasting (p < 0.001) and the interaction chemical treatment*storage (p < 0.001) did not affect μSBS; all silane-containing primers showed significant drop in μSBS after aging. Significance: MDP and/or silane-based solutions affect the physicochemical properties of blasted-zirconia. An MDP-based primer is fundamental to achieve a stable resin-zirconia bonding, but the chemical reactivity of MDP is impaired when this molecule is present in a multicomponent system.