Effect of an MDP-containing ceramic primer application on adhesion to a ZLS ceramic with or without prior acid etching

This study evaluated if using an MDP-containing ceramic primer combined with acid etching or without improves the microshear bond strength of resin cement to a zirconia-reinforced lithium silicate ceramic (ZLS). A total of 32 ZLS ceramic plates (Vita Suprinity) were prepared and divided according to the following adhesive procedures: primer (P), silane (S), hydrofluoric acid etching + primer (HFP), or hydrofluoric acid etching + silane (HFS). Resin cement was inserted and photo-cured into starch tubes (0.96 mm × 1 mm) over the treated ceramic surfaces. Half of the specimens were tested (microshear bond strength – µSBS) after 24 h and the other half after aging (90 days in distilled water and 10,000 thermocycles) (10 tubes/slice, n = 40). Pre-test failures were recorded and failure mode images were performed in a scanning electron microscope (SEM). Ceramic surfaces underwent as-sintered, HF etching, ceramic primer, or silane applications and were observed in SEM and had the contact angles analyzed. The data for bond strength, failure mode and number of pre-test failures were analyzed by ANOVA, t-tests, and Chi-square tests. HFS and HFP treatments showed similar and highest µSBS means in both baseline and aged conditions, and its bond strength was maintained after aging. The failure mode and number of pre-test failures were proven treatment-dependent. HF modified the ceramic surface and led to the lowest contact angle. MDP-containing ceramic primer without previous HF etching did not produce long-term bonding between ZLS and resin cement and did not improve the bond strength when HF etching was used.