Bond strength to high-crystalline content zirconia after different surface treatments

The aim of this study was to evaluate the effect of primers, luting systems and aging on bond strength to zirconium oxide substrates. Eighteen zirconia discs (19.5 x 4 mm) were polished and treated (n = 3) either with a MDP primer (Md) or with a MDP and VBATDT primer (MV). In the control group (n = 3) no surface chemical treatment was performed. Zirconia specimens were cemented to prepolymerized composite discs utilizing resin cements - RelyX Unicem or Panavia 21 (RU and Pa, respectively). After 24 h, samples were sectioned for microtensile testing and returned to water at 37 degrees C for two different periods before being tested: 72 h or 60 days + thermocycling (5-55 degrees C/5000 cycles). Bond strength testing was performed at 1 mm/min. Values in MPa were analyzed through ANOVA and Tukey's Studentized Range (HSD) (p > 0.05). The application of MV primer resulted in the highest bond strength (22.77 MPa), statistically superior to Md primer (12.78 MPa), and control groups presented the lowest values (9.17 MPa). When luting systems were compared, RU promoted the highest bond strength (16.07 MPa) in comparison with Pa (13.75 MPa). The average bond strength decrease after aging (9.35 MPa) when compared with initial values (20.46 MPa). The results presented by this in vitro study suggest that a chemical surface treatment based on the MDP and VBATDT combination may improve bond strength between zirconia and luting system, without any previous mechanical treatment, depending on the luting system used. This chemical treatment may result in a reliable alternative to achieve adequate and durable bond strength.