Impact of acidic monomer type and concentration on the adhesive performance of dental zirconia primers

This study evaluated the influence of acidic monomer type (phosphate–PAM or carboxylic–CAM) and concentration on the adhesive performance of single-solution model dental zirconia primers to yttria-stabilized polycrystalline dental zirconia ceramic. The acidic monomers 1,3-glycerol dimethacrylate phosphate (PAM) or mono-2-(methacryloyloxy)ethyl maleate (CAM) were added to a photocurable (di)methacrylate co-monomer at mass fractions of 10%, 20%, 40% or 60%, with constant 40% mass of ethanol. The degree of CC conversion (DC) of the primers was measured using mid-infrared spectroscopy. Zirconia bonds were assessed by shear bond strength test after two aging conditions: water storage for 24 h or thermal cycling (3,000 cycles in water at 5 °C and 55 °C). DC data were submitted to one-way ANOVA for each monomer type. Bond strength data were submitted to two-way ANOVA for each aging condition. Bond strengths at 24 h and after thermal cycling were compared using t-tests (α=0.05 for all analyses). Lower DC was observed for increased acidic monomer concentrations. The bond strengths of PAM-based primers were generally higher than CAM-based materials, irrespective of acidic monomer concentration or aging condition. After thermal cycling, the bond strengths for PAM-based primers were still higher compared with CAM-based primers, although CAM-based materials generally had more stable zirconia bonds. In conclusion, both the acidic monomer type and concentration had a significant impact on the adhesive performance of the primers. The primer with 40% of phosphate methacrylate showed the best overall bonding performance to dental zirconia.