Optimization of a Zirconia Bonding System Using Acidified Hydrogen Peroxide（H₂O₂／HCl）Treatment and Two-bottle Primers Containing Zirconium Alkoxide and γ-MPTS

Abstract

Zirconia is highly chemically stable, making it difficult to achieve reliable adhesion to resin cement. In this study, a zirconia bonding system was optimized by hydrophilizing the zirconia surface using acidified hydrogen peroxide treatment (hydrochloric acid [HCl] added to 30 wt％ hydrogen peroxide [H₂O₂]) and by combining a two-bottle zirconia primer containing zirconium alkoxide with a two-bottle silane primer containing c‑methacryloyloxypropyltrimethoxysilane (γ‑MPTS).Mirror-polished zirconia specimens were immersed at 80℃ for 10-30 min, and water contact angles were measured. The contact angle decreased with increasing HCl concentration and immersion time, reaching the minimum after treatment with 30 wt％ H₂O₂＋3 N HCl for 30 min. Specimens treated under this condition were primed and bonded, and shear bond strength was compared at c-MPTS working concentrations of 0.021─0.100 mol/L. The maximum bond strength was 8.4±1.1 MPa at 0.061 mol/L, and the failure mode shifted from interfacial failure to mixed failure with resin cement remnants. The optimized zirconia bonding system showed significantly higher bond strength than a commercial 10‑methacryloyloxydecyl dihydrogen phosphate (MDP)-based bonding system (6.0-6.4 MPa；p<0.05), suggesting that the optimized system may provide greater chemical bonding performance than the conventional MDP-based approach.