Optimization of a zirconia bonding system: A simple and practical approach to surface modification

Background Zirconia is widely used in dental restorations due to its excellent mechanical properties and biocompatibility. However, because of its chemical and mechanical stability, achieving strong adhesion with resin cement remains a challenge. This study aimed to develop and evaluate a simplified zirconia bonding system designed to enhance chemical bonding strength without requiring complex procedures or specialized equipment. Materials and Methods Mirror-polished zirconia specimens were prepared and immersed in solutions of 30 mass% hydrogen peroxide (H₂O₂) containing 0, 1, 2, or 3 N hydrochloric acid (HCl) at 80°C for 10, 20, or 30 minutes. The water contact angles were measured to assess surface hydrophilicity. Subsequently, the treated zirconia surfaces were coated with a zirconium alkoxide-containing primer, followed by different volumes (10, 20, 30, and 50 µL) of γ-methacryloyloxypropyltrimethoxysilane (γ-MPTS) primer. Resin cement was bonded to the surfaces, and macro-shear bond strength was tested. The performance of the optimized bonding protocol was compared with that of a commercial 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based system. Results The water contact angles of the oxidized zirconia surfaces treated for 30 min with 30 mass% H ₂ O ₂ -containing 3 N HCl significantly decreased. The optimized zirconia bonding system treated with the 30 µL γ-MPTS primer exhibited a maximum bond strength of 8.4 MPa—significantly higher than that of the commercial MDP-based system (6.0–6.4 MPa, p  < 0.05). Conclusions The chemical bonding strength of the optimized zirconia bonding system developed in this study was superior to that of a commercial MDP-based system.