Enhancing resin bonding to zirconia-glass composite surfaces: Comparative evaluation of ceramic primer coating strategies

The poor interfacial adhesion between dental zirconia and resin composites remains a critical limitation affecting the long-term clinical performance of zirconia-based restorations. This study constructed a novel zirconia-glass composite surface through melt-infiltration of SiO2-Li2O-Al2O3 glass, systematically evaluating the influence of different ceramic primers coating on the resin bonding strength. Three surface coating treatments were applied to acid-etched composite surfaces: Monobond N (silane+10-MDP), Clearfil Ceramic Primer Plus (silane+10-MDP), or Z-Prime Plus (10-MDP-only), with control groups consisting of airborne-particle abrasion treated zirconia with identical primers and an untreated group. The experiment results demonstrated that all glass-infiltrated and primed groups (GHM, GHC, GHZ) exhibited significantly enhanced immediate shear bond strengths (>30 MPa) compared to the airborne-particle abrasion groups. After 5000 thermal cycles, groups treated with the combined silane and 10-MDP primers (GHM, GHC) demonstrated remarkable bond stability, outperforming the group receiving the 10-MDP-only primer (GHZ). This superior performance was attributed to the enhanced wetting properties of the composite surface, as all primer formulations achieved consistently low contact angles (∼20°) on the acid-etched substrate, effectively mitigating their intrinsic wettability differences. Advanced spectroscopic analyses employing XPS and FTIR techniques elucidated a synergistic bonding mechanism in Group GHM and Group GHC, featuring simultaneous formation of Si-O-Si covalent bonds with the glass infiltrate layer and P-O-Zr coordination bonds with the zirconia substrate. This study demonstrates that applying a composite primer containing both silane and 10-MDP to the zirconia-glass interface improves bonding performance and stability under laboratory conditions. These findings merit further study to assess their clinical applicability.