Concentration-Dependent Synergistic Interfacial Interactions Between Multifunctional Acrylate and Silane Coupling Agents in an Organic–Inorganic Nanohybrid Material

Synergistic effects of a multifunctional acrylate and a long-chain silane coupling agent were investigated in an organic–inorganic nanohybrid material. We tested the bond strength of nanohybrid composites treated with experimental primers containing silane coupling agents—3-methacryloxypropyl trimethoxysilane (γ-MPTS) or 8-methacryloxyoctyl trimethoxysilane (8-MOTS)—with or without multifunctional acrylates—trimethylolpropane triacrylate (A-TMPT) or dipentaerythritol hexaacrylate (A-DPH). Shear bond strength was evaluated after 24 h of water storage at 37 °C. Untreated control and silane-only groups exhibited low shear bond strengths (e.g., control: 2.4 ± 2.0 MPa) and failed exclusively at the adhesive interface. While addition of A-TMPT did not significantly improve bond strength, addition of A-DPH produced significantly higher shear bond strengths. Highest strength was achieved with 30% 8-MOTS and A-DPH (22.4 ± 6.1 MPa), followed by 20% γ-MPTS and A-DPH (19.0 ± 7.0 MPa), and A-DPH groups produced cohesive failures. Regardless of the silane used (γ-MPTS or 8-MOTS), incorporating A-DPH in the primer consistently yielded superior bond strengths, indicating a promising strategy for improved adhesion for such nanohybrid systems. These findings provide new insights into optimizing resin–filler interfacial interactions and may contribute to the development of restorative materials with improved long-term clinical durability.