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.

This study investigated the effects of varying concentrations of two distinct silane agents, 8-methacryloxyoctyl trimethoxy silane (8-MOTS) and 3-methacryloxypropyl trimethoxy silane (γ-MPTS), on their initial bonding efficacy to feldspathic ceramic (FC), lithium disilicate glass-ceramic (LD) and polymer-infiltrated ceramic (PIC) specimens, in 10% increments for concentrations ranging from 10% to 40%. Shear bond strengths between the ceramic substrates and the luting material were assessed following 24 h incubation in distilled water. For FC, the median value of shear bond strength peaked at 20% of γ-MPTS (7.4 MPa), while 8-MOTS exhibited a concentration-dependent increase, reaching its highest value at 40% (13.1 MPa). For LD, γ-MPTS above 10% yielded similar strength median values (10.2 MPa), whereas 8-MOTS at 30% (15.8 MPa) and 40% (13.4 MPa) yielded higher strength values than at 10% (2.9 MPa) and 20% (4.1 MPa), with the highest median value exhibited at 30%. For PIC, both γ-MPTS and 8-MOTS demonstrated similarly low bond strength values which were not significantly different from the non-silane-treated specimens. When applied on silica-based FC and LD, silane revealed a concentration-dependent bonding effect, with 8-MOTS exhibiting superior bond strength to γ-MPTS. However, PIC, characterized by a high inorganic filler content, demonstrated limited bondability with both silanes.

This study evaluated the effects of silane coupling agents with different spacer chain lengths on the bonding performance and long-term stability of feldspathic ceramics. Feldspathic ceramic surfaces were treated with silane coupling agents featuring short (1-MMS), medium (3-MPS), and long (8-MOS) spacer chains at concentrations of 0.01, 0.03, and 0.07 mol/L. Shear bond strength was measured immediately and after 1 day, as well as 1, 3, 6, and 12 months. Surface wettability was evaluated using contact angle measurements, and chemical interactions were analyzed using Fourier-transform infrared spectroscopy (FTIR). Contact angles of 1-MMS showed high values (~58°) across all concentrations, whereas 8-MOS exhibited a concentration-dependent increase up to 61.1 ± 2.1°. FTIR spectra of the silane solutions showed distinct methacryloyl-related bands (1726 and 1321 cm⁻¹) for 1-MMS and 3-MPS, whereas 8-MOS produced only a broad band without distinct peaks, suggesting differences in the state of the silanes in solution after activation. Short-spacer 1-MMS at 0.07 mol/L produced high immediate adhesion (>10 MPa), reached 23.7 MPa at 3 months, and maintained 13.0 MPa at 12 months. Bond strength peaked at 3 months in all groups, including the non-silanized control, when cohesive failure within the ceramic predominated; after 12 months, 8-MOS at 0.07 mol/L retained 11.0 MPa, with cohesive failure within the resin cement in approximately half of the specimens. The spacer chain length of silane coupling agents influences the balance between interfacial coupling and surface hydrophobicity. Short spacers are associated with stronger initial bonding, whereas longer spacers increase surface hydrophobicity and may contribute to improved durability.