Effects of a Hydrophilic Collagen-Reactive Monomer on Dentin Bond Durability

This study investigated a dilution system comprising a novel hydrophilic aldehyde-based diluent monomer, N-vinyl formamide (NVF), in combination with a hydrophobic aldehyde-based diluent monomer, formyl phenyl acrylate (FA). The binding capability of NVF to dentin collagen was examined by attenuated total reflection–Fourier transform infrared spectroscopy, hydroxyproline release under collagenase degradation, and thermogravimetric analysis. The cytotoxicity of NVF was also evaluated. Hydrophilic NVF and hydrophobic FA resin monomers were incorporated into experimental 2-step etch-and-rinse adhesives (EAs) in various percentage proportions (0, 30/0, 20/10, 10/20, and 0/30). The degree of conversion, tensile, and flexural strengths of the EAs were evaluated with 8 and 16 wt% water incorporation to examine their coordination with water. An optimal EA group was selected by comprehensive physical properties to investigate its bonding performance via microtensile bond strength testing. Infiltration properties of the EA were examined by nanoleakage testing, Masson trichrome staining, confocal laser scanning microscopy, and micro-Raman spectroscopy from the external direction perpendicular to the interface and the pulp chamber–interface direction. In situ zymography was performed to further validate the inhibitory effect of the NVF-FA system on the endogenous hydrolytic activity of dentin. The results demonstrated that NVF covalently binds to dentin collagen, thereby improving its proteolytic, hydrolytic, and thermal stability. In addition, NVF is biocompatible within clinically acceptable standards. When compared with HEMA, the combination of hydrophilic-hydrophobic aldehyde monomers significantly enhanced polymerization and mechanical properties under wet conditions. These alternatives led to significantly better bond strength, depth of infiltration, and interface sealing, before and after aging. The present study proposes a novel dilution system that enhances infiltration and protection of the collagen matrix. An EA incorporating this dilution system shifts from traditional passive diffusion to specific infiltration guided by characteristic functional groups. This has significant clinical relevance for improving adhesive durability and effectiveness.