Effect of Dentinal Water on Bonding of Self-etching Adhesives

Objectives: The purpose of this study was to evaluate the effects of dentin wetness on the bond strengths of one-bottle and two-step self-etching adhesives using the microtensile bond test and SEM. Methods: The microtensile bond strength of resin to dentin was measured using two one-bottle self-etching (Optibond All-in-One/Kerr and SI-R20603/Shofu) and two two-step self-etching adhesives (Imperva FL-Bond II/Shofu and Clearfil Protect Bond/Kuraray) for wet-dentin (control) or a dry-dentin substrate. Wet-dentin is the normal substrate for bond testing and dry-dentin was dehydrated in a desiccator at different drying times (5, 10, 20, 40, or 60 min) before bonding. The bond strengths were evaluated by two-way ANOVA and Fisher's PLSD test (p<0.05). We used simple regression analysis for the drying-time of the dentin substrate vs. the bond strength. After the bond testing, the fractured surfaces were examined by SEM. Results: Although no correlation (p>0.05) was found for two-step self-etching adhesives, the bond strength of the dry-dentin was significantly (p<0.05) increased with the increase in the drying-time for one-bottle adhesives. With increased drying-time, the amount of water-bubbles was decreased for one-bottle adhesives, however, no bubble formation was seen in two-step adhesives in any group. Conclusion: Nanoleakage, especially for water droplets in hydrophilic adhesives can mostly be attributed to the presence and continuous supply of water from the dentin/tubules or smear layer by osmosis. The differential bond strength and bubble formation of one-bottle self-etching adhesives must be due to a difference in the moisture content of dentin. This effect may depend on the “hydrophilicity” of adhesives.