Abstract:

Objective To explore the promotion effect on remineralization of demineralized dentin of urushiol primer applicated in acid-etch-rinse adhesives， and to clarify its impact on the longevity of dentin adhesion. Methods Ninety-six freshly extracted，caries-free third molars were selected to prepare the dentin specimens. Following acid etching with 37% phosphoric acid gel， the specimens were randomly divided into blank control group， 0.3%， 0.7%， 1.0%， and 1.5% urushiol groups， and positive control group（acetone solvent）. The treated samples were placed in modified simulated body fluids for remineralization for 14 and 28 d. Attenuated total reflection Fourier transform infrared spectroscopy（ATR-FTIR） was used to detect the relative mineralization mass of minerals in the dentinal tubules in various groups， and X-ray Diffractometery and Energy Dispersive spectrometer were used to analyze the dentin surface material compositions in various groups. Scanning electron microscope（SEM） was used to observe the surface morphology of the specimens in various groups， Vickers hardness tester was used to measure the microhardness of the dentin surface in various groups， and microtensile strength （μTBS） was used to examine the effect of the bond strengthes in various groups. Results Compared with blank control group， the conversion rate of adhesive double bonds by primer in positive control group was decreased， but the difference was not significant （P>0.05）； but the conversion rates of adhesive double bonds by primer in 0.3%， 0.7%， 1.0%， and 1.5% urushiol groups were increased （P<0.05）. The SEM results revealed that at 14 and 28 d， compared with bland control group， a minimal membranous deposit in dentinal tubules was seen in positive control group， minimal mineralization displayed in 0.3 % urushiol group， significant deposition of loose mineral particles with blocking the tubule orifices was found in 0.7% urushiol group， noticeable mineral precipitates exhibited in 1.0% urushiol group， and relatively empty dentinal tubules were seen in 1.5% urushiol group. The microhardness results showed that at 14 d after remineralization， compared with blank control group， the microhardness in positive control group showed no significant improvement（P>0.05）， while the differences in 0.3%， 0.7%， 1.0% and 1.5% urushiol groups were statistically significant （P<0.05）； at 14 d after remineralization compared with positive control group， the microhardness of dertin in 0.7 % and 1.0% urushiol groups were increased（P<0.05）； at 28 d after remineralization， compared with blank control and postive control groups， the microhardness in urushiol groups were significantly increased （P<0.05）， espectially in 0.7% to 1.5% urushiol groups （P<0.05）. In the μTBS test， at 14 d after remineralization， compared with postive control group， the μTBS in 0.3%， 0.7%， 1.0% and 1.5% urushiol groups were increased（P<0.05）； at 28 d after remineralization， the μTBS in blank control group was the lowest； compared with blank control group， there was no significant difference in the μTBS in postive control group（P>0.05）； compared with positive control group， the μTBS in 0.3%， 0.7%， 1.0%， and 1.5% urushiol groups were increased （P<0.05）， espectially in 0.7%，1.0， and 1.5% urushiol groups （P<0.05）. Conclusion Natural-derived urushiol， as a novel primer， can pretreat the demineralized dentin substrates， and facilitate collagen cross-linking within the dentin matrix； moreover， it leverages the phenolic hydroxyl groups within its structure to attact calcium and phosphate ions， envelope dentin collagen fibers to promote remineralization， in order to enhance the strength of the resin-dentin bonding interface.

Key words: Urushiol, Dentin, Adhesion, Remineralization, Hydroxyapatite