Influence of natural and synthetic metalloproteinase inhibitors on bonding durability of an etch-and-rinse adhesive to dentin

The aim of the present study was to evaluate the effect of natural (green tea (Camellia sinensis) GT) and synthetic (chlorhexidine-CLX) metalloproteinase inhibitors on the microtensile bond strength (µTBS) of an etch-and-rinse adhesive to dentin, after 24 h and 6 months of water storage (WS). Thirty human dentin specimens were conditioned with 37% phosphoric acid for 15 s, rinsed for the same amount of time and dried gently. They were then divided into 3 groups, according to the solution to be applied to the dentin surface (n=10): GT, 2% CLX, or NT (none, as control). CLX and GT solution (20 μl) were applied for 60 s and dried gently with absorbent paper. The adhesive system (Adper Single Bond 2, 3M ESPE) was then applied according to the manufacturer's instructions, and a 4-mm composite resin block was built. After 24 h, at 37 °C, resin–dentin blocks were sectioned into 1-mm2 sticks that were assigned into two µTBS test conditions: after being stored in water for 24 h or after 6 months. Data were submitted to repeated-measures two-way ANOVA and Tukey's test, with a 5% significance level. The failure pattern was described in percentage terms. The results showed that the µTBS values in the NT group were significantly higher compared to the GT values. The application of CLX resulted in intermediate µTBS values, which were not statistically different from NT or GT. There was no significant difference between the µTBS values in the two time points of analysis for CLX and GT groups while the NT group showed a significant decrease over time. After 6 months of WS, all groups had µTBS values statistically similar among themselves. It can be concluded that in a short-term evaluation, chlorhexidine showed no interference on bond strength to dentin, while green tea did. After a long-term evaluation, both metalloproteinase inhibitors, chlorhexidine and green tea, were capable of maintaining bond strength stability.