The enzymatic degradation of the hybrid layer protein content is one of the processes responsible for the functional breakdown of the adhesive interface. Therefore, the inhibition of the dentin matrix endogenous proteases, released and activated after the dentin demineralization, has been investigated as a strategy to improve the resin-dentin bond stability. Polyphenols are better known by their antioxidant action, but many of these phytochemicals are also inhibitors of matrix metalloproteinases (MMPs). They are of particular interest because they are extracted from natural sources, and one of them, still not investigated in the context of the adhesive dentistry, is the naringenin. Thus, the aim of this study is to investigate the effect of naringenin on the in situ activity of MMPs and on the ultimate bond strength of dentin matrices. One hundred dentin specimens (0.5mm´2.0mm´5.0mm or 1.0mm´1.0mm´5.0mm) will be cut from the crown of sound human molars. The specimens will be completely demineralized and the initial total MMPs activity of each specimen will be assessed using Sensolyte. Then, the specimens will be divided into 5 groups (n=20) in such way that the mean MMP activity of all groups will be similar (ANOVA, p>0.05). According to the groups, the specimens will be treated for 60 seconds with deionized water (control), 98% ethanol, 200 µM naringenin, 300 µM naringenin or 5% glutaraldehyde, followed by abundant water rinse. Total MMPs activity will be reassessed in 10 specimens also used for the analysis of hydroxyproline release, and the remaining 10 specimens will be subjected to a mechanical test to determine the ultimate bond strength of the dentin matrices. Each response variable data set (n=10/group) will be evaluated as to the adherence to the normal curve and homoscedasticity. Based on these premises, adequate tests will be selected, and the statistical inferences will be made at the 5% level of significance.
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