The use of cavity disinfectants with composite resins has raised important questions regarding their potential adverse effects on bond strength. The purpose of this study was to evaluate the effect of cavity disinfection on the bond strength of composite resin to dentin. Buccal surfaces of 64 caries-free extracted human third molars were ground flat by diamond flat-end cylinder bur, polished with a series of silicon carbide abrasive papers and mounted in autopolymerizing acrylic resin. They were randomly distributed into four groups (of 16). In group 1 (control group), dentin surfaces were treated with 35% phosphoric acid, Permagen primer and Permagen bonding resin and no disinfectant was used. In group 2, cavity disinfectant was applied and acid etching, priming and bonding procedures were performed as in group 1. In group 3, cavity disinfectant was applied after acid etching. In group 4, cavity disinfectant was applied as in group 3, but it was rinsed off before priming and bonding procedures. Then a Teflon mould 3 mm thick and 4 mm in diameter was attached to the dentin surfaces, filled with composite resin and light polymerized. After the specimens had been thermocycled, shear bond strengths were determined. Application of the disinfectant before or after acid etching significantly reduced the shear bond strength of composite to dentin (P<0.05). Rinsing off the cavity disinfectant before the bonding procedure did not affect the bond strength (P>0.05). The use of cavity disinfectant with composite resin restorations can influence the dentin bond strength.
In-office and at-home bleaching techniques are widely used methods for the whitening of teeth. However, the safety of these techniques has not been clarified yet. The aim of the current study is to investigate the in-office- and at-home-bleaching-induced structural and quantitative changes in human enamel and dentin at the molecular level, under in vitro conditions. The Fourier transform mid-infrared (mid-FT-IR) spectroscopic technique was used to monitor bleaching-induced structural changes. Band frequency and intensity values of major absorptions such as amide A, amide I, phosphate (PO(4)), and carbonate (CO(3)(-2)) bands, for treatment groups and control, were measured and compared. The results revealed that both procedures have negligible effects on dentin constituents. In office-bleached enamel, in addition to demineralization, a decrease in protein and polysaccharide concentrations, mineral-to-protein ratio, and the strength of hydrogen bonds around NH groups, as well as a change in protein secondary structure were observed. The protein structure changed from beta-sheet to random coil, which is an indication of protein denaturation. However, no significant variations were observed for at-home bleached enamel. The control, at-home, and in-office bleached enamel samples were differentiated with a high accuracy using cluster analysis based on FT-IR data. This study revealed that office bleaching caused deleterious alterations in the composition and structure of enamel that significantly affected the crystallinity and mineralization of the tissue. Therefore, at-home bleaching seems to be much safer than in-office bleaching in terms of molecular variations.
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