Abstract
This in vitro study evaluated the effect of sodium bicarbonate and sodium ascorbate on the microtensile bond strength of an etch-and-rinse system to bleached bovine enamel. Sixty bovine enamel blocks (4x4 mm) were flattened and randomly allocated into 5 groups: G1 (negative control): without treatment; G2 (positive control): bleached with 35% hydrogen peroxide (HP); G3: bleached and stored for 7 days in artificial saliva before restorative procedures; G4: bleached and treated with 10% sodium bicarbonate solution for 5 min; G5: bleached and treated with 10% sodium ascorbate hydrogel for 15 min. HP gel was applied twice (20 min each, except in G1) and the adhesive restorations were performed. After 24 h, the specimens were sectioned into sticks and submitted to microtensile bond strength testing with a crosshead speed of 0.5 mm/min (n=12). As a complementary visual observation, the enamel surfaces of the G1 and G2 specimens were evaluated with scanning electron microscopy. Data were analyzed by one-way ANOVA (p<0.05). The means (standard deviation) were: G1: 24.22±7.74; G2: 18.29±5.88; G3: 40.88±7.95; G4: 19.95±5.67 and G5: 24.43±6.43. Adhesive failures were predominant in all groups. The comparison between the treatments indicates that waiting 7 days after bleaching is still the most effective approach. When this waiting period is not possible, application of sodium ascorbate or sodium bicarbonate seems to be a good alternative. Therefore, the practicality of obtaining sodium bicarbonate in the bleaching kits and its higher stability enables its clinical use.
Highlights
Pigmentation of dental structures is one of the most common clinical issues related to aesthetics in dentistry
The application of 10% sodium bicarbonate solution (G4) and 10% sodium ascorbate hydrogel (G5) recovered the microtensile bond strength values after bleaching since the mean values were similar to the negative control group G1 (p>0.05), which showed an intermediate performance
There was a reduction in the bond strength of G2 compared to G1. This decrease in the bond strength may be attributed to changes in the enamel surface, such as precipitation that may negatively influence the adhesive process [16] or perhaps due to the presence of residual oxygen which inhibits the full polymerization and proper penetration of the resin tags [1,4,5]
Summary
Pigmentation of dental structures is one of the most common clinical issues related to aesthetics in dentistry. The general approach is to defer any adhesive restorative procedure for a time interval ranging from 24 h to 4 weeks after bleaching [1,4,5,6,7], because reduction of the bond strength is temporary. Aiming to reduce this time interval, the antioxidant products were introduced as an interesting strategy since they can remove or reduce the residual oxygen [8,9]. Ozelin et al [11] concluded that this substance must to be applied for at least 60 min to improve bond strength values, which hinders its clinical practice
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