Abstract
The aim of this study was to evaluate the possibility of fluoride solutions applied to enamel to protect pulp cells against the trans-enamel and transdentinal cytotoxicity of a 16% carbamide peroxide (CP) bleaching gel. The CP gel was applied to enamel/dentin discs adapted to aicial pulp chambers (8 h/day) during 1, 7 or 14 days, followed by fluoride (0.05% or 0.2%) application for 1 min. The extracts (culture medium in contact with dentin) were applied to MDPC-23 cells for 1 h, and cell metabolism (MTT assay), alkaline phosphatase (ALP) activity and cell membrane damage (flow cytometry) were analyzed. Knoop microhardness of enamel was also evaluated. Data were analyzed statistically by ANOVA and Kruskal-Wallis tests (α=0.05). For the MTT assay and ALP activity, significant reductions between the control and the bleached groups were observed (p<0.05). No statistically significant difference occurred among bleached groups (p>0.05), regardless of fluoride application or treatment days. Flow cytometry analysis demonstrated 30% of cell membrane damage in all bleached groups. After 14 days of treatment, the fluoride-treated enamel presented significantly higher microhardness values than the bleached-only group (p<0.05). It was concluded that, regardless of the increase in enamel hardness due to the application of fluoride solutions, the treated enamel surface did not prevent the toxic effects caused by the 16% CP gel to odontoblast-like cells.
Highlights
Two-thirds of the patients subjected to tooth bleaching techniques complained about postoperative tooth hypersensitivity [1]
The data obtained in the present study, which are in line with previous investigations [7,8], showed similar reduction in cell metabolism for all experimental groups in which 16% carbamide peroxide (CP) gel was used, even after a single application of the product to the enamel surface
Min et al [21] reported that odontoblast-like MDPC-23 cells exposed to high concentrations of hydrogen peroxide (HP) exhibit a significant increase in intracellular reactive oxygen specie (ROS) production, which cause intense oxidative stress in this cell line
Summary
Two-thirds of the patients subjected to tooth bleaching techniques complained about postoperative tooth hypersensitivity [1] This negative side effect may be explained, at least in part, by the inward hydrogen peroxide (HP) movement through enamel and dentin, which, in turn, causes inflammatory pulp reaction when in contact to the pulp cells [2,3]. Some studies have shown that the application of bleaching gels on enamel causes protein matrix disruption by free radical oxidation as well as mineral loss [10] These superficial defects increase enamel porosity, which enhances trans-enamel diffusion of HP to reach deep areas of the dentin and pulp chamber [11]. At-home tooth bleaching using low concentrations of carbamide peroxide (CP) gels, such as 10% or 16%, has been considered as a more friendly treatment
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