Effect of remineralization product on the microhardness and surface roughness of enamel after bleaching agents

Abstract

PURPOSE: To evaluate the effect of toothpaste containing sodium fluoride, a commercially available remineralization product, on the microhardness and roughness of enamel after whitening with two different concentrations of hydrogen peroxide. METHODS: 32 premolar teeth extracted for orthodontic reasons were collected. Initial microhardness and roughness values were measured. All samples were immersed in a coffee solution for 1 week to simulate coloration in the oral environment and ensure standardization. Then, the second microhardness and roughness measurements were obtained. Two samples were separated, and the remaining ones were divided into three groups; Group 1: Group 2: Samples treated with Beka HP 30% bleaching agent; Group 3: Samples kept in distilled water. For Groups 1 and 2, the bleaching procedure was applied in three sessions of 15 minutes each, following the manufacturer's instructions. Afterward, measurements of all samples were repeated. To examine the reversibility of surface changes following the bleaching process, a demineralization-remineralization (pH) cycle was applied. Subsequently, microhardness and roughness measurements were repeated, and two samples from each group were set aside for FE-SEM Field emission scanning electron microscope analysis. A total of eight samples underwent FE-SEM analysis at x1,000 and x5,000 magnifications. Data were analyzed using two-way ANOVA and Kruskal-Wallis tests. RESULTS: Initial microhardness values of all samples were the highest values, with a decrease observed after the bleaching procedure. Even though the microhardness of the samples increased in Groups 1 and 2 after the pH cycle, there was no significant difference (P< 0.05). While the roughness values of the samples decreased after the discoloration (P> 0.05), they increased after the pH cycle and there were significant differences between the 4th measurement and the other measurements (P< 0.05). CLINICAL SIGNIFICANCE: The bleaching agent causes changes in the structure of the enamel and reduces microhardness and roughness values. However, remineralizing agents applied during the pH cycle may have a positive effect on microhardness.