Effect of three nanobiomaterials on microhardness of bleached enamel

OBJECTIVES: The aim of this in vitro study was to evaluate the effect of incorporating three different nanobiomaterials into bleaching material on microhardness of bleached enamel. MATERIALS AND METHODS: The crowns of 24 extracted sound human molars were sectioned. Sixty enamel specimens (2 × 3 × 4 mm) were selected and divided into five groups (n = 12): Group 1 received no bleaching procedure (control); Group 2 underwent bleaching with a 40% hydrogen peroxide (HP) gel; Groups 3, 4, and 5 were bleached with a 40% HP gel modified by incorporation of bioactive glass (BAG), amorphous calcium phosphate (ACP) and hydroxyapatite (HA), respectively. The enamel microhardness was evaluated. The differences in Knoop microhardness data of each group were analyzed by one-way ANOVA, followed by post hoc Tukey tests. RESULTS: Significant differences were observed between the study groups. The enamel microhardness changes in Groups 1, 3, 4, and 5 were significantly lower than that of Group 2 (p < 0.001). CONCLUSIONS: Within the limitations of this study, it can be concluded that incorporation of each one of the three tested biomaterials as remineralizing agents might be effective in decreasing enamel microhardness changes subsequent to in-office bleaching.

[Effect of bleaching on microhardness of two nanofilled and one microhybrid composite resins]

Discolored teeth can be treated by various techniques, including direct composite resin veneers, indirect porcelain veneers, ceramic crowns and bleaching agents. The aim of this study was to evaluate the effect of at-home and in-office bleaching agents on the surface microhardness of one microhybrid [Point 4] and two nanofilled [Filtek Supreme and Premise] composite resins. Opalescence PF with 20% carbamide peroxide and Opalescence Quick with 35% carbamide peroxide were used as at-home and in-office bleaching agents, respectively. Fifty samples from each composite resin, including Point 4 microhybrid, Premise and Filtek Supreme nanofilled composites resins were prepared and exposed to bleaching agents. For each composite resin the samples were randomly divided into five groups of 10 and designated as: control, two-week at-home, four-week at-home, one-time in-office and two-times in-office bleaching groups with two-week intervals. After the appropriate bleaching procedures on samples of each group, microhardness measurements were carried out on each sample. Data was analyzed using ANOVA and post hoc Tukey HSD test [p value < 0.05]. There were significant differences in mean surface microhardness values of each composite resin type. No significant differences were observed in mean microhardness values of Point 4 between four-week at-home and one-time office, Filtek Supreme between two-week at-home and four-week at-home, and Premise between one-time in-office and two-time in-office bleaching groups. Under the limitations of the present study, it was concluded that the microhardness of three composite resins tested in the present study were affected by bleaching agents