Effect of Nano-Tricalcium Phosphate and Nanohydroxyapatite on the Staining Susceptibility of Bleached Enamel

Objective . This study was designed to evaluate the effect of nano-tricalcium phosphate (n-TCP) and nanohydroxyapatite (n-HAP) on prevention of restaining of enamel after dental bleaching. Methods . Forty bovine incisors were bleached with 20% carbamide peroxide for two weeks. Afterward, they were divided into five groups based on remineralization solution: no treatment (control), 10% n-TCP, 5% n-TCP, 10% n-HAP, and 5% n-HAP. Each group was daily immersed for 10 minutes in the restaining solution (tea) and for 3 minutes in the remineralization agent, respectively. This protocol was repeated for five days. Subsequently, three digital photographs (baseline, after bleaching, and after restaining) were analyzed by Adobe Photoshop software. The obtained L ∗ , a ∗ , b ∗ , and Δ E parameters were compared using ANOVA and Wilcoxon and Bonferroni tests. Results . After bleaching, there were significant changes in tooth colors ( P < 0.001) while, after restaining and immersion in remineralization solutions, there were no significant differences in L ∗ , a ∗ , and b ∗ values of different groups ( P > 0.05). However, Δ E of 10% TCP was significantly lower than the control ( P = 0.02) while there were no significant differences between the other groups ( P > 0.05). Conclusion . 10% n-TCP could significantly maintain the resultant color and reconstruct the enamel structure after bleaching.