Effect of nano-carbonate apatite to prevent re-stain after dental bleaching in vitro

Objectives: This study examined the effect of nano-carbonate apatite (n-CAP) to prevent re-staining and the change of enamel surface after dental bleaching in vitro. Methods: Twenty-four bovine specimens were bleached for 2 weeks with 10% carbamide peroxide (CP). After bleaching, the specimens were divided into the following four groups: distilled and deionized water (DDW, negative control), 10% n-CAP, NaF (positive control) and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP, positive control). Each group was subjected to pH cycling for 7 days. The specimens were treated for 4 min 3 times per day and re-staining was induced naturally by artificial saliva in the remineralization process. After pH cycling, the changes in colour were evaluated with spectrophotometry and scanning electron microscopy (SEM). The difference in colour between before and after pH cycling was evaluated using an ANOVA and Tukey test. Results: After pH cycling, the colour difference of n-CAP group was significantly lower than that of the DDW and CPP-ACP groups (p < 0.05). SEM showed that n-CAP particles were deposited regularly on the damaged surface compared to the other groups. Conclusion: 10% n-CAP could significantly maintain the initial colour and protect the damaged enamel structure after bleaching.