Objectives: The aims of this study were to evaluate inhibition effects of nano-carbonate apatite (n-CAp) dentifrice for post-bleach staining and to compare efficacy of color measurement between spectrophotometer and digital image analysis. Methods: The enamel specimens were bleached with a 35% Hydrogen peroxide gel. The compositions of experimental dentifrice were as follows: 0%, 5% and 20% n-CAp and commercial nano-hydroxyapatite dentifrice. The bleached specimens were treated for 24 hours with dentifrice slurries. The treated specimens were stained in an extrinsic staining solution composed of TSB broth, containing Sarcina lutea, for a 72 hours. The color changes in each specimen were measured before and after extrinsic stains using a spectrophotometer and a digital camera. After taking a digital image using a camera, Casmatch stickers were used to evaluate the in change whiteness with a correction for each image. Results: Extrinsic staining showed much stronger stain relapse in the group treated without n-CAp than in those treated with the 5 and 20% n-CAp solution, which maintained a glossy appearance. After extrinsic staining over a 72 hour period, digital image analysis showed that the control group had an approximately 68% lower gray value, while the n-CAp groups showed an approximate 75% decrease. In both cases, a 5 and 20% concentration, the efficacy of stain inhibition was similar (p<0.05). Spectrophotometric analysis showed that the control and hydroxyapatite group were decreased E value about 80%, while the n-CAp groups were decreased about 83 and 86% respectively low and high concentration, because it was quits difficult to focus on a precise ROI on the specimen. Conclusion: The dentifrice containing nano-carbonate apatite effectively inhibits extrinsic stain after inoffice bleaching by hydrogen peroxide. Moreover, the digital image analysis is the simple and powerful method for color measurement better than spectrophotometer.
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