Milk and milk products, such as cheese, have been shown to exhibit anticariogenic properties in human and animal models. CPP-ACP shows an anti-caries effect by suppressing demineralization, enhancing remineralization, or possibly a combination of both. The purpose of this study was to evaluate the effect of CPP-ACP paste on demineralization by observing the treated tooth surface using an FE-SEM. The specimens were prepared by cutting enamel and dentin of bovine teeth into blocks. A few specimens were stored in 0.1 M lactic acid buffer solution for 10 min and then in artificial saliva (negative control). The remaining specimens were stored in a 10 times-diluted solution of CPP-ACP paste or a placebo paste containing no CPP-ACP for 10 min, followed by 10 min immersion in a demineralizing solution (pH = 4.75, Ca) twice a day before storage in artificial saliva. After treatment of the specimens for 3, 7, 21 and 28 days, they were fixed in 2.5% glutaraldehyde in cacodylate buffer solution, dehydrated in ascending grades of tert-butyl alcohol, and then transferred to a critical-point dryer. The surfaces were coated with a thin film of Au in a vacuum evaporator, and were observed under field emission-scanning electron microscopy (FE-SEM). The SEM observations revealed different morphological features brought about by the various storage conditions. Demineralization of the enamel and dentin surfaces was more pronounced with the longer test period in the control and negative control specimens. On the other hand, enamel and dentin specimens treated with CPP-ACP paste revealed slight changes in their morphological features. From the morphological observations of the enamel and dentin surfaces, it could be considered that the CPP-ACP paste might prevent demineralization of the tooth structure.

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The purpose of this study was to determine the elastic modulus of enamel during bleaching procedure with the use of an ultrasonic device. Enamel sections were obtained from freshly extracted bovine incisors. Specimens were exposed to 10％ carbamide peroxide for two hours, followed by an application of a fluoride-containing toothpaste for five minutes and stored in artificial saliva (pH 7.0). An ultrasonic device was used to measure the sound velocities of longitudinal and shear waves as well as elastic modulus. The mean elastic modulus of bleached enamel decreased with time, from 15.5 GPa to 10.1 GPa. Conversely, the elastic modulus of bleached enamel followed by application of a fluoride-containing toothpaste increased with time, from 15.2 GPa to 20.2 GPa. Results of this study indicated that a decrease in elastic modulus associated with bleaching occurred, and that fluoride-containing toothpaste reversed this effect.

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