Effects of Different pH Conditions on Enamel Erosion Repair by Nano Fluorapatite Pastes

The effects of different pH conditions on enamel erosion repair by nano fluorapatite (n-FA) pastes were evaluated in this study. Eighteen human dental enamel blocks with artificially-induced erosion were randomly divided into three groups that were coated with n-FA pastes with 3 different pH values (pH < 1, pH = 4.5 and pH = 7.5, respectively) for 15 minutes. SEM, XRD, XPS, Vickers microhardness test and mass measurement were performed for the enamels before and after treatment. A layer of enamel-like fluoride substituted hydroxyapatite was observed on the surface of all the samples. After treatment by n-FA pastes with 3 different pH values (pH < 1, pH = 4.5 and pH = 7.5), the Vickers micro-hardness value was respectively changed to 125.9 HV, 252.1 HV and 304.9 HV from 241.3 HV of the artificial enamel erosion, and mass loss was 0.75 mg/mm(2), 0.41 mg/mm(2) and 0.30 mg/mm(2), respectively. SEM analysis showed that the surface of the enamels treated by n-FA pastes with pH 7.5 and pH 4.5 was smoother than those treated by n-FA pastes with pH < 1. These results suggested that the pH value had significant effects for the repairment of enamel erosion with n-FA pastes. This study demonstrated that the n-FA paste with neutral pH value (7.5) for enamel erosion repair would not only significantly enhance the enamel surface hardness, but also avoid the enamel mass loss and increased surface roughness.