Acid resistance of human enamel by brushing with and without abrasive dentifrice.

Daily brushing with and without abrasive dentifrice pieces of was performed on the ground surfaces of human enamel attached to resin plates which were exposed to the oral cavities of 4 subjects for 8 weeks. The difference in acid resistance between a pair of enamel pieces obtained from the same tooth was examined with atomic absorption spectrometry. After etching with a lactate buffer solution at pH 4.5, the amount of Ca dissolved from the enamel in each pair by brushing without dentifrice was significantly lower than that when brushing with an by abrasive paste. Under SEM, the brushing with paste caused prism structures to appear clearly on the enamel surface, while brushing without dentifrice caused a nonbacterial organic film, i.e., salivary pellicle, to cover the surface. These results indicate that the pellicle is protected by mineral deposits when brushing without dentifrice but brushing with an abrasive paste tears off the unmineralized pellicle. Brushing without dentifrice induces a stronger resistance to acid on the enamel surface.