Abrasion of human enamel by brushing with a commercial dentifrice containing hydroxyapatite crystals in vitro

Automatic toothbrushing with a commercial dentifrice containing hydroxyapat ite (HAP) crystals was performed on the tangential polished surfaces of sou nd human enamel, mainly consisting of biological apatite similar to HAP, fo r 10 min in vitro. The X-ray diffraction peaks of HAP, brushite (DCPD), and monetite (DCP) crystals were detected from the dentifrice. After brushing, the enamel surfaces were observed with a scanning electron and a confocal scanning laser microscope. The brushing caused larger abrasive loss and mor e remarkable roughness of the enamel surfaces following the broad traces of brush bristles and the exposure of prism structures than brushing with a d entifrice containing only DCPD, which we previously reported. We claim that the fine granular-shaped HAP crystals of the dentifrice indicated as an ac tive ingredient for preventing enamel caries possess stronger abrasivity of sound enamel than the DCPD and DCP as abrasives on account of their Mohs h ardness values rather than sizes and shapes. The HAP crystals of dentifrice s may not occlude the small defects of early caries enamel, but erode them more strongly as an abrasive than the other abrasives.