Fluoride and mineral redeposition in outermost layers of bovine enamel during surface softening

Mineral and fluoride concentration changes in the outermost layers of bovine enamel (depth less than 1 micron) were measured after demineralization in unbuffered hydroxyethylcellulose gels of pH = 5.4 with an intrinsic fluoride concentration of about 0.02 ppm. A combination of two nuclear analytical techniques, Rutherford backscattering spectrometry (RBS) and proton-induced gamma ray emission spectrometry (PIGE) was applied to determine the Ca/P molar ratios and F depth profiles, respectively. When compared to deeper layers, a reduced loss of mineral content is observed for the depth range of about 0-0.1 micron corresponding well with a F concentration increase from about 500 to about 5,000 ppm in the same range. These findings are interpreted as a fluoride-induced partial remineralization of the superficial surface layer during an overall demineralization process.