Diffusion of fluoride ions in dental enamel at pH 7

The penetration and uptake of both radioactive (18F) and stable fluoride (19F) in bovine enamel were investigated. Buffered pH 7 NaF solutions were employed. Penetration profiles of both 18F and 19F in enamel were determined by using a sectioning technique. 18F and 19F concentrations decreased exponentially with increasing penetration distance. The uptake of 18F in enamel can be described by a power function of the immersion time, with an average power of 0.76. The results agree reasonably with our previously published theoretical model for the diffusion in enamel, based on simultaneous diffusion in enamel pores and in the hydroxyapatite crystallites. The diffusion coefficients of fluoride ions in enamel obtained from the application of the model to the results presented here, were: D = 0.9 x 10(-17) cm2/s in the crystallites and D' = 3.3 x 10(-10) cm2/s in the enamel pores. An average penetration depth of fluoride ions at pH 7.0 of 8 micron in 4 hours has been calculated.