DIFFUSION OF FLUORIDE IONS IN DENTAL ENAMEL AT PH-7

Abstract

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 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 a 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 F- in enamel obtained from the application of the model to the results presented were: D = 0.9 .times. 10-17 cm2/s in the crystallites and D'' = 3.3 .times. 10-10 cm2/s in the enamel pores. An average penetration depth of F- at pH 7.0 of 8 .mu.m in 4 h was calculated.