Uptake of fluoride by human surface enamel from ammonium bifluoride and consequent reduction in the penetration in vitro by caries-like lesions

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In-vitro fluoride uptake by mid-coronal, premolar enamel surfaces from topically-applied solutions of NH 4HF 2 was determined using a multi-electrode system for fluoride and calcium analyses. In tooth surfaces dehydrated with 100 per cent ethanol before the topical application of 1 per cent aqueous NH 4HF 2, there was a 2–3-fold increase in fluoride concentration up to a depth of 50 μm and fluoride enhancement to a total depth of 100 μm into the enamel. Caries-like lesions were induced in vitro in both treated and untreated enamel by the use of acidified, 6 per cent hydroxymethyl-cellulose gel containing 0.04 per cent hydroxyapatite at pH 4.5. After 120 days exposure, the mean depth of lesion penetration in the controls was 149 (±34) μm. No lesions occurred in half the treated specimens; in specimens with lesions, the mean depth of penetration was 19 (± 3) μm. Thus, NH 4HF 2 was a potent inhibitor of caries-like lesion formation in vitro.