Fluoride Deposition in Enamel from Monofluorophosphate Application

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Abstract
In vitro topical application of sodium monofluorophosphate (MFP) to enamel causes very limited fluoride enrichment. Thus, only a few hundred ppm fluoride penetrated to a depth of 5 μm after a 5 min application even when the acidity was decreased from pH 7.0 to 4.4 or the concentration varied from 0.4 to 1.5 M. Greater penetration was seen at pH 3.2. More fluoride penetrated into the enamel from a neutral MFP solution than from a neutral sodium fluoride solution that contained the same amount of fluoride ion. Most of the fluoride in the enamel was already ionic after 5 min. Fluorapatite formation could not be demonstrated immediately after a 5 min application but was observed after a 24 h posttreatment incubation. Greater penetration of fluoride and enhanced formation of fluorapatite resulted when the application time was increased to 6 h. Neutral ammonium MFP was more reactive than neutral sodium MFP.