Enamel fluoride uptake affected by site of application: comparing sodium and amine fluorides

In enamel fluoride uptake studies, the most frequently sampled site is the middle third of the buccal surface. Because different parts of the enamel surface vary in fluoride concentration, the present study investigated fluoride uptake at contrasting sites using two different topical agents. One was a neutral aqueous solution of sodium fluoride containing 2% w/w of fluoride, and the second was an aqueous solution of two amine fluorides containing 1% w/w of fluoride. The enamel of 10 pairs of clinically sound extracted human premolars was etched initially and after treatment with one of these agents on the cervical and middle thirds of the buccal surface and on the proximal surface, yielding the pre- and post-treatment fluoride concentrations of these sites at depths of 5 and 10 microns from the surface. Enamel treated with the amine F solution had significantly higher fluoride uptakes at all sites compared to the NaF-treated specimens. The differences in uptake from the two agents varied with site, being smallest for the buccal middle third enamel and greatest for the proximal enamel. It is suggested that these results relate to possible differences in enamel maturation or to the presence of initial proximal caries, and the greater affinity of amine fluoride for porous enamel. The findings emphasise the importance of obtaining site-specific data in the study of fluoride in enamel.