The response of intact and experimentally altered human enamel to topical fluoride

Abstract

Intact enamel, treated for 1 min with dilute phosphoric or hydrochloric acid and then exposed to phosphate fluoride followed by 24 hr washing in a metastable calcium phosphate solution, acquired larger amounts of fluoride in greater depth than similarly fluoride-exposed unetched enamel. More fluoride was deposited after treatment with 0.05 M than 0.01 M phosphoric acid, while treatment with 0.01 M acetic acid was ineffective. Enamel deprived of organic constituents by extraction with ethylenediamine acquired similar amounts of F as enamel treated with 0.01 M phosphoric acid. Analyses of teeth, F treated in vivo and extracted 1 wk later confirmed that mild etching with phosphoric acid greatly increased the deposition of F. The enamel thus treated was not visibly altered. Analyses of aqueous washings suggested that the deposited F was present primarily as fluorapatite, and that the minute amounts of enamel which dissolved as a result of the treatment were attributable to formation of CaF 2, and not to enamel demineralization. It was concluded that the combined treatment of mild etching with phosphoric acid and topical application with acid phosphate fluoride is worthy of a clinical trial.