Fluoride Deposited by Topical Applications in Enamel

Abstract

A single topical treatment with three different fluoride-containing systems on human enamel resulted both in an enrichment of the F content in the enamel and an accumulation of F reaction products on the enamel surface. The aim of this study was to quantify the fluoridation of an APF gel and two F-containing lacquers and to measure the amounts of KOH-soluble fluoride and acquired fluoride separately. Blocks of intact enamel were treated with the topical agents and subsequently exposed to 1 M KOH for 24 h. No measurable amount of fluoride was dissolved from the control specimens of intact enamel by this treatment. Results are presented from experiments with the three different fluorides applied to natural surfaces of the same tooth. The amount of fluoride in the KOH solutions for the APF gel and Duraphat® was comparable (≈ 20 μg · cm^-2); Fluor Protector® deposited more than twice this amount. The layer thickness of CaF₂ based on KOH-soluble fluoride was quantified. The acquired amount of fluoride in the enamel after exposure to KOH was not related to the pH value of the agent nor to the total amount of fluoride deposited on and in the enamel. The total amount of aquired fluoride in the enamel – 30 μm thick layer – was 4, 9 and 10 μg cm^-2, respectively, for APF gel, Duraphat and Fluor Protector; the total amount of KOH-removable fluoride and acquired fluoride in the specimens was 28, 38 and 60 μg cm^-2, respectively. The contact time plays a dominant role in the fluoridating effect in deeper layers (5–30 μra) in the enamel as well as for the amount of CaF₂ deposited in the enamel surfaces for agents at the same pH value.