Fluoride acquisition on and in human enamel during topical application in vitro.

Fluoride acquisition during topical fluoride treatment was studied after different time intervals, at different concentrations and at different pH. The effects of pretreating the enamel with Ca++, and of pre-etching were also tested. Four experimental groups of repeated measures design were established. Chemical assessments were made of the amounts of fluoride formed on (as alkali soluble fluoride, i.e., calcium fluoride) and in enamel (as firmly bound fluoride). The depositions on enamel were also demonstrated by SEM. The amounts of alkali soluble fluoride on enamel increased with time, concentration, pH-decrease and calcium availability. The time of exposure seemed to be the major factor. The amounts of fluoride deposited on enamel outranged by far (greater than 70%) the amounts of fluoride acquired in the enamel. The formation of alkali soluble fluoride on enamel is probably limited by the availability of calcium ions. It is suggested that the fluoride on enamel may protect the enamel surface and serve as a reservoir of fluoride.