Abstract
Equilibration in 1M KOH for 24 hr of from 0.6 to 30 μg ml −1 of CaF 2 and different amounts of fluorapatite resulted in dissolution of the CaF 2 while the fluorapatite remained intact. CaF 2 was also selectively dissolved from mixtures of CaF 2 and pre-fluoridated powdered human enamel. No fluoride was dissolved from blocks of intact enamel treated in 10 ml of KOH for 24 hr, but most of the fluoride deposited from topical treatments was lost by this treatment. Findings on enamel blocks treated with topical solutions of acidulated phosphate fluoride and NH 4F showed that the fluoride retained after exposure to KOH was not related to the initial uptake. Scanning electron microscopic examinations of F-treated enamel surfaces verified the removal of CaF 2 by KOH. The concentrations of Ca, P and F in the KOH solution after equilibration with different amounts of CaF 2, hydroxyapatite and fluorapatite showed that rapid release of F and Ca from CaF 2 depressed dissolution of the apatites, and that the system was governed by the solubility products of CaF 2 and Ca(OH) 2. It is concluded that 1M KOH can be used for the assessment of the CaF 2 formed from topical treatments in in vitro systems.
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