The State of Fluorine in Dentifrice Systems

Abstract

Using ¹⁸F in an adsorption and desorption technique and by means of chemical F analyses, it has been possible to establish a distribution pattern for F in dentifrice systems.

When a dentifrice is dispersed in water, parts of the F remain in the dentifrice in a) inactive form, or b) adsorbed form; parts are in solution, as c) ionic F, d) undissociated HF, or e) as complexed F; parts are present in the enamel surface presumably as f) CaF₂, or g) as Ca₅(PO₄)₃F, or h) as adsorbed complexes. Some F is possibly acquired by the enamel by means of i) exchange processes.

The results obtained compare reasonably well with theoretical expectations, indicating that the deposition of F in the enamel is a matter of physico-chemical solubility. The solubility product of fluorapatite seems to be a governing principle. No relationship was established between the fluoride ion concentrations (activities) and the uptake of F in the enamel. It was suggested that not only the chemical composition of a dentifrice but also its physical properties, are of importance for the behaviour of F in dentifrice systems.

An acidulated, NaF-containing dentifrice has been found to possess superior parametric values as compared to Na₂PO₃F-containing dentifrices. A neutral, NaF toothpaste containing methylmetacrylate and liquid paraffin, retained 27 % of its F-content in the dentifrice phase whereas only 4% was deposited in the enamel powder.