Electron spectroscopic studies of interactions between superficially-applied fluorides and surface enamel

Despite comparable acidities and fluoride concentrations, distinctly different characteristics of fluoride deposition and enamel degradation were observed. In the sequence of the amine hydrofluorides, this may possibly be due to the increasing cation polarity. Thus, by the concomitant rise in the dissociation constants of the compounds, the increasing effectiveness of fluoride accumulation is due to the presence of more free fluoride in solution. On the other hand, sodium fluoride shows behavior comparable to that of the unsaturated amine hydrofluoride. Presumably, specific interactions between the cations and surface apatite may favor fluoride deposition. Under present conditions of treatment, however, neither sodium nor quaternary ammonium cations are deposited in significant amounts on tooth surfaces. Thus, the behavior of fluoridizing agents cannot be understood only by their properties in bulk solution. Obviously, specific reaction mechanisms between surface-adjacent solutions and enamel apatite must be considered. Similar reactions have been studied extensively in connection with corrosion problems. The investigations clearly demonstrated that, for the interpretation of mechanisms, all relevant parameters must be considered: the ionic composition of solutions, the temperature, the time of treatment, etc. Thus, a series of additional experiments will be necessary for more insight into the reaction mechanisms of fluoride on superficial dental enamel. The consequence of the present studies is that the cariostatic effect of superficially applied fluoridizing agents cannot be discussed in terms of fluoride accumulation only.