[Fluoride ions and apatite recrystallization of apatite in enamel]

The authors discuss the basic process on which the principle of fluoridation in based--i.e. the mutual exchange of F- ions and the OH- group in hydroxyapatite of enamel. Model investigations assessing the energy difference between hydroxyapatite and F- and fluorapatite and the OH- group indicate that fluorapatite tends to release steadily fluoride ions and to change into hydroxyapatite. This tendency, apparently inopportune from the aspects of caries prevention, ensures, however, a permanent low F- level above the enamel surface. The presence of F- ions facilitates recrystalization of apatite in the initial caries stage. The investigation tries to throw new light, from the point of view of theoretical chemistry at a molecular level, on the mechanism of remineralization, one of the most important ways which implements the preventive action of fluoride.