Current Concept on the Anticaries Fluoride Mechanism of the Action

The paper discusses a possible new concept of the role of fluoride and its mechanism of action in caries prevention. In the past fluoride inhibition of caries was ascribed to reduced solubility due to incorporation of fluoride (F–) into the enamel minerals (firmly bound fluoride or fluorapatite). Based on the new findings, it appears that fluoride, either released into or present in the fluid phase bathing the hard tissue, is more important for the reduction of caries development and progression. There is convincing evidence that fluoride has a major effect on demineralization and remineralization of dental hard tissue and that it interferes with acid production from cariogenic bacteria. The provision of dissolved fluoride is the key to successful therapy. The source of this fluoride could either be fluorapatite or calcium fluoride (CaF2) (like) precipitates, which are formed on the enamel and in the plaque after application of topical fluoride. The precipitates of calcium fluoride do not dissolve quickly as was initially believed. Calcium fluoride coating at neutral pH by pellicle proteins and phosphate is the main reason for this. The dissolution of the fluoride from calcium fluoride is pH dependent. At lower pH, the coating is lost and an increased dissolution rate of calcium fluoride occurs. The CaF2 , therefore, act as an efficient source of free fluoride ions during the cariogenic challenge. These are subsequently incorporated into the enamel as hydroxyfluorapatite or fluorapatite

Effect of Amine Fluoride on Enamel Surface Morphology

In this in vitro study, examination of the enamel surface morphology after topical application of an amine fluoride solution with different fluoride (F) content was carried out. Sound human enamel slabs were treated with an amine fluoride solution containing either 1.0, 0.5 or 0.25% F for 3 min. during 3 days. All slabs were examined using scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDS) qualitative analysis. The globular precipitates were revealed in all treated specimens, regardless of F content. The distribution of the deposits was more homogeneous in groups treated with higher concentrations; however, the globules were larger and more cubical in groups treated with lower fluoride concentrations. These larger globules could be less soluble and thus serve as a fluoride reservoir for a more extended period and so they could contribute to the caries preventive effect in professional topical products with lower fluoride concentration. Following the 24-hour treatment with KOH the precipitates could be removed; however, the enamel surfaces covered with the precipitates were less degraded than the untreated enamel. The EDS qualitative analysis showed that the intensities of fluoride signals were increased with the higher concentration of fluoride in an amine fluoride solution, while the intensities of calcium signals were decreased. The enamel surface precipitates were alkali-soluble, but we were not able to demonstrate that they are pure calcium fluoride