• http://www.ncbi.nlm.nih.gov/pubmed/17333303?dopt=Abstract
• http://www.newmediaexplorer.org/chris/Pizzo-2007.pdf

Role of water fluoridation in caries prevention: current key issues Systemic vs topical effect of fluoride

A dogma has existed for many decades, that fluoride acts mainly preeruptively with its incorporation into the hydroxyapatite crystals, leading to the formation of fluorapatite, a less soluble enamel apatite [12].

Research over the last 20 years, however, has changed our understanding of this concept [6, 12, 15, 23]. A number of studies showed that the differences in fluoride concentration in surface enamel between permanent teeth from low-fluoride and fluoridated areas were minimal, whereas an inverse relationship between fluoride levels in enamel surface and caries experience was not found [12, 15].

Several laboratory investigations have clearly demonstrated that the presence of low levels of fluoride (0.03 ppm or higher) in saliva and plaque fluid reduces the rates of enamel demineralization during the caries process and promotes the remineralization of early caries lesions [11, 12, 15].

On the other hand, the level of fluoride incorporated into enamel by systemic ingestion was proved to have no significant effect in preventing/reversing caries [11]. Moreover, the reexamination of clinical/epidemiological data from early and recent CWF studies supported the current view that the cariostatic effect of fluoride is almost exclusively posteruptive and the mechanism of action is topical [12, 15, 23].

A person living in a fluoridated community, in fact, may increase this level to about 0.04 ppm several times during the day [23]. In addition, it has been found that fluoride may also affect oral plaque bacteria by the interference with acid production [3, 6, 11]. The implications of these concepts are that frequent exposure to low concentration of fluoride in the oral cavity is the most important factor in preventing/controlling caries; on the other hand, the anticaries effects of systemic fluoride are recognized to be minimal [6, 11, 23, 38].