Post-eruptive changes in the fluoride concentrations of human tooth surface enamel

Systemic versus Topical Fluoride

The actual mechanism of fluoride action is still a subject of debate. A dogma has existed for many decades, that fluoride has to be ingested and acts mainly pre-eruptively. However, recent studies concerning the systemic effect of fluoride supplementation concluded that the caries-preventive effect of fluoride is almost exclusively posteruptive. Moreover, epidemiologists have cast doubt on the validity of the 'old' studies dealing with fluoride use. The concept of the posteruptive fluoride effect is supported by in vitro and in situ investigations demonstrating that the mode of action of fluoride can be attributed mainly to its influence on de- and remineralization kinetics of dental hard tissues. Therefore, topical fluoride application (e.g. in the form of fluoridated dentifrices) should be encouraged. There are still important questions open that need to be answered despite existing knowledge about the caries-preventive effect of fluoride.

Fluoride concentrations of the surface enamel of children living in an optimally fluoridated community

The present study was undertaken in a community, where the tap water has been optimally fluoridated since 1959 (1.0-1.2 ppm). The material consisted of 92 children and adolescents including 30 sibling-couples. The mean age of the participants was 11.8 +/- 2.45 (SD) yr. 56 children had consumed fluoridated water all their life, the others only a part of the developmental period of their permanent dentition. Enamel biopsies were taken from 212 permanent teeth and 33 primary teeth by etching the tooth surface for 6 or 30 s. The etch depth was calculated from the mean of dissolved enamel calcium and phosporus. The fluoride concentration in the outermost enamel was almost similar in the teeth of the lifelong residents and the rest of the children. Towards the deeper layers the amount of fluoride decreases depending on its availability during the development of the enamel. There was no striking similarity neither in the fluoride concentration nor in the amount of dissolved enamel between the siblings when compared with the other children. The posteruptive incorporation of fluoride takes place only on the outermost surface of the enamel. The results suggest that in subsurface layers the fluoride exposure during tooth formation is the dominating determinant of enamel fluoride concentration.

Rational use of fluorides in caries prevention. A concept based on possible cariostatic mechanisms

The aim of this review has been to suggest that future fluoride preventive programs should be based on what is at present known about the possible cariostatic mechanisms of fluoride. The relative role of enamel fluoride in caries prevention has become increasingly questioned during the last two decades. No significant relationship has been demonstrated between caries experience of the individual and fluoride content of the enamel. Furthermore, the fluoride content in surface enamel between teeth developed in low and "optimal" fluoride areas is too small to explain any significant effect on dissolution rate of the enamel. As the major explanation for the cariostatic effect of fluoride must therefore be sought in its local effect on the oral environment, the possible effects on plaque colonization, composition and metabolic activities are discussed. The effect of even low concentrations of fluoride in the liquid phase on enamel dissolution is described, and it is concluded that the major cariostatic effect of water fluoridation, fluoride tooth paste and mouth rinses can probably be ascribed to regular increases in fluoride ion activity in the oral fluids. The effect of high concentrations of topical fluoride solutions is thought to be a result of a slow dissolution of calcium fluoride deposited in initial caries lesions, whereby an increased fluoride ion concentration is maintained locally for longer periods of time. Finally, the clinical consequences of these considerations are described.

A 3-year clinical trial into the effect of fluoride content and toothpaste abrasivity on the caries inhibitory properties of a dentifrice

The effect of reducing the abrasivity of toothpaste on dental caries was observed in a 3-year clinical trial involving 1106 11-13-year-old Berkshire schoolchildren were divided into three groups; Group 1 were allocated a low abrasivity paste containing 0.8% sodium monofluorophosphate, Group 2 a paste of conventional abrasivity also containing 0.8% sodium monofluorophosphate and Group 3 a low abrasivity non-fluoride paste. After 3 years the net DMFS increments (clinical and radiographic scores combined) were 4.22 in Group 1, 4.72 in Group 2 and 6.43 in Group 3. The differences between Groups 1 and 3 and between Groups 2 and 3 were highly significant (P less than 0.001). The mean increment in Group 1 was lower than in Group 2 but did not reach statistical significance. Reducing the abrasivity of the toothpaste had no meaningful effect on the standard of oral hygiene and prevalence of gingivitis as measured by the Gingival and Plaque Indices.

Lead in enamel and saliva, dental caries and the use of enamel biopsies for measuring past exposure to lead

Enamel biopsies taken from schoolchildren in a community where exposure to lead was a health hazard were analyzed for lead and fluoride. The children with high enamel lead had significantly higher caries scores than the children with low enamel lead, in spite of the fact that the high lead group also was higher in enamel fluoride. There was no increase in enamel lead with age. The lead in saliva was only a fraction of that in blood. Infants with lead poisoning showed higher saliva lead than a normal infant. The use of the lead in enamel biopsies and in saliva for measuring exposure to lead is discussed.