surface enamel of residents of fluoridated and non-fluoridated areas was limited.
Therefore, it is difficult to explain the 50% reduction of caries observed, on the basis
of the fluoride level in the surface enamel. Furthermore, there has been no study to
show any clear-cut inverse relationship between fluoride content of surface enamel
and dental caries.
All the available evidence is that caries results from the presence of an acidogenic
plaque on elements of the tooth mineral. The diffusion of acidic components into the
tooth mineral is accompanied by the reverse diffusion of components of the mineral.
During the carious process there is a preferential loss of calcium, accompanied by
dissolution of magnesium and carbonate. The first clinical sign of enamel caries is the
so-called 'white spot' lesion, where an apparently sound surface overlies an area of
decalcification. The remineralization effect of fluoride has since come into favour. It
has been reported that attacked enamel could re-harden on exposure to saliva and that
softened enamel could be re-hardened by solutions of calcium phosphates in vitro.
However, it is now known that it is the presence of fluoride in the oral cavity, and in
particular, its presence in the liquid phase at the enamel-plaque interface, that is of
most importance.
In the past it was thought that the systemic action of fluoride was important for caries
prevention. This view has completely changed and it is now known that it is the
topical action of fluoride that is essential for caries prevention. It is the presence of
fluoride in the liquid phase at the plaque-enamel interface that is of most importance.
Studies have shown that even low levels of fluoride (0.10 ppm) were effective in
preventing the dissolution of enamel. It has been stated that the activity of the fluoride
ion in the oral fluid that is important in reducing the solubility of the enamel rather
than a high content of fluoride in the enamel. Saliva, the fluid that bathes the teeth has
been extensively studied. The level of fluoride in saliva is thought to be important for
caries prevention and it has been shown that caries susceptible subjects had salivary
fluoride levels of <0.02 ppm, whereas caries resistant subjects had levels of >0.04
ppm.
Key Points
Fluorides
- It is the activity of the fluoride ion in the oral fluid that is of most importance in
reducing enamel solubility rather than having a high content of fluoride in surface
enamel. - A constant supply of low levels of intraoral fluoride, particularly at the saliva/
plaque/enamel interface, is of most benefit in preventing dental caries.
There are a vast number of fluoride products that are available for systemic and
topical use. They can be applied professionally by the dental team or by the patient at
home.
Water fluoridation
This is a systemic method of providing fluoride on a community basis. Over 300
million people worldwide receive naturally or artificially fluoridated water. 1.0 ppm
fluoride was shown by Dean to be the optimum level in 1942. This was in a pre-
fluoride era and perhaps the optimum level needs to be reviewed. There have been