There is a lot of anti fluoride hysteria that wants to eliminate water fluoridation, which has eliminated a cash cow for dentists = frequent cavities = fillings. The rise in fluoride made dental incomes decline as dental health improved. (sugar in soda drinks kept them alive). This paper notes that cleaning teeth and applying a topical solution and holding for 5-10 minutes and then washing is best. High fluoride toothpaste is also better than adding to water. The water method is automatic, while tooth painting = dental visit costs.
https://www.ncbi.nlm.nih.gov/books/NBK587342/
There are areas with high natural fluoride, that can stain teeth, but there is no apparent reduction in IQ in those areas. Most free fluoride is grabbed by teeth from the blood and is laid down as hydroxy fluoro apatite where it makes the tooth structure more competent as a solid by minutely filling the matrix so it has fewer flaws that bacterial acids can use to open gaps. https://en.wikipedia.org/wiki/Fluorapatite
I have never seen any study showing that the fluoride from the blood can have any influence on the teeth.
The enamel of the teeth does not have blood vessels, so it cannot "grab fluoride" from blood. As far as it is known, the biomineralized calcium phosphate is always hydroxyapatite. When the hydroxyapatite of the enamel of the teeth is in contact with a solution containing fluoride ions, there is a passive ion exchange process (i.e. not mediated by biological enzymes) which results in partial replacement of the more soluble hydroxyapatite with the less soluble fluorapatite.
There is no doubt that using a tooth paste with fluoride or washing the mouth with a fluoride solution can prevent caries.
However there has never been any evidence whatsoever that drinking fluoride has any beneficial effect, beyond that of the teeth being washed by the fluoride solution before ingesting it. On the contrary, it is well known that too much fluoride in the drinking water interferes with bone growth, as it happens in some countries where the drinking water is naturally rich in fluoride.
If dentists are so interested in challenging the water fluoridation narrative so that they can do more fillings - why do they offer that tooth painting?
Probably because cavities aren't a cash cow for dentists. More expensive crown and veneer procedures, and other elective procedures, are the cash cows.
