Skeletal fluorosis is well known to occur in regions where the natural drinking water has high fluoride content, e.g. in some regions from India and China.

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I am not aware of any study about the incidence of fluorosis in places where the drinking water is fluoridated artificially, but it would be very difficult to do such studies, due to the lack of comprehensive past statistics, to the many confounding factors and because only few of the existing cases are detected. When someone heals a bone fracture they almost never do additional complex tests to determine if it was normal for the fracture to happen or its likelihood was increased by a condition like fluorosis.

In any case no such studies are really needed, because when you have an activity like ingesting fluoride, for which there is absolutely no evidence of benefits and no known mechanism by which it could provide benefits, but there is weak evidence that it might be harmful and there are known mechanisms by which it may be harmful, then there is no rational doubt whether that activity should be done or not.