[dypsilon]

There is a paper linked on Wikipedia stating that studies conducted in Germany showed that "Water fluoridation was followed by a decrease of caries, and interruptions in fluoridation were followed by increasing caries levels." but also "There was a significant caries decrease down to the lowest DMFT (2.0) since 1959 in spite of the fact that only F-poor water was available over years [...] explained by changes in caries-preventive and environmental conditions."

https://onlinelibrary.wiley.com/doi/abs/10.1034/j.1600-0528....