[chaorace]

To be clear: drinking water sources often contain flouride and swallowing water is generally not optional. The source can be natural or artificial, but the outcome will be the same if you get an unusually excessive amount during developmental years. As with all nutrients, too much will inevitably become bad for you (thankfully, in the case of flouride, the therapeutic index is quite generous)

With all of this being said, once you're an adult there's no longer any particularly viable pathways from the bloodstream to your outer teeth, so flouride in the body becomes mostly disconnected from flouride in the teeth (and vice versa). Flouride's effects on the body are less well understood, albeit only because we struggle to measure such apparently small effects on a general population.