[Secret Agent Man]

not all fluoride is equal.

sodium fluoride is a waste byproduct of other chemical processes, is toxic to humans, and that is what is put in drinking water and toothpaste.

calcium fluoride is what the body needs to help your teeth and bones. it is not an industrial byproduct and is much more expensive compared to sodium fluoride, and so it is not used by water departments and toothpaste makers.

[Olog-hai]

They sell NaF in pills for cavity prevention and osteoporosis treatment. AFAIK, the most common actual water fluoridation agent is hexafluorosilicic acid (H₂SiF₆)

Since NaF has an estimated lethal dose between 5 and 7 grams for an adult human, that’s not too toxic. CaF₂ is insoluble in water; it has to be produced by the body versus being ingested. Fluoride poisoning, incidentally, involves CaF₂ being produced by the body in excessive quantities, resulting in hypocalcemia.