For the sake of argument, let’s accept the claim that fluoride strengthens teeth. Topical application to the teeth would seem to make sense. Putting fluoride in the water you drink, use for cooking, and shower/bath in, with the hope that some fluoride would make it to your teeth, makes far less sense.
Many people have thyroid problem and in some cases it may be due to Fluoride. Fluorine is in the same chemical family as Iodine.
https://pubchem.ncbi.nlm.nih.gov/periodic-table/
Iodine is used by the thyroid to make the T3 and T3 hormones that control your metabolism. T3 has three Iodine atoms, T4 four. If an iodine receptor is clogged with fluorine then it can’t accept iodine.
I’ve installed a reverse osmosis water purifier for drinking water. It takes out everything. Unfortunately, it also takes out calcium and magnesium which are good for your bones. So, I have recently added another cannister to the water system to re-introduce minerals to my drinking water.
Unfortunately, it also takes out calcium and magnesium...
Magnesium is also needed to regulate blood pressure. Since I started taking Magnesium my BP has gone into the normal range.