No joke. That is a major money maker. There is minimal cost per-use and your insurance pays $200 for it (my last one was $186.00 for instance). The dentists would be crazy not to recommend them as of often as possible.
Fluoride "rinses" are likely up there too. Rinse for a few seconds and they charge the insurance $50 or something for it.
However you don’t swallow mouth rinses like Act, so any nonobvious issue is also greatly reduced.
I personally intend to stay vigilante to dihydrogen monoxide poisoning.
Thus showing that something is toxic doesn't mean it's something you should never consume. And note that fluoridation started because it was observed that the people in areas with higher natural levels benefited.
To be fair, the quantity of fluorine that would kill you if you consumed it is too small to notice. What's saving you from the fluoride isn't that there isn't enough fluorine to be dangerous - it's that the fluorine is accompanied by things that make it less dangerous.
Table salt is 60% highly toxic chlorine, but you're free to coat your food in it because it's 40% sodium, too. In combination, they're fine and in fact necessary to life. Consumed separately in equal amounts, either would kill you. The quantity isn't what matters.