Humans may have a u-shaped curve relationship with fluoride, where some fluoride is not harmful and may serve a role.

“there are some some studies that show that with excess fluoride bone density increases but bones do not become stronger they can actually become more brittle and there are other studies which show that when lower amounts of fluoride are used that perhaps there is an improvement in the strength of the bones so i think that there is a sweet spot for fluoride just like so many things this is probably a u-shaped curve meaning that zero fluoride is probably not great for humans we've probably been always been exposed to some it's an element that occurs naturally in the human diet in our environments there's a sweet spot sweet spot is probably below what most people are getting right now in my belief and then as you get to be too much fluoride you see systemic manifestations that are quite pathological fluorosis in the teeth bones etc”