Tangential anecdote: I had a co-worker in India who grew up in a region with excessive naturally occurring fluoride in the groundwater. As a result, he had blotchy dark brown teeth - not stained, the substructure of the teeth were brown all the way through. The side effect was that the teeth were substantially stronger than regular teeth, as were presumably his bones. My understanding is that extremely high fluoride can mess with bone and tooth development in the embryo, with lower levels only showing up as the cosmetic blotches but no developmental issues.