How wide-spread is this problem?

The US Public Health Service estimates that 1 in 5 children have dental fluorosis. (By the way, all native reservations in the US have mandatory fluoridation, resulting in very high incidents of dental fluorosis in those areas.) Realistic figures are as high as 80% in some areas in the US and as high as 69% in Canada. Studies have been conducted directly linking bone tissue damage to children with dental fluorosis. Fluorosis is the first visible sign that destructive effects of fluoride are also occurring in bone, connective tissue, immune and enzyme functions.