Fluoride in the water: Too much of a good thing?

In the early 1900s, a young dentist named Frederick McKay moved to a Colorado town where the residents' teeth - though in some cases stained chocolate brown - had far less decay than was typical back then. He and other researchers eventually linked the phenomenon to fluoride in the town's drinking water - a eureka moment that would usher in what is often called one of the 10 great public health achievements of the 20th century.