About three-fourths of the water that comes from community water supplies in the US is fluoridated, meaning that it has the mineral fluoride added to it. This mineral has been found to prevent and reduce the decay of tooth enamel, which leads to cavities. Although water naturally contains fluoride, it is at lower levels than is believed to be optimal for dental health. Fluoridation of water in the US was introduced in 1945, and health experts have ranked the practice as one of the 10 greatest public health works of the 20th century.
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