Fluoride is a chemical found in many substances. In the human body, fluoride acts to prevent tooth decay by strengthening tooth enamel and inhibiting the growth of plaque-forming bacteria. After researchers discovered this characteristic of fluoride, fluoridation--the process of adding the fluoride to public water supplies--began. It all started with Frederick S. McKay, a Colorado Springs, Colorado, dentist, in the early 1900s. McKay noticed that many of his patients had brown stains, called "mottled enamel," on their teeth. McKay set out to find the cause, helped by researcher Greene V. Black (1836-1915) of Northwestern University and other dentists. By 1916, McKay believed the mottling was caused by something in the patients' drinking water. By 1928, he concluded that mottling was linked to reduced tooth decay. In 1931, at the suggestion of an Alcoa chemist in Bauxite, Arkansas, McKay verified that drinking water from places with a...