Fluoride is a chemical found in many substances. In the human body, fluorideacts 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. By1928, 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 high degree of tooth mottling containedunusually high levels of naturally occurring fluoride. H. Trendley Dean, a dentist with the United States Public Health Service, also studied the connection between mottling and fluoride in the 1930s. By the early 1940s, Dean andhis research team had established that one part per million was the ideal level of fluoride in drinking water, substantially reducing decay while not causing mottling. Following safety tests on animals, the Public Health Service conducted field tests. In 1945 the public water systems of Newburgh, New York,and Grand Rapids, Michigan, became the first ever to be artificially fluoridated with sodium fluoride. Simultaneously, a group of Wisconsin dentists led by John G. Frisch inaugurated fluoridation in their state. Results of these tests seemed to show that fluoridation reduced dental cavities by as much as two thirds. Based on those results, the United States Public Health Service recommended in 1950 that all United States communities with public water systemsfluoridate. Later that year the American Dental Association (ADA) followed suit, and the American Medical Association added its endorsement in 1951. Eventhough virtually the entire dental, medical, and public health establishmentfavored fluoridation, the recommendation was immediately controversial and has remained so. Opponents objected to fluoridation because of possible healthrisks (fluoride is toxic in large amounts) and concerns about being deprivedof the choice whether or not to consume a chemical. While referenda have blocked fluoridation in a number of communities, nearly 60 percent of people inthe United States now drink fluoridated water. Fluoridation is also practicedin about thirty other countries. The initial claims that fluoridation of drinking water produced two-thirds less tooth decay have been modified to about20 to 25 percent reduction. Other ways of applying fluoride have been developed. In the 1950s Procter and Gamble had the idea of adding the chemical to toothpaste. First, researchers at Indiana University had to find a way to keepstannous fluoride from bonding with toothpaste abrasives. Once this problem was overcome, Procter & Gamble introduced its new "Crest--with Fluoristan"in 1956, launched with an advertising blitz that included the popular line "Look, Mom--no cavities!" Four years later, P&G scored a coup when the ADACouncil on Dental Therapeutic gave Crest its seal of approval as "an effective decay-preventive dentifrice." The ADA now estimates that brushing with fluoride-containing toothpaste reduces tooth decay by as much as 20 or 30 percent. In addition to toothpaste, fluoride can also be taken in tablet form and as a solution either "painted" directly onto the teeth or swished around as amouthwash. Recently, a team of British scientists have been working on developing a vaccine to prevent tooth decay, which could one day serve as an alternative to fluoridation. A plant-based substance, the vaccine is "painted" on the teeth and prevents tooth decay by eliminating bacteria from the mouth.