A dentist named Frederick S. McKay opened his practice in 1901 in Colorado Springs and soon noticed something odd about his patients: many of them had brown, mottled teeth, very ugly but also highly resistant to decay.

McKay collected water samples from several areas where brown teeth were common and sent them to a chemist who examined them using a new technique, spectrographic analysis. The chemist found concentrations of fluoride in the samples as high as 12 parts per million, and researchers quickly confirmed in epidemiological studies that fluoride was the cause of the brown teeth.

The New York Times reported the finding on June 14, 1931, above left, the first time the newspaper mentioned fluoride in connection with drinking water.

By 1938, researchers had also confirmed McKay’s other observation: that drinking fluorine-contaminated water resulted in reduced numbers of cavities. The Times took no notice until Oct. 15, 1943, near the end of a 600-word account of a conference of the American Public Health Association.

“School children using domestic waters containing as little as one part per million of fluoride,” the article reported, “experienced only half to a third as much dental decay as comparable groups using water that contains no fluoride.”

In 1944, The Times reported that the New York State Department of Health would undertake an experiment by fluoridating the city water supply in Newburgh to a level of one part per million and comparing its dental health with that of Kingston, where the water would remain fluoride-free.

By 1951, when the health department officially recommended fluoridation, dozens of water systems across the nation had been fluoridated.

But New York City moved slowly. The Times began covering a dispute that would continue for the next 14 years. On Oct. 1, 1965, the newspaper published a 44-word article reporting that “fluoridation of New York’s water supply, a matter of bitter debate for several years, began quietly today.”

When the newspaper first mentioned the substance in 1931, it called fluoride the “ravisher of living tissues and disrupter of bone structure.”

Today, according to the Centers for Disease Control and Prevention, more than 60 percent of Americans use fluoridated water.

A version of this article appeared in print on November 17, 2009, on page D7 of the New York edition

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