In 1931 at the University of Arizona Agricultural Experiment Station M. C. Smith, E. M. Lantz, and H. V. Smith discovered that when given drinking water supplied with fluorine, rats would develop tooth defects. Further testing by H. T. Dean and E. Elove of the United States Public Health Service confirmed this report, and stated that what is known as mottled tooth.
Mottled tooth is a condition in which white spots develop on the back teeth.
Gradually the white spots get darker and darker until the tooth is eroded completely. A strong uproar was heard when this was released and people wanted all fluorine out of their water. But later tests concluded that communities with high levels of fluorine in their drinking water suffered less dental cavities. In 1938, with this information, Dr. Gerald Cox of the Mellon Institute began to promote the addition of fluoride to public water systems, claiming that it would reduce tooth decay, however there were two major obstacles in his path, The American Medical Association, and The American Dental Association. Both associations wrote articles in their journals about the dangers of fluoridation of water supplies.