Henry Trendley Dean (August 25, 1893 - May 13, 1962) was and American dentist and pioneer investigator of water fluoridation in the prevention of tooth decay. He received his dental degree from St. Louis University in 1916. During World War I, he served with the United States Army until 1919, when he returned to his practice. In 1921, he entered the United States Public Health Service and was stationed in several US Marine Corps hospitals until 1931 when he was placed in charge of dental research at the National Institute of Health, advancing to director of the dental research section in 1945. After World War II, he directed epidemiologic studies for the Army in Germany. When Congress established the National Institute of Dental Research in 1948, Dean was appointed its director, a position he held until retiring in 1953. He helped establish that high amounts of fluorine in drinking water caused mottled enamel on the teeth, while at the same time precipitating lower rates of dental caries (cavities). The rest of his professional life was spent finding the optimal level of fluorine that would prevent tooth decay yet avoid staining teeth. He died in 1962 at the age of 68, after a long-time battle with asthma and emphysema.