Dr. Louise Reiss, who directed a study that examined hundreds of thousands of baby teeth during the cold war and helped persuade the world’s leading powers to ban nuclear testing in the atmosphere, died Jan. 1 at her home in Pinecrest, Fla. She was 90, writes the New York Times. Dr. Reiss and her husband Eric, also a physician, founded the Greater St. Louis Citizens’ Committee for Nuclear Information, and worked with schools of dentistry in St. Louis, MO, to collect and analyze baby teeth for elevated rates of strontium 90. The study showed that radioactive fallout from nuclear testing was getting into the nation’s food supply and ultimately working its way into human bones and teeth. The study ultimately found that children born in St. Louis in 1963 had 50 times as much strontium 90 in their teeth as children born in 1950 — before most of the atomic tests. The U.S. conducted 206 atmospheric tests before a ban on atmospheric tests was agreed between the U.S. and the Soviet Union.