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.

Her son, Eric, confirmed her death.

Dr. Reiss and her husband, Eric, both physicians, were founding members of the Greater St. Louis Citizens’ Committee for Nuclear Information, which joined with the schools of dentistry at Washington University in St. Louis and St. Louis University in 1959 to create the Baby Tooth Survey.

The goal was to show that radioactive fallout from nuclear testing was getting into the nation’s food supply and ultimately working its way into human bones and teeth. And the study succeeded.

Dr. Reiss was named director of the project and, along with her husband, worked with other scientists in the project’s laboratory.