Excerpts from an interesting report in The Appendix:
Scientists suspected that radiation from the above-ground atomic weapons tests taking place from 1945 onward could pose a significant health risk to the populace, but no one knew how much radiation human bodies were absorbing... Bone samples were one avenue by which accumulation in the body could be measured. However, the limited samples of bone available from autopsied adults provided a small and erratic body of data.
To avoid these problems, Kalckar proposed turning to a different source of samples: children’s baby teeth. Near-term prenatal incisor teeth (in other words, children’s front baby teeth or “milk teeth”) took up high levels of radioisotopes during their formation, yet renewed their cells at a far slower rate than bone. Therefore, baby teeth could provide a stable snapshot of radiation absorbed by human bodies in a given geographic area around the time of a child’s birth. Since children tend to shed incisor teeth around the
CNI initiated the Baby Tooth Survey in December of 1958 with a grant from the United States Public Health Service.. aimed to collect 50,000 teeth a year from children in the St. Louis area...Adults in St. Louis who took part in the study as children recall the lure of the I GAVE MY TOOTH TO SCIENCE buttons sent out to participant children, a visible marker of honor and belonging. Kids’ notes bear this out: “Dear Sir,” one reads, “I lost my pin, will you please send me another one? I sent for it last week. Plus this one? Thank you.”
More information about the study and its results at the link, and at this article from the Washington University School of Dental Medicine.