Researchers at the University of Washington and Pacific Northwest National Laboratory have used atom probe tomography to map fluoride distribution in tooth enamel at the atomic scale, comparing samples from a 22-year-old and a 56-year-old. The findings were published on December 19, 2024 in Communications Materials. Enamel cannot self-repair, and its mineral composition changes with age, contributing to increased brittleness, particularly near the outer surface where cracks originate. The technique produces a 3D map of individual atoms within the repetitive crystalline structures of enamel, which are ten thousand times smaller than the width of a human hair. The team analysed three regions within those structures: the crystal core, a shell coating the core, and the inter-shell space. In the older tooth, fluoride levels were elevated across most regions, with the highest concentrations in the shell regions. The researchers interpret this as evidence that fluoride from toothpaste and drinking water accumulates in enamel over time, though this was a proof-of-concept study using only two teeth. Next steps include examining how enamel protein composition changes with age. The study was funded by the National Institutes of Health and Colgate-Palmolive Company, among others.