Researchers at the University of Washington and Pacific Northwest National Laboratory have used atom probe tomography to map fluoride distribution at the atomic level in enamel samples from two human teeth, one from a 22-year-old and one from a 56-year-old. The findings, published December 19, 2024 in Communications Materials, show that fluoride levels were higher across most regions of the older tooth's enamel, with particularly elevated concentrations in the shell regions surrounding each crystalline structure. Enamel is composed of minerals arranged in repetitive structures ten thousand times smaller than the width of a human hair. Previous lab-scale methods could not resolve this level of detail. Atom probe tomography produces a 3D map of individual atoms within a sample, allowing the team to compare element composition across three distinct zones: the core of each crystalline structure, the shell coating the core, and the space between shells. The study is described as a proof of concept, and the researchers note that the sample size is limited. The results suggest that fluoride from toothpaste and drinking water is incorporated into enamel over a person's lifetime, though the clinical implications of this accumulation remain to be established. The team plans to investigate how protein composition in enamel changes with age, which was the original focus of the research before fluoride distribution became the dominant finding.