More than 80,000 American service members remain missing from previous wars, most from World War II. When remains are found, their age often makes identification difficult—but not impossible.
Even without a name, fingerprints, or facial features, our history leaves indelible marks on us, locked in the atoms of the toughest structures in our bodies: the enamel of our teeth. Subtle differences in tooth chemistry could help determine the identity of fallen soldiers and other human remains—if we can learn to read that history.
Now, a collaboration between geography and dentistry researchers aims to find ways to map a person’s remains to the region where they grew up, based on slight differences in tooth enamel that are determined by the composition of local tap water.
While the researchers’ immediate goal is to help identify fallen soldiers, the project has the potential to strengthen the field of forensic investigation as a whole, according to Gabe Bowen, PhD, professor of geology and geophysics at the University of Utah and the lead on the project. “The ultimate goal is to produce a resource that will be very broadly useful,” Bowen says. “Cold cases, border crossers, humanitarian crises—any situation where we end up with individuals of unknown identity.”
The waters of home
The researchers’ identification scheme hinges on differences in the oxygen atoms of tooth enamel.
More than 99 percent of the oxygen atoms in the world—and in our teeth—contain exactly eight protons, eight neutrons, and eight electrons. But a small minority of oxygen atoms have two extra neutrons, making them slightly heavier. These different varieties of oxygen are called isotopes.
The amount of heavy oxygen in tooth enamel is different from person to person, depending on how much heavy oxygen was present in their environment when their teeth formed.
“Most of the oxygen in our tooth enamel gets into our body through the water that we drink and the food that we eat,” Bowen says. “To the degree that those are local, that’s where the signal is coming from.” After the enamel forms, those location-specific differences are permanent.
Critically, the amount of heavy oxygen in groundwater changes between regions of the country in predictable ways. When a cloud rises from the ocean and moves over the land, water molecules containing heavy oxygen are slightly more likely to fall as rain.
This means that the Gulf Coast, which is right next to the ocean, has the most heavy oxygen in its water. The Rockies have the least; by the time the clouds get to the mountains, they’ve already dropped much of their heavy oxygen.
The research team confirmed these general patterns by rigorously testing groundwater across the U.S. for heavy oxygen.
The molar code
The next step? Teeth, and a lot of them.
To match someone’s teeth to where they grew up, the researchers are amassing a database of teeth donated by volunteers nationwide and comparing their enamel composition to groundwater data. They’re using wisdom teeth, which are commonly removed in modern dental care.
“I think it’s beautiful that in the natural progression of people’s treatment, we would be removing these teeth anyway,” says Michael Bingham, clinical research coordinator in the School of Dentistry at the University of Utah. “We can take something that would, in theory, be discarded, and use it to do this beautiful project of reuniting families with their service members’ remains.”
While the researchers need more tooth donors to get a comprehensive map, their results so far are promising. According to Bowen, differences in the amount of heavy oxygen in tooth enamel are very strongly associated with differences in drinking water. This strong association increases the chance of being able to map a set of remains to a particular region of the country.
Bingham adds that the level of public enthusiasm for the project is inspiring. “It’s been cool to see the swell of support from patients,” he says. “Anybody you talk to is like, ‘I’m really excited to be a part of the project. How can I help?’”
Making a change
While much work remains to be done, Bowen is hopeful that the project will make a real difference for forensic analysis, seeing it as a way to put his enthusiasm for geochemistry to immediate use.
“Isotopes are fascinating,” Bowen says. “They connect all these environmental, human, and ecological systems that surround us and are changing all the time. And this is a very real and applied problem that I think a lot of people can connect with. It’s a way of leveraging some of the more esoteric work and bringing it into a context where it can make a difference in peoples’ lives.”