Geologists and dentists create dental database to help identify missing military remains

More than 80,000 American soldiers are missing from past wars, mostly from World War II. When remains are found, decomposition often makes identification difficult, but not impossible.

Even without names, fingerprints or facial features, our histories remain locked in the atoms of the hardest tissue in our bodies: tooth enamel, leaving an indelible mark. Subtle variations in the chemical makeup of teeth could help pinpoint the identities of fallen soldiers and other remains — if we can decipher that history.

Now, a collaboration between geography and dentistry researchers is aiming to find a way to place a person’s remains in the area where they grew up, based on subtle differences in tooth enamel that are determined by the composition of the local tap water.

While the researchers’ immediate goal is to help identify fallen soldiers, the project has the potential to enhance the entire field of forensic investigation, according to Gabe Bowen, a professor of geology and geophysics at the University of Utah and FIND-EM project leader.

“The ultimate goal is to create a resource that’s very broadly useful,” Bowen said, “for cold cases, people crossing borders, humanitarian crises — any situation where you encounter unidentified individuals.” (You can read about Bowen’s work here, including a 10-day solo cross-country flight in 2019 to collect water samples for isotope analysis.)

Hometown Water

The researchers’ identification plan relies on isotopic differences in oxygen atoms in the tooth enamel.

Over 99% of the oxygen atoms in the world, and in your teeth, contain exactly 8 protons, 8 neutrons, and 8 electrons. However, a very small number of oxygen atoms contain two extra neutrons, making them slightly heavier. These different types of oxygen are called isotopes.

The amount of heavy oxygen in tooth enamel varies from person to person, depending on how much heavy oxygen was present in the environment when the teeth were formed.

“Most of the oxygen in tooth enamel gets into the body through the water we drink and the food we eat,” Bowen says. “If it’s localized, that’s where the signal comes from.” Once the enamel is formed, those differences in different locations are permanent.

Importantly, the amount of heavy oxygen in groundwater varies predictably between different parts of the country: when clouds rise from the ocean and move over land, water molecules containing heavy oxygen are slightly more likely to fall as rain.

This means that the waters along the Gulf Coast, adjacent to the ocean, have the most heavy oxygen, while the Rocky Mountains have the least, and by the time the clouds reach the mountains, they have already lost much of their heavy oxygen.

The team confirmed this general pattern in rigorous testing of groundwater across the United States for the presence of heavy oxygen.

Molcode

What’s next? Teeth, and lots of teeth.

To match a person’s teeth to the place they grew up in, the researchers are collecting a database of teeth donated by volunteers across the country and comparing the composition of their enamel with data from groundwater. They are using wisdom teeth, which are typically removed in modern dental care.

“I think it’s great that the natural progression of treatment is that we would have had to extract these teeth anyway,” said Michael Bingham, clinical research coordinator at the University of Utah School of Dentistry. “It’s taking something that would have theoretically been discarded and putting it to use in this incredible project of reuniting families with military remains.”

While the researchers need more tooth donors to create a comprehensive map, the results so far are promising. Bowen says that differences in the amount of heavy oxygen in tooth enamel are very strongly correlated with differences in drinking water. This strong correlation raises the possibility of mapping sets of remains to specific regions of the country.

The level of enthusiasm shown by the public for this project is impressive.

“It’s been great to see the growing outpouring of patient support,” Bingham said. “Everybody I talk to is like, ‘I’m so happy to be a part of this. How can we help?'”

While there is still a lot of work to be done, Bowen hopes that this project will bring about a change in forensic analysis and sees it as an immediate way to put his passion for geochemistry to use.

“Isotopes are fascinating,” Bowen says, “They connect all the environmental, human and ecological systems that surround us and are constantly changing. It’s a very real, applicable problem that I think a lot of people can relate to. This is a way to take some of the more esoteric research and bring it into a situation where it can make a difference in people’s lives.”