September 27, 2005
By Lisa Ellis
InteliHealth News Service
INTELIHEALTH – Scientists routinely use radiocarbon dating to estimate the age of fossils and archeological remains. Now a team from the United States and Sweden has developed a technique to analyze human teeth and pin down most people’s age within 1.6 years.
The scientists believe the method may help to identify people killed in Hurricane Katrina.
The technique measures the amount of radioactive carbon 14 in tooth enamel. It takes advantage of a “pulse” of carbon 14 that entered the atmosphere during nuclear testing from the mid-’50s to 1963.
“That pulse went up quite quickly in eight years or so and it’s been slowly decreasing since then,” explained Bruce Buchholz, Ph.D., a scientist with the Lawrence Livermore National Laboratory in California who was involved in the study.
Spreading around the globe, the carbon reacted with oxygen to form carbon dioxide, researchers noted in their study, published September 15 in the journal Nature. Plants absorbed the gas through photosynthesis, and so the radioactive carbon entered the food chain and eventually was eaten by humans.
As a result, teeth formed during this period show predictable amounts of carbon 14, reflecting the levels of the isotope in the atmosphere at the time a particular tooth was formed, Buchholz said. Once formed, the carbon 14 level in dental enamel does not change.
Because specific teeth, such as incisors or molars, are formed at particular ages, the amount of carbon 14 in a tooth therefore can be used to calculate age within an average of 1.6 years, he said.
That’s an improvement over the most commonly used techniques for dating adult skeletal remains, which can estimate age within five to 10 years based on tooth wear, the Nature article said.
When there’s a doubt about age, carbon levels can be measured in two teeth formed at different times, Buchholz said.
Pathologists at the Karolinska Institute in Stockholm, co-authors of the article, already have used carbon 14 dating to help identify bodies from the southeast Asian tsunami earlier this year, Buchholz said.
“If a body is out in warm water for a couple of weeks, you can’t tell if the person was 20 years old or 60 years old because of the deterioration,” he said. “This [technique] is a filter to make it easier to identify a body from a list of missing persons.”
Lawrence Livermore Laboratory, operated by the University of California for the U.S. Department of Energy, has passed on the information about carbon 14 dating to U.S. officials involved with the Hurricane Katrina rescue. So far, Buchholz said, there has been no request for assistance in identifying anyone.
“I’m not sure how much they will use it,” he said. “It depends on the bodies found and the lack of identifying information. There appear to be fewer victims than initially thought.”
Carbon 14 dating does have one notable limit. It can narrow down age only for people who still were forming teeth after open-air nuclear testing began in 1955.
Since the enamel of wisdom teeth is formed at about age 12, this means that anyone born before 1943 will have no carbon 14 in the teeth, the Nature article explained.
In the Nature study, Karolinska pathologists obtained teeth from 22 individuals and processed them by dissolving all soft tissue, including all dentin and pulp, Buchholz said. Then they shipped the remaining enamel to the Livermore laboratory.
Livermore scientists analyzed the enamel using a mass spectrometer, Buchholz said. This machine can measure tiny changes in the amount of an isotope by counting atoms rather than waiting for radioactive decay, which occurs very slowly, he said.
In the future, the first lengthy step — separating the enamel — may not be needed. Buchholz said he recently tried just sawing a piece of enamel off a tooth, and this worked fine.
This could speed up the process if it’s needed to help identify Katrina victims. “I don’t have any teeth yet,” Buchholz said. “I suspect that I will receive some eventually.”