September 14, 2005

True Age Revealed in Tooth Enamel

LONDON -- Tests of nuclear bombs conducted in the 1950s have had an unexpected benefit for forensic scientists.

A permanent record of the fallout from above-ground tests is embedded in tooth enamel and allows scientists to estimate the age of a person at the time of death more precisely.

Jonas Frisen, of the Karolinska Institute in Stockholm, who developed the method, said it has already been used to help identify people who died in the Indian Ocean tsunami last year.

American researchers are also offering to determine the age of unidentified victims of Hurricane Katrina with the technique.

"It is a simple method to determine the age of an individual by measuring the level of the compound in teeth," Frisen said in an interview.

Until now forensic scientists studied the skeleton and the wear on teeth to determine the age of a person, which was accurate to about 5 to 10 years.

But by looking at the amount of radioactive carbon-14 in the tooth enamel, scientists can correctly predict a person's age to within roughly 1.6 years.

Tooth enamel is formed at distinct times during childhood and contains only 0.4 percent carbon. So concentrations of it in teeth reflect the amount in the atmosphere when the enamel was formed.

When nuclear testing began in 1955 it increased the amounts of carbon-14 in the atmosphere. Regardless of where the tests were done the levels very quickly became uniform around the globe, so the technique can be used to determine the age of people around the world.

But it does not work for individuals born before 1943 because their teeth were already formed by the time the nuclear tests began.

Carbon-14 found its way into teeth after being incorporated into plants and entering the food chain. After 1963, when above-ground nuclear testing was stopped, levels began to drop.

Scientists can compare the amount of carbon-14 in tooth enamel to records of how much was in the atmosphere to get an accurate time of when the tooth was formed.

Frisen, a cell biologist, and his colleagues were studying the age of cells in the body when they realized carbon-dating tooth enamel could help forensic scientists.

The researchers, who reported their findings in the science journal Nature, said using the technique is no more difficult than doing a blood test.