Teeth are a window into our past, storing a record of the environmental pollutants and radiation they've encountered. Now scientists are developing tools to use teeth enamel to test how much radiation a person has been exposed to in the case of a major emergency, like a dirty bomb explosion.

"Dental enamel is quite a remarkable material," said Barry Pass, a professor in the College of Dentistry at Howard University in Washington, D.C. "There's a world of information in the tooth."

When a person is exposed to radiation, the energy can create free radicals in the body. These are atoms that have an extra unpaired electron, which makes them unstable – in healthy tissue, they can harm regular molecules by stealing electrons and damaging DNA.

But free radicals can be a useful indicator of how much radiation a person has come in contact with. Scientists are working on perfecting a process called Electron Paramagnetic Resonance (EPR) that can measure levels of free radicals in substances like teeth.

The technique could prove especially useful in gauging how much harm has been done after a major release of radiation from an accident or a radiation dispersal device, often called a dirty bomb.

The process works like this: Scientists need a small sample of a tooth – basically a tiny piece that can be carved out with a dental drill, and doesn’t damage the remaining tooth. Then they apply microwave energy to the sample. Free radicals will absorb microwave energy, so scientists can measure how much energy is left after passing through the tooth fragment to estimate how many free radicals are present.

"These free radicals are generated in proportion to the radiation exposure," Pass explained this month at a meeting of the American Physical Society in Washington, D.C. "The absorption of microwave energy is proportional to the concentration of these free radicals."

The method does have its drawbacks, though. For one thing, the tooth sample must be extracted by a dentist using dental tools. It takes time and trained personnel, not to mention a small chunk of tooth. None of these are ideal for a very quick assessment after an emergency.

"Ideally what we want for rapid triage is something that's non-invasive," Pass said. "You want to be able to get unambiguous data so you can triage or break down the victims into subclasses. You want to be able to operate in a variety of environments by minimally-trained individuals."

Another shortcoming is the fact that most EPR processes can only detect relatively high radiation levels. This is fine for getting a rough idea of the worst cases after a catastrophe, but scientists would also like to use tooth enamel to test background levels of radiation that people experience in the course of regular life, and to track changes in radiation exposure over a lifetime. This data would be especially useful for studies correlating radiation exposure with cancer risk, for example.

Researchers hope their sensitivity levels will increase with more powerful machines that can blast the samples with higher-frequency microwave energy.