Radiant plasma may combat cavities.

Here's a new way to flash a smile: Waft a glowing plasma of charged particles onto your teeth. Researchers in the Netherlands and the United States have shown that a radiant vapor made from electrically zapped helium gas quickly kills colonies of the main bacterial culprit in tooth decay.

The finding might ultimately lead to improved dental-office techniques for stopping--and possibly even reversing--early-stage decay caused by Streptococcus mutans or other microbes and for disinfecting hard-to-reach areas between teeth, says David R. Drake of the University of Iowa College of Dentistry in Iowa City.

Unlike plasmas, including the sun's corona, that exist only in a vacuum and reach temperatures of thousands to millions of degrees, the newly demonstrated bactericidal plasma forms in room-temperature gas.

A handheld stylus, originally devised by Eva Stoffels of the Eindhoven (Netherlands) University of Technology, creates the plasma. Helium gas flows through a glass tube around a sharp tungsten needle. A powerful electric field at the needle's tip shatters helium atoms to create the swarm of electrically charged ions and electrons that constitute the plasma, explains physicist John Goree of the University of Iowa.

As these ions and electrons mix with air just beyond the needle tip, the speedy electrons, which cause the plasma's glow, slam into components of the helium-air mixture. The collisions generate highly reactive, short-lived products, such as lone oxygen atoms from shattered oxygen molecules, that can kill bacteria. The researchers are planning tests to verify that gums aren't damaged.

Stoffels, Drake, Goree, and physicist Bin Liu, also of University of Iowa, describe their new approach and stylus in the August IEEE Transactions on Plasma Science.--P.W.