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Cool plasma packs heat against biofilms

The plasma probe is applied to an extracted tooth. (DTI/Photo courtesy of USC)
Beth Dunham, USA

Beth Dunham, USA

Fri. 12 June 2009


LOS ANGELES, CA, USA: In the search for new ways to safely fight tenacious biofilm infections, researchers at the University of Southern California’s (USC) School of Dentistry and Viterbi School of Engineering have developed a new tool that could revolutionise many facets of medicine.

According to Parish Sedghizadeh, Assistant Professor of Clinical Dentistry and Director of the USC Center for Biofilms, biofilms cultivated in the root canal of extracted human teeth were easily destroyed with a pencil-sized plume of plasma on the tip of a small probe that remained at room temperature.

Chunqi Jiang, a Research Assistant Professor in the Ming Hsieh Department of Electrical Engineering and co-author of the study, explained that plasma, the fourth state of matter, consists of electrons, ions and neutral species, and is the most common form found in space, stars and lightning. But while many natural plasmas are hot, or thermal, the probe developed for the study is a non-thermal, room-temperature plasma that’s safe to touch. The researchers placed temperature sensors on the extracted teeth before treatment and found that the temperature of the tooth increased by only 5°C after 10 minutes of exposure to the plasma.

The cooler nature of the experimental plasma comes from its pulsed power supply. Instead of supplying a steady stream of energy to the probe, the pulsed power supply sends 100-nanosecond pulses of several kilovolts to the probe once every millisecond, with an average power of less than 2 watts. According to the plasma emission spectroscopy obtained during the experiments, atomic oxygen [a single atom of oxygen, instead of the more common O2 molecule] appears to be the antibacterial agent, Prof. Jiang explained.

Prof. Sedghizadeh said that the oxygen-free radicals might disrupt the cellular membranes of the biofilms, causing their demise and that the plasma plume’s adjustable, fluid reach allowed disinfection even in the hardest-to-reach areas of the root canal.

Given that preliminary research indicates that non-thermal plasma is safe for surrounding tissues, Prof. Sedghizadeh commented that he was optimistic about its future dental and medical uses. Much like the spread of laser technology from research and surgical applications to routine clinical and consumer uses, plasma could change everything, especially as non-thermal plasmas carry no risk of tissue burns and eye damage that lasers do, he said.

(Edited by Claudia Salwiczek, DTI)

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