Cool plasma packs heat against biofilms

Though it looks like a tiny purple blowtorch, a pencil-sized plume of plasma on the tip of a small probe remains at room temperature as it swiftly dismantles tough bacterial colonies deep inside a human tooth. But it's not another futuristic product of George Lucas' imagination. It's the exciting work of USC School of Dentistry and Viterbi School of Engineering researchers looking for new ways to safely fight tenacious biofilm infections in patients - and it could revolutionize many facets of medicine.

Two of the study's authors are Chunqi Jiang, a research assistant professor in the Ming Hsieh Department of Electrical Engineering-Electrophysics, and Parish Sedghizadeh, assistant professor of clinical dentistry and Director of the USC Center for Biofilms. "Nanosecond Pulsed Plasma Dental Probe" appears in the June 2009 issue of Plasma Processes and Polymers.

Sedghizadeh explained that biofilms are complex colonies of bacteria suspended in a slimy matrix that grants them added protection from conventional antibiotics. Biofilms are responsible for many hard-to-fight infections in the mouth and elsewhere. But in the study, biofilms cultivated in the root canal of extracted human teeth were easily destroyed with the plasma dental probe, as evidenced by scanning electron microscope images of near-pristine tooth surfaces after plasma treatment.

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, Jiang said. 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 for just five degrees after 10 minutes of exposure to the plasma, Jiang said.

The cooler nature of the experimental plasma comes from its pulsed power supply. Instead of employing 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 less than 2 Watts, Jiang said.

"Atomic oxygen [a single atom of oxygen, instead of the more common O2 molecule] appears to be the antibacterial agent," according to plasma emission spectroscopy obtained during the experiments, she said.

Sedghizadeh said the oxygen free radicals might be disrupting the cellular membranes of the biofilms in order to cause their demise and that the plasma plume's adjustable, fluid reach allowed the disinfection to occur 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, Sedghizadeh said 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 since nonthermal plasmas don't harbor the risks of tissue burns and eye damage that lasers do, he said.

"Plasma is the future," Sedghizadeh said. "It's been used before for other sterilization purposes but not for clinical medical applications, and we hope to be the first to apply it in a clinical setting."

"We believe we're the first team to apply for biofilm disinfection in root canals," Jiang added. "This collaboration is very unique. We're attacking frontier problems, and we're happy to be broadening our fields."

Source: University of Southern California (news : web)

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Jun 11, 2009
I wonder if this could be used for a consumer dental hygiene device? The ability to totally disinfect your teeth and gums would basically eradicate a lot of dental diseases.

Jun 11, 2009
Or make you very prone to infection...
Humans have never lived in a sterile environment, and I doubt there are any advantages in doing so.

Jun 11, 2009
" for surrounding tissues..."
Could this technology be used to treat pneumonia? Insert an endoscope with camera and plasma probe into the lung. POW! biofilm destroyed!

Jun 11, 2009
I don't get it. If atomic oxygen disrupts bacterial cell membranes, how does it not disrupt human cell membranes? Furthermore, isn't atomic oxygen so reactive, that it would cause extensive damage even worse than ozone? Maybe a safer and cheaper "therapy" would be to just pump the patient's mouth full of ozone. That'll take care of all the bacteria, all right...

Jun 13, 2009
PinkElephant is right; I would expect "collateral damage" if the probe is used carelessly. However, in a root canal, this is not an issue; hard tooth material would be removed mechanically in a conventional procedure, so minor surface disruption is not a big deal.

Jun 15, 2009
Nice ! This low temperature use of plasma will
have many applications in the treatments of

Good to see a few plasma physicist still around.

Jun 26, 2009
I wonder if this could be used for a consumer dental hygiene device? The ability to totally disinfect your teeth and gums would basically eradicate a lot of dental diseases.

Try rinsing with glycerin. It is so hygroscopic that it dehydrates bacteria on contact. Seems to be an excellent gum tonic. Tastes good, too. Food-additive safe; I brush with just glycerin all the time now. No spitting required.

I think, from the sensation on the surface of teeth and gums, that it wipes out biofilms, too. Swish around the back of the tongue for INSTANT sweet breath.

Lots of other uses; e.g., excellent treatment for psoriasis or any other skin problem.

Aug 20, 2009
I watched on a show on this and how plasma could be a force field for solid objects and waves such as microwaves (which are hypothesized that there will be microwave guns in the future).

Aug 21, 2009
Humans have never lived in a sterile environment, and I doubt there are any advantages in doing so.

Very good point, as someone else said this would be good in the field of dental hygiene though, but we should not be using this on at home or in public areas, unless other technologies decrease our vulnerability of disease, infections and illness. Which is very likely in the field of nanotechnology.

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