Wiping Out Tooth Infections: Cool Plasma Packs Heat Against Biofilms
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The plasma probe is applied to an extracted tooth. (Credit: Image
courtesy of University of Southern California)
ScienceDaily (June 15, 2009) — 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.
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 plasma 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."
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