Low Energy Nanosecond Pulsed Plasma Sterilization for Endodontic Applications

The development of effective and safe methods for root canal disinfection, including mechanical, chemical and laser techniques, remains an important problem, and complete eradication of bacteria from the root canal system with minimum tissue trauma is still a serious challenge for endodontists. Recently, a pulsed, hollow-electrode based plasma dental probe has been developed to sterilize the root canal system during endodontic treatment. Driven by 100 ns, 1 kHz, 6 kV electric pulses, the plasma dental probe generates a room temperature, several centimeter long, ~2 mm in diameter, tapered cylindrical plasma plume in ambient atmosphere when a flow of He/(1%)O₂ mixture exits the probe nozzle at 3 L/min. In preliminary experiments we observed 100% killing of the test organism Bacillus atrophaeus on nutrient agar plates with an exposure time of 60 s. The applied pulsed plasma has an average power ~2 W (energy per pulse, 1-2 mJ). The surface temperature of the nutrient agar directly under the plasma exposure increased from 22degC to 33degC in 3 min. Similar plasma plumes, operating close to room temperature, have been shown to inhibit bacterial growth without damaging skin. Measurements by plasma emission spectroscopy imply that active species (especially atomic oxygen) play an important role in the plasma sterilization process, and nanosecond electric pulses with optimal pulse conditions can be a highly efficient method for generating these radicals. Therefore, a nanosecond non-thermal plasma dental probe may prove to be a simple, safe, and effective procedure for root canal sterilization.