Characterization Study of a Helium Cold Atmospheric-Pressure Plasma Jet and Its Application in Plasma-Mediated Root Canal Irrigation

Abstract

This study focuses on the design and optimization of a cold atmospheric-pressure plasma (CAP) jet, particularly targeting plasma-mediated root canal irrigation for smear layer removal and Enterococcus faecalis disinfection. The dielectric barrier discharge (DBD)-based CAP jet, powered by a bipolar pulsed power supply, was systematically optimized by varying applied voltage, frequency, and helium gas flow rate to achieve optimal plasma parameters. The CAP jet, operating in a buoyant axisymmetric jet configuration, exhibited a transition from laminar to turbulent flow at helium flow rates exceeding 4 slpm corresponding Reynolds number of ~400. optical emission spectroscopy (OES) was utilized to identify species generated and determine plasma parameters, with the collisional–radiative (CR) model revealing a nonequilibrium nature characterized by electron density ( ${n} {_{e} }~\sim ~10{^{{1}}} {^{{3}}}$ cm ${}^{\text {-3}}$ ), electron temperature ( ${T} {_{\text {re}}}~\sim ~0.35$ eV), and plasma gas temperature ( ${T} {_{g} }~\sim $ 305 K) under optimized conditions (4.5 kV, 20 kHz, 4 slpm). Fifty-Six mandibular premolars divided into four groups equally were irrigated with Normal saline solution (control) and CAP jet for 2, 5, and 10 min, respectively. Scanning electron microscope (SEM) imaging and disinfection analysis demonstrated significant improvements in smear layer removal and a ~5 log reduction in E. faecalis count, respectively. Smear layer removal was evaluated using the Kruskal–Wallis test, followed by Dunn’s post hoc analysis, whereas differences in bacterial load reduction across various CAP treatment times were analyzed using one-way ANOVA with Tukey’s honest significant difference (HSD) test for multiple comparisons. Safety considerations for medical applications, including gas temperature, leakage currents, and ozone emissions, were also evaluated according to DIN-specification 91315 (General requirements for plasma sources in medicine). These results underscore the promising application of plasma-mediated root canal irrigation, offering minimally invasive dental procedures, providing a foundation for further development and clinical translation in endodontics.