Innovative Curved-Tip Reactor for Non-Thermal Plasma and Plasma-Treated Water Generation: Synergistic Impact Comparison with Sodium Hypochlorite in Dental Root Canal Disinfection

Abstract

Non-thermal plasmas (NTPs), known as cold atmospheric plasmas (CAPs), hold great potential for diverse medical applications, including dentistry. However, traditional linear and rigid dielectric barrier discharge reactors used for NTP generation encounter limitations in accessing oral cavities and root canals. To address this issue, we have developed an innovative NTP reactor featuring an angled end for improved accessibility. The central copper electrode, with a 0.59 mm diameter and adjustable length for desired angulation, is coated with zircon powder (ZrSiO₄) to ensure stable NTP generation. This central electrode is housed within a stainless steel tube (3 mm internal diameter, 8 mm external diameter, and 100 mm length) with a 27° angle at one end, making it ergonomically suitable for oral applications. NTP generation involves polarizing the reactor electrodes with 13.56 MHz radio frequency signals, using helium gas as a working medium. We introduce plasma-treated water (PTW) as an adjunctive therapy to enhance biofilm eradication within root canals. A synergistic approach combining NTP and PTW is employed and compared to the gold standard (sodium hypochlorite, NaOCl), effectively neutralizing Enterococcus faecalis bacteria, even in scenarios involving biofilms. Moreover, applying NTP in both gaseous and liquid environments successfully achieves bacterial inactivation at varying treatment durations, demonstrating the device's suitability for medical use in treating root canal biofilms. The proposed NTP reactor, characterized by its innovative design, offers a practical and specific approach to plasma treatment in dental applications. It holds promise in combatting bacterial infections in root canals and oral cavities.

Keywords: bacteria; ceramic; non-thermal plasma; plasma-treated water; root canals; veneering.

Figure 1

Placement of the NTP-generating reactor inside the mouth, illustrating its application in the most profound areas: (a) upper molar and (b) lower molar.

Figure 2

(a) Preparation of the mixture for the coating of the central electrode. (b) The mixture and corresponding angle cover the central electrode. (c) Non-thermal plasma reactor. (d) Schematic diagram. (e) The NTP reactor test device was applied to a root canal model.

Figure 3

A 3D printed transparent tooth model with the following images: (a) top view showing the simulated root canal, (b) lateral view, (c) presentation of the cast and dentin, (d) dentin mounted on the model, (e) dentin and cast showing the stamp, and (f) biofilm growth.

Figure 4

Experimental conditions applied to the 3D models of root canals.

Figure 5

(a) SEM micrograph of the raw powder. (b) SEM micrograph of the processed powder.

Figure 6

Diffractogram of the powder used for the coating of the central electrode.

Figure 7

Temperature measurements with two graphs: (a) effect of applied power concerning distance; (b) effect of applied power concerning time.

Figure 8

The inactivation of Enterococcus faecalis bacteria under various conditions. (a) Control at 10⁶ CFU/mL. This image illustrates bacterial growth without any treatment. (b) Concentration of 10⁶ CFU/mL treated with NTP. The treated area is highlighted by a circle, demonstrating bacterial inactivation. (c) Control at 10⁵ CFU/mL. This image displays bacterial growth without NTP treatment. (d) Concentration of 10⁵ CFU/mL treated with NTP. Once again, the treated area is marked with a circle, showcasing bacterial inactivation at this concentration.

Figure 9

Survival graph of biofilms in the biomodels under different conditions.

Figure 10

Longitudinal section of root canal analysed by SEM: (a) Dentin fully colonized by Enterococcus faecalis. Biofilms under various treatment conditions: (b) α, (c) ε, (d) ε + ε, (e) γ, (f) η, (g) γ + ε, (h) η + γ, and (i) Treatment η + ε. Arrows indicate changes in cellular morphology, alterations, and debris.