Cold Plasma Therapy Of Tooth Root Canal Infected With Enterococcus Faecalis Biofilms In Vitro

Plasma is the fourth state of matter, which is general produced by ionizing the gas. The history of plasma research in many industrial and military aspects, such as nuclear power, material modification, material etching, lighting, etc. has more than100years. In recent years, the atmospheric pressure low temperature plasma in medical therapy areas, such as the sterilization, blood coagulation, teeth whitening, cancer therapy, tooth root canal treatment, treatment of fungal infections, have made great development. The objective of the study was to investigate in vitro the feasibility of using a cold plasma treatment of a root canal infected with Enterococcus faecalis biofilms.Materials and Methods:Colony Forming Units (CFU) counting, Scanning Electron Microscopy (SEM) and Laser Scanning Confocal Microscopy (LSCM) were employed to observe the process of the growth, development and formation of Enterococcus faecalis biofilm in root canal. Moreover, we compared the Enterococcus faecalis biofilm disinfect efficacy of cold plasma and clinical medicine (calcium hydroxide (Ca(OH)2)) by CFU, SEM and LSCM respectively. In addition, we studied the disinfection efficacy of two kinds of different plasma excitation device (Alternating Current dielectric barrier discharge plasma (ACCP) and direct current glow discharge plasma (DCCP)) and detected the reactive species in plasma by optical emission spectra (OES). The mechanism of plasma disinfection was analyzed and discussed in this study.Results:After7days of culturing, the E. faecalis biofilm successfully formed in the root canals, with numerous mycelia cross-linking. After10minutes of cold plasma treatment, the E. faecalis biofilm was successfully disinfected and we observed that the regular structure of the biofilm was destroyed and replaced with ruptured bacteria. Compared with the Ca(OH)2, cold plasma had a significantly higher antimicrobial efficacy. Moreover, ACCP showed a more sufficient antimicrobial efficacy than DCCP. The OES results revealed that the low temperature plasma contains variety of reactive species such as atomic oxygen, hydroxyl radicals, singlet oxygen and free electrons, etc., which can effectively inactivate E.faecalis biofilm.Conclusion:Compared with the Ca(OH)2, cold plasma had a significantly higher antimicrobial efficacy. Moreover, ACCP showed a more sufficient antimicrobial efficacy than DCCP. We believe that the effective inactivation of E. faecalis biofilm can be attributed to the reactive species in the atmospheric nonthermal plasma jet.