Effect Of Nonequilibrium Plasma Against Endodontic Bacterial Biofilms In Vitro

Purpose:It has reported that the nonequilibrium plasma has super antibacterial activity against microorganisms. It exists at room temperature and atmospheric pressure, and does not inflict thermal damage to host tissue. The short-lived reactive species generated by plasma are not harmful, and can reach the minor irregular parts. Accordingly, the nonequilibrium plasma is an interesting novel biomedical application that is attractive for medical use. In our previous studies, nonequilibrium plasma was effective in killing Enterococcus faecalis (E. faecalis) biofilms in vitro. No significant difference was detected in killing activity between nonequilibrium plasma and conventional root canal irrigant. It is of value to combine nonequilibrium plasma with chlorhexidine digluconate (CHX), which becomes to nonequilibrium CHX plasma. Hence, the aim of the present study was to evaluate the antibacterial effect of root canal disinfection and sealing, nonequilibrium plasma, and nonequilibrium CHX plasma against endodontic bacterial biofilms in vitro.Methods:E. faecalis and subgingival plaque suspensions were inoculated into sterile cover slips, bovine dentin discs, prepared human single-rooted teeth, and dentinal tubules for incubation at37℃under the anaerobic conditions, to establish the in vitro endodontic bacterial biofilms. The infected specimens were subjected to root canal disinfection and sealing, nonequilibrium plasma, and nonequilibrium CHX plasma for different exposure times. After treatment, the bacterial biofilms were stained with fluorescent viability dyes and examined by confocal laser scanning microscopy (CLSM) for3-dimensional reconstruction analysis. The proportions of bacterial biofilm cells killed by disinfecting treatments were calculated with using of the software Imaris.Results:The3-dimentional reconstruction CLSM images showed that the majority of endodontic biofilm cells were killed by root canal disinfection and sealing, nonequilibrium plasma, and nonequilibrium CHX plasma. The nonequilibrium CHX plasma was more active in killing biofilm bacteria compared with conventional canal irrigating agent2%CHX and nonequilibrium plasma (P<0.05). The proportions of dead cells subjected to the disinfecting approaches increased significantly with the increasing exposure (P<0.05). Remarkably more bacteria were killed in young endodontic biofilms than that in old biofilms (P<0.05).Conclusions:The nonequilibrium CHX plasma killed more biofilm cells in vitro and thus shows promise as an additional approach in infection control during endodontic therapies, in order to obtain the successful root canal treatment and save more teeth. However, more further studies will focus on the biocompatibility and the antibacterial mechanisms of nonequilibrium CHX plasma against endodontic bacterial biofilms.