In vitro studies of the antimicrobial effect of non-thermal plasma-activated water as a novel mouthwash.

The aim of this study was to evaluate the antimicrobial effects of non-thermal plasma-activated water (PAW) as a novel mouthwash in vitro. Three representative oral pathogens - Streptococcus mutans, Actinomyces viscosus and Porphyromonas gingivalis - were treated with PAW. The inactivation effect was evaluated using the colony-forming unit (CFU) method, and the morphological and structural changes of a cell were observed by scanning electron microscopy and transmission electron microscopy (TEM). The physicochemical properties of PAW were analysed, and its influence on the leakage of intracellular proteins and DNA was evaluated. The results showed significant reduction of Streptococcus mutans within 60 s, of Actinomyces viscosus within 40 s, and of Porphyromonas gingivalis in less than 40 s. Scanning electron microscopy and TEM images showed that the normal cell morphology changed by varying degrees after treatment with PAW. Intracellular proteins (280 nm) and DNA (260 nm) leaked from all three species of bacteria after treatment with PAW. Reactive oxygen species (ROS), especially atomic oxygen (O), hydroxyl radical (˙OH), and hydrogen peroxide (H2 O2 ), were generated and led to strong oxidative stress and cell damage. These results suggest that PAW has potential use as a novel antimicrobial mouthwash.

Cold plasma-induced surface modification of heat-polymerized acrylic resin and prevention of early adherence of Candida albicans.

Atmospheric-pressure cold plasma was applied to process the surface of heat-polymerized acrylic resin. Changes to the physical properties and early adherence of Candida albicans were investigated. Alternating current cold plasma with Ar/O2 as working gas was used. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to study the possible mechanism. Experimental results showed that after plasma treatment, the contact angle of acrylic resin significantly decreased. There were no significant differences in roughness, flexural strength and elasticity modulus, but microhardness was significant improved in the treated group. More importantly, the early adherence of Candida albicans on the surface was reduced after plasma treatment. Cold plasma seemed to be a promising and convenient strategy of preventing the early adherence of Candida albicans on acrylic resins, which would greatly benefit potential dental applications.

Evaluation of Cold Plasma Treatment and Safety in Disinfecting 3-week Root Canal Enterococcus faecalis Biofilm In Vitro.

INTRODUCTION: Although endodontic infection is caused by multi-bacteria species, Enterococcus faecalis is usually isolated in chronic apical periodontitis. The aim of this study was to evaluate the effectiveness and mechanical safety of cold plasma therapy in disinfecting 3-week E. faecalis biofilms. METHODS: Teeth with 3-week E. faecalis biofilm were treated with AC argon/oxygen (Ar/O2) cold plasma for various treatment times and compared with those treated with Ca(OH)2, 2% chlorhexidine gel, and Ca(OH)2/chlorhexidine for a week. Antimicrobial efficacy was assessed by colony-forming unit method. Scanning electron microscopy was used to assess the morphologic changes of E. faecalis biofilm by plasma. Confocal laser scanning microscopy was used to confirm the viability of the biofilm after the plasma treatment. Microhardness and roughness changes of root canal dentin caused by plasma were verified with Vickers Hardness Tester and 3D Profile Measurement Laser Microscope, respectively. RESULTS: There were no detectable live bacteria after 12 minutes of cold plasma treatment. This was further confirmed by scanning electron microscopy and confocal laser scanning microscopy results. Microhardness and roughness of root canal dentin showed no significant difference after plasma treatment. CONCLUSIONS: Atmospheric pressure cold plasma is an effective therapy in endodontics for its strong sterilization effect on fully matured biofilm within a few minutes. Meanwhile, it has an accepted mechanical safety for its low temperature and not affecting the microhardness and roughness of root canal dentin significantly.

[Evaluation of two different cold plasma treatments on root canal infected with enterococcus faecalis biofilms].

OBJECTIVE: To compare the bactericidal efficacy of two different cold plasma (glow discharge and dielectric barrier discharge) treatments on root canal infected with Enterococcus faecalis biofilms in vitro. METHODS: One hundred and twenty teeth infected with Enterococcus faecalis biofilm in the roots for seven days were divided into twelve groups randomly. Two served as negative control group (gas only, no discharge). Five were teeth treated by dielectric barrier discharge cold plasma and the other five were treated by glow discharge cold plasma. The treatment time in each five groups was 2, 4, 6, 8 and 10 min, respectively. The disinfection of Enterococcus faeccalis biofilm was evaluated by colony forming unit (CFU) counting. The plasma component produced by different devices was analyzed by optical emission spectroscopy (OES). RESULTS: Comparing the two plasma treatments, the plasma produced by dielectric barrier discharge had better bactericidal effect than that produced by glow discharge at different treatment time (P < 0.05). The advantage was obvious with the time getting longer. The OES indicated that active components of the two type plasmas were similar. But the peak of excited Ar atom of dielectric barrier discharge was twice as that of glow discharge. CONCLUSION: The cold plasma produced by dielectric barrier discharge has more bactericidal efficiency in the treatment of root canal infected with Enterococcus faecalis biofilms.