Abstract
Objective To investigate the effectiveness of plasma sterilization in reducing bacterial contamination and controlling biofilms in dental unit waterlines. Materials and Methods Ten identical dental chair units (DCUs) were used. Five DCUs were installed with an automated plasma sterilization system (PSS) and the other five were kept as nontreated controls (CTL). Water flushed from the airotor line served as the output water of the dental unit waterlines (DUWLs). Water samples were collected at the beginning and on a weekly basis for 4 months. Water was analyzed for bacterial contamination (CFU/mL). Scanning electron microscopy (SEM) was used to investigate the amount of biofilm in the waterlines. Biofilm viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays. All statistical analyses were performed using the Mann–Whitney U test. A value of p < 0.05 was considered significant. Results The DCU output water was found to be heavily contaminated with bacteria. Plasma sterilization effectively reduced bacterial contamination from an average of 212 CFU/mL to 8 CFU/mL. During the entire period of 4 months, the level remained below 500 CFU/mL, the standard level recommended by the Centers for Disease Control and Prevention (CDC) of the USA. The reduction in the bacterial count was significant compared with the CTL group (p < 0.05). Plasma sterilization could not eradicate the existing biofilms in the waterlines, and it did reduce biofilm mass and viability. Moreover, treatment with plasma sterilization did not induce a change in the composition of microorganisms, as analyzed by Gram staining. Conclusion Plasma sterilization, which is part of electrochemically activated water, effectively reduces bacterial contamination and reduces biofilms in dental unit waterlines.
Highlights
Dental chair units make use of water as a coolant for highspeed rotary dental instruments and for washing the mouth during the dental procedure. e input water of a dental chair unit can be derived from different sources: either directly from municipal water or from a separate water reservoir
Dental chair unit input water was heavily contaminated with bacteria ranging from an average of 4,800 to 30,440 CFUs/ mL. ere was not a significant difference in the bacterial count of input water between the plasma sterilization system (PSS) and the nontreatment control group (Figures 1(a) and 1(b)). roughout the entire period of 4 months, the dental unit output water was found to be heavily contaminated with bacteria. e maximum bacterial counts were as high as an average of 35,400 CFUs/mL
Scanning electron microscopy revealed the presence of bacterial biofilms covering the inner surface of the waterlines in the control group (Figure 3). e biofilm mass was strongly reduced in the PSS group (Figure 3)
Summary
Dental chair units make use of water as a coolant for highspeed rotary dental instruments and for washing the mouth during the dental procedure. e input water of a dental chair unit can be derived from different sources: either directly from municipal water or from a separate water reservoir. E input water of a dental chair unit can be derived from different sources: either directly from municipal water or from a separate water reservoir. Once it enters the dental chair unit, the water will be flushed through the complex small tubing system to supply the airotor handpiece and air-water syringe. E dental chair unit output water has been reported to be highly contaminated by microorganisms [1]. E microorganisms in the tubing system form biofilms which continuously release microorganisms that contaminate output water. E main obstacle to eliminate effectively microorganisms in DUWLs is the formation of biofilm that aggravates resistance to a wide range of disinfection methods.
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