Abstract
Because of some disadvantages of chemical disinfection in dental practice (especially denture cleaning), we investigated the effects of physical methods on Candida albicans biofilms. For this purpose, the antifungal efficacy of three different low-temperature plasma devices (an atmospheric pressure plasma jet and two different dielectric barrier discharges (DBDs)) on Candida albicans biofilms grown on titanium discs in vitro was investigated. As positive treatment controls, we used 0.1% chlorhexidine digluconate (CHX) and 0.6% sodium hypochlorite (NaOCl). The corresponding gas streams without plasma ignition served as negative treatment controls. The efficacy of the plasma treatment was determined evaluating the number of colony-forming units (CFU) recovered from titanium discs. The plasma treatment reduced the CFU significantly compared to chemical disinfectants. While 10 min CHX or NaOCl exposure led to a CFU log10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. In conclusion, the use of low-temperature plasma is a promising physical alternative to chemical antiseptics for dental practice.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. The yeast Candida albicans can cause oral infections. The oral cavity of most denture wearers is colonized with C. albicans forming biofilms. The yeast protects itself from chemical influences by secreting slime (extracellular polysaccharides). The treatment of these biofilms is difficult, because denture brushing is seldom performed as a daily routine by elderly people with acceptable efficacy. Chemical cleansing (sodium hypochlorite, chlorhexidine) with immersion baths is the first choice for denture plaque control, but cannot operate with sufficient efficacy on biofilms because of the protective slime. We quantify microorganisms using colony forming units (CFU ml-1, usually given logarithmically). The effectiveness of antimicrobial substances is contrasted with other reduction factors (CFU before treatment vs CFU after treatment, usually given logarithmically).
Main results. The plasma treatment reduced CFU significantly more than chemical disinfectants. While ten minutes of CHX or NaOCl exposure led to a CFU log10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. Scanning electron microscopic images show that plasma completely destroyed the yeast cells (see figure). NaOCl treated cells look rugose. In contrast, CHX treated cells looked as undamaged as the untreated controls. In the end, plasma is more effective than chemical disinfectants.
Wider implications. The possibility of using DBD plasma to treat a whole denture is ideal for denture cleaning. Therefore, atmospheric pressure plasma may become an alternative to chemical cleansing. Plasma could also offer the opportunity to treat Candida infections directly, which is also important outside of dentistry.
Figure. C. albicans biofilms on titanium discs after treatment with (A) chlorhexidine digluconate, (B) with sodium hypochloride, (C) with DBD (dielectric barrier discharge) plasma and (D) with VDBD. Magnification 5000fold.