Aim. Dental biofilms play a major role in the pathogenesis of many dental diseases. In this study, we evaluated the synergistic effect of atmospheric pressure plasma and different agents in dentistry on the reduction of biofilms. Methods and Results. We used monospecies (S. mutans) and multispecies dental biofilm models grown on titanium discs in vitro. After treatment with one of the agents, the biofilms were treated with plasma. Efficacy of treatment was determined by the number of colony forming units (CFU) and by live-dead staining. For S. mutans biofilms no colonies could be detected after treatment with NaOCl or H2O2. For multispecies biofilms the combination with plasma achieved a higher CFU reduction than each agent alone. We found an additive antimicrobial effect between argon plasma and agents irrespective of the treatment order with cultivation technique. For EDTA and octenidine, antimicrobial efficacy assessed by live-dead staining differed significantly between the two treatment orders ( ). Conclusions. The effective treatment of dental biofilms on titanium discs with atmospheric pressure plasma could be increased by adding agents in vitro. 1. Introduction Plasma is the fourth state of matter besides the solid, liquid, and gaseous states. It is an ionized gas consisting of ions, a broad spectrum of radicals, ultraviolet irradiation, electric fields, and ozone, which are responsible for its antimicrobial efficacy [1]. Atmospheric pressure plasma is also called nonthermal plasma, because it can achieve body temperature [2]. This allows medical application to humans by small plasma hand device on humans [3]. Plasma medicine is a new scientific field, and many research groups investigated various applications, for example, to the treatment of dental diseases like periodontitis [4], peri-implantitis [5], and caries and denture stomatitis [6] as well as dermatological diseases and chronic wounds [1, 7, 8]. Most applications were based on the antimicrobial effect of plasma to disinfect the skin, implants, and other medical devices. To date antiseptics have been commonly applied in these cases. Plasma is especially interesting for fields with a dissatisfactory standard therapy or where an effective therapy does not exist, for example, peri-implantitis therapy in dentistry. The antimicrobial efficacy of plasma could be increased by raising the electrical input power [9, 10]. However, plasma should also be tissue tolerable and applicable to humans. As with any active substance the balance between efficacy and tolerability needs to be found. To
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