# Applications of Cold Atmospheric Pressure Plasma in Density
###### Abstract  
Plasma is an electrically conducting medium that responds to electric and magnetic fields. It consists of large quantities of highly reactive species, such as ions, energetic electrons, exited atoms and molecules, ultraviolet photons, and metastable and active radicals. Non-thermal or cold plasmas are partially ionized gases whose electron temperatures usually exceed several tens of thousand degrees K, while the ions and neutrals have much lower temperatures. Due to the presence of reactive species at low temperature, the biological effects of non-thermal plasmas have been studied for application in the medical area with promising results. This review outlines the application of cold atmospheric pressure plasma (CAPP) in dentistry for the control of several pathogenic microorganisms, induction of anti-inflammatory, tissue repair effects and apoptosis of cancer cells, with low toxicity to healthy cells. Therefore, CAPP has potential to be applied in many areas of dentistry such as cardiology, periodontology, endodontics and oral oncology. Keywords:cold atmospheric pressure plasma; antimicrobial agent; plasma medicine; dentistry +
Footnote †: journal: Medical  
of thousands K, while the heavy particles (ions and neutrals) have a much lower temperature [2]. Plasma can be also generated under different pressure conditions, including atmospheric pressure [1]. In the last decade, atmospheric pressure plasmas have become a very attractive tool for material processing applications because they are generated in an open environment and can be easily implemented in online processing. However, working at atmospheric pressure has some disadvantages. For instance, gas breakdown at atmospheric pressure occurs at much higher electric field, typically in the order of ten of kV cm\({}^{-1}\)[1]. Additionally, if special precautions are not taken, the atmospheric plasmas have the tendency to become thermal i.e., hot plasmas that can damage heat sensitive materials or burn living tissues [2]. A gas discharge in which a dielectric layer covers one or both electrodes is called Dielectric Barrier Discharge (DBD) and it was first introduced by Siemens--in 1857--for the production of ozone. Large number of DBD systems has been reported [3] with the planar and cylindrical geometries as the most common employed configurations. Figure 1a depicts a typical planar DBD reactor, while Figure 1b shows the so-called floating electrode DBD (FE-DBD) [4; 5]. The plasma, in this case, is formed between an insulated high voltage electrode and a target (human skin or living tissue), which acts as a floating counter electrode. Due to the current limitation caused by the charge accumulation on the dielectric surface, the gas temperature in DBD can be quite low (about the room temperature), which makes it adequate for biological applications [4]. However, the plasma in DBD devices is confined into small gaps between two electrodes (usually in the order of few mm), which is a disadvantage for some applications. For instance, FE-DBD was successfully used in a number of clinical trials for the treatment of skin diseases, to control melanoma development, blood coagulation and antisepsis of open wounds [5]. However, it is not suitable for plasma application inside the human body's cavities, such as tooth root canals or internal organs. On the other hand, in the so-called atmospheric pressure plasma jets (APPJs) the plasma generated into a dielectric enclosure (tube or syringe) is expelled through a small orifice into the ambient atmosphere by gas flow (usually a noble gas). The ejected plasma forms a plasma plume that extended several cm into the air and can be easily directed to a target. Figure 2 shows a drawing of the APPJ concept. In the past decade many APPJ configurations, different electrodes arrangements and excitation schemes have been reported in the literature. More details about APPJs and their characteristics can be found in some recent review papers [6; 7; 8].