## 1 Introduction  
The biomedical application of cold atmospheric pressure plasmas (CAPP) has grown in the past decade, being studied for diverse purposes, such as application as a biomaterial and medical equipment decontamination, wound treatment, cancer treatment, and biofilm and inflammation control [1, 2]. Applying energy to a neutral gas can cause it to become electrically conductive, capable of emitting electromagnetic radiation and very sensitive to externally applied fields. The gas in such a state is known as plasma (physical plasma) and is composed by molecules, ions, and electrons that produce UV (ultra violet), reactive oxygen species/reactive nitrogen species (ROS/RNS) and can operate at body temperature [3; 4; 5]. Its efficiency against microorganisms seems to be driven mostly by hydroxyl and oxygen groups, better produced in devices working with atmospheric gas and, together with the other physical components (UV, heat, electromagnetical field), can vary according to the device's parameters [1; 2; 6]. Plasma can be generated by different devices and discharge principles. Among them, plasma torch and plasma jet (cold atmospheric pressure plasma jet) produce a plasma plume and operate mostly with argon and helium or a mixture of gases. Other configurations, such as dielectric barrier discharge (DBD), floating electrode dielectric barrier discharge (FE-DBD), and surface micro-barrier discharge (SMD) devices can operate with air [7]. This variability, added to the different possibilities of parameters combinations for the reactor itself and the different types of cells and surfaces applied, makes it hard to compare results and requires repetitive safety tests in the studies. Reactive oxygen species (ROS) can be found intra or extracellularly in superoxide form (O\({}_{2}\)\({}^{-}\)), peroxide (H\({}_{2}\)O\({}_{2}\)) or hydroxyl radical (OH\({}^{-}\)) and, together with reactive nitrogen species (RNS) interact with intracellular amino acids influencing in processes like cell aging, degeneration, and inflammatory damage or, in low concentration, be protective against oxidative stress, microbial agents, and induce mitogenic response [8; 9]. Super production of ROS can trigger tumor suppressor gene and oncogene mutation [9]. The variation on plasma dose can either stimulate, inhibit, or cause DNA damage that cannot be repaired by cell cycle repair mechanisms [7]. The oxidative stress, together with a local dysbiosis, is responsible for tissue destruction on periodontal disease. Hyperactivated polymorphonuclear can over-release ROS that can kill invading pathogens but also be cytotoxic to host cells, leading to proinflammatory mechanisms, and inducing osteoclastogenesis [10]. A therapy that could not only inactivate periodontal pathogens but additionally balance the oxidative stress, reducing inflammation without cell damage, would be desirable for periodontitis. The literature has shown a positive plasma effect on _P. gingivalis_ (ATCC 33277) planktonic cells [11], and monospecies biofilm grown for 15 days [12]. We have previously shown that CAPP treatment was effective against planktonic growth of _P. gingivalis_ (ATCC 33277) and dual-species biofilm (_Porphyomonas gingivalis + Streptococcus gorontii_) from 1- to 7-min treatment with no cytotoxic effects (in vitro) or tissue damage (in vivo) [13]. With these favorable results, we were intrigued with the plasma effect on oral cells' DNA and the response of a more virulent strain of _P. gingivalis_ (HW24D-1) in a single species biofilm. The DNA damage can be accessed by different assays, from micronucle to comet assays, detection of phosphorylated histone H2 AX, or even static cytometry [7; 14]. Static cytometry, or image DNA cytometry is an internationally recognized evaluation method for neoplastic transformation of oral cells, and cervical cancer diagnosis that evaluate Feulgen' stained cells in an image software [15; 16].