# Low-Temperature Plasma as an Approach for Inhibiting a Multi-Species Carigenic Biofilm
## 1 Introduction  
Even though dental caries have become less prevalent in developed countries and are delimited to some sectors of the population [1], it is still prevalent in underdeveloped countries, especially in children up to six years of age [2, 3, 4]. Dental caries are caused by a combination of factors, including the frequent consumption of sucrose combined with a dental biofilm composed of acid-producing microorganisms [5, 6]. The cariogenic dental biofilm is formed by highly organized diverse microbial communities enmeshed in a polysaccharide-rich matrix and adheres to the dental surface [7]. The microbial community is linked to a chain of interactions that can regulate pathogenicity and resistance to antibiotics [8]. The extracellular matrix can function as the first line of defense against the effect of antibiotics and for the transfer of genes among microorganisms [9]. Microorganisms in the biofilm can be up to a thousand times more resistant to antibiotics when compared to free-floating cells [10]. The formation of the cariogenic biofilm is an ongoing process withnumerous stages. First, the acquired pellicle is formed, followed by the primary colonization, later proliferation of adhered microorganisms, secondary co-aggregation, and finally the biofilm maturation process [11]. For disease progression to occur, microorganisms need a source of carbohydrates from the diet, exposure time to acidic pH, and a susceptible host. Oral bacteria ferment these carbohydrates, producing acids, thus beginning the disease stage. Thereafter, acid-producing and low-pH-tolerant bacteria begin to increase their population within the acidic environment, causing demineralization of the tooth surface and, eventually, the formation of cavities [12; 13; 14; 15]. Sucrose is a variogenic carbohydrate obtained from the diet capable of stimulating biochemical and physiological changes in oral biofilm. Moreover, carbohydrates can alter the formation of the cariogenic biofilm. Carbohydrates may also change the phenotype during the formation of the cariogenic biofilm [16; 17]. The pH reduction causes a selection of acidophilic and acidogenic microorganisms, which results in an even more cariogenic environment [18]. In addition, sucrose can participate as the substrate for extracellular polysaccharides production [19]. Some studies have proven the ability of sucrose to reduce concentrations of calcium (Ca), inorganic phosphorus (Pi), and fluoride (F) in oral biofilms [20]. These ions are of crucial importance and are linked to the remineralization of enamel and dentin [20; 21]. Streptococci make up more than 80% of the initial constituents of biofilm and are responsible for the initial colonization process. _S. sanguinis_ and _S. goroduii_ are amongst the initial species to inhabit the dental surface [22]. These microorganisms can express adhesin molecules on the cell surface with binding capabilities [23]. Furthermore, they are capable of adhering through their fimbria in the saliva-coated hydroxyapatite layer [24]. For this reason, they compete for attaching to the same receptors offered by the host [23]. The development of caries may be associated with the growth of _S. mutans_ and lactobacillus, as well as a decrease in the general diversity of other species that colonize the oral cavity [25; 26; 27]. Interactions between species of oral streptococci can play a significant part in this change. When in large quantities in dental biofilm, some streptococci may have a beneficial characteristic capable of antagonizing _S. mutans_[28]. This antagonism can be demonstrated when these microorganisms are identified and listed by molecular identification methods, which allows greater clarity in the study of the microbiota associated with dental caries [28]. An in vitro experiment using molecular biology techniques demonstrated this antagonism, indicating that _S. sanguinis_ and _S. goroduii_ are directly involved with _S. mutans_ for dominance over a given niche [19]. While _S.