# Applications of Cold Atmospheric Pressure Plasma in Density
## 4 CAPP Application in Endodontics  
Endodontic infection occurs in the tooth root canal system that gets exposed to the oral environment. The microorganisms can reach the intra-radicular region from a carious lesion or after a traumatic injury to the coronal tooth structure [79]. Primary endodontic infections are caused by polymicrobial biofilms dominated by aerobes and facultative anaerbes microorganisms [80]. The persistence of _Enterococcus faecalis_ in the root canal system is the main cause of post-treatment infection followed by _Fusobacterium_ and _Propionibacterium_[80, 81].  
Endodontic infection treatment involves removing of remnants vital or necrotic tissues, the elimination of microorganisms within the root canal system, and removal of hard tissue debris that is formed during root canal instrumentation. The root canal disinfection is considered the pivot of this therapy [81]. NaOCl solution is commonly used to clean and disinfect the root canal due to its antimicrobial activity, however, it can also affect vital pulp and decreases the mechanical resistance of dentin [82].  
Some studies have shown that CAPP is able to inhibit the persistent root canal microorganism _Enterococcus faecalis_. [PERSON] et al. [83] evaluated the effect of CAPP against _E. faecalis_ suspensions spread on the surface of sterile glass slides. They observed that CAPP was able to reduce the number of colonies forming unities after 2 min of exposure. They also observed that the antimicrobial effects are time-dependent and the exposure for 3 min showed the best results. In situ studies using dental tissue as the surface for biofilm formation could better represent the root canal system. [PERSON] et al. [84] reported that the viability of _E. faecalis_ biofilms formed on the surface of tooth fragments were significantly reduced after exposure to He-CAPP or He/O\({}_{2}\)-CAPP for 4, 6 and 8 min.  
The association of He-CAPP with other substances can also be a strategy for clinical application. [PERSON] et al. [85] observed that Ar/O\({}_{2}\)-CAPP treatment for 12 min eliminated 3-week _E. faecalis_ biofilms without changes of root canal dentin. [PERSON] et al. [86] observed that He-CAPP jet flowing through 3% hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) showed better effects against _E. faecalis_ biofilms formed inside extracted teeth root canals when compared to He-CAPP alone. Optical emission spectroscopy analysis showed that stronger emission lines of atomic oxygen and hydroxyl radical in the He/H\({}_{2}\)O\({}_{2}\)-CAPP when compared with He-CAPP.  
More recently, the indirect CAPP treatment also appeared as an alternative for the disinfection of root canals system, although few information is available so far. [PERSON] et al. [87] showed that plasma-treated water (PTW) can be used as an endodontic irrigant.  
The in-situ experiment showed that PTW was able to disinfect the root canal experimentally infected with _E. faecalis_ without adverse effects to oral mucosa.  
The study on the CAPP effects against _Propionibacterium_ is scarce in the literature. According to [PERSON] et al. [88] CAPP exposure inactivated _P. acnes_ cells in suspensions and biofilm formed on glass slides. They also observed that the antimicrobial effect increases with time.  
No study reporting the antimicrobial effects of CAPP against _Fusobacterium_ could be found in the literature. However, CAPP has already showed antimicrobial activity against other Gram-negative and anaerbes oral pathogens as _P. gingivalis_[68].  
The aim of endodontic treatment is to eliminate the pathogenic microorganisms and prevent reinfection, avoiding clinical failures. The studies shown that CAPP can be an alternative to the conventional irrigant solutions which can damage healthy tissues. The antimicrobial effect of plasma jet seems to be correlated with the time of exposure and the working gas. Then, an efficient protocol should be developed to the use of CAPP in the endodontic clinical routine.