# Different Approaches to the Regeneration of Dental Tissues in Regenerative Endodontics
## 4 Discussion  
The American Association of Endodontists has set three goals, whose achievement determine the degree of success of regenerative therapy. The primary goal is the elimination of periapical periodontitis and clinical symptoms. The secondary desirable goal is the thickening of root walls and/or continued root maturation. Finally, the third goal is a positive response to pulp sensibility testing [53]. There have also been requirements set that must be met by a selected case in order to start the RET procedure. The basic stipulation is a permanent tooth with necrotic pulp and immature root that does not need a post for final restoration [51]. The treated patient should be compliant and not exhibit signs of allergy to medicaments used during the procedure [49]. A complete endodontic diagnosis includes preoperative radiographic examination, thermal sensitivity pulp tests, electric pulp testing, and percussion testing [91]. Extraoral and intraoral examinations must be conducted to check for signs of lymphadenopathy or swelling. The positive result of the regenerative protocol depends on various circumstances, which are considered below. An infected immature permanent tooth with an open apex exhibits greater potential to achieve a positive result of endodontic treatment than mature teeth, due to rich vascularization, a significant supply of dental pulp stem cells (DPSC) [61], the reservoir of stem cells from apical papillae (SCAP), and their ability to produce the primary odontoblasts involved in apexogenesis [12; 20; 21; 92]. However, one of the major problems of necrotic immature teeth is controlling the infection by obtaining a complete eradication of bacterial biofilm in the complex root canal system. In cases of atypical root canal morphology accurate treatment planning is now facilitated by the possibility of performing non-invasive three-dimensional imagining with micro-computed tomography (microCT), cone-beam computed tomography (CBCT), peripheral-quantitative computed tomography (pQCT), and spiral computed tomography [93; 94]. The intracanal disinfection is considered to be an essential step of regenerative dentistry, due to the fact that infection prevents pulp tissue reparation and regeneration, and also may cause the damage of stem cells in periapical tissues [95; 96]. Careful selection of irrigants seems to be significant, because of their various antimicrobial properties, different reaction with tissues, root canal lubrication, and debris removal [97; 98]. The most common protocol to control infection is root irrigation with sodium hypochlorite (NaOCl) and EDTA or chlorhexidine, then canal system filling with antibacterial Ca(OH)\({}_{2}\) or triple antibiotic paste [99]. The major irrigation solution in endodontic treatment is sodium hypochlorite, with a broad antibacterial and antifungal spectrum. In vitro studies showed that NaOCl in a concentration ranging from 1% to 5.25% is effective against biofilm formed by highly resistant _Enterococcus faecalis_, however, a large amount of the solution, and irrigation time up to 5 min, are required [49, 100]. Moreover, a recent study proved that the impact of NaOCl on the mechanical properties of dentin depends on concentration and irrigation time [101]. It is also well accepted that higher concentrations of sodium hypochlorite have a toxic effect on the survival of stem cells from the apical papilla (SCAP). Therefore, current regenerative endodontics guidelines recommend using 1.5%-3% NaCl [52, 53], as this concentration of the irrigant exhibited minimal harmfulness for SCAP and odontoblasts [102]. The noxious effect of NaOCl could be reversed by the usage of 17% EDTA after NaOCl irrigation, thus it may be beneficial for tissue preservation, as well as to enhance SCAP survival [103]. In contrast to sodium hypochlorite, EDTA has the ability for smear layer removal from instrumented root canal walls.