# Different Approaches to the Regeneration of Dental Tissues in Regenerative Endodontics
## 4 Discussion
It could be avoided by replacing minocycline with cefaclor [116], or removed in double antibiotic paste (DAP) [117,118]. Recent research has indicated that both TAP and DAP decrease the survival of stem cells of the apical papilla (SCAP) when used in a concentration greater than 1000 mg/mL as a canal dressing [114,119]. The other recommended canal medication, calcium hydroxide, showed improvement of SCAP proliferation [103,120] and no cytotoxic properties [119]. Calcium hydroxide preserves its antimicrobial character over long periods, thus it effectively eradicates bacteria from the infected root dentine [121,122]. [PERSON] et al. reported that usage of calcium hydroxide as a canal dressing for a long period of time may lead to weakening root dentine and increasing the possibility of root wall fracture [123]. Nevertheless, the latest study on root susceptibility to fracture after long-term calcium hydroxide treatment, revealed that root fracture might be more associated with root stage development than the use of the examined material [124]. It was suggested that the intra-canal medicaments recommended in current standardized regenerative treatment do not achieve adequate elimination of bacteria in simulated necrotic immature root canals [125]. The next step in REP is the periapical tissues laceration with a hand file to induce bleeding into the canal space. This procedure should be carried out with local anesthesia, and without a vasoconstrticrator. The flowing blood may bring mesenchymal stem cells [126], immunoglobulins, cytokines, and growth factors, such as PDGF, TGF, IGF, and EGF [69]. Another purpose is blood clot formation, which may act as a scaffold [51]. Most of the available data indicated that intracanal bleeding plays a key role in pulp-dentin complex repair [127], however, some studies have demonstrated that cases with the tissue laceration step omitted had successful outcomes as well [127,128]. [PERSON] et al. [129] showed that using blood clotting in the treatment protocol resulted in improved healing outcomes, formation of dentin in the root canal, and also vascularized tissue. Optimally, the top of the blood clot should reach 2-3 mm underneath the cementoenamel junction (CEJ) [130]. Once this is accomplished, a mineral trioxide aggregate (MTA) cement is placed over the blood clot or scaffold to seal the root canal space, and prevent bacterial invasion [83]. MTA exhibits a bioinductive capacity, reparative properties [131], and biocompatibility to tooth tissues [103,132]. An interesting result was provided by research aimed at evaluating histologically the newly generated tissue after RET. The study demonstrated MTA's ability for apical closure induction and resolution of periapical lesions in immature teeth [129]. Nevertheless, MTA is considered to have a potential for discoloration of coronal dentine, when used as a canal sealer [133,14,134]. This brings a major esthetic concern for anterior teeth treatment. Alternatives to MTA, such as Biodentine can be used to avoid the risk of this negative outcome [135,136,137,135]. According to the American Association of Endodontists, to achieve a good coronal seal, a 3-4 mm layer of glass-ionomer should cover the MTA, followed by bonded resin restoration [53]. In fact, it is worth mentioning that recent research revealed a higher shear bond strength value between calcium silicate-based cement (such as Biodentine and MTA) overlaid with resin-based composite than glass ionomer [138,139,140,141]. According to [PERSON] et al. [140], placing the glass ionomer cement over the capping material is not recommended. Long-term follow-up studies are required to establish reliable outcomes the success rate of regenerative endodontic procedures [51], however, there are no standardized recall protocols [49]. A complete follow-up should include a radiographic and clinical examination. The periapical radiographs allow verifying the increase of root length and width of root walls, and also the resolution of an apical radiolucency [48,142].