# Different Approaches to the Regeneration of Dental Tissues in Regenerative Endodontics
## 4 Discussion
In addition, research has demonstrated that EDTA solution significantly increases the release of growth factors into root canal space, and might, therefore, play a role in the promotion of cells to recruitment and differentiation [49, 104, 105]. In 2016, [PERSON] et al. showed that irrigation of either 1.5% NaOCl + 17% EDTA, or 2.5% NaOCl + 17% EDTA significantly enhanced the release of TGFb1 in comparison with the result of irrigation only, with 17% EDTA. This resulted in the migration of dental papilla stem cells (DPSC) on the growth factors inside the root canal [31]. It is worth mentioning that a recent study on the immunohistochemistry analysis of failed cases indicated that intraradicular disinfection may not be efficient for preventing extraradicular biofilm formation, which may result in the persistence of apical inflammation [106]. According to a data analysis performed by [PERSON] et al., in 68% of clinical case reports there was no mechanical instrumentation of the canal walls [107]. Some studies have suggested that complete instrumentation may be unfavorable for regenerative treatment, by removing vital tissues from the apical area of the canal and also weakening root walls [49, 108]. Nevertheless, mechanical debridement seems to be required for biofilm structure removal, because its remaining causes persistent inflammation, and significantly decreases the chance of regenerative procedure success [104, 109]. [PERSON] and [PERSON]'s recent case report presented a regenerative endodontic treatment for an immature necrotic #18 tooth with arrested root development. At the first appointment, the mesial canals were instrumented to the working lengths to size 45 K-file, and the distal canal to size 120 K-file. At the second appointment, each canal was formed into a 0.05 taper with K-files by step-back preparation [109]. Another study, conducted on seven permanent teeth with necrotic pulps and apical periodontitis, included mechanical instrumentation with hand K-files to #20, and following preparation with Pro-Taper Universal rotary files, also to #20 to the working length on the first visit. On the second treatment visit the canals were enlarged with rotary files to #40, #30, and #20 tip size, depending on the tooth and root location, and then the patency of the canal foramen was checked with a #15 K-file [69]. Both clinical studies achieved symptoms of remission and apical lesion healing. The apical foramen width seemed to affect the outcomes of RET in teeth with necrotic pulp, nevertheless, the minimum diameter has not been determined. It was found in an animal study that revascularization can occur with an apical foramen as small as 0.32 mm [110]. It was suggested that the large size of the apical foramen may be beneficial for cell migration from the apical area into the root canal, to create a new tissue [51]. There are different data available that show various approaches to apical foramen size preparation; e.g., [PERSON] and al. [111] enlarged the foramen to a #35 K-file, and [PERSON] and [PERSON] [112] to a #60 K-file. Recent studies demonstrated that the most successful treatment was conducted with a foramen width of 0.5-1.0 mm [113]. To sustain disinfection and curative processes during the inter-visit period, it is necessary to fill prepared root canals with canal medications. The American Association of Endodontists proposed using in REP, either a calcium hydroxide paste or an antibiotic paste [53]. The antibiotic medicament, commonly known as a triple antibiotic paste (TAP), contains a combination of ciprofloxacin, minocycline, and metronidazoleae. Even though TAP exhibits a wide antibacterial spectrum [114], and numerous case reports involving antibiotic root dressing have demonstrated a positive outcome of regenerative procedures [49], TAP has some disadvantages worth consideration. Antibiotic usage is always associated with the risk of systemic allergic reaction [51]. Tooth structure discoloration is one of the side effects caused by the minocycline included in triple antibiotic paste [115].