## 4 Discussion  
Recently, REP has gained popularity due to its potential to induce neotissue formation in the root canal space and hard tissue formation [1]. Its primary objective is to enable the healing of apical periodontitis and to help achieve other goals affecting tooth maturation [30]. Tooth maturation involves regaining normal pulpal physiological functions, which are evaluated in terms of continued root development, immune competency, and normal nociception [30]. [PERSON] et al. [18] suggested that all teeth with immature roots (Cvek Class 1-4 (25)) that do not need intraadicular restoration could be treated with REP. The NaOCl concentration used for disinfection irrigation contributes to the treatment success. We used 4% NaOCl in combination with 20 mL of 17% EDTA. [PERSON] et al. [9] demonstrated that dentin conditioning with high concentrations of NaOCl exerted a profound negative effect on the survival and differentiation of stem cells of the apical papilla in vitro; however, the use of 17% EDTA following NaOCl irrigation minimised the aforementioned effect. [PERSON] et al. [4] reported that 1.5% NaOCl was associated with a higher risk of failure, whereas a higher concentration of NaOCl (6%) and the complete strength of double antibiotic paste were associated with greater increase in root development. We used a modified triple antibiotic paste (TAP) as an intracanal medication since the majority of previous studies have reported high success rates with TAP [4; 31; 32]. The originally suggested TAP included minocycline, which caused discoloration. Therefore, researchers suggested to discard or replace it with another type of antibiotics [31]. The scaffold is another clinical factor that contributes to REP success. Although the clinical advantages of PRF over blood clots are debatable, we used PRF as a scaffold in all cases. Moreover, the use of blood concentrates as an alternative source for blood clots may have several advantages, including the increased concentration of growth factors [33], resolution of clinical signs and symptoms of apical periodontitis, and continued root development [2; 14]. Comparative clinical studies have indicated that root lengthening is significantly more frequent in REPs using PRF than in those using blood clots [34; 35]. In comparison with the blood clot scaffold, PRF induced greater apical closure [3] and lesser root canal obliteration [36]. This is a better outcome since obliteration may exert an adverse effect on future endodontic treatments. [PERSON] et al. [36] demonstrated no need for prior apical bleeding for successful REP with PRF. Nonetheless, bleeding was evoked in the present study prior to PRF insertion to ensure the continuity of the PRF with apical tissues. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Characteristics of Continued**} & \multicolumn{3}{c}{**Anterior**} & \multicolumn{3}{c}{**Posterior**} \\ \cline{2-7}  & **Mean** & **Median** & **IQR** & **Mean** & **Median** & **IQR** \\ \hline RRA & 26\% & 25\% & 15\% & 39\% & 38\% & 30\% \\ Length & 6\% & 4\% & 7\% & 11\% & 10\% & 7\% \\ \hline \hline \end{tabular}  
* RRA, radiographic root area; IQR, interquartile range.  
\end{table} 
Table 1: Continued development (increase in RRA and length) of the anterior and posterior roots. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Type of Teeth**} & \multicolumn{3}{c}{**Apical Closure Status**} \\ \cline{2-7}  & **Complete** & \multicolumn{3}{c}{**Incomplete**} & \multicolumn{3}{c}{**Unchanged**} \\ \cline{2-7}  & **Posterior** & **Anterior** & **Posterior** & **Anterior** & **Posterior** & **Anterior** \\ \hline Number of teeth & 19 & 10 & 2 & 16 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The distribution and frequency of apical closure status. Moreover, a recent meta-analysis by [PERSON] and [PERSON] [30] reported that the success rate of REP was significantly greater with blood concentrates than with blood clots.