## 1 Introduction  
The high success rate of periapical healing and continued root development in teeth subjected to regenerative endodontic procedures (REPs) [1; 2; 3; 4] is well documented. A recent retrospective study identified the predictors of success and provided insights into the clinical factors contributing to success. These factors include substances that come in direct contact with pulpal stem cells, namely, sodium hypochlorite (NaOCl), intracanal medications, and biocearamic placed on the top of a blood clot [4]. The optimal NaOCl concentration is controversial, and researchers have proposed various concentrations ranging from 1.5% to 6% [4; 5; 6; 7; 8; 9]. The American Association of Endodontists recommends a concentration of 1.5% [10], whereas the European Society of Endodontology position statement lists concentrations ranging between 1.5% and 3.0% [11]. This necessitates a thorough understanding and assessment of the materials and components employed in REPs for an ideal clinical outcome [4].  
[PERSON] and [PERSON] [5] demonstrated the suitability of a blood clot as a scaffolding medium. The blood clot has long been considered a classical scaffold. Nonetheless, other scaffolding materials suitable for REPs have recently been suggested, such as blood concentrates, synthetic polymers, and ceramic materials. Platelet-rich fibrin (PRF) is a second-generation platelet concentrate [12], and its application and protocols were developed by [PERSON] et al. [13]. It is a non-thrombosed autologous mesh that serves as a reservoir for the slow and continuous release of growth factors over 7 to 28 days [14; 15]. It incorporates leukocytes, platelets, and a wide range of key healing proteins into a dense fibrin matrix. The use of blood concentrates is preferred over blood clots since the amount of evoked bleeding from the apical tissues is inadequate to fill the entire canal space, and an unstable blood clot may break down upon the coronal placement of a bioceramic material [16]. PRF is preferred to avoid the potential difficulties associated with blood clots, including inadequate intracanal bleeding, insufficient blood volume, or the breakdown of blood clots [9; 16; 17].  
A vast number of case reports and series on REP have been published since 2001 [3; 18; 19]. However, there are insufficient studies evaluating the outcomes of REPs performed using PRF. Further, most reports on REP describe the treatment of anterior teeth and premolars [20]. Researchers have recently reported on the potential of successful REPs in posterior teeth with pulp necrosis [21; 22; 23]. No study has compared the effect of tooth location (anterior vs. posterior), root development, and apical closure on the outcomes of REP. Therefore, we aimed to report on the clinical outcomes of REPs performed using PRF scaffolds in the anterior and posterior teeth. Further, we compared the outcomes in anterior and posterior teeth (radiographic length, radiographic root area [RRA], and apical closure) based on the criteria suggested by [PERSON] et al. [24] and [PERSON] et al. [4].  
The null hypothesis was that there is no difference in the outcomes between the anterior and posterior teeth.