# Regenerative Endodontics as the Future Treatment of Immutative Permanent Teeth
## 1 Introduction  
Conventional endodontic treatment of permanent teeth with incomplete root development is impossible, due to the significant risk of complications, including root fracture (the walls are thin and the roots are short) or the accidental injection of fluids or filling materials beyond the wide root apex. In the endodontic management of immature teeth, two methods are generally accepted: keeping all or part of the pulp alive, allowing the root to develop naturally (apexogenesis), or--if the pulp is non-vital--stimulating the formation of a hard barrier in its apical part, using appropriate substances inserted into the canal (apexification) [1, 2]. The apexification method has many disadvantages. When calcium hydroxide is applied, repeated placement of intracanal medicaments is necessary, which carries the risk of reinfection, and thorough instrumentation inside the root canalmay cause weakening of the canal walls [3; 4]. The application of new materials that are an alternative to calcium hydroxide, e.g., MTA or Biodentine, eliminates the problem of intracanal medicament replacement. However, none of these substances stimulates further root development. They only constitute a mechanical barrier, closing the root canal lumen. Thus, treatment is a filled root canal with wall thickness and length developed naturally before pulp necrosis. However, some reports of apical papilla survival after REP in humans and dogs may indicate that root regenerative processes are possible [5; 6]. However, in most cases, the tooth does not show adaptation for long-term functioning, as there is a risk of root wall fracture; the greater the risk, the earlier the stage of its development at the time of pulp damage. According to [PERSON] et al. [7], this complication occurs with equal frequency in restorations reinforced with a root-canal post as well as with composite material alone.  
The regenerative endodontic procedure, proposed in 2004 by [PERSON] [8], currently attracts great interest. In the literature, one can find interchangeably used terms, such as revascularization or revitalization. These names stand for biological procedures to stimulate the restoration of tooth tissues, including the pulp-dentine complex and root formation [9]. For this process to occur, three essential components must be present in the root canal: a scaffold for newly forming tissue, stem cells, and growth factors [10]. The key processes that occur in the root canal after regenerative procedures are angiogenesis, reinnervation, and the differentiation of cells responsible for root development [11]. This leads to the formation of vital pulp-, bone-, cementum- or periodontal-like tissue in the canal and thus, root formation [12; 13; 14; 15]. The expected therapy outcome is a tooth whose anatomical structure and functional capacity are close to physiological ones [16; 17]. In addition, there are numerous reports in the literature about the effectiveness of REP for immature teeth with necrotic pulp [17; 18; 19].  
This study aims to review the literature and present the latest methods of regenerative endodontics, including the results of research, and propose a possible treatment protocol.