Sources of information and search strategy
A comprehensive search was conducted to ensure that as many studies as possible were identified through electronic searching.
For the search strategy, the following electronic databases were consulted: 1) PubMed and 2) Web of Science, covering the past 10 years, using the following MeSH keywords: “apical closure”, “open apex”, “immature teeth”, “permanent teeth”, “platelet-rich fibrin”, “MTA”, “non-vital traumatised immature permanent”, “pulp necrosis”, “dental pulp regeneration”.

Boolean operators were used, such as: “immature” NOT “mature”, “permanent” NOT “temporal”, “Blood Clot” OR “Platelet-rich Fibrin”.

Eligibility Criteria
The selection of articles for this study was conducted by applying the following selection criteria (Table 1).
All identified articles were assessed according to the title, keywords, and abstract to exclude those not relevant to the review question.

Selection of studies
The search process yielded a total of 635 articles. After applying the filter of “publications from the last 10 years”, 135 articles were excluded, leaving 500 articles remaining. After removing duplicates in both databases (218 articles), a total of 282 publications remained.
The remaining publications were filtered for “randomised controlled trials” and “clinical trials”. In PubMed, the search was reduced to 17 articles, while in Web of Science, it was reduced to 212, resulting in a total of 229 articles.
Following selection of the articles by title and abstract, 53 were chosen for full-text review. Twelve of these were excluded for being systematic reviews; three for involving non-human samples; four of them, for being in vitro studies; seven, for having a follow-up period of less than three months; and the remainder, for other reasons. Thus, only eight were selected for full-text review, and all of these were included in the present study (Figure).

Characteristics of the studies
For this search, various types of studies were consulted, excluding, as previously mentioned, systematic reviews. Furthermore, sample size, case follow-up, and aetiology have also been considered (Table 2).
Patient characteristics
The sampling unit in these studies is the immature necrotic permanent tooth. A total of 227 immature necrotic permanent teeth are included The majority are maxillary incisors (193), although mandibular incisors (1), premolars (5), maxillary molars (3), and mandibular molars (25) have also been studied (Table 2).

Revascularisation technique
In half of the studies selected for this review, pulp revascularisation was performed by inducing bleeding (blood clot formation) (BC)^2,8-10. Only one study utilised platelet-rich fibrin (PRF)¹¹ and another employed platelet-rich plasma (PRP)¹². The remaining two were conducted using platelet-rich fibrin in half of the sample, and in the other half, blood clot induction was performed^13,14 (Table 3).
Use of MTA
Of the eight studies selected for this review, five used MTA exclusively to create a coronal plug2, ^11-14.

Two other studies divided the sample into two groups, using MTA in one group and either Bioceramic Root Repair⁸ or EndoSequence Bioceramic Putty⁹ in the other. Only one study used NeoMTA Plus¹⁰ (Table 3).

Intracanal medication
Triple antibiotic paste (TAP) was used in five studies⁹,¹¹–¹⁴. Another study used TAP in half the sample and Ca(OH)₂ in the rest¹⁰. In one study, either Ca(OH)₂ or 2% chlorhexidine digluconate gel was used⁸. In the eighth study included in this review, tetracycline and triamcinolone were used as intracanal medication² (Table 3).

Discolouration
Four studies reported the occurrence of coronal discolouration, either caused by MTA or after blood clot induction^2,8,11,14. Only one study reported the absence of coronal discolouration, coinciding with the use of NeoMTA Plus10. Three studies made no reference to the presence or absence of discolouration^{9,12.13</sup(Table 3).}

Failures / exclusion
A total of 54 treatments failed. Failures could be early or late⁸. The former (19) are characterised by an absence of bleeding on induction or failure to form a blood clot; whereas in the latter group (11 teeth), patients exhibited persistent clinical symptoms. Others failed due to severe resorption (3) or non-attendance at follow-up visits (1)².
Other unfavourable outcomes included root resorption (1 case), association with the sinus tract (1), sensitivity to percussion (2), and persistence or increase in the size of the apical radiolucency without symptoms (3)¹⁰. In some cases, failure was due to the need for additional treatment (3) or incomplete healing (4)⁹ (Table 3).

Regenerative therapy has demonstrated excellent success rates³ and has proven to be the technique offering the greatest benefit for the long-term management of non-vital permanent teeth¹¹.
Revascularisation is a promising approach for treating immature incisors, helping to restore sensitivity and promote apical closure², increase dentinal wall thickness11 and at least preserve the alveolar bone in terms of socket preservation. Further studies are needed to determine the ideal conditions for revascularisation, such as trauma type, age, and apical foramen width².

The success of revascularisation is considered to depend on reducing bacterial load¹⁸. The main reported side effect was discolouration, seen only in damaged teeth. The most consistently observed radiographic finding was narrowing of the apical diameter³. Yang et al. (2022) followed up at 6, 12, 24, and 36 months, showing further radiographic evidence of healing in immature necrotic teeth¹⁶.
In a prospective study, Wikström et al. (2022) reported successful pulpal revitalisation, with resolution of clinical and radiographic signs and continued root development.

Continuous root development was observed in 60% of the teeth in which the procedure was performed, with failed cases being associated with the absence of bleeding (n=19) and persistent infections (n=11)8
⁸, as well as crown fractures¹⁹.

Use of MTA
In the study by Tawfeek et al. (2023) demonstrated that clinical and radiographic success, whether using NeoMTA or conventional MTA (WMTA), was 100%. Discolouration was detected in only one tooth with NeoMTA (9.1%) and in three teeth (27.3%) with MTA, but the difference between the groups was not statistically significant¹⁵.
Similarly, Ajram et al. (2019) demonstrated that the regenerative endodontic technique is feasible and can be successfully performed using Ca(OH) and MM-MTA5. In the randomised clinical trial by Abuelniel et al. (2020), it was demonstrated that teeth treated with MTA exhibited significant discolouration from 6 to 18 months of follow-up. It was observed that 23 of the 25 teeth treated with MTA had developed discolouration at the 6-month follow-up visit²⁰.

The case series conducted by Hajizadeh et al. (2019), illustrated 12-month follow-ups of revascularisation in three necrotic immature teeth using MTA as a coronal barrier. The treatments were considered successful, as the teeth were functional, all unfavourable signs and symptoms were alleviated, and some degree of root development was achieved17.
In the study conducted by Sajjad et al. (2022), 40 cases were treated with MTA and 32 were successful. A complete resolution of signs and symptoms was observed, with absence of periapical radiolucency, in most cases, elongation of root length, increased thickness of the root canal walls, and apical closure²¹.
Use of platelet-rich fibrin, platelet-rich plasma, and stimulation of the blood clot

The randomised controlled trial (RCT) conducted by Rizk et al. (2020), demonstrated that the teeth in which platelet-rich fibrin was used (examined group) exhibited a statistically significant increase in radiographic root length and width, an increase in periapical bone density, and a reduction in apical diameter compared to the control group (in which bleeding was induced, resulting in the formation of a blood clot). At the end of the follow-up period, all treated teeth were negative in the sensitivity test. The control group exhibited greater coronal discolouration compared to the examined group¹⁴.

In the prospective case series by Nawal et al. (2020), immature necrotic permanent maxillary anterior teeth (n=6) underwent pulp regeneration using platelet-rich fibrin. None of the teeth demonstrated improved responsiveness to pulp sensitivity tests at the end of the 5-year follow-up; however, all exhibited a reduction in apical diameter (mean of 30.96%), which was statistically significant. An increase in root thickness (40.20%) and root length (13.18%) was also observed⁷.
Ragab et al. (2019) stated, in their RCT, that the use of platelet-rich fibrin is effective for controlling the placement of MTA at the desired level, with only slight pressure exerted on the MTA during placement; It is also stated, however, that the use of platelet-rich fibrin may not be necessary for pulp revitalisation in immature permanent anterior teeth¹³. Similarly, Sakthivel et al. (2020) confirmed that platelet-rich fibrin is an ideal biomaterial for regeneration⁶.

In the RCT conducted by Rizk et al. (2020), they conducted a 12-month follow-up (n=24). Platelet-rich fibrin demonstrated a marginal increase in radiographic root length and width, periapical bone density, and a reduction in apical diameter. No statistically significant differences were observed when compared with the blood clot. The treated teeth did not respond to the sensitivity test at the conclusion of the study. The blood clot exhibited a statistically significantly greater degree of coronal discolouration compared to the platelet-rich fibrin group¹⁴.
Ragab et al. (2019) stated, in their randomised clinical trial, that the blood clot was important for creating vital tissue within the empty sterile canals¹³.

In the prospective clinical trial conducted by Markandey et al. (2022), a follow-up period of 12 to 24 months was conducted, yielding the following results: the use of a blood clot, platelet-rich plasma, and platelet-rich fibrin demonstrated similar potential for the healing of periapical lesions and apical closure, as well as for radicular wall thickness and root length in immature teeth²².
Platelet-rich plasma is superior to platelet-rich fibrin and induced bleeding with regard to the healing of periapical wounds; however, they produce comparable outcomes in terms of lateral wall thickening, root lengthening, and response to vitality tests²³.
A disadvantage of platelet-rich plasma and platelet-rich fibrin techniques is that additional time is required to extract and centrifuge blood prior to its introduction into the root canals²³.

Canal disinfection
Sakthivel et al. (2020) confirmed that revitalisation of an immature necrotic infected tooth is possible under conditions of complete canal disinfection⁶.

Biradar et al. (2023) once again demonstrated the role of antibiotics in creating a favourable environment for the growth of pulpal and periapical tissues; furthermore, they make particular mention of triple antibiotic pastes (TAP), which play an important role as intracanal medicaments in regeneration and revascularisation procedures¹². Hajizadeh et al. (2019) stated that the concentrations of medicaments are important in achieving a balance between canal disinfection, the release of growth factors from the dentine matrix, and the survival/proliferation of stem cells from the apical papilla¹⁷. It should be noted that triple antibiotic paste is a highly effective antimicrobial agent; however, high concentrations of this mixture may have a detrimental effect on the survival of stem cells²⁴.

Ragab et al. (2019) stated, in their RCT, that ciprofloxacin and metronidazole in addition to sodium hypochlorite are effective in controlling infection, although in some cases an extension of the treatment period is required¹³.

Adverse effects
Higher concentrations of antibiotic medications, as well as Ca(OH)2, may cause adverse effects on the mechanical, physical, and chemical properties of radicular dentine; that is, it may negatively affect fracture resistance in the cervical third of the roots^25,26.

When used at high concentrations, antibiotic medicaments (TAP) may demonstrate superior antimicrobial properties compared to Ca(OH)2. However, high concentrations of TAP have been associated with several complications, such as antibiotic resistance, high cytotoxicity, and discolouration of the teeth¹⁰.
There is a low incidence of adverse effects. The most frequently reported drawback in the reviewed publications was tooth discolouration caused by MTA.
Endodontic regeneration failed in some cases due to discolouration and recurrent caries, crown fracture4 or loss of the coronal restoration of the treated teeth⁹.

According to this literature review, pulp revitalisation demonstrates high survival rates in the treatment of immature necrotic permanent teeth, with satisfactory clinical and radiographic outcomes.
Revascularisation facilitates improved apical closure, increased dentinal wall thickness, and greater root length. It also preserves the alveolar bone.

Randomised clinical trials are required to compare the effect of platelet-rich fibrin and induced bleeding on the long-term revitalisation of teeth with necrotic pulp and open apices. Platelet-rich plasma results in superior apical healing, with root lengthening and thickening of the dentinal walls.
Clinical and radiographic success can be achieved using either MTA or Ca(OH2). One of the principal challenges of pulp revitalisation is coronal discolouration. NeoMTA is a material that has demonstrated less discolouration compared to conventional MTA. Likewise, it has been shown that the use of platelet-rich fibrin results in less discolouration than induction of bleeding and clot formation.
Triple antibiotic paste is a highly effective antimicrobial agent; however, high concentrations may have a detrimental effect on the survival of stem cells.
Although current research in regenerative therapy is highly promising, its outcomes remain unpredictable due to the histological nature of the regenerated tissue. Consequently, further studies are required to assess the follow-up and efficacy of each of these treatments.