Orthograde Apical Barrier in Non-Vital Immature Permanent Teeth: A Precision-Preservation Narrative Review of Clinical Pathways, Procedural Determinants, and Evidence Gaps

1. Introduction

The permanent dentition can be rendered non-vital before root formation is complete, most often as a consequence of dental trauma, untreated caries or developmental dental anomalies in children and adolescents [1,2]. Dental trauma is a principal causative factor, as it may interrupt the apical blood supply (partially or completely) through displacement of the tooth or crushing of the surrounding blood vessels, so that pulp necrosis ensues when this supply is not re-established. Traumatic dental injuries of permanent teeth are a global health problem, with statistics indicating that one billion people worldwide are affected [3] and that approximately one third of these injuries involve immature teeth that may proceed to pulp necrosis [4]. In a study at Damascus University, traumatic injuries accounted for approximately 11% of cases, of which 40% involved immature permanent teeth; delay in seeking treatment—recorded in nearly half of the cases—was closely associated with pulpal and periapical complications, particularly asymptomatic apical periodontitis, while avulsion and complicated crown fractures were the most common injuries leading to pulp necrosis [5]. Dental caries constitutes a second major cause: bacteria and their metabolic by-products penetrate the pulp and provoke inflammation and fibrosis, and where the bacterial insult is not removed, chronic inflammation diminishes the pulp’s reparative capacity until the entire root canal system becomes involved [6]. Developmental anomalies represent a further aetiology, notably dens invaginatus and dens evaginatus [7,8]; in the former, the pulp is separated only by a thin layer of hard tissue, predisposing to early necrosis after eruption, whereas in the latter an enamel-covered tubercle—containing pulp tissue in up to 43% of cases—may fracture under occlusal trauma, exposing the pulp and arresting further root development [8].

When the pulp becomes necrotic in such an immature tooth, the function of Hertwig’s epithelial root sheath is disrupted and root development ceases, leaving a tooth with a short root, thin and divergent dentinal walls, a wide root canal and an open (often blunderbuss) apex [1]. This anatomical configuration produces an unfavourable crown-to-root ratio and markedly reduced resistance to fracture, while the absence of an apical constriction makes conventional obturation, working-length determination and effective disinfection particularly demanding [9].

For decades, the management of these teeth relied on long-term calcium hydroxide apexification to induce a calcified apical barrier. Although effective in forming a barrier, this approach requires many months and multiple visits and has been associated with a time-dependent weakening of radicular dentine and a clinically relevant risk of cervical root fracture [10]. The introduction of hydraulic calcium silicate cements as artificial apical barriers transformed this field, enabling single- or two-visit creation of an apical plug, immediate obturation and reported success rates broadly comparable or superior to those of calcium hydroxide [11,12]. More recently, regenerative endodontic procedures have emerged as a biologically attractive alternative that may permit continued root maturation; however, the longer-term and comparative evidence base remains incomplete, and apical barrier treatment is still widely regarded as the first-line orthograde option when revascularisation is not indicated or not feasible [13,14].

Despite the popularity of the apical-plug technique, the literature addressing it is heterogeneous and procedurally fragmented: individual studies tend to focus on a single variable—material type, plug thickness, irrigation, condensation method or outcome—without situating it within the complete clinical pathway. Several procedural steps that are specific to the immature tooth are frequently under-reported. The purpose of this narrative review is therefore to integrate the contemporary evidence across the entire treatment sequence from diagnosis, isolation, disinfection and the procedural determinants of apical-plug formation, to the choice of material, the definitive restoration, the patient- and operator-related factors that influence the outcome of apical plug treatment, and treatment outcome itself, and to identify, throughout, the questions that remain unresolved. Particular emphasis is placed on distinguishing between laboratory and clinical evidence, and on highlighting the procedural variables that most plausibly influence the clinical result.

In precision and preservation-based pediatric dentistry, apical barrier therapy should be understood not merely as apexification with a newer material, but as a structured decision pathway that preserves compromised immature permanent teeth when regenerative treatment is not appropriate, while requiring accurate diagnosis, procedural skill, definitive restoration, and equitable access to follow-up care.

Methods of the Narrative Review

This narrative review was developed through targeted searches of PubMed/MEDLINE, Scopus, Web of Science, Cochrane Library, and Google Scholar up to [insert final search date]. Search terms included combinations of: “immature permanent teeth,” “open apex,” “apexification,” “apical barrier,” “apical plug,” “mineral trioxide aggregate,” “MTA,” “Biodentine,” “bioceramic putty,” “calcium silicate cement,” “regenerative endodontics,” “pediatric endodontics,” “dental trauma,” “irrigation,” “intracanal medicament,” “rubber dam isolation,” “working length,” “CBCT,” “fiber post,” and “coronal restoration.” English-language clinical studies, randomized trials, systematic reviews, guidelines, laboratory studies, and relevant case reports were considered when they informed the clinical pathway or procedural determinants of apical barrier therapy. Because this was not designed as a systematic review, no formal meta-analysis or risk-of-bias assessment was performed. Evidence was narratively synthesized according to the clinical sequence of diagnosis, treatment selection, isolation, disinfection, plug formation, restoration, follow-up, and evidence gaps.

2. Management of Non-Vital Immature Permanent Teeth by Apexification with Apical Barrier

2.1. Indication

Apexification is indicated as one of the most widely accepted therapeutic approaches for the management of non-vital immature permanent teeth (with a Cvek root-development stage of II to IV) with or without a periapical lesion [15,16] to form a calcified barrier at the apex to ensure a tight seal of the root canal, prevent overfilling and promote healing of the periapical tissues [17,18].

Notably, the dental literature lacks clear criteria for the apical dimension at which a tooth is considered to have an open apex; this depends largely on the criteria of individual controlled randomised clinical studies. Recent studies have considered the minimum dimension at which a tooth is classified as immature to range between 0.6 and 1 mm, depending on tooth type (the range narrows posteriorly) and on the intended type of treatment (regenerative procedures require larger dimensions). It is also worth noting that some studies relied on the radiographic appearance of the tooth itself, considering it immature if its root was shorter than expected, its walls were divergent, or the apical lumen was wider than the canal lumen [12,15,16,19,20,21].

2.2. Calcium Hydroxide Apexification

The use of calcium hydroxide [Ca(OH)₂] paste as a repeated, long-term intracanal dressing was observed to induce apical closure [3]. The alkalinity of calcium hydroxide stimulates the stem cells of the periapical papilla to transform into cementum- and dentine-forming cells, and apical formation continues through the deposition of hard tissue in the apical region in cases where the teeth are asymptomatic with radiographic signs indicating closure of the apical foramen [4,22]. This technique is distinguished by its excellent ability to disinfect the root canal owing to the high alkalinity of calcium hydroxide [10,23]. However, it has drawbacks, namely the need for multiple treatment visits over a long period of between 9 and 24 months [24], as well as a decrease in fracture resistance over time at the level of the pre-cervical dentine (the mechanically weakest region in immature teeth) because of the reaction of calcium hydroxide with dentine and the dissolution of its organic components, which alters the nature of the acidic proteins and proteoglycans that act in dentine as binding agents between the collagen network and hydroxyapatite crystals, rendering the dentine more brittle and potentially leading to cervical root fracture and the risk of complete tooth loss [10,25]. Immature permanent teeth with a Cvek root-development stage of I have been identified as a negative prognostic factor for such fractures when treated with calcium hydroxide dressings, with fracture rates ranging from 77% in the least mature teeth to 27% in the more mature teeth; the deficiency of root development was observed to be more influential than the duration of calcium hydroxide dressing use [16,26].

2.3. Apical Barriers

Another effective technique was developed as an alternative to calcium hydroxide apexification, working to induce the formation of apical hard tissue with the aid of an artificial barrier at the apex to assist closure of the root canal in teeth with open apices—known as the apical plug, using calcium silicate materials.

Calcium silicate cements have been distinguished from conventional calcium hydroxide dressings by numerous advantages, such as enhanced compressive strength, reduced solubility after setting, improved sealing ability to prevent bacterial ingress, antibacterial activity against facultative anaerobes, an excellent capacity to induce the formation of mineralised tissue, and a positive biological interaction with the surrounding dental tissues, all of which remain unaffected by contact with tissue fluids or blood [27,28,29]. However, these materials also have some limitations, such as high cost, difficulty of mixing and handling, the potential to cause tooth discolouration, a long setting time, and the considerable waste associated with materials available in capsule form [30,31,32].

This technique yields excellent results in periapical tissue healing and radiographic signs indicating closure of the apical foramen [12,33]. It is distinguished by the immediate closure of the open apex, which substantially reduces treatment duration, in addition to its excellent biocompatibility arising from the use of highly biocompatible calcium silicate cements, which improves their interaction with the periapical tissues by stimulating cell proliferation and differentiation [12,21,34].

2.4. The Practical Stages of Apical Plug Formation

2.4.1. Diagnostic Considerations and the Limitations of Pulp Testing

Establishing a correct pulpal diagnosis is the prerequisite that determines whether a tooth is a candidate for apical barrier at all, yet this is uniquely difficult in immature teeth. Conventional thermal and electric sensibility tests are widely regarded as unreliable in immature permanent teeth, principally because the myelinated nerve fibres of the pulp—and the plexus of Raschkow at the pulpo-dentinal junction—are not fully developed until several years after eruption [35]. Consequently, a vital but immature tooth may fail to respond to the electric pulp test, producing false-negative results, while the subjective nature of these tests and the limited cooperation of young patients further reduce their diagnostic accuracy [36]. This limitation is compounded after trauma, where sensory function may be temporarily lost even when the vascular supply is intact [37].

Because sensibility tests assess innervation rather than blood supply, they do not reflect the true vitality of the pulp. For this reason, a diagnosis of pulp necrosis should never be based on a single test, but should integrate the history, clinical examination, multiple special tests and radiographic findings [38]. This is especially important in immature teeth following trauma, where revascularisation of the pulp remains possible and a premature decision to intervene endodontically would needlessly arrest root development. Vitality-based methods that assess pulpal blood flow rather than innervation—such as pulse oximetry and laser Doppler flowmetry, and more recently transmitted-light plethysmography—have shown encouraging diagnostic accuracy in young permanent incisors and may, in time, offer a more reliable basis for decision-making in this group, although they are not yet routine [39]. In practice, serial monitoring and confirmation of necrosis by unambiguous clinical or radiographic signs of infection remain the most defensible approach before committing an immature tooth to apical barrier.

Radiographic examination complements sensibility testing and is indispensable for staging root development, locating the apex and assessing the periapical tissues. Conventional two-dimensional periapical radiographs remain the first-line and routine modality, yet their diagnostic yield in the immature, frequently traumatised tooth is limited: the superimposition of anatomical structures and the two-dimensional compression of a three-dimensional object mean that early periapical lesions, root fractures and resorptive defects on the buccal or palatal surfaces may go undetected, and a substantial proportion of cases show clinical signs without corresponding radiographic evidence [40]. Cone-beam computed tomography (CBCT) overcomes many of these limitations by providing three-dimensional, high-resolution visualisation of the root, the open apex and the surrounding bone, and is particularly valuable in this group for determining the true extent of the periapical lesion, detecting concomitant root fractures after trauma, characterising and monitoring external and internal inflammatory resorption, and estimating the thickness of the residual dentinal walls—information that directly informs the decision between apexification, regenerative treatment and extraction [41]. Contemporary trauma guidelines accordingly recommend CBCT, used selectively, for the assessment of root and crown–root fractures and lateral luxations, where it localises the fracture and defines its extent and direction more reliably than periapical views [42]. Because children are more susceptible to the stochastic effects of ionising radiation, CBCT should never be a routine substitute for conventional radiography but should be justified case by case and acquired with the smallest field of view and lowest dose compatible with the diagnostic task, in accordance with the ALARA principle [43].

The optimal radiographic diagnosis and follow-up protocols for immature teeth undergoing apical barrier treatment nevertheless remain undefined: the selective indications for CBCT in this context are extrapolated from the general trauma literature rather than from studies of these teeth, and whether its additional three-dimensional information meaningfully alters treatment decisions or outcomes—enough to justify the added radiation burden in this radiosensitive group—has not been established. This issue represents a notable evidence gap.

2.4.2. Isolation of the Immature, Frequently Traumatised Tooth

Effective rubber dam isolation is the standard of care for any non-surgical endodontic procedure, providing an aseptic field, protecting the airway, and improving access and visibility [44]. In the immature tooth, however, isolation is frequently complicated by factors peculiar to this group: the tooth may be incompletely erupted with a short clinical crown, and—because so many of these cases arise from trauma—the crown is often fractured, leaving insufficient sound structure to retain a clamp. Where the bulge of the tooth lies at or apical to the gingival crest, there are no undercuts to prevent the clamp sliding coronally [44].

Several adaptations address these difficulties. A pre-endodontic build-up of the broken-down crown with composite or glass-ionomer re-establishes four walls, facilitating both clamp retention and a sound access cavity [45]. Alternative strategies include etching the enamel to bond small composite spots that grip the clamp, isolating several teeth together, anchoring the dam to adjacent teeth, or stabilizing it with fragments of dam material passed beneath the contact points instead of a clamp [44]. A specific and important caution applies to the recently traumatized tooth: where the periodontal ligament is injured, and the tooth is mobile, apically directed wedging forces from a clamp at the cemento-enamel junction can, in rare instances, displace or even avulse the tooth, so clamp placement must be gentle and, where possible, transferred to adjacent teeth [46]. Adequate isolation is not a trivial preliminary: contamination of a recently disinfected canal by oral fluids undermines the very disinfection on which apical barrier depends.

It should be noted, however, that these isolation strategies are supported only by case reports and expert opinion; the influence of the isolation method on the outcome of apical barrier in immature teeth has not been investigated clinically and remains a notable evidence gap.

2.4.3. Access Cavity Preparation

In laboratory studies, the traditional access cavity has been considered more suitable than the conservative access cavity for treating immature permanent teeth with apical plugs, since the total porosity of the apical plug with traditional access cavities was significantly lower than with conservative access cavities. Straight-line access in traditional cavities facilitates placement of the MTA plug. In contrast, in conservative cavities, contact between the plug-transfer and condensation instruments and the chamber walls may restrict straight-line access to the apex, leading to a more porous fill than in traditional cavities [47].

No clinical study was found comparing the effect of access-cavity design on the outcomes of treating non-vital immature permanent teeth. It is worth noting that these cases are often associated with traumatic fracture injuries [5], such that a wide access is automatically secured along the fracture line.

2.4.4. Working-Length Determination

Determining the working length is crucial to ensure accurate canal preparation, disinfection and filling. Periapical radiographs are used for this purpose without electronic apex locators in immature permanent teeth, since the absence of an apical constriction gives unreliable readings; canals larger than #80 were unreliable to measure because of the potential influence of periapical tissue fluids on the electronic apex locator reading [48,49]. Periapical radiographs are therefore preferred for this purpose [50].

Re-confirmation of the working length before the plug-formation visit is recommended when a long period elapses between treatment visits—particularly in infected cases, owing to the possibility of external resorption—or if the procedure is taken over by a different clinician, or if circumstances require modification of the original working length (such as a new traumatic injury between visits), or if the patient reports pain at a point shorter than the previous length, or in the event of loss or replacement of the coronal restoration between appointments, which may alter the length and the previous reference point [50].

It is worth noting that the use of electronic apex locators in determining the working length and maintaining it during the preparation of closed-apex canals has helped to reduce post-operative endodontic pain, owing to a reduction in the inadvertent irritation of the periapical tissues; endomotors with an integrated apex locator and an apical auto-reverse function limit apical extrusion of debris and the consequent release of inflammatory mediators in the periapical tissues, and have been associated with less post-operative discomfort and lower analgesic consumption [51].

It remains unknown, however, whether the more recent generations of electronic apex locators can be used with the large-sized hand and rotary files required for working-length determination and minimal mechanical preparation in immature permanent teeth, and how this would compare with the conventional radiographic method in terms of reducing post-operative pain following apical-plug treatment.

2.4.5. Minimal Mechanical Preparation of the Immature Canal to Receive an Apical Plug

Mechanical preparation of the root canals in immature permanent teeth is a controversial subject. Many researchers agree that conventional mechanical preparation may weaken the thin walls of immature teeth, increasing the risk of future root fracture; chemical cleaning alone using irrigants such as sodium hypochlorite is therefore preferred, to reduce structural damage and preserve the vital stem cells in the apical region. From another perspective, minimal mechanical preparation may be necessary to improve removal of the smear layer and necrotic pulp remnants and to eliminate the reverse taper established in the coronal and middle thirds, ensuring that irrigants and plug-formation instruments reach the apical third—provided this is done with great care and without additional weakening of the root walls. Modern techniques such as the XP-endo Finisher and Gentlefile files have provided safer alternatives, allowing access to complex areas within the canal while removing a relatively small amount of dentine compared with conventional files, as shown by laboratory studies using micro-computed tomography (micro-CT). The current principle can be said to rest on balancing preservation of tooth structure with adequate canal debridement, with a tendency to minimise or avoid excessive mechanical preparation in immature permanent teeth except when strictly necessary [12,14,16,52].

2.4.6. Irrigants Used in Apical Barrier Treatment

Sodium hypochlorite is considered the gold standard among irrigants; it is an excellent solvent that dissolves living and necrotic organic pulp tissue and has effective activity against endodontic micro-organisms and biofilms [53]. There is insufficient research on the optimal time, volume, and concentration for treating non-vital immature permanent teeth.

Sodium hypochlorite at a concentration of 5.25% was used because it has greater antibacterial activity and an enhanced ability to dissolve necrotic tissue while reducing the time required for irrigation compared with the 2.5% concentration—that is, a more effective procedure in a shorter time, which is extremely important when treating children [54,55]. It is worth noting that using 5.25% hypochlorite in the chemical preparation of the immature canal followed by a plug of one of the calcium silicate cements has a high success rate, ranging between 84% and 92% depending on the cement used as the apical plug [50]; the success rate rose to 100% after one year of follow-up when 1.3% hypochlorite was used followed by Q-Mix irrigant, with both solutions activated by ultrasonic tips and followed by MTA or Biodentine [12]. In immature teeth with open apices, higher NaOCl concentrations must be balanced against the risk of extrusion and cytotoxic injury; therefore, concentration, delivery depth, needle design, flow rate, and activation method should be considered together rather than interpreted as isolated variables.

There are some variations in the irrigation methods for non-vital immature permanent teeth during apexification, but these did not affect the overall outcomes or survival rates; a systematic review of apexification studies showed that all clinical studies relied on sodium hypochlorite at various concentrations as the principal irrigant, after which chlorhexidine gluconate (CHX) was used in 20% of studies, while ethylenediaminetetraacetic acid (EDTA) was used in 80% of studies [16].

Incorporating EDTA into the irrigation regimens of non-vital immature canals has numerous advantages; it chelates calcium ions within the mineral dentine crystals, thereby limiting surface demineralization and exposing the organic dentine matrix. As a result, growth factors stored within the dentine matrix—such as TGF-β, BMP, VEGF, and other bioactive molecules sequestered during dentine formation—are released. The release of these factors allows their diffusion within the root canal, acting as biological signals that stimulate the migration, proliferation, and differentiation of stem cells, in addition to supporting angiogenesis and the formation of mineralized tissue, thereby assisting apical closure [56,57,58]. Furthermore, by removing the smear layer, EDTA increases the penetration of calcium silicate particles into dentinal tubules, thereby enhancing the stability of the apical plug and its push-out bond strength [59].

Regular replacement of the irrigant and the use of a large volume are essential to ensure maximal antibacterial efficacy [60]; nevertheless, there was variability among apical barrier studies regarding the volumes of irrigant used and the protocols employed in disinfecting immature canals [16].

2.4.7. Irrigant Activation in Non-Vital Immature Permanent Teeth

Irrigant activation is of particular importance in non-vital immature permanent teeth, as it helps to improve the irrigant’s ability to remove necrotic tissue remnants, the smear layer and the bacterial load from areas inaccessible to conventional instruments. Activation of irrigants by various means (such as passive ultrasonic irrigation or modern instruments such as the XP-Endo Finisher or lasers) shows greater efficacy in increasing the penetration of solutions and enhancing their contact with the entire wall of the immature canal, thereby improving biofilm removal [61,62]. Achieving effective cleaning in these teeth raises the chances of success of endodontic treatment and reduces the need for additional mechanical preparation that may weaken the already weak root structure [63]. Nevertheless, no clinical studies have compared short- and long-term outcomes with and without activated irrigation.

The use of the XP-Endo Finisher in irrigant activation is an advanced and effective step for improving the cleaning of root canals in immature permanent teeth [64]. An in-vitro study showed that this file removes intracanal dressings from immature canals more effectively than conventional needle irrigation and ultrasonic activation [61]. Likewise, another in-vitro study showed that activating EDTA solution with the XP-Endo Finisher increases the release of transforming growth factor beta-1 (TGF-β1) from dentine, enhancing the biological dimension in conservative revitalisation protocols, especially with reduced EDTA irrigation time to avoid adverse effects on the thin dentine of immature teeth [65].

Laser-activated irrigation has been investigated as an advanced method for enhancing disinfection, specifically in immature permanent teeth. Photon-induced photoacoustic streaming (PIPS), which employs an Er: YAG laser to generate cavitation and photoacoustic shock waves, and the more recent shock wave-enhanced emission photoacoustic streaming (SWEEPS), produce a three-dimensional streaming of the irrigant that may improve its penetration and contact with the canal walls without the need for additional mechanical preparation—an attractive property in the thin-walled immature canal. In simulated immature-tooth models, however, laser-activated protocols have shown variable superiority over passive ultrasonic and sonic activation: studies have reported comparable or only marginally better removal of intracanal medicaments and dissolution of periapical organic tissue, with no consistent advantage of one laser modality over the other [66,67]. The evidence, therefore, suggests that while laser activation is a promising adjunct for disinfecting the immature canal, its benefit over established activation methods in this specific group remains to be clearly demonstrated.

A caution regarding the final irrigant used before plug placement. Beyond the disinfection protocol itself, the choice of the final irrigant left in contact with the canal walls immediately before the apical plug is condensed merits attention, since it conditions the dentine surface to which the calcium silicate cement will bond and set. Laboratory evidence indicates that the irrigant preceding placement influences the push-out bond strength and sealing ability of the subsequently placed cement, and that this effect is material-dependent: chlorhexidine, when left in contact with ProRoot MTA, significantly reduces its push-out bond strength to dentine and is associated with increased microleakage and a shift towards adhesive failure at the cement–dentine interface, whereas the bond strength of Biodentine is not impaired—and may even be enhanced—under the same conditions [68]. This effect appears to be material-dependent, as the bond strength of Biodentine is not impaired—and may even be enhanced—under the same conditions [68]. A further consideration is that the interaction of residual chlorhexidine with sodium hypochlorite produces a precipitate (para-chloroaniline) that can interpose at the dentine interface and compromise the seal of the obturation [69]. Although these findings derive largely from mature-tooth models rather than immature teeth specifically, they imply that the final irrigation protocol should be selected with the intended plug material in mind) avoiding a chlorhexidine final rinse where an MTA plug is to be placed, in favour of inert alternatives such as saline (so as not to jeopardise the apical seal on which the success of apical barrier depends.

Finally, bearing in mind that most studies did not test different disinfection methods for non-vital immature canals in clinical studies, success rates were generally high; nevertheless, the cellular and bacterial status of immature permanent teeth after treatment remains imprecisely known, as none of the studies reported performing bacterial sampling of immature canals as a standard method for verifying the efficacy of disinfection before the filling stage [16]. This evidence gap extends to the clinical role of irrigant activation in this group: although the laboratory data summarised above are encouraging, there is a lack of clinical studies evaluating whether the choice of activation method influences clinically meaningful outcomes such as post-operative pain or the radiographic healing of periapical lesions in non-vital immature permanent teeth treated with apical plugs.

2.4.8. Intracanal Dressings

Intracanal dressings are a fundamental pillar in apical barrier treatment of immature permanent teeth, working to reduce the bacterial load, stimulate healing and support apical barrier formation. Intracanal dressings are commonly used in apical barrier protocols to reduce bacterial load, control exudate, and prepare the canal environment before plug placement; however, their necessity, optimal material, and duration remain unresolved. Calcium hydroxide is the most common dressing and has proven effective in forming the apical barrier over an average period of 3–12 months; it is also antibacterial and well tolerated by the periapical tissues and the stem cells of the apical papilla, but prolonged use may weaken the dentine walls and increase the risk of root fractures, warranting caution [70,71].

Triple antibiotic paste (metronidazole, ciprofloxacin, minocycline) has proven highly effective in disinfecting the root canals of non-vital immature teeth, showing the ability to eliminate bacteria resistant to calcium hydroxide, making it a promising option, especially in cases with a high bacterial load [71]. Its use as a short-term dressing (two to four weeks) before apical closure or regenerative procedures helps to obtain a clean canal environment suitable for healing [72].

The endodontic literature mentions the use of corticosteroid dressing (Ledermix paste) as an adjunctive dressing for managing severe luxation trauma cases by inhibiting root resorption, with a positive effect on treatment outcomes [73].

In addition to its role in disinfection, the intracanal dressing clinically is used as a preparatory step before placing the apical plug (with materials such as MTA or bioceramic materials), as it helps to reduce bleeding and exudate and ensures the canal is dry and prepared for tight placement of the plug, which improves the apical seal and long-term treatment success [50,74].

It is worth noting that in a previous study [12], no calcium hydroxide dressing was used in the management of non-vital immature permanent molars; instead, Q-Mix irrigant was used to irrigate the immature canals and was activated in a single-visit procedure immediately before placing the apical plug, and this method achieved high clinical and radiographic success. Here, the question is raised regarding the optimal type of intracanal dressing for non-vital immature permanent teeth, the appropriate duration, and the necessity of its use in apical barrier treatment, this requires future controlled randomised clinical studies.

A new intracanal dressing composed of calcium silicate (calcium silicate–based intracanal medicaments) has recently appeared, such as Bio-C Temp, which has shown promising properties, including high biocompatibility, the ability to stimulate cells and release growth factors from dentine, and the potential to support healing processes. Despite these properties, the current evidence remains mostly laboratory-based or experimental, with a clear lack of long-term clinical studies supporting its use within apical barrier protocols [75].

2.4.9. Drying and Moisture Control of the Immature Canal Before Plug Placement

Before the apical plug is condensed, the canal must be freed of residual irrigants, blood, and periapical exudate, since excess fluid interferes with the adaptation and condensation of the material and may dilute it or promote its extrusion through the open apex. In the wide, open-apex canal, this is more demanding than in the mature tooth: paper points may not reach or adapt to the apical third, and periapical fluid can continue to seep coronally through the patent foramen. Drying is therefore usually achieved with large-diameter paper points, occasionally supplemented by flexible micro-cannulas or apically positioned absorbent points, provided active bleeding is absent before placement. A point of distinction specific to these materials is that hydraulic calcium silicate cements (unlike conventional gutta-percha and sealer) require ambient moisture to hydrate and set; an excessively desiccated environment is therefore neither necessary nor desirable, and the objective is the control of excess moisture rather than complete dehydration of the dentine [76,77]. Laboratory evidence indicates that canal moisture conditions influence the push-out bond strength and apical sealing of bioceramic and MTA-based materials, with a normal-moisture or controlled-dry state generally favoring adhesion over a frankly wet canal. However, the optimum varies between cements [78,79].

Notably, almost all of this evidence derives from in vitro models, and the optimal moisture protocol for the immature canal specifically—and its influence on clinical outcomes—has not been established.

2.4.10. Apical Plug Formation Techniques

The formation of the apical plug refers to the appropriate delivery and condensation of the material into the apical third of the canal to create an artificial apical barrier, after preparing and drying the canal [80]. The material is usually placed at the canal orifice after mixing, then a manual vertical plugger is used to progressively compact and adapt the material to the required thickness within the apical third; the plugger diameter is 50% of the apical diameter to ensure effective condensation without the need for excessive force that may displace the material or damage the canal walls [81]. Several other specialised, non-conventional methods have been described in the literature, including the following:

Material-delivery techniques

Lentulo spiral. An old technique that delivers and distributes the material directly into the immature canal by loading it onto the lentulo spiral [82].

Amalgam carriers. The material is introduced into the orifice of the immature canal using an amalgam carrier and packed into the apical third using manual vertical hand pluggers [83], large gutta-percha cones [84], large paper points [85] or large hand files [86].

Dedicated carriers such as the Micro Apical Placement (MAP) System. The MAP System allows precise delivery of the plug material to the apical third via a fine, flexible, guided metal cannula, reducing the likelihood of material packing during condensation from the orifice towards the apex without the need for excessive canal enlargement; the material is then injected into the apical third and condensed using manual vertical pluggers [12,80,87].

Thermafil carriers. A seldom-used technique in which the plug material is placed on the tip of the carrier, which is then inserted into the canal to deliver and condense the material in the apical third; it is used mainly with curved immature canals [88].

Modified cannula. A patented Syrian device available in multiple sizes to suit immature teeth, consisting of a flexible plastic tip that can carry the plug material and a flexible, closed-tip metal plunger that pushes the material once it reaches the appropriate location and condenses it [80].

Plug-condensation techniques

Condensation using the XP-Endo Shaper. A portion of the plug material is placed using the dedicated carrier, then the XP-Endo Shaper is introduced into the canal to 1 mm short of the working length at 800 rpm in a counter-clockwise direction; on reaching the working length it is gently withdrawn while the file continues to rotate, ensuring homogeneous distribution of the material, and this process is repeated three times [47,81].

Condensation using indirect ultrasonic activation of the manual vertical plugger. The plug material is placed in the canal in three increments (2 mm, then 2 mm, then 1 mm); during condensation of the increments with the manual vertical plugger, a fine ultrasonic tip (such as CPR-1) is activated in direct contact with the plugger—without the plugger touching the dentinal walls—while compacting the material into the apical third. The ultrasonic tip may be used at low, medium or high power [47,81,89], provided the duration of ultrasonic activation does not exceed 8 s, to avoid increased porosity or reduced microhardness in certain materials such as MTA [90].

Prefabricated BioRoot inlay. Described in two case reports, this principle is based on taking a light-body impression of the immature canal, then embedding this impression in heavy-body to leave an imprint of the canal in the heavy-body. After removing the light-body impression, the canal imprint in the heavy-body is filled with plug material; once set, the heavy-body is trimmed to obtain a custom piece of plug material ready for direct placement in the canal with an appropriate sealer [91,92].

Building on this concept, an in vitro study using three-dimensionally printed root canal models of immature permanent teeth developed the idea further by incorporating a fibre post into a BioCeramic putty plug: the post, bonded to the set putty, serves as a handle by which the prefabricated plug can be carried, tried into the canal and withdrawn, after which a sealer is applied and the unit is reseated, with the same fibre post subsequently used to support the definitive coronal–radicular restoration. That study, which compared different cementation systems for bonding the fibre post to the BioCeramic putty, reported the highest pull-out bond strength with a total-etch dual-cure resin cement, and on the basis of its discussion proposed this post-retained prefabricated-plug approach as a means of combining apical sealing with internal reinforcement of the thin-walled immature root [93].

A contradiction was found in the literature regarding the quality of apical plugs condensed by different techniques: plugs formed by delivering the material directly to the apical third and condensing it produced a better seal than those formed with an amalgam carrier that pushes the material into the coronal third to be subsequently packed into the apical third [80]. Condensation of MTA increments combined with indirect ultrasonic activation, or use of the XP-Endo Shaper to distribute the plug material, increased the proportion of voids and porosity in apical plugs performed on extracted teeth [47]; conversely, indirect ultrasonic activation at high or medium power was found to reduce the marginal leakage of MTA plugs [89]. It was also found that both the XP-Endo Shaper and indirect ultrasonic activation reduced the external voids of plugs formed from other calcium silicate cements (Biodentine, NuSmile NeoPUTTY and Well-Root PT) performed on three-dimensional printed immature-canal analogues [81]. This raises the question of the optimal method of forming the apical plug (including its delivery and condensation) for each material; nevertheless, there is no additional information on this subject, and it requires further research on the other methods and a study of the clinical effect of this factor.

Previous studies have described the possibility of using the apical matrix placement technique before condensing the apical plug; this matrix is usually made from collagen sponge, demineralised freeze-dried bone powder or platelet-rich fibrin, to support plug formation in very wide canals or those with divergent apical walls before introducing the apical plug material [94,95,96]. This technique helps to reduce extrusion of the plug material beyond the apex, and there is scant information for short-term follow-up periods that it does not affect radiographic healing [95]. However, there are no systematic reviews or long-term studies comparing the use of this technique with its non-use and with extrusion of the plug material beyond the apex. It is self-evident that the limit of the root filling is only to the level of the apical foramen, and the extrusion of materials beyond the apex (whether the apical matrix or the filling material) requires long-term follow-up and a study of its effect on the healing of periapical lesions and bone repair in the periapical region.

The apical barrier technique may itself affect post-operative pain as a short-term outcome determinant: a single gutta-percha cone with a bioceramic sealer has been reported to cause less immediate post-operative pain than a bioceramic-putty apical plug in necrotic immature incisors [64].

2.4.11. Thickness of the Formed Apical Plug

The optimal thickness of the apical plug is one of the decisive factors in ensuring the seal and strength of teeth with open apices. Forming an apical plug 3–5 mm thick achieves an adequate seal and reduces push-out of the apical plug in laboratory studies [97]. Increasing the thickness of apical plugs from 1 mm to 3 mm reduces marginal leakage [98], whereas the seal of Biodentine and bioceramic putty plugs may not be affected by plug thickness provided it is not less than 3 mm [99]. As the thickness of MTA or Biodentine plugs increases towards a complete fill, the fracture resistance of the immature permanent tooth decreases [100,101], whereas a plug 3–6 mm thick reduces the risk of fracture [100]. An apical plug thickness of less than 4 mm increases the likelihood of clinical failure one and a half times because of apical leakage [50]. Accordingly, it is recommended to form an apical plug of no less than 4–5 mm regardless of the calcium silicate cement used [50,102].

Within the literature reviewed for this narrative synthesis, no clinical studies were identified that directly compared outcomes. No clinical evidence was found favoring a complete fill or a 4–5 mm plug for immature permanent teeth based on their degree of development. Logically, however, in cases of immature permanent teeth with extensive breakdown requiring a coronal–radicular restoration, it is preferable to keep at least the coronal half of the immature canal empty to support the broken-down coronal structures with a coronal–radicular restoration such as fiber posts [103].

2.4.12. Materials Used as Apical Plugs

Calcium silicate cements are commonly used as apical plugs [103,104] owing to their biocompatibility, bioactivity and excellent physico-chemical properties [105,106].

Mineral trioxide aggregate (MTA) is considered the first calcium silicate cement to be applied in the field of root canal system treatment and is the most studied bioactive material to date. MTA was developed starting from Portland cement and possessed good biocompatibility and a high capacity for apical sealing. The inherent limitations of MTA include its long setting time, high cost and potential to cause tooth discolouration [104].

Further bioactive materials were developed in the late 2000s and early 2010s, possessing biological properties similar to MTA, such as antibacterial activity, low cytotoxicity and a moderate inflammatory response [107,108]. These modern materials—such as Biodentine, the bioceramic EndoSequence Root Repair Material (ERRM), BioAggregate and calcium-enriched mixture (CEM)—have been used extensively in clinical practice [109].

Bioceramic compounds are defined as hydrophilic calcium silicate–based materials that form hydroxyapatite after setting; they are a class of pre-mixed, ready-to-use bioactive materials characterised by good operational performance and a low risk of discolouration of dental structures [110].

Bioceramic compounds are classified by viscosity into the putty form—commercially available as EndoSequence BioCeramic Putty (equivalent to iRoot BP Plus and TotalFill RRM Putty)—and the sealer form, commercially available as EndoSequence BioCeramic Sealer (equivalent to iRoot SP and TotalFill Sealer).

BioAggregate, CEM, TheraCal LC, EndoSequence Fast-Set Putty and BC Sealer HiFlow are mentioned as modern calcium silicate materials used as apical plugs; the use of calcium phosphate as an apical plug has also been recorded [111,112].

Comparable clinical results with high success rates were found for both MTA and Biodentine as apical plugs when treating non-vital immature permanent molars with medium-sized periapical lesions in children; post-operative pain one day after treatment was lower in the MTA plug group, whereas treatment time was shorter in the Biodentine group, and some cases in the Biodentine group showed a calcified tissue barrier apical to the plug that did not appear in the MTA group [12].

A similar clinical study found that Biodentine was better in short-term outcomes (3 months) as an apical plug for the healing of periapical lesions compared with MTA and calcium phosphate cement, whereas calcium phosphate cement was best in terms of radiographic healing in the long-term outcomes (9 months); a criticism of this study is its failure to specify whether the teeth involved were anterior or posterior [112].

A recent similar clinical study including maxillary central incisors found that both MTA and BioCeramic Putty were comparable in terms of resolution of clinical symptoms after treatment, whereas BioCeramic Putty outperformed MTA in terms of radiographic healing of periapical lesions in terms of the bone density restored at the lesion site [21].

A retrospective study was conducted on children under 16 years of age whose non-vital immature permanent incisors were treated, and found that the success rate reached 84% for MTA, 88% for Biodentine and 92% for TotalFill Putty after 12 months of apical barrier procedures. All materials achieved excellent clinical performance in apical barrier procedures; the use of MTA was associated with the highest rate of crown discolouration, whereas Biodentine was most associated with extrusion beyond the apex. It was also observed that not using local anaesthesia during placement of the apical plug had no adverse effect on the quality of execution or the clinical outcome. This study also showed that operator-experience-related factors—such as treatment performed by an experienced clinician or by the same clinician throughout the treatment stages—had a greater effect on treatment quality and final outcomes than the type of material itself, as cases performed by trainees or by more than one clinician were associated with higher failure rates and lower quality of performance [50].

Despite the breadth of materials now available as apical plugs, the comparative clinical evidence in immature permanent teeth remains limited and heterogeneous. Direct comparisons are derived largely from in vitro models, short-term clinical studies (3–12 months) or retrospective data, and the reported success rates of the principal materials are closely clustered and difficult to separate; no long-term randomised clinical trials have directly compared the newer pre-mixed bioceramic putties with MTA and Biodentine in this group. This uncertainty is compounded by inconsistent outcome criteria and uncontrolled confounders (such as tooth location, lesion size and follow-up duration) which limit comparison across studies.

2.4.13. Management of the Residual Canal Space and the Definitive Restoration

A caution regarding irrigation of the residual canal after plug placement. Where the apical plug is placed and the remainder of the canal is irrigated in the same or a subsequent visit (before obturation or restoration) the irrigant brought into contact with the already-set cement merits consideration. An in vitro study on set ProRoot MTA demonstrated that contact with 2% chlorhexidine significantly increased marginal leakage and impaired the sealing ability of the hardened cement [113]. Although this evidence derives from a furcal-perforation model rather than from apical plugs specifically, the underlying principle is directly transferable: once a calcium silicate apical plug has set, flushing the residual canal with chlorhexidine may compromise the very apical seal on which the success of apical barrier depends, and an inert final rinse such as saline is therefore preferable in contact with the set plug. The influence of post-placement irrigation on the seal of calcium silicate apical plugs has not been investigated directly, and represents a further procedural variable warranting dedicated study.

Apical closure is only one half of the prognosis; a sound, well-sealed coronal restoration is equally decisive, both to prevent coronal microleakage (a recognised cause of endodontic failure) and to compensate for the structural fragility of the immature tooth [114]. The thin, divergent dentinal walls and the weak pre-cervical dentine leave these teeth highly susceptible to cervical fracture, which is among the principal causes of late tooth loss after apical barrier [16,74].

In most cases, where coronal tooth structure is largely intact, the canal space coronal to the apical plug is obturated conventionally with gutta-percha and a suitable sealer, and the access cavity is then restored with a bonded resin composite, which both seals the canal coronally and restores function and aesthetics. A post is not routinely required in such teeth, and is reserved for situations in which extensive loss of coronal tissue demands additional retention and reinforcement.

Two restorative principles follow from this. First, as mentioned previously, sufficient canal space should be preserved coronal to the apical plug to allow placement of an intra-radicular fibre post when the coronal tissue is extensively broken down; a complete fill that leaves no room for a post may be counter-productive in such cases [115,116]. Laboratory evidence indicates that restoring simulated immature teeth with a fibre post and composite resin after a calcium silicate apical plug increases their fracture resistance, supporting the concept of internal reinforcement of the thin-walled root [115]. Second, because the most widely used plug materials—particularly MTA—carry a recognised potential for crown discolouration, contact between the cement and the coronal dentine should be avoided, the pulp chamber cleaned of residual material, and consideration given to sealing the coronal dentine to mitigate aesthetic impairment in these often anterior, aesthetically critical teeth [117]. The timing and choice of definitive restoration should therefore be planned from the outset, as an integral part of the treatment, rather than as an afterthought once apical closure has been confirmed.

Two evidence gaps follow. First, the irrigant most appropriate for cleansing the residual canal coronal to the set plug before restoration is undefined. As noted earlier, the final rinse in contact with the set cement can affect its seal, yet the optimal choice has not been established for each combination of plug material and restorative or reinforcement technique. Second, the evidence for internal reinforcement is largely confined to in vitro testing of conventional fiber posts. In contrast, alternative strategies—customized or short composite-resin posts, three-dimensionally printed root substructures, and bondable polyethylene-fiber systems (e.g., Ribbond)—remain poorly characterized both in the laboratory and, especially, clinically, with no studies linking them to the long-term survival of apexified immature teeth with apical barrier. Both warrant standardized in vitro comparison and prospective clinical evaluation.

3. Factors Affecting the Outcomes of Apical Barrier Treatment

3.1. Effect of Operator Experience on Treatment Outcomes

Operator experience is a decisive factor in the success of root canal treatment, as studies have shown that higher technical competence during the various stages—isolation, access-cavity preparation, mechanical and chemical debridement, placement of intracanal dressings and canal filling—is directly associated with increased healing rates [118,119,120]. It is worth noting that some research has indicated that patient satisfaction is higher when treatment is received from experienced specialists, underscoring the importance of clinical skill in improving the treatment experience [119,121,122].

Current evidence suggests that, once an appropriate calcium silicate material is selected, outcomes may be influenced as much by procedural quality, continuity of care, coronal restoration, and operator experience as by the material itself. However, this operator effect remains insufficiently tested in prospective clinical studies.

The treatment failure rate was found to increase almost two-fold when apical closure or filling was performed by less experienced clinicians, and treatments carried out over more than one appointment or by different clinicians were more prone to failure. This is attributed to a lack of continuity of care and variation in skill level, particularly in cases where the temporary restoration is lost or contaminated between visits [50].

It is worth noting that most systematic studies that evaluated apical barrier treatment outcomes were conducted in specialised centres by highly experienced practitioners, which limits the generalisability of their findings to general practice, where the vast majority of endodontic treatments worldwide are performed in general clinics—often without the aid of the surgical microscope or specialist instruments. This may explain the discrepancy in success rates between academic studies and real-world clinical practice [2,16].

3.2. Effect of Child Cooperation

Treatment may be further complicated by high levels of dental fear and anxiety in children, particularly with regard to local anaesthesia, which may cause problems in patient cooperation and increase the stress of patients and parents [123,124]. Similarly, each stage of endodontic treatment may represent a new and unfamiliar experience for the patient [125]. It is therefore important to document the challenges of patient cooperation, as they may also affect the quality of endodontic treatment [48], in addition to the fact that children are susceptible to dental fatigue during the long treatment periods associated with traumatic dental injuries [126].

A retrospective study confirmed that child cooperation was among the factors most influencing the success of endodontic treatments performed in children [48]. The child’s behaviour during treatment, the difficulty of direct visualisation of the immature permanent tooth, and the precision of placing the material in the ideal location may also increase the risk of tooth discolouration [16].

Moreover, uncooperative children required a longer overall duration of the apical barrier procedure, irrespective of the apical barrier method employed [64].

3.3. Effect of the Severity of the Traumatic Injury or the Cause of Pulp Necrosis as a Prognostic Factor

Traumatic dental injuries increase the risk of early loss of immature permanent teeth; evidence indicates that luxation injuries adversely affect the prognosis of fractured teeth. Isolated crown fractures show high rates of pulp survival, whereas the presence of a concomitant injury to the supporting tissues leads to a marked increase in the likelihood of pulp necrosis owing to disruption of the neurovascular bundle at the apex and impairment of the pulpal blood supply. These injuries are also associated with an increased likelihood of subsequent complications such as inflammatory root resorption and periapical inflammation, which may negatively affect long-term treatment success. It is believed that injury to the periapical tissues and the periodontal ligament weakens the capacity for natural biological repair and affects the revascularisation process, thereby reducing the chances of healing and worsening the clinical prognosis of the injured teeth [7,127,128]. Nevertheless, a meta-analysis showed scope for bias, as the studies conducted on non-vital immature permanent teeth include teeth that became non-vital because of traumatic injuries and teeth that became non-vital for other reasons, without clarifying the effect of this factor on long-term treatment outcomes; this analysis nonetheless reported high survival rates for all treated non-vital immature permanent teeth included overall [2]. Another systematic review, including studies with long follow-up periods, indicated that the severity of the dental trauma itself—such as complete avulsion—may affect the long-term prognosis of the teeth more than the treatment technique used in managing the immature permanent tooth [16].

3.4. Effect of the Presence of Root Resorption

Immature permanent teeth are rapidly susceptible to root resorption because of the wide dentinal tubules that allow bacterial penetration [129]. Inadequately disinfected canals are more prone to inflammation or external root resorption, particularly those whose canals are associated with long periods between pulp-extirpation and filling appointments, which may lead to a change in apical anatomy and consequently a change in the working length. A retrospective study indicated that the presence of root resorption before the start of treatment is associated with a 3.5-fold increase in the likelihood of treatment failure [50].

3.5. Effect of the Level of the Root Filling on Success

The level of overfilling, underfilling or adequate filling when using MTA plugs in apical barrier treatments did not affect the overall clinical and radiographic success [73], and there were no notable differences in periapical lesion healing between non-vital immature permanent teeth filled with MTA plugs to an over-extended level or within the ideal limits [130]. This may be explained partly by the good biocompatibility of MTA [131] and by the ability of MTA to induce the deposition of mineralised tissue at the site of application [132].

Notably, extrusion of the bioceramic material beyond the apex was not associated with increased post-operative pain in the treatment of immature permanent teeth [64].

There are no recent studies that have precisely evaluated the outcomes of over- or under-filling using the more modern calcium silicate cements such as Biodentine or BioCeramic, and the long-term effects of extrusion of calcium silicate cements remain imprecisely evaluated to date [16].

3.6. Effect of the Presence of Periapical Lesions on Treatment Success

The absence of a pre-operative apical radiographic lesion significantly improves the outcomes of endodontic treatment in teeth with closed apices [119], and the size of the apical lesion negatively affects the outcomes of treatment with the single-cone technique with bioceramic sealer in teeth with closed apices [133]. For non-vital immature permanent teeth treated with MTA plugs, the presence of a large lesion (grade 3–5 on the PAI score) increases the failure rate two- to four-fold [134], whereas the presence or absence of apical lesions in immature permanent teeth treated by apical barrier using bioceramic putty was found not to affect the success rate [135].

4. Assessment of the Outcomes of Apical-Plug Endodontic Treatment in Immature Permanent Teeth, Follow-Up Duration and Prognosis

Apical barrier treatment had generally better clinical and radiographic success rates among all available endodontic treatments for non-vital immature permanent teeth [136].

Clinical success is defined as the functional retention of the teeth without any signs of self-reported pain, pain on percussion or palpation, pathological tooth mobility, abnormal periodontal probing depth, swelling or fistula formation. Radiographic success is defined as evidence of healing of periapical tissue inflammation (if present) and the absence of any pathological signs on radiographs, such as internal or external root resorption. These criteria are based on most of the recent guidelines and systematic reviews concerned with the long-term outcomes of apical barrier treatments [2,16,137].

Radiographic assessment is usually the principal and only objective method used to evaluate the outcomes of endodontic treatments. Radiographic assessment is performed using intraoral radiographs according to a set of criteria for determining the status of the apex, and these criteria are considered the gold standard in measuring the outcomes of endodontic treatments in immature permanent teeth [16].

The periapical index (PAI index) is considered the most widely used criterion in recent studies that evaluated the outcomes of treatment with apical plugs in terms of the presence or absence of periapical bone inflammation at the initial assessment [12,21,138]; it comprises five scores, with PAI 2 and PAI 3 designated as the cut-off between apical health and the presence of apical disease [139].

The most important radiographic outcomes recorded in studies concerned with apical barrier were healing of apical lesions, apical closure (formation of a calcified tissue barrier), the absence of radiographic signs of fracture, and the absence of signs of internal or external root canal resorption; high success rates were recorded, ranging between 81% and 100% [10,29,101,125,127,128].

Opinions vary regarding the ability of apical-plug treatment to promote radiographic root growth in non-vital immature permanent teeth. Some studies confirmed that the use of MTA as an apical plug did not contribute to an increase in root length [2,12,16], whereas Biodentine plugs showed a slight increase in the root in a limited number of cases [12]. Another study observed that the use of MTA as an apical plug led to only slight increases in root length compared with revascularisation procedures after a one-year follow-up period [140], while some case reports indicated that the use of MTA or bioceramic putty as apical plugs led to an increase in root length of a distance equal to or exceeding 2 mm [141,142].

It is worth noting that post-operative pain was reported as a secondary short-term outcome variable of endodontic treatment of immature permanent teeth using apical plugs, and was often measured by its presence or absence or using the visual analogue scale (VAS) [64]; the most important clinical outcomes obtained were the absence of local signs of infection (fistula and abscess), the absence of symptoms, and a low incidence of root fractures [12,16,21].

Discolouration of immature permanent teeth treated with MTA apical plugs was considered a treatment complication owing to its effect on aesthetics [16]; however, the occurrence of discolouration with resolution of the clinical and radiographic symptoms of the treated tooth is not considered a treatment failure [143].

The European Society of Endodontology recommends following up non-vital immature permanent teeth at 3, 6, 12, 18 and 24 months, then annually for five years [13,16]; nevertheless, recent studies have provided a shorter follow-up duration for the included samples, with only short-term outcomes ranging between nine months and three years [12,21,50,112,138]. Table 1 demonstrates the strength of evidence by procedural step. More robust studies are warranted to strengthen the evidence-based approach.

5. Equity, Training, and Global Implementation Considerations

Apical barrier therapy should not be viewed solely as a material-driven technique. In many health systems, the prognosis of immature permanent teeth is shaped by delayed trauma care, limited access to specialists, the cost of bioceramic materials, the availability of rubber dam isolation, radiographic resources, behavioral support, and the clinician’s training. A precision-preservation model, therefore, requires not only selecting the appropriate calcium silicate material but also ensuring that children can access timely diagnosis, skilled endodontic care, definitive restoration, and long-term follow-up. Without these system-level conditions, technologically advanced procedures may widen rather than reduce disparities. Future research should therefore report not only healing and survival but also access barriers, treatment delays, operator training level, setting of care, cost, retreatment burden, and child-centered outcomes. Table 2 outlines the decision boundary between apical barrier versus regenerative endodontics, as the setting of care is valuable for pediatric dentists or endodontists.

6. Limitations of This Review

This manuscript is a narrative review rather than a systematic review; therefore, formal risk-of-bias assessment, meta-analysis, and quantitative grading of certainty were not conducted. The reviewed literature is heterogeneous with respect to case definition, root-development stage, tooth type, etiology of necrosis, lesion size, material selection, plug placement technique, restoration type, follow-up interval, and outcome criteria. In addition, many procedural recommendations are derived from laboratory studies using simulated immature teeth, and their clinical relevance remains uncertain. These limitations should be considered when interpreting recommendations on irrigation, activation, plug placement, moisture control, reinforcement, and material selection.

7. Conclusions and Future Directions

Apical barrier with hydraulic calcium silicate cements is a predictable, well-established treatment for non-vital immature permanent teeth, offering immediate apical closure, a short treatment duration, and high clinical and radiographic success across the principal materials (MTA, Biodentine, and pre-mixed bioceramic putties). The evidence reviewed here suggests that, within this material class, the choice of cement is generally less decisive for the outcome than the quality of disinfection, the adequacy and condensation of the plug, the definitive coronal restoration, and—consistently—the experience of the operator.

Nevertheless, the treatment pathway is supported by evidence of uneven strength, and several questions remain genuinely open. The principal evidence gaps identified throughout this review are summarised below, ordered along the clinical pathway, and together they define the most pressing directions for future research:

• Diagnosis and the radiographic protocol. No validated reference standard exists for confirming pulp necrosis in the immature tooth: sensibility tests are unreliable in this group, while the more objective perfusion-based methods still lack defined thresholds and validated protocols for open-apex teeth. In parallel, the optimal radiographic protocol—and the specific indications for CBCT in apexification, including its value for monitoring barrier formation and periapical healing—has not been established for these teeth and is largely extrapolated from the general trauma literature.
• Isolation. The strategies described for isolating the immature, frequently traumatised tooth derive almost entirely from case reports and expert opinion; the influence of the isolation method on the outcome of apexification has not been investigated clinically.
• Disinfection end-point and irrigant activation. The microbiological status of the immature canal at the time of plugging is essentially unknown, as no studies have used bacterial sampling to verify disinfection before filling, and the optimal irrigant concentration, volume and activation protocol for these wide, thin-walled canals remain undefined. Whether the method of irrigant activation—ultrasonic, sonic or laser-activated—influences clinically meaningful outcomes such as post-operative pain or radiographic healing has likewise not been tested clinically.
• Working-length determination. It is unknown whether the more recent generations of electronic apex locators can be used reliably with the large-sized files required in immature teeth, and how this would compare with the conventional radiographic method in terms of accuracy and post-operative pain.
• Intracanal dressing. Whether an intracanal dressing is necessary at all, and, if so, which material and for how long, has not been resolved by controlled clinical trials, particularly given single-visit protocols that omit calcium hydroxide yet report high success rates.
• Plug formation, thickness and moisture control. The laboratory literature is contradictory regarding which delivery and condensation methods minimise porosity and leakage, and these findings differ between materials; the optimal plug thickness as a function of root-development stage, the trade-off between apical seal and the canal space required for coronal–radicular reinforcement, and the ideal moisture protocol before plug placement all lack direct clinical evidence, and the clinical relevance of these in vitro differences has not been tested.
• Material comparison and the operator effect. No long-term randomised trials have directly compared the newer pre-mixed bioceramic putties with MTA and Biodentine in immature teeth, and several recently introduced cements are used as apical-plug materials on the basis of laboratory or anecdotal evidence alone. Because retrospective data suggest that operator-related factors may influence outcome more than the choice of material, future trials should account for operator experience so that the true effect of the material can be isolated.
• Post-placement irrigation, the definitive restoration and reinforcement. The irrigant left in contact with the set plug—both before obturation of the residual canal and before the definitive restoration—can affect the apical seal, yet the optimal final rinse has not been defined for each combination of plug material and restorative or reinforcement technique. Moreover, the evidence for internal reinforcement is largely confined to in vitro testing of conventional fibre posts, whereas alternative strategies—customised or short composite-resin posts, three-dimensionally printed root substructures and bondable polyethylene-fibre systems—remain poorly characterised, with no studies linking them to the long-term survival of apexified immature teeth.
• The apical-sealing technique and adjuncts. The apical-sealing technique itself may affect short-term outcomes such as post-operative pain, and adjuncts such as the apical matrix have not been evaluated in long-term or comparative studies, including their effect on periapical healing when material is extruded beyond the apex.
• Standardised outcome reporting. Heterogeneity in case definition, root-development staging, follow-up and success criteria limits comparison across studies; a consensus framework for reporting apexification outcomes is needed, alongside well-designed randomised controlled trials with adequate follow-up.

Until such evidence is generated, clinical decisions should rest on the balance of preserving tooth structure, achieving thorough disinfection, forming an adequate and well-condensed apical plug of at least 4–5 mm, and providing a definitive restoration that addresses the inherent fragility of the immature tooth—all delivered, ideally, by an experienced operator.

Future studies should include child- and family-centered outcomes, such as pain experience, dental anxiety, number of visits, need for sedation or general anesthesia, school absence, esthetic satisfaction, quality of life, and caregiver treatment burden. These outcomes are particularly important because apical barrier therapy is often performed after traumatic injury in children and adolescents, and biological success alone may not fully capture the treatment’s impact.