Abstract
This article will provide a summary of causes of incomplete root end closure and the implications of this on endodontic treatment. The limitations and benefits of traditional and more contemporary materials including the use of bioceramic cements are considered. The apical barrier technique is described in detail for teeth with immature apices utilising a variety of bioceramic cements and regenerative endodontic procedures with an overview of appropriate instruments to successfully complete the procedure.
Learning Objectives
To highlight the causes of incomplete root end closure and the implications of this
To describe the variety of materials that can be used to endodontically manage teeth with incomplete root end closure
To outline the apical barrier technique used to obturate teeth with wide apical foramen
Introduction
Teeth with immature apices are those which have not had complete root end closure. This is usually due to several external factors with the most common being dental trauma. 1 Traumatic dental injuries are a frequent occurrence in children and young adults, making up 5% of injuries in this patient group, with the majority of injuries occurring before the age of 19. 2 Other causes of failed root development include caries-induced pulpal necrosis, teeth with developmental defects such as dens evaginatus and, less frequently, the use of chemo and/or radiotherapy in paediatric cancer patients who were treated with these modalities during the development of the permanent dentition.3,4 The difficulties in managing teeth with immature root development is that the apex is usually wide and obturation can be difficult as there is no apical stop. The dentine walls of the root are thin so condensing a filling material in the root space to create an optimal seal can be challenging and risky. The treatment of teeth with immature root development can be time consuming and requires substantial technical skill from the operator. Historically, non-setting calcium hydroxide was used to induce a hard tissue barrier at the apex, to prevent overextension of the root filling material. 5 This process involved multiple appointments over numerous months to dress the canal space with calcium hydroxide until an apical barrier formed. This treatment showed reliable outcomes with success rates above 95%.6,7 However, the long-term use of calcium hydroxide has shown an increased risk of cervical root fractures, particularly in immature teeth.8,9 As such there has been a move away from processes that may further jeopardise the longevity of the tooth. Figure 1(a) is a radiograph showing a traumatised maxillary left central incisor with an immature apex. This tooth was treated by apexification with long term use of calcium hydroxide. Figure 1(b) shows the development of the root apex and the presence of a hard tissue barrier within the pulp space.
Bioceramic cements or calcium silicate-based cements have been available for over 20 years and are now used more frequently to form apical plugs in the endodontic management of immature teeth. 10 Bioceramic cements have numerous benefits over traditional calcium hydroxide but of course do come with some limitations, as shown in Table 1.11-14 The use of bioceramic cements has been advocated as the treatment modality of choice for non-vital anterior teeth with incomplete root development. 15 This paper will discuss clinical management techniques of teeth with immature apices utilising the apical barrier technique with a variety of materials and techniques.
Benefits and limitations of bioceramic cements
Maintaining pulp vitality
A significant effort should be made to maintain pulp vitality in both mature and immature teeth. The endodontic management of teeth with open apices can require skill and is often time consuming. Avoiding endodontics in teeth with immature apices is important as these teeth have the ability to continue root development and allow for closure of the apex. 16 Clinically, we see this in cases of dental trauma, usually with luxation injuries, root fractures or complex and non-complex crown fractures. In cases of traumatic pulpal exposure, partial pulpotomies should be considered as the treatment of choice to maintain pulp vitality.17,18 The European Society of Endodontology has published further guidance to help in the management of deep carious lesions and carious pulpal exposure with the use of pulp caps and pulpotomies. 19 Again the aim of this guidance is to maintain pulp vitality and prevent possible complex endodontic treatment. In both instances of traumatic and carious pulpal exposure, bioceramic cements have been advocated ahead of more traditional calcium hydroxide materials. Figure 2 shows a complex crown fracture on a right maxillary central incisor tooth which was treated with a Cvek partial pulpotomy using Biodentine™ (Septodont, Saint Maur des Fosses, France).
Necrotic pulps
If the pulp is irreversibly damaged and efforts to maintain the vitality have failed, then the necrotic pulp requires endodontic intervention. In immature teeth with open apices the use of bioceramic cements is now the gold standard treatment modality. Bioceramic cements are based on tricalcium and dicalcium silicate which come in multiple forms: powder and liquid which require mixing, pre-mixed pastes or premixed putty forms. ProRoot® MTA (Dentsply Tulsa Dental, Tulsa, OK, USA) was one of the earliest developed bioceramic materials, followed by the development of newer bioceramic materials, such as Biodentine, MTA Angelus® (Angelus, Londrina, Brazil), and TotalFill® BC RRM™ Putty (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland). The more modern bioceramics have negated some of the initial drawbacks of early bioceramic materials with easier handling, shorter setting times and less discolouration.
The root canal system should be disinfected chemically; mechanical shaping should be avoided if possible. Some authors have advocated placing a collagen sponge beyond the apex which creates a physical barrier against which the bioceramic material can be condensed.21,22 This can be technically difficult to place and risks introducing pathogens/foreign body response apically; the authors of this paper would not advocate such a technique.
The bioceramic can then be delivered into the root canal system with specific carriers and hand pluggers (Figure 3). Table 2 shows advantages and disadvantages of three commonly available carrier devices.
Comparison of three commonly available carriers for bioceramic cements
Once the first increment is placed, the bioceramic is gently condensed to the appropriate length with pre-measured hand pluggers, or large sized paper points matched to the apical foramen. The benefit of using paper points is that they wick away moisture from the bioceramic and allow easier handling of the material. The pluggers should be measured 2mm short of the apex to prevent unnecessary extrusion of material beyond the apex. After the first few increments a radiograph can be taken to assess the apical plug to ensure appropriate length control and compaction at the apex before more material is placed. It becomes harder to correct extension the more material is placed. If the apical plug is short or poorly compacted, more bioceramic can be placed/compacted. If there are significant voids the material can be washed out with sterile water.
The total length of plug should be approximately 5–6mm in length. On completion of the apical plug the walls of the canals should be cleaned to ensure no excess bioceramic is visible (this may lead to discolouration when mineral trioxide aggregate [MTA] is used). The remaining portion of the canal can be filled with a post or heated gutta percha (GP) and the access cavity restored to achieve a good coronal seal.
As discussed above, MTA has limitations of a long setting time and a risk of potential discolouration. Other bioceramics are available but many of these have the same handling issues. Biodentine has been introduced as an alternative to MTA as it has a relative short setting time and a reduced risk of discolouration. 20 However, no material is ideal. Biodentine is thixotropic and this can make handling more difficult as the material becomes more liquid if over-manipulated. In comparison to MTA, it has a radiopacity similar to dentine and therefore interpreting it on radiographs can also be a challenge.
The latest development is the introduction of bioceramic putties. They have similar indications to conventional premixed bioceramics and bioceramic pastes. In theory, they have improved handling characteristics, are radiopaque, and have relatively short settings times. They are used in a similar method to MTA and Biodentine in the apical barrier technique but require no spatulation or mixing.
Apical barrier technique: step-by-step
Stage 1: Estimate working length (WL). This is most accurately undertaken using a combination of an electronic apex locator (EAL) and WL radiograph.
Stage 2: Complete decontamination of the root canal. The emphasis should be on chemical decontamination with very little instrumentation undertaken or advisable. Sodium hypochlorite remains the gold standard irrigant.
Stage 3: Placement of bioceramic plug: Measure a plugger that can be fitted within 1–2mm of the apex Measure a delivery device that fits snugly 2–3mm from the apex (see Figure 4) Place first 2–3 increments of bioceramic at the predetermined WL and condense Take test radiograph to confirm the first apical plug is in the correct position If happy, backfill the canal with at least 5mm of bioceramic (to allow future apical amputation if necessary)
Stage 4: Backfill the remaining canal with either warm flowable GP or post and/or core material.
Figures 5 and 6 show two cases of teeth with immature apices treated with MTA using the apical barrier technique. Following the completion of the MTA plug, the canals were backfilled with warm, flowable GP below the level of the cementoenamel junction (CEJ). In these cases, the GP can be sealed with at least 2mm intermediate restorative material (IRM) if bleaching is required. The remaining pulp space was filled with glass ionomer cement (GIC) and a direct composite resin restoration was used as the final layer. The differing radiopacities of the materials can be seen on the radiographs.
Figure 7 shows the process of root canal retreatment of an upper left central incisor utilising a bioceramic putty. Bioceramic putties are used in the same technique as conventional MTA but are said to have easier handling properties and some offer faster setting times. Figure 7(c) shows the first increment of bioceramic putty and Figures 7(d) and 7(e) show the completed apical plug.
Limitations of apical barrier technique
The benefits of the apical barrier technique have been described above. Unfortunately, no one technique is perfect and there are some limitations of this method of treatment. Additional training is required to be able to competently complete this technique. Alongside the extra training, additional material and equipment (bioceramic cement, carriers and pluggers, and high-powered magnification) may be required which can be costly. The use of bioceramic materials with this technique can be sensitive and underfills and overfills can be common (see Figure 6). Ultimately the teeth remain vulnerable to fracture as this technique does not induce root growth or augment the root dentine.
Regenerative endodontics
Apical barrier techniques to obturate open apices do not induce any further root formation. An alternative to the above-described techniques are revascularisation or regenerative endodontic procedures. The aim of this technique is to induce stem cells into the pulp space from the apical papilla beyond the root apex. These stems cells can develop into differing cell types with the potential of replacing damaged structures like dentine, the dentine-pulp complex, and root structures.23,24 The results of the regenerative procedures can cause the resolution of pain and inflammation, heal the periapical lesion, and increase root length and thickness which in theory is expected to improve root strength. 25
Teeth deemed suitable for regenerative endodontics are those which are restorable and have incomplete root formation with necrotic pulps. Teeth which will require posts should not be treated with regenerative endodontics as the post will occupy the root canal space. A suggested protocol for regenerative endodontics is described in Table 3. A diagrammatic representation of the regenerative endodontic procedure, showing treatment of an upper left central incisor with regenerative endodontics, can be seen in Figures 8 and 9.
Suggested protocol for regenerative endodontics, from the European Society of Endodontic position statement 25
As described in Table 3, the aim of this treatment modality is to regenerate the pulp. However, histological studies have shown that regeneration may not actually take place, rather cementum and fibrous tissue is found within the canal.26,27 Currently the evidence to support regenerative procedures being superior to apexification is inconclusive. 28 Larger patient cohorts with longer follow-up periods are required to determine the success of these treatment modalities.
Conclusion
The management of teeth with immature apices is a clinical challenge. Historic treatment techniques yielded good success rates, however also had the risk of cervical root fractures rendering teeth unrestorable. Modern techniques have overcome some of these historic issues. In the first instance pulp vitality should be maintained wherever possible to avoid complex endodontic treatment. If the pulp does indeed become necrotic then there are several techniques available to manage immature permanent teeth. Clinicians should be aware of the limitations and advantages of each of these techniques. The most recent addition to the armamentarium in attempting to revascularise teeth is an exciting prospect. With greater research and longer-term case follow up this may be the treatment modality of choice for immature teeth in the future.