Abstract
Difficulties encountered during endodontic treatment can be a cause of frustration for both clinician and patient. Complications such as iatrogenic perforation, ledge formation, canal blockage, instrument separation and untreated anatomy may impact the outcome of endodontic treatment. Clinicians should understand how each of these complications can occur, be prevented and predictably rectified. It is also important for clinicians to understand the impact of a specific complication on treatment prognosis and to appreciate how this may differ in each case. There may be scenarios where a complication does not significantly affect the prognosis, whereas in other situations, the same complication will be detrimental to the outcome of treatment. An appreciation of the clinical factors which determine prognosis is important, so that the correct intervention is chosen, and the patient is correctly informed of the likely sequelae.
Keywords
Learning Objectives
To be able to recognise incidents of iatrogenic perforation, ledge formation, canal blockage, instrument separation and untreated anatomy
To understand the impact of these endodontic complications on treatment prognosis
To understand the management options for endodontic complications
Introduction
Complications in relation to endodontic treatment are a common occurrence in dentistry. These may occur at any stage of endodontic management: diagnosis, treatment planning, access, instrumentation, irrigation and obturation. The subsequent restorative procedure is equally critical to the success and longevity of the root treated tooth.
Clinicians should be aware of the most common complications, how they can be prevented and how to manage them when they arise. A case specific assessment during treatment planning will help clinicians to anticipate the challenges for each individual treatment and reduce the incidence of complications. Identifying and communicating the specific challenges of each case to the patient is also essential and provides an opportunity to obtain valid consent.
Not all endodontic complications are ‘catastrophic’. With appropriate management, many can be predictably rectified without any significant impact on treatment outcome. Clinicians should be aware of how specific complications can impact prognosis. Conveying this information to the patient at all stages of the process is critical to reducing the likelihood of a complaint. Referral to an endodontic specialist should be discussed where appropriate and a good working relationship is of benefit to both the patient and the clinician.
This article discusses important endodontic complications, how they may affect prognosis, and how they should be managed.
Perforation
What is this?
In endodontics, perforation can be defined as the creation of a mechanical or pathologic communication between the root canal system and the outside of the tooth.
The American Association of Endodontists (AAE) have classified perforations according to the site: 1
Apical perforation: A perforation in the apical one-third of the root
Furcation perforation: A perforation in the furcal area of the tooth
Strip perforation: A complete penetration of the root canal wall due to excessive lateral tooth structure removal during canal preparation; this usually occurs in curved roots or roots with surface invaginations
Furcation perforations are related to complications during access, whilst strip- and apical perforations are related to complications caused during instrumentation.
How does this affect the prognosis?
The main determinants of prognosis related to perforations are size, location, time until intervention and the choice of repair material. 2 Small perforations can be more predictably sealed than large perforations. Supra- and sub-crestal perforations have superior prognoses to those at crestal level. Time will allow bacterial colonisation of the perforation site to take place, which will in turn lead to bone and periodontal attachment loss, essentially creating an endodontic-periodontal lesion; infection at the perforation site is the most important prognostic modifier. Outcome studies have reported success rates for subcrestal perforations were as low as 40% and it was noted that the presence of pre or intra-operative perforations increased tooth loss by nearly 300%.3,4
In many ways, the effect of size, location and time until repair on perforation prognosis are interlinked as they will combine to accelerate the progression of hard and soft tissue destruction.
Based on these factors, it can be inferred that a small furcal perforation which is expediently repaired will have little effect on the outcome of treatment, assuming the repair procedure can be completed satisfactorily. In these cases, the perforation repair simply prevents bacterial contamination of the site and subsequent bone loss.
A large furcal perforation which has become infected will eventually lead to hard and soft tissue attachment loss, meaning the perforation site communicates with the oral cavity. These perforations will be harder to repair as they are no longer confined to the periodontal attachment apparatus. Here, the objective of treatment is to regenerate the bone at the perforation site and obtain reattachment of the periodontal tissues. This is clearly less predictable.
Over-preparation of the coronal root canal space during instrumentation may lead to strip perforation on the inner aspect of the curvature. This is more likely when inadequate straight-line access has not been obtained and when large rigid rotary instruments, such as Gates Glidden burs, are used overzealously. Preparation for a post may also lead to strip perforation.
Transportation of the root canal in the apical third may lead to apical perforation. This will usually occur on the outer canal wall of the root just beyond the apex of curvature. Whilst the prognosis of the perforation repair in itself is good, the location of the perforation makes the repair more difficult, but more importantly, it is often not possible to complete the cleaning, shaping and filling of the uninstrumented part of the canal. This is of significant importance in infected cases.
How can this be treated?
Contemporary bioceramic materials have revolutionised the repair of perforations. Whilst much of the data on perforation repairs relates to the use of Mineral Trioxide Aggregate (MTA), the evolution of more user-friendly materials, such as Biodentine and bioceramic putty cements, has greatly increased the options available to clinicians. 5
These materials appear to have improved the prognosis of perforation repair and reduced the influence of the main clinical factors which were historically considered to impact treatment outcome. 6 A systematic review has shown the success rate for perforation repair with MTA to be 80.9%. 7
Long standing infection at the perforation site will lead to bone destruction. Therefore, early repair is one of the most critical factors in optimising outcomes. When this is not possible at the time of treatment, every effort should be made to prevent microbial contamination. The use of non-setting calcium hydroxide paste at the perforation site followed by the provision of an optimal coronal seal is imperative if the patient is to be referred for further treatment.
Furcal perforations most commonly occur in maxillary molars. However, the prognosis of furcal repairs in maxillary molars is superior to that observed in mandibular molars (see Figure 1). The use of a resorbable matrix (for example, collagen sponge) to pack the bioceramic material against may be useful in cases where there has been considerable bone destruction adjacent to the perforation. Strip perforations may be managed similarly.
When the perforation has occurred in the apical third and it has not been possible to clean the entire root canal space, the canal may be filled with a bioceramic material to the level of the perforation. Subsequently, root end surgery may be required.
A patient presented with acute pain and swelling in the upper left molar region. Tooth 26 had recently had a metal ceramic crown placed. Clinical examination revealed a mid-buccal sinus tract at the gingival margin with associated pocketing of 6 mm. A pre-operative periapical radiograph revealed existing root fillings in the 26 and 27. Periapical and furcal disease associated with the 26 was evident (1a). A diagnosis of chronic suppurative apical periodontitis associated with a previously root treated tooth was reached. Upon careful access through the metal ceramic crown (1b), a perforation (red arrow) was detected adjacent to the first mesio-buccal root canal (1c). The perforation site was repaired with MTA and during the root canal retreatment procedure, the second mesio-buccal canal was also located (yellow arrow, 1d), after which four canals were chemo-mechanically prepared, cleaned and obturated. A radiograph taken at the 1-year review revealed evidence of healing of the periapical and furcation lesions (1e)
Ledge formation and canal blockage
What is this?
A ledge is an iatrogenically created irregularity (platform) in the root canal that impedes access of instruments (and in some cases irrigants) to the apex. This results in insufficient instrumentation and incomplete obturation. 8
Ledge formation is caused by overzealous instrumentation against the outer wall of the canal just after a curvature. This may be attributable to inadequate straight line access and/or coronal flaring, lack of careful use of precurved small instruments to create a glide path, aggressive instrumentation with larger rigid instruments, inappropriate filing technique (particularly when using cutting tipped instruments) or a combination of these factors.
The greater the curvature of the canal, the greater the risk of ledge formation. Continued erroneous technique once a ledge has been formed will exaggerate the complication and make correction less feasible. Eventually, perforation may result. If the problem cannot be resolved, the canal beyond the ledge will remain uncleaned and unfilled.
Canal blockage by dentin chips and/or pulp tissue debris is an obstruction in a previously patent canal that prevents access and complete disinfection of the most apical part of the root canal system. The blocked canal may contain infected compacted dentinal mud, residual pulp tissue and/or remnants of root filling materials (in cases of retreatment). 8
This complication is more likely to occur in narrow canals. The main contributing factors are lack of adequate irrigation, excessive instrumentation in a dry canal, inadequate cleaning of the file flutes between uses and not carrying out patency filing. Vital cases where abundant pulp tissue is present may be more susceptible to blockage.
How can these be treated?
The key focus for the management of ledge formation is prevention. Careful assessment and planning using high quality pre-operative radiographs (or small volume CBCT) is fundamental to reducing this iatrogenic complication. When a canal is considered to be susceptible to ledge formation, great care must be taken to plan the access cavity and canal preparation coronal to the curvature. Copious irrigation and the careful use of pre-curved flexible stainless steel hand files (ISO 08 and 10) to reach the working length is essential. Great care is required when moving from ISO size 10 to 15 as there is a 50% increase in the diameter of the file between these instruments. Similarly, there is a 25% increase from ISO 15 to 20. The increase in rigidity when trasnitioning between these files makes ledge formation more likely.
This issue may be overcome by the use of glidepath files which create adequate canal parameters for the subsequent use of Ni-Ti rotary or reciprocating instruments.
Canal blockages almost always occur at the apex of the canal. As mentioned previously, these are more likely in vital and/or narrow canals. Abundant irrigation with sodium hypochlorite and/or EDTA throughout the procedure, together with the use of pre-curved small stainless-steel hand files (ISO 08 and 10) will minimise the risk of blockage. Patency filing will ensure the canal is maintained throughout cleaning and shaping. When the canal has been blocked, the same principles of management apply as to that of a ledge (see Figure 2).
A ledge can form when an endodontic file straightens in a curved canal (red arrow, 2a). A small hand file such as a size 10 K-file can be gently pre-curved at the tip (2b) and used to bypass the ledge and locate the original canal path. Once the tip is apical to the ledge, it is moved in and out of the canal utilising small amplitude push-pull movements. The file must remain in the region apical to the ledge defect during this stage. If the file is moved coronal to the ledge prematurely, there is a risk of re-engaging the ledged area, which may worsen the ledge and make it more difficult for the subsequent file to follow the path of the original canal (blue arrows show the correct motion of the file, 2c)
Instrument separation
What is this?
Instrument separation can be defined as the event where a root canal instrument fractures and remains inside the canal, potentially obstructing further cleaning, shaping and filling.
When this occurs, the treating clinician may often be overwhelmed with how to appropriately manage the patient. Clear and informative communication is essential to minimise the risk of a complaint. Prompt referral to a specialist may be necessary in many cases.
Instrument separation may occur with hand or engine-driven instruments and either due to cyclic fatigue and/or torsional failure. Cyclic fatigue occurs when an instrument is rotated in a curved canal whilst undergoing multiple tensile and compressive stresses. Torsional failure occurs when the tip of the file binds in the canal whilst the instrument continues to rotate. Generally, coronal fractures of instruments are more likely to be due to cyclic fatigue whilst apical fractures are more often due to torsional stresses. Stainless steel hand instruments will generally separate due to torsional failure but engine driven Ni-Ti instruments will usually fail due to a combination of torsional and cyclic fatigue.
The incidence of instrument fracture has been reported to be between 0.7 and 7.4%. 9 It can be considered that root canal anatomy is a critical factor contributing to instrument fracture, and the multi-planar curvatures frequently observed in the mesial roots of molar teeth appear to be predisposed to this. Based on the current literature, it would appear that mandibular molars are the most commonly affected teeth. Restricted access may act as a further complicating factor.
How does this affect the prognosis?
The prognosis of a tooth where instrument separation has occurred is largely dictated by the absence or presence of infection within the root canal space. The instrument itself does not cause failure, moreover, it may prevent adequate cleaning and shaping of the canal. Clinicians should take some time to consider both the pre-operative status of the tooth (vital or necrotic) and the stage at which the instrument fracture has occurred when evaluating the impact on prognosis.
If instrument fracture occurs at the apex after the canal has been thoroughly disinfected, and/or the tooth has a vital pulp, the prognosis of treatment is less likely to be significantly affected. However, if the canal was infected and was not cleaned adequately prior to the instrument fracturing, then the likelihood is that the instrument will prevent the elimination of bacteria beyond the obstruction and lead to failure.
The literature in relation to the impact of instrument fracture on treatment outcome is highly variable. Matched pair (case-controlled) studies have shown no significant difference in the success rate of teeth with retained fractured instruments.10,11 However, it would appear that the presence of a pre-operative radiolucency is of significant importance to success rates, highlighting the relevance of intra-canal infection. 12
How can this be treated?
The management options for a tooth with a fractured instrument include removal, bypass, leaving in in situ and monitoring or surgical management.
The decision on which approach to take will be based on the pre-operative status of the tooth, stage of treatment at which the fracture occurs, location of the fractured instrument, the retained length and the type/material of the instrument. Careful consideration of these factors together with the relative risks of each management option is required.
Successful removal of the instrument is largely dictated by the ability to visualise it; this can normally only be achieved with a surgical operating microscope or high magnification loupes with appropriate coaxial lighting.
Instrument removal is most frequently carried out with the use of specifically designed ultrasonic tips. A circumferential staging platform is first created around the coronal part of the instrument. Ultrasonic energy is then applied to the instrument to ‘unscrew’ the file and remove it. Frequent irrigation and drying of the canal is required to maintain good visualisation. When the instrument fragment is long and/or the alloy is of a softer type, the ultrasonic energy may not be able to adequately reach the tip of the file which is locked into the dentine of the canal walls. In these cases, instrument removal devices may be used which are essentially designed with an appropriately sized tube which seats over the instrument. The instrument is wedged against the inner aspect of the tube after which the tube together with the bound instrument are unscrewed together. A study has shown that with these techniques, instruments can be removed in 87 % of cases. 13
When considering when to remove an instrument, consideration should be given to how much dentine removal may be required to obtain straight line access and then remove the file; excessive dentine removal may lead to perforation or excessive weakening of the tooth. In instances where the root dentine is particularly thin, or the file lies beyond a significant curvature, bypassing or leaving the file may be considered. A retained fractured instrument may have less impact on treatment outcome than the perforation which could occur as a result of attempting removal of the file.3,4 Therefore, care and good judgement should be used by the treating clinician before trying to heroically retrieve a fractured file, which may not significantly affect the endodontic outcome, especially when managing a vital case (see Figures 3 and 4).10,11,14
A patient was referred for recurrent pain which localised to tooth 36. A periapical radiograph revealed a fractured file in the mesial root of the tooth. This was located in the mid- and apical region of the root. The previous root filling had voids and was short in both roots; there was associated periapical disease (3a). The root filling material was removed and the fractured file could be visualised with the use of a dental operating microscope. The file was subsequently removed with the use of a dedicated ultrasonic tip (3b). Root canal retreatment was completed and a post-operative radiograph confirmed three well obturated canals. An orthodontic band was placed to decrease the risk of fracture whilst awaiting the provision of a definitive cuspal coverage restoration (3c)
A patient attended complaining of pain which was localised to tooth 46. A periapical radiograph revealed a fractured file in the apical third of the mesial root. The canals had been previously filled and a periapical lesion was evident involving the mesial and distal roots, as well as the furcation region; crestal bone loss was also noted mesially (4a). A diagnosis of chronic apical periodontitis associated with a previously root treated tooth, with an additional finding of a fractured instrument, was made. During root canal retreatment, an attempt was made to remove the fractured instrument. However, its position was beyond the curvature in the mesiobuccal canal (the curvature was clinically more acute when compared with the 2-dimensional appearance in the pre-operative periapical radiograph). It was decided that the risk of iatrogenic damage during file removal was high, as too much tooth structure would have to be sacrificed in order to achieve this. The apical position of the file also presented a higher risk of perforation. The options were discussed with the patient and it was agreed to accept the retained file. The mesiobuccal canal was cleaned and shaped to the level of the file. Bypass was attempted but could not be achieved. The compromised result with the mesiobuccal canal was somewhat mitigated by the complete cleaning and shaping of the mesiolingual canal to full length. This was followed by the placement of a well adapted composite core. A metal ceramic crown was placed by the general dental practitioner. The patient was only able to attend for review after 4 years; the follow-up radiograph shows complete healing of the periapical lesion (4b)
Untreated anatomy
What is this?
Missed canals during endodontic treatment are an important cause of treatment failure. Persistent or emerging infection within the untreated root canals may not cause immediate failure.
The limitations of two-dimensional radiographic imaging, lack of adequate magnification, variation in normal root canal anatomy, effect of calcification and operator skill can all contribute to canals being missed.
How does this affect the prognosis?
In teeth with apical periodontitis, missing a canal is likely to influence the prognosis of treatment significantly. The incidence of apical periodontitis in teeth with untreated canals has been shown to be as high as 82.6% 15 -98%. 16
The impact may be slightly reduced when the missed canal is confluent with another canal in the same root and shares a single apical foramen. However, in these cases, there may be ‘late’ failure as the microbes in the untreated canal eventually overcome the apical root filling material.
Studies have assessed the incidence of missed canals and this appears to be in the order of 12%.15,16 Maxillary first molars most frequently have untreated canals with the second mesiobuccal canal most commonly missed. Other canal configurations that may be missed include the second mesiobuccal canal in the second maxillary molar, second distal canal in mandibular first molar, middle mesial canal in mandibular molar, lingual canal in lower incisor teeth and second or third canals in premolar teeth.
How can this be treated?
Teeth with untreated canals may be amenable to non-surgical retreatment. Unlocated canals may be successfully identified with the use of small volume CBCT scanning prior to the treatment.
Magnification with coaxial lighting, achieved with an operating microscope or high magnification loupes together with a good understanding of pulp chamber anatomy are essential to predictably locate all of the root canals in any particular tooth. A study demonstrated that endodontists were able to find the second mesiobuccal canals in maxillary first molars in 17.2%, 62.5% and 71.1% of cases when using no magnification, loupes and the operating microscope respectively. 17
Instruments such as dedicated ultrasonic tips, LN and Endo tracer burs are invaluable for modifying the pulp chamber and identifying elusive canals (see Figure 5).
The strategic removal of dentine will reveal hidden anatomy such as the elusive second mesiobuccal canal of maxillary first molars (5a-c) and the mid-mesial canal in mandibular molars (5d). Ultrasonic tips such as the Start-X #2 (DentsplySirona) can be used to conservatively remove dentine over the canal orifices (5e), this provides the clinician with more control compared to using a bur
Conclusion
The management of complications during endodontic treatment is part and parcel of life as a clinician. Assessing each case and tailoring the treatment planning process to anticipate and reduce the risk of iatrogenic complications is the most fundamental step in improving the predictability of endodontic treatment. The specific challenges of each case should be discussed with the patient in advance of the treatment and this key step will help to reduce the impact of complications should they arise.
Various clinical factors will significantly influence the impact of treatment complications. Essentially, the objective of endodontic treatment is to prevent or eliminate infection from the root canal system. Therefore, if these objectives cannot be achieved following a complication then the prognosis will be reduced. Clinicians should consider the pre-operative status of the pulp when considering the impact on a specific case. Furthermore, if the complication is not managed expediently, intra-canal infection may ensue and have a detrimental effect on treatment outcome. Reassurance and open communication with patients is an essential component of managing endodontic complications. With the correct management, serious sequelae can be avoided and the root canal treated tooth retained.