Ng YL, Mann V, Rahbaran S Outcome of primary root canal treatment: systematic review of the literature – Part 2. Influence of clinical factors. Int Endod J. 2008; 41:6-31 https://doi.org/10.1111/j.1365-2591.2007.01323.x
Siew K, Lee AH, Cheung GS. Treatment outcome of repaired root perforation: a systematic review and meta-analysis. J Endod. 2015; 41:1795-1804 https://doi.org/10.1016/j.joen.2015.07.007
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Incidents and accidents influence the outcome of root canal treatment, irrespective of the operative techniques used. The unjustified removal of dental hard tissues may promote structural failure of the root canal treated tooth or recontamination of the intra-canal space. Iatrogenic errors, particularly those associated with the loss of working length due to blockages, can impede adequate cleaning, shaping and filling of the root canals. This can influence the treatment of apical periodontitis as well as tooth retention. This case series discusses common incidents and accidents that can occur during root canal treatment, as well as their possible management.
CPD/Clinical Relevance: Operators should be aware of the possible intra-operative complications during root canal treatment and factors to prevent their occurrence.
Article
Root canal treatment encompasses the management of intra-canal contents, including dental pulp (vital and/or necrotic) and, when present, contamination in the form of biofilms on the root canal wall. An inert material is subsequently placed into the root canals. Technical factors that are associated with improved treatment outcomes during the management of primary apical periodontitis include root fillings without voids and the filling extending to within 2 mm of the radiographic apex of the root.1 The apical extent of the root filling is also a significant factor associated with higher success rates in re-treatment cases.2Figure 1 illustrates technically adequate and inadequate root canal fillings. The absence of peri-apical pathosis prior to treatment, and the provision of a suitable definitive restoration after treatment have a positive effect on root canal treatment outcomes.1,2 Conversely, intra-operative factors, such as perforations and other technical errors, have a negative effect on treatment outcomes.
Figure 1.
(a) Root canal-treated maxillary right first molar teeth (UR6). Technically adequate root filling within 2 mm from the radiographic apex and without visible voids. (b) Technically inadequate root canal filling by being shy from the desirable apical position and presenting with voids.
A crucial consideration is the position of a root canal filling and its density, observable in post-operative radiographs. The appearance of a root filling reflects not only the root canal filling process per se, but also the quality of the root canal preparation and suggests that iatrogenic errors have been avoided. The present case series will focus exclusively on intra-canal procedural accidents and incidents during root canal treatment, particularly those relating to the instrumentation stage. Incidents where the deviation of the access cavity occurs, but where there is no communication with the extra-radicular space, and accidents, where an access cavity is associated with perforations, are unexpected events; however, only accidents result in significant damage. An incident should always be considered a ‘near miss’ and requires prompt identification and adequate management, which may include referral to an endodontist when further damage is likely to occur. An incident may progress to an accident if not managed appropriately. Furthermore, the identification of intra-canal incidents is important in that it is an opportunity for the operator to practice self-reflection; to prevent and avoid such iatrogenic errors in the future.
Case presentations
Tooth structure loss
Mechanical preparation of the root canal requires the use of hand and/or engine-driven instruments to remove root canal contents, prepare a path for delivering disinfecting solutions and medicaments, and create a root canal shape that can be filled predictably to the desired technical standards.
Preservation of tooth tissue and structure is essential during the mechanical preparation of the root canal. The inappropriate use of diamond burs during access cavity preparation can lead to the weakening of the most coronal part of the root canal if the mesio-distal and bucco-lingual inclinations of the tooth are not recognized. This alignment may be impeded by the presence of extra-coronal restorations (Figure 2) and overcutting may occur if instruments of excessive size are used. This can increase the risk of subsequent tooth fracture. Coronal and mid-root incidents include perforations, defined as communications between the root canal system and the external surface.3 Clinically, these can be identified by the presence of persistent bleeding, pain, erratic readings of the apex locator or observed on radiological examination. The haphazard use of cutting instruments (Figure 3), in particular within the furcation area of multi-rooted teeth where the thickness of dentine is reduced, and strip perforations, may occur at various root levels (Figures 4 and 5). The latter is also associated with the tendency of files to straighten at the mid-root level of curved canals.
Figure 2. Post-operative radiograph of maxillary right second premolar tooth (UR5) being a distal abutment of a fixed prosthesis. The access cavity was prepared through the pre-existing restoration resulting in misalignment of the diamond bur. During root canal treatment, repair with a glass ionomer cement was carried out, in the absence of communication with the peri-radicular tissues (arrow). Reproduced with kind permission of John Wiley & Sons.Figure 3.
(a) Radiograph of mandibular right premolar tooth (LR4) following root perforation and completion of root canal treatment. Intra-operative and post-operative (b) Incident pre-empted by the mesial inclination of the tooth and intra-canal calcification.Figure 4. Pre-operative and post-operative radiographs. (a) Mandibular left first molar tooth (LL6) following root canal treatment. (b) A furcal perforation in the coronal third of the mesial root is evident in the post-operative radiograph with the presence of a furcal radiolucency, and scatter of radiopaque root canal filling material (arrow). Referral to an endodontist for management ensued. Case courtesy of Dr Laura Petroff, Adelaide, Australia.Figure 5. Post-operative radiograph of a maxillary right first molar tooth (UR6) following root canal treatment. Strip perforation in the middle of the mesial root is evident as radiopaque root canal filling material consisting of gutta-percha points is visible (circle).
Outcomes for the management of perforation depend on several variables, namely the size, position, time and material of repair.4 Periodontal complications can ensue if a perforation is in proximity to the crestal bone.4 Perforations of limited size, those not in proximity to the periodontal attachment, and prompt treatment are associated with better outcomes. The use of hydraulic calcium silicate cements, such as mineral trioxide aggregate, is associated with improved outcomes when compared with other materials, including glass ionomer cements.5
Blockages
Access to the apical terminus may be hindered by debris and/or foreign materials, which can impede the cleaning and filling of the area apical to the obstruction; intra-canal biofilms may persist and cause a chronic inflammatory response in the periapical tissues.6 In the absence of intra-canal contamination, i.e. no apical periodontitis, or if this incident occurs at a late stage of chemo-mechanical instrumentation, the consequences of canal blockage may be limited, since the biofilm was already disturbed before the blockage. However, the inability to recognize this complication mid-treatment may compel the operator to try to regain the previous working length, which can lead to ledging and possible perforation of the root canal walls.
Foreign bodies, such as restorative materials, may inadvertently fall into the canal space. This can negatively influence healing in the presence of apical periodontitis (Figures 6 and 7). Removal of unsupported loose material, and/or dental tissue debris, is key to preventing this particular incident from occurring, whereas patency filing, i.e. passing a small file through the apical foramen,3 helps to maintain the apical terminus free of debris while also preventing the loss of the desired working length.3 Dental tissues, including pulp, calcified matter and detached dentine, can create blockages by being pushed and packed during instrumentation. This is not as readily discernible as radiopaque foreign bodies in radiographs and, thus, may not necessarily be readily detected by the operator.
Figure 6. Root canal treatment of a mandibular right second molar tooth (LR7) with C-shaped morphology. (a) Pre-operative; (b) intra-operative and (c) post-operative imaging. Following shaping, radiopaque material consisting of amalgam had fallen into the apical third of the root canals. The root canal filling was completed using gutta-percha and sealer coronally to the metallic obstruction. No influence on the outcome in the absence of a peri-apical radiolucency, which would be suggestive of no or limited microbial contamination, should be expected.Figure 7.
(a) Mandibular right first molar tooth (LR6) re-treatment. Pre-operative panoramic radiograph and intra-operative peri-apical radiograph. (b) Radiopaque material consisting of amalgam has fallen into the apical third of the three roots. In the presence of peri-apical radiolucencies associated with the mesial and disto-lingual roots, the obstructions will have a negative influence on the technical aspects of treatment and, subsequently, healing of the pre-existing apical pathosis is unlikely. To be noted, pre-operative radiographic assessment of teeth using panoramic radiography before root canal treatment is insufficient to inform the operator about possible intra-operative challenges.
The use of instruments, such as large stainless steel files, which are stiff and have cutting edges, in the presence of curvatures, is associated with the risk of transportation,7 which is the removal of canal wall structure on the outside wall of the curve.3 Excessive apical pressure and inappropriate movement of hand files should also be avoided as these too can contribute to transportation. Endodontic files are active tangentially to the outside apical curve, owing to the restoring force causing the instrument to return to its original shape when bent. In the apical part of curved canals, common incidents include the formation of ledges, an artificial irregularity created on the surface of the root canal wall that impedes the placement of instruments to the apex of an otherwise patent canal,3 and zips, a teardrop shape in the apical foramen following transportation of the outer wall.3 The latter makes filling of the apical terminus less predictable as zips lead to the formation of hourglass-shaped apical preparations, which makes it difficult to fit master points that are tapered. Deviations from root canal anatomy and eventual loss of working length when using nickel–titanium engine-driven instruments may occur if they are maintained in the same corono-apical position for longer than 1–3 seconds because of their tendency to straighten when bent.8
A priori evaluation of root curvature based on published checklists is essential before initiating root canal treatment. Among these, the American Association of Endodontists Case Difficulty Assessment Form9 and the EndoApp tool10 consider the role of root curvature severity and the presence of S-shaped canals among the features that increase the level of treatment difficulty. Management by a specialist is justified in highly complex cases. Once an incident has occurred, regaining access to the anatomical terminus will require prompt referral to an endodontist and may not always be achieved. Subsequent outcomes and management modalities will depend on the original diagnosis and the medical history of the patient (Figures 8–12).
Figure 8. Mandibular right first molar tooth (LR6) endodontic recall radiograph. Blockage and transportation are evident in mesial canals. Although technically inadequate, in the absence of a radiolucency, the treatment should be considered successful owing to the absence of apical pathosis and symptoms.Figure 9.
(a) Maxillary left first premolar tooth (UL4) with S-shaped roots. Pre-operative radiograph. (b) Post-operative radiograph showing transportation and loss of working length in both root canals. Healing of the pre-existing apical pathoses is unlikely.Figure 10.
(a, b) Mandibular left lateral incisor tooth (LL2). (c) Pre-operative radiographs available from the referring dentist. Working length determination radiograph confirming apical transportation and perforation. (d) Post-operative radiograph. (e) One-year recall demonstrating no changes in the periradicular radiolucency. As the patient is asymptomatic and receiving bisphosphonate therapy, no further intervention was considered apart from recall.Figure 11.
(a) Management of canal transportation with perforation on a maxillary right first molar tooth (UR6), mesial root. Pre-operative peri-apical radiograph following the referral. (b) Pre-operative cone beam computed tomography imaging confirming the diagnosis as transportation visible in the dataset (arrow). (c) Intra-operative radiograph with a file in the transported canal. (d) Intra-operative radiograph with a file in the original canal. (e) Post-operative radiograph with a root canal filling evident in the original canal.Figure 12.
(a) Management of canal transportation with perforation on a maxillary left second premolar tooth (UL5). Pre-operative peri-apical radiograph following referral from the general practitioner. (b) Pre-operative cone beam computed imaging showing the shape of the root canal. (c) Intra-operative radiograph illustrating canal transportation (file in situ). (d) Intra-operative radiograph illustrating the location of the original canal (file in situ). (e) Post-operative radiograph illustrating root canal filling of the iatrogenic canal and the original canal.
Engine-driven instruments are liable to fracture. The management of fractured files requires prompt disclosure of the incident and discussion of the management options with the patient. These will depend on the pre-operative status of the tooth, with symptoms and/or the presence of apical pathosis prompting further intervention. Intra-operative management will vary depending on the type, number and position of the fractured files, as well as the root canal morphology of the tooth affected. For instance, a fractured instrument apical to a curvature makes removal less predictable. Referral to an endodontist should be part of the discussion in the shared decision-making process. The management of fractured instruments is shown in Figures 13–17. An operating microscope may be necessary to visualize the fractured instrument, while an ultrasonically powered instrument is used to remove dentine around the fractured file, to free any binding areas. Once the file is loose in the canal, a micro loop can grasp it for removal. Failure to adequately manage biofilm beyond fractured instruments in the root canal is related to negative outcomes in most clinical scenarios. This is one of the additional challenges during root canal re-treatment as the instrument sometimes cannot be visualized on a pre-operative radiograph because the root canal filling material prevents the fractured instrument being seen. Following removal of the blockage and adequate root canal treatment, positive outcomes should ensue. Another method to manage fractured instruments is to perform a bypass because sometimes there are spaces between the fractured instrument and the canal wall, since most rotary instruments are triangular in shape. A smaller instrument, such as a ISO size 06 or 08 k-file, can be used to carefully cut around the fractured instrument and progress to the desired working length. The area beyond the fractured instrument will now be accessible to the disinfecting solutions and medicaments and theoretically, root canal treatment should provide a positive outcome. Finally, if the instrument is located at the apical part of the root canal and cannot be bypassed or removed and there is apical periodontitis, surgical endodontics can be performed to remove the fractured instrument and any biofilm present. The use of cone beam computed tomography could help in the diagnosis of some of these complications, as illustrated in the cases included in the present report (Figures 11–17).
Figure 13.
(a) Removal of fractured spiral filler in maxillary right central incisor tooth (UR1). Pre-operative radiograph following the referral. (b) Post-operative radiograph with root canal filling of adequate standard. Case courtesy of Dr Yoseif Haddad, Welland, Ontario, Canada.Figure 14.
(a) Root canal re-treatment a maxillary right first molar tooth (UR6). Pre-operative periapical radiograph following the referral showing an inadequate root filling and a fractured file in the mesio-buccal root (circle). (b) Working length determination radiograph at ‘0 reading’ of the electronic apex locator demonstrating fractured file bypass. (c) Post-operative radiograph with file in a more apical position and embedded in the root canal filling (circle).Figure 15.
(a) Removal of fractured rotary file in a maxillary left first molar tooth (UL6). Pre-operative radiograph showing a fractured file in the distobuccal root. (b) Post-operative radiograph with root canal filling of adequate standard. Case courtesy of Dr Pantea Motearefi (Adelaide, Australia).Figure 16.
(a) Tooth extraction following fracture of files. The pre-operative radiograph of LL6 shows the presence of two file fragments in the mesial root (arrow). (b) Post-extraction radiograph. Note that extraction of teeth with fractured files should not be considered the most desirable treatment modality, especially in the absence of apical pathosis as in the present case. During a candid discussion with the patient, the incident should be disclosed and referral to a specialist should be part of the management modalities considering that prevention of tooth loss is the ultimate goal in endodontics.Figure 17. Root canal re-treatment of a three-rooted mandibular right first molar tooth (Tooth 46). (a) Pre-operative radiograph showing inadequate root filling, intra-canal posts in the mesial and distal roots and a fractured file in the disto-lingual root, together with an apical radiolucency associated with the mesial root. (b) Working length determination radiograph for distal roots. (c) Post-operative radiograph. (d) One-year recall peri-apical radiograph showing complete healing of the apical pathosis.
Discussion and conclusion
As the cleaning and disinfection of the root canal space is not assessable post-operatively, research highlights that the single most important treatment factor influencing success is the apical extent of the root filling, which implies that both the canal preparation as well as the root filling have been completed adequately.2,7 Operators may realize at the obturation stage that working length loss may have occurred. This commonly arises during chemo-mechanical instrumentation when using stainless steel files owing to the formation of ledges and/or packing of debris of moderate radiopacity including dentine. In the authors' experience, referring colleagues purport that their inability to regain the original working length is due to the ‘calcification’ of the most apical part of the root canal. It is worth noting that this is not biologically plausible in the absence of viable pulp cells. The latter is the case after instrumentation and irrigation with sodium hypochlorite of the root canal and/or the presence of apical periodontitis.
Dental practitioners should observe that they ‘do no harm’. Prevention of intra-canal complications requires choosing the most appropriate and less invasive procedure based on the best available evidence. In the emergency management of symptomatic pulpitis, for example, a coronal pulpotomy will suffice.11 Instrumentation of inflamed root canal contents is unjustified to relieve symptoms, as intra-procedural errors are associated with the presence of ‘hot pulps,’ where pain control and visibility, due to bleeding, are often limited.
Similarly, practising according to previously established protocols plus generating referrals based on the case complexity is crucial for reducing clinical incidents in practice.9,10
The disclosure of significant clinical errors, including intra-canal accidents, is a clinician's responsibility to patients. Some, such as fractured files, are easy to identify radiographically; however, not every technical mishap will be promptly noticed by the operator. While a threshold of what should be reported has not been established, unimportant incidents may not necessarily need to be disclosed to patients because it is more likely to cause them distress rather than benefit.12 However, operators should be candid when clinical errors occur, as this will allow the provision of adequate post-operative care and the timely management of ensuing complications.12
