Why might endodontic treatment fail? And what can be done?

Why might endodontic treatment fail?

Even though it is a widely successful procedure, there are a variety of reasons why endodontic treatment may fail. These include poor aseptic control during treatment, insufficient chemo-mechanical preparation, and suboptimal obturation of the canals. However, root canal anatomy is complex and, even in adequately filled teeth, infection can persist due to extra-radicular sources of infection such as periradicular biofilms, foreign body extrusions and self-sustaining cystic lesions.[iii]

Reinfection may also occur if there is a breakdown of the coronal seal, as this can result in microleakage, in addition to errors which occurred during the initial procedure such as instrument separation or perforations, as well as resistant microorganisms such as E. Faecalis.[iv]

Diagnosis and prognosis

Should an endodontically treated tooth require further treatment, it’s important to confirm the diagnosis ensuring there are no non-odontogenic causes of the patient’s symptoms, assess the likely origin of the infection, and decide whether the patient may be a suitable candidate for non-surgical retreatment.

As part of the clinical assessment, particular attention should be paid to the restorability of the tooth, determining whether coronal tooth structure is sufficient. However, if this is not the case, such as when there are medical contraindications to extraction, non-surgical retreatment can be performed as long as an aseptic environment can be maintained throughout the procedure.[v]

For accuracy in diagnosis and treatment planning, it is important to carry out a thorough radiographic examination. In addition to revealing root canal morphology and periradicular radiolucency, radiographs can indicate procedural errors, the quality of obturation, and the quality of the coronal seal.[vi] The use of CBCT could also be considered pre-operatively, when justified, as it may help formulate a diagnosis and enhance the management of the tooth.[vii]

As with primary root fillings, teeth that have undergone root canal retreatment should be reviewed on an annual basis until completely healed. If teeth become symptomatic, or the lesion stays the same size or has not completely resolved within four years, apicectomy or extraction should be considered as next steps.[viii]

Retreating root canals

Because root canal treated teeth are usually restored with a permanent restoration, non-surgical endodontic retreatment can be a more complex procedure as accessing the tooth can be a challenge. It is thus integral that magnification and illumination are adequate, to detect subtle colour changes between restorative materials and dentine. In addition to this, obturation material must be removed to facilitate adequate disinfection of canals.

When restoration margins are sound, access cavities can be created through the restoration. However, in many cases, the coronal restoration must be removed if it is defective (to evaluate any underlying pathology and restorability of the tooth), if locating the canals is difficult, or if underlying pathology is detected during access. If posts are present, it is advised the case is referred to a more experienced practitioner (i.e. specialist). Whilst diamond and long neck burs will help operators traverse through the majority of restorative material, ultrasonics enable the removal of subtle materials closer to the floor up the pulp chamber, reducing the risk of perforation.

Gutta-percha (GP) can be removed using hand and mechanical rotary and/or reciprocating instruments and solvents. The technique used to remove the GP will be influenced by the obturation technique, the extent of voids, curvature of the canal, and how narrow the canals are. The pre-operative radiograph should be used to determine these factors.

Following this, canal patency should be established and treatment should then follow a similar process to that of initial treatment. Clinicians should pay special attention when obturating the canals though, as cracks are more likely to occur in retreated teeth. Achieving a restoration with a good coronal seal and resistance is essential, for long-term survival of the endodontically treated tooth.[ix]

Staying up-to-date

Up-to-date knowledge is critical when providing endodontic retreatment. As such, the British Endodontic Society (BES) is hosting the first in a series of hands-on workshops on 22^nd February 2025 entitled “Endodontic Retreatment: a British Endodontic Society Hands-on Workshop”, which aims to improve delegates’ clinical and decision-making skills in this area. Furthermore, the BES has created ‘A Guide to Good Endodontic Practice’, which is a fantastic resource for clinicians to refer to. It reviews the basic principles of endodontics, and takes the reader through the decision-making process that leads to endodontic intervention.

Endodontics often offers successful outcomes, however, retreatment is sometimes necessary. Clinicians must assess cases carefully and decide whether to treat or refer to a specialist.

For more information about the BES, or to join, please visit the website www.britishendodonticsociety.org.uk or call 07762945847

[i] Ng YL, Mann V, Gulabivala K. Tooth survival following non-surgical root canal treatment: a systematic review of the literature. Int Endod J. 2010 Mar;43(3):171-89. doi: 10.1111/j.1365-2591.2009.01671.x. PMID: 20158529. https://pubmed.ncbi.nlm.nih.gov/20158529/

[ii] Fransson, Helena, and Victoria Dawson. “Tooth survival after endodontic treatment.” International Endodontic Journal 56 (2023): 140-153. https://onlinelibrary.wiley.com/doi/10.1111/iej.13835

[iii] BES. Guide to good endodontic practice. Accessed October 2024. https://britishendodonticsociety.org.uk/news/39/a_guide_to_good_endodontic_practice

[iv] BES. Guide to good endodontic practice. Accessed October 2024. https://britishendodonticsociety.org.uk/news/39/a_guide_to_good_endodontic_practice

[v] BES. Guide to good endodontic practice. Accessed October 2024. https://britishendodonticsociety.org.uk/news/39/a_guide_to_good_endodontic_practice

[vi] BES. Guide to good endodontic practice. Accessed October 2024. https://britishendodonticsociety.org.uk/news/39/a_guide_to_good_endodontic_practice

[vii] Patel, Shanon, et al. “European Society of Endodontology position statement: the use of CBCT in endodontics.” International endodontic journal 47.6 (2014): 502-504.

[viii] BES. Guide to good endodontic practice. Accessed October 2024. https://britishendodonticsociety.org.uk/news/39/a_guide_to_good_endodontic_practice

[ix] BES. Guide to good endodontic practice. Accessed October 2024. https://britishendodonticsociety.org.uk/news/39/a_guide_to_good_endodontic_practice