A More Precise Way to Re-treat Root Canals

Dr. Manor Haas


The clinical outcome of teeth with well-done root canal treatments and proper restorative treatments (as indicated) has been shown to be very high, often with success rates around 90% and survival rates at nearly 95%.1-5 That being said, there are still some root canal treatments that fail and require nonsurgical endodontic re-treatment.

With the incorporation of enhanced instruments, including dental microscopes and cone beam imaging, failing root canals can now be more precisely diagnosed and re-treated. Conventional 2-D radiographs (ie, periapicals and Panorex radiographs) are limited in what information they provide. It’s not uncommon to be presented with a case that was previously endo treated but has apical pathology that is only seen in 3-D imaging and not in traditional 2-D radiographs.6,7 (Figures 1 and 2 demonstrate such a case.) Hence, no longer do we need to make educated guesses with the limited information provided to us with traditional imaging.1,8

In addition to the information that 3-D imaging provides, we can visually evaluate the inside of the tooth with great precision. We can achieve this with enhanced magnification, such as high-magnification loupes with an overhead light, or, better yet, a dental operating microscope. Using these tools means that we do not have to look into a dark hole in the tooth (the endo access). With such magnification, we can determine if there’s a fracture or locate untreated and/or calcified canals that are often associated with lesions in failing root canals. A common example is that of the untreated MB2 canal in maxillary molars. I discussed the significance of the MB2 canal and where and how to look for it in the June 2018 edition of Dentistry Today.6

Figure 1. A 2-D periapical radiograph of a symptomatic tooth No. 14 does not show pathology. Figure 2. A 3-D image of tooth No. 14 shows an apical lesion over an untreated MB2 canal.
Figure 3. Buccal view of tooth No. 3. Figure 4. A preoperative 2-D periapical, showing tooth No. 3 with an MB root “J-shaped” lesion (red arrows).

The following case highlights how the incorporation of 3-D imaging and enhanced microscopic magnification helped diagnose, treatment plan, and manage a failing root canal treatment. This would not have been possible prior to the availability of 3-D/CBCT imaging and dental microscopes.7,9

Case Background and Diagnosis

The patient in this case presented for evaluation and management of pain upon biting on tooth No. 3. The tooth was root canal treated about 15 years earlier and had been heavily restored. As seen in Figure 3, other than gingival recession, there was nothing significant noted about the soft tissues over the tooth. No deep, isolated periodontal pockets were noted either. However, things did not appear normal radiographically. There was a clear (inverted) “J-shaped” lesion along the length of the MB root (Figure 4). Traditionally, J-shaped lesions have been considered an indication of a vertical root fracture. In fact, the kind of lesion seen in this case could be considered “textbook” for a root fracture.1
So, now arises the diagnostic and treatment planning question: What exactly is the problem with tooth No. 3? And how should it be managed?

Clinical Management: The Conventional Approach
In years past and, in fact, still nowadays, clinicians would not be able to diagnose the endo pathology if only 2-D imaging was used. And, if the endo was indeed deemed to be failing, one would often have to re-treat all the roots and canals in hopes of making sure no problematic canals are left behind: a “just in case” kind of approach. This is due to uncertainty and what I consider the “shotgun” approach.

Figure 5. Axial view, showing the lesion centered around the untreated MB2 canal in tooth No. 3. Figure 6. Coronal view, showing intact buccal and palatal bone and an apical lesion over the untreated MB2 canal.
Figure 7. Sagittal view, showing the MB apical lesion. Figure 8. A volume rendering of the buccal view of the tooth No. 3 site, with no vertical bone loss.

This conventional approach means that the dentist/endodontist might not treat what needs to be treated because of not being able to see the apical pathology. Or, he or she might over-treat the tooth by treating all the canals, even if not all of them had a problem.

A New and More Precise Approach: Diagnosis and Treatment Plan
In order to precisely diagnose the situation with tooth No. 3, a limited field CBCT 3-D scan was performed (J. Morita USA). As seen in Figures 5 to 8, the exact nature of the MB lesion was determined. It was centered over the apical exit of an untreated MB2 canal. Unlike what the 2-D periapical radiograph showed, the lesion did not run the length of the MB root. Also, there was no isolated site of vertical bone loss. As such, the lesion was not consistent with that of a vertical root fracture. Furthermore, no apical pathology was seen over the DB and palatal roots. This information was key because it changed the diagnosis and treatment plan. Instead of a probable root fracture diagnosis and likely extraction (or root amputation) as a treatment, the recommended treatment involved saving the tooth.

Possible treatments included nonsurgical root canal retreatment or apical surgery. Re-treatment was recommended in this case in order to manage the MB intra-canal infection that was the source of the apical infection vs simply treating the apical infection surgically and leaving bacteria in the MB root system.

Clinical Treatment
With the help of a dental operating microscope (ZEISS), the tooth was accessed conservatively and centered only over the MB1 and MB2 orifices. Under the enhanced magnification and illumination of the microscope, the endo access and pulp chamber could easily be viewed. At this time, it was important to confirm the absence of any internal fractures. The untreated MB2 canal was located and treated, along with the MB1 canal. Both canals were treated with hand files (C-files [Dentsply Sirona]) along with mechanized NiTi files (ProTaper Next [Dentsply Sirona]). Canal lengths were determined with the use of an electronic apex locator (ProMark [Dentsply Sirona]). During the procedure, sodium hypochlorite was used as a lubricant and medicament. No gutta-percha solvent was used. Once instrumentation was complete, the canals were flushed with more sodium hypochlorite, dried, and then irrigated with EDTA/chlorhexidine (QMix [Dentsply Sirona]). The MB root was medicated with calcium hydroxide (Root-Cal [Endo Tech]) that was delivered with a lentulo spiral, and the endo access was closed with a temporary restoration (Cavit [3M]).

Figure 9. The initial view of endo access,
showing the calcified site of the untreated MB2 in tooth No. 3.
Figure 10. The instrumented MB1 and MB2 canals, medicated with calcium hydroxide.
Figure 11. Intra-access view of the MB1 and MB2 canals, obturated. Figure 12. A radiograph, showing the final obturation of the MB1 and MB2.
Figure 13. The endo access in tooth No. 3 was restored with amalgam following endo re-treatment. Figure 14. One-year followup, showing (1) the absence of the pre-op MB vertical lesion (red arrows), and (2) the obturated MB2 canal (blue arrow).

After one week, the patient returned, and the intra-canal medication was removed by irrigating the canals with sodium hypochlorite. The canals were obturated with gutta-percha and a resin-based cement (AH Plus [Dentsply Sirona]). The small endo access was then restored permanently by the referring dentist. As seen in the one year follow up, the preoperative MB apical lesion healed, and the patient was asymptomatic (Figures 9 to 14).

Traditionally, the case presented would likely be deemed as hopeless. Its J-shaped root lesion has been, and still is, considered to be indicative of a vertical root fracture. Without having to raise an exploratory surgical flap or perform an exploratory endodontic access, we were able to easily and precisely determine the exact nature of the lesion as only apical and not running the full length of the MB root. Furthermore, with the 3-D scan, we were able to determine the exact location of the endo-related pathology as only over the MB root and not over the DB and palatal roots. This helped greatly in treatment planning and managing the case. After so many years since the initial endodontic treatment, if there was infection associated with these 2 roots, then one would expect apical pathology over them. But none was noted, and there was a clear reason for the apical lesion to only be over the MB root: the untreated MB2 canal. Hence, only the MB root was re-treated. Furthermore, it was important to re-treat the MB1 canal and not just the untreated MB2. That is because of the known communications between the MB1 and MB2 canals in the form of isthmuses. See the June 2018 Dentistry Today article, “The Infamous MB2 Canal.”6

Table 1 compares conventional re-treatment with the more precise re-treatment approach highlighted in this article.

We no longer have to make educated guesses about the etiology of symptoms associated with failing root canals. And we do not need to take a shotgun approach to nonsurgical root re-treatment by automatically re-treating all the roots and canals. Instead, we can and should consider treating only what our modern-day tools show as the source of the problem. Doing so is more conservative, less invasive, and may also be less expensive for patients (if one bills per treated canal).


  1. Dorn SO, Cheung GSP. Management of endodontic emergencies. In: Hargreaves KM, Berman LH. Cohen’s Pathways of the Pulp. 11th ed. St. Louis, MO: Elsevier; 2016:706-721.
  2. Iqbal MK, Kim S. For teeth requiring endodontic treatment, what are the differences in outcomes of restored endodontically treated teeth compared to implant-supported restorations? Int J Oral Maxillofac Implants. 2007;22(suppl):96-116.
  3. Fernández R, Cardona JA, Cadavid D, et al. Survival of endodontically treated roots/teeth based on periapical health and retention: a 10-year retrospective cohort study. J Endod. 2017;43:2001-2008.
  4. Setzer FC, Kim S. Comparison of long-term survival of implants and endodontically treated teeth. J Dent Res. 2014;93:19-26.
  5. Burry JC, Stover S, Eichmiller F, et al. Outcomes of primary endodontic therapy provided by endodontic specialists compared with other providers. J Endod. 2016;42:702-705.
  6. Haas M. The infamous MB2 canal: how to find and treat it. Dent Today. 2018;37:90-93.
  7. Haas M. The use of 3-D imaging is changing: endodontic diagnoses and treatments. Dent Today. 2016;35:135-140.
  8. Lin YH, Lin HN, Chen CC, et al. Evaluation of the root and canal systems of maxillary molars in Taiwanese patients: a cone beam computed tomography study. Biomed J. 2017;40:232-238.
  9. Low KM, Dula K, Bürgin W, et al. Comparison of periapical radiography and limited cone-beam tomography in posterior maxillary teeth referred for apical surgery. J Endod. 2008;34:557-562.

Dr. Haas is a certified specialist in endodontics and lectures internationally. He is a Fellow of the Royal College of Dentists of Canada and is on staff at the University of Toronto Faculty of Dentistry and the Hospital for Sick Children. He maintains a full-time private practice limited to endodontics and microsurgery in Toronto. He can be reached at haasendoeducation.com.

Disclosure: Dr. Haas reports no disclosures.

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