Nonsurgical Endodontic Retreatment: Exploring Promising Prognoses With Contemporary Techniques

When presented with a tooth whose previous endodontic treatment has failed, clinicians and patients face a crucial decision point. The options are to attempt nonsurgical endodontic retreatment (NS RETX), perform apical surgery, or consider extraction with or without replacement. This decision goes beyond a simple procedural choice and must incorporate shared decision-making involving discussions of risks and benefits of alternatives, prognostic effects, and economics. This article focuses on nonsurgical retreatment as a viable treatment option. The authors encourage readers to seek further study on apical surgery as another alternative to extraction.

The natural dentition maintains the integrity of the oral environment, preserves alveolar bone, and provides superior tactile feedback and proprioception, which are crucial for efficient mastication and overall oral health.¹ Additionally, the psychological benefits of tooth retention, often leading to higher satisfaction and confidence, cannot be underestimated.²

In current dental practice, however, a perception exists among many clinicians that dental implants offer superior long-term prognoses compared to endodontic retreatment.³ This notion may be influenced by the more stringent outcome measures utilized in the endodontic outcomes literature, which typically require the absence of both clinical and radiographic pathology, compared to the extract–implant approach, where the outcome measures tend to focus on survival rather than success.^4,5

A recent retrospective study at University of North Carolina at Chapel Hill School of Dentistry reviewed endodontically treated teeth that were replaced by implants.⁶ The researchers found that over half of the teeth extracted due to endodontic failure could have been potential candidates for retreatment, underscoring endodontic retreatment as an underutilized option for saving a substantial proportion of compromised teeth deemed untreatable.

Endodontic Failure: Causes and Diagnoses

Endodontic treatment failures are primarily attributed to the persistence of microorganisms within the root canal system, particularly in the apical region. A number of gram-positive cocci, rods, and filaments have been identified to form biofilms on the canal walls, resisting antimicrobial measures and contributing to persistent infections.⁷ In particular, Enterococcus faecalis is the most consistently reported organism persisting in non-healing apical lesions after endodontic treatment.^8,9 Interestingly, these gram-positive, facultative anaerobic cocci are more frequently seen in secondary infection than primary infection.¹⁰ The remarkable ability of E faecalis to survive in the presence of intracanal antibiotics and form biofilms in a nutrient-deprived environment makes it classifiable as an opportunistic pathogen.¹¹

Other significant causes of endodontic failures include missed or untreated canals, which harbor residual bacteria that can lead to reinfection.¹² Incomplete debridement and inadequate obturation are also frequent culprits, as they allow for bacterial survival and colonization within the canal system.¹³ Furthermore, procedural errors such as instrument fractures, perforations, or coronal leakage due to faulty restorations can compromise the seal of the root canal system, providing pathways for bacterial ingress and subsequent failure (Figure 1).¹⁴ Consequently, periapical lesions are formed by the patient’s immune-mediated response to these microbial and inflammatory elements.

Effective diagnosis of endodontic treatment failures relies on a combination of clinical evaluation and advanced imaging techniques. Regular follow-up appointments allow clinicians to monitor the healing process, identify any emerging symptoms, and detect radiographic signs of failure such as persistent or developing periapical radiolucency.¹⁵ Cone-beam computed tomography (CBCT) allows for 3-dimensional visualization of teeth and their adjacent tissues and has become an invaluable tool in evaluating postoperative outcomes. Multiple studies show that CBCT provides more accurate detection of subtle periapical radiolucent changes, poor-quality root filling, and complex root anatomies than periapical radiographs.^16-18 Combining modern imaging tools with diligent follow-up allows for earlier diagnosis of periapical disease.

Preoperative Factors Influencing Retreatment Prognosis

Several preoperative factors significantly influence the prognosis of nonsurgical endodontic retreatment. One critical factor is the presence of apical periodontitis. Similar to primary root canal therapy (RCT), the presence of preoperative apical periodontitis negatively impacts success rates following NS RETX, reducing the success rate from 93% to 80%.^12,19 Large radiolucencies are particularly problematic, as they often indicate a greater microbial bioburden or long-standing infections with evolved microbial communities, making them highly challenging to treat effectively.²⁰

The presence of clearly defined issues or technical errors in the initial RCT also plays a crucial role in determining the predictability of retreatment outcomes. Studies have shown that the retreatment outcome is often inversely associated with the quality of the initial treatment.¹⁹ When the causes for primary endodontic failure are obvious and correctible, such as a missed canal or incomplete obturation, the retreatment prognosis tends to be more predictable, as the necessary corrective measures can be directly targeted (Figure 2 through Figure 5).

Unmanaged complications, such as pre-existing perforations, significantly affect the outcomes of nonsurgical retreatment.¹⁹ Patients presenting with a perforation that was not appropriately managed initially have less-predictable retreatment outcomes. The presence of a perforation introduces complexities in sealing the root canal system and controlling infection, which can compromise the overall success of the retreatment.

The remaining tooth structure is another critical factor influencing the success of nonsurgical retreatment. Research by Al-Nuaimi et al indicates that teeth with more than 30% of their initial volume of coronal tooth structure intact fare much better following retreatment than teeth with less than 30%.²¹ Adequate remaining tooth structure provides better structural integrity and support for the restoration, which is essential for the long-term success of the treated tooth. In contrast, teeth with significant loss of coronal structure are more susceptible to fractures and other complications, which can undermine the success of the retreatment.

NS RETX With Modern Techniques

In a survival analysis performed by Salehrabi and Rotstein using data from Delta Dental insurance claims, the 5-year survival rate among the nearly 5,000 teeth that underwent NS RETX was found to be 89%.²² When looking at teeth that were not only present, but clinically functional and without symptoms or radiographic pathologies, studies have yielded variable results. A meta-analysis by Torabinejad et al reported a range of 74% to 85% 4- to 6-year success rate among eight studies published between 1998–2008.²³ The variation could be affected by patient population, clinical settings (hospitals/dental schools/private practices), treatment protocol, and evaluation criteria. However, even the most recent study reported in the meta-analysis (82% success rate among 229 patients) was fairly dated and only included treatments completed between 1998 and 2001, before the widespread adoption of modern techniques.¹⁹

Modern endodontic techniques, including advances in visualization, instrumentation, and materials, have significantly improved the standard of care and predictability of outcomes in both primary nonsurgical RCT and retreatment. One of the most impactful advancements in modern endodontics is the use of surgical operating microscopes. Recent data shows that more than 90% of endodontists report using an operating microscope in their practice,²⁴ a substantial increase from 1999, when only 52% utilized this equipment.²⁵ The high magnification and superior illumination of these instruments allow clinicians to visualize complex canal morphologies, such as isthmuses, accessory canals, and microfractures, for which magnifying loupes or similar devices may be inadequate. Moreover, the ergonomic design of microscopes helps clinicians maintain a comfortable posture, improving focus and reducing fatigue during long procedures.

Rotary and reciprocating instruments made from nickel-titanium have largely replaced traditional stainless-steel files in canal preparation. Their greater flexibility and durability allow for more efficient and effective cleaning and shaping, especially in curved canals.²⁶ The adaptation of advanced irrigation protocols, including ultrasonic activation, has further enhanced the debridement and disinfection of the canal system. Ultrasonic instruments have working ends that are 5 to 10 times smaller than the smallest round burs available, and their narrow profile and abrasive coatings enable precise excavation of dentin when removing mineralized obstructions.²⁷ These features ensure a thorough yet conservative means of removing obstructions, which are often the primary cause of persistent infections and treatment failures.

Currently, gutta-percha (GP) is used for endodontic obturation. A 1997 survey involving 48 US dental schools reported that cold lateral condensation was the most commonly taught technique in predoctoral courses.²⁸ There has been a recent shift in trend to the use of thermoplastized GP in endodontic obturation. The concept of heating GP to produce a homogenous, stable, compatible material that adapts to the root canal system was first introduced by Schilder in the 1960s, and this was followed by the development of other heated GP obturation techniques such as continuous wave obturation, injectable gutta-percha, and carrier-based techniques.²⁹ Studies demonstrate that these thermoplastized techniques achieve a higher density of GP in the apical region and produce fewer voids, resulting in superior replication of the root surface compared to cold lateral condensation methods.³⁰

Along with 3-dimensional diagnostic radiographs and the latest generation of sealant and coronal restoration materials, the integration of contemporary techniques has markedly improved the success rates and predictability of retreatment outcomes. A recent study from the University of Pennsylvania on treatments completed between 2017 and 2020 in the postgraduate and faculty practices found a markedly higher survival rate (92.4%) for nonsurgically retreated teeth than previously reported.³¹ Another prospective study examined teeth treated specifically with modern techniques at Baylor College of Dentistry; all treatments followed a standardized treatment protocol featuring current advancements, namely operating microscopes, nickel-titanium rotary files, ultrasonic irrigation, and a thermoplastized technique for obturation.³² The authors found that nonsurgical retreatment using contemporary techniques significantly improved patients’ quality of life and chewing ability over time, with a success rate of 90.4% after 2 years. This improvement in prognosis might even be an underestimation. Previous studies often measured success by the number of roots rather than the number of teeth, which tends to overestimate success rates. Since all teeth in this study were multirooted, the success rate would likely have been higher if the unit of evaluation was per root rather than per tooth.

Conclusion

The advancement of modern endodontic techniques has ushered in a new era of improved outcomes for NS RETX. Traditional methods, which relied heavily on manual instrumentation, limited visual aids, and basic irrigation and obturation techniques, often yielded variable success rates. Factors affecting retreatment prognosis include apical periodontitis, initial treatment quality, unmanaged complications, and the amount of remaining tooth structure. However, the incorporation of advanced technologies such as operating microscopes, nickel-titanium rotary files, ultrasonic irrigation, thermoplastic obturation techniques, and more accurate diagnostic tools like CBCT has significantly enhanced clinicians’ ability to successfully retreat endodontic failures. The improved visualization, precision, and thoroughness provided by current methodologies means that many teeth previously deemed untreatable are potentially salvageable with modern nonsurgical retreatment techniques. Recent studies indicate that these contemporary approaches result in higher survival and success rates (92.4% and 90.4%, respectively), offering a compelling case for prioritizing nonsurgical retreatment as a promising option in cases of primary endodontic failure.

ABOUT THE AUTHORS

Ruojun Esther Wu, DMD Candidate
Harvard School of Dental Medicine, Boston, Massachusetts
Brooke Blicher, DMD, Certificate in Endodontics

Assistant Clinical Professor, Department of Endodontics, Tufts University School of Dental Medicine, Boston, Massachusetts; Lecturer, Department of Restorative Dentistry and Biomaterials Science, Harvard School of Dental Medicine, Boston, Massachusetts; Co-founder, Pulp Nonfiction Endodontics; Private Practice limited to Endodontics, White River Junction, Vermont

Rebekah Lucier Pryles, DMD, Certificate in Endodontics
Assistant Clinical Professor, Department of Endodontics, Tufts University School of Dental Medicine, Boston, Massachusetts; Lecturer, Department of Restorative Dentistry and Biomaterials Science, Harvard School of Dental Medicine, Boston, Massachusetts; Co-founder, Pulp Nonfiction Endodontics; Private Practice limited to Endodontics, White River Junction, Vermont

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