Endodontic Treatment Outcomes

Learning Objectives

After reading this chapter, the student should be able to:

  • 1.

    Describe signs of successful and unsuccessful root canal treatment.

  • 2.

    Describe the most common modalities used to determine success or failure.

  • 3.

    State the approximate range of expected outcomes of routine, uncomplicated root canal treatment based on pretreatment conditions.

  • 4.

    State predictors of success and failure.

  • 5.

    Identify endodontic and nonendodontic causes of treatment failure.

  • 6.

    State the outcomes of retreatment, endodontic surgery, and intentional replantation.

  • 7.

    State the outcomes of fixed partial denture and single tooth implant treatments.

  • 8.

    Approach treatment planning of root canal failure, recognizing the advantages and disadvantages of different treatment modalities.


The primary goals of endodontic treatment are to provide patients with the best possible long-term outcomes regarding function, comfort, and esthetics. From a biologic perspective, this encompasses the prevention or cure of apical periodontitis. Prevention will be the focus for treating teeth presenting with pulpal inflammation, such as irreversible pulpitis. This can be achieved by maintaining aseptic conditions utilizing hygienic protocols and rubber dam isolation to prevent any oral microorganisms or bacteria present in caries from entering the root canal system during or after root canal treatment.

The objective for treating teeth with infection present within the root canal system is to significantly reduce the microbial load and to prevent recontamination. This is achieved by a disinfecting phase, including thorough mechanical instrumentation, antimicrobial irrigation, and medication, as well as a sealing phase including root canal filling and placing permanent restoration. Complete root filling should largely eliminate the habitat for microorganisms, so that any residual microorganisms after treatment can be expected to perish as a result of the harsh environmental conditions of a well-sealed root canal root canal system, or at least rendered dormant. Finally, restorations preventing coronal leakage should disallow bacterial recontamination and achieve functional and esthetic rehabilitation.

Optimal outcomes are dependent on attaining these technical goals. However, as a result of the complexity of root canal systems, , less than perfect instrumentation, and root filling techniques, as well as the impossibility to render permanent restorations leakage free indefinitely, the guaranteed elimination of microorganisms from the root canal systems cannot be achieved under certain circumstances.

The purposes of this chapter are to (1) define success and failure, (2) describe methods used for the evaluation of endodontic outcomes, (3) provide outcome rates, including success and survival, (4) explain the signs and symptoms of negative outcomes, (5) discuss factors influencing outcomes, and (6) compare the outcomes of initial nonsurgical root canal treatment with those of nonsurgical retreatment, surgical retreatment (endodontic surgery), and alternative treatments, such as single tooth implants.

Definitions of Success and Failure

A successful outcome of root canal treatment may have a different meaning to different stakeholders involved in the treatment, including patients, dentists, and third-party payers.

Patients will expect the elimination of symptoms, comfortable chewing function, satisfying esthetics, reassurance that symptoms may not recur, and that their tooth does not pose a risk of causing systemic disease. Insurance companies may judge the outcome by the access to care provided, the quality of care, cost efficiency, and the longevity of the treatment rendered.

Dentists are primarily concerned with the delivery of optimal care, predictable elimination of disease as measured clinically and radiographically, and fair compensation. In addition, they engage in aligning all stakeholders’ expectations. Dentists should also reevaluate the technical quality of treatment and the long-term outcome in terms of preventing and eliminating apical periodontitis.

For endodontically treated teeth with previously vital pulps and no preexisting apical lesion, success entails that the tooth remains asymptomatic and no periapical pathosis develops after treatment. Failure will involve new symptoms and/or the appearance of a periapical lesion. For a tooth with a diagnosis of pulp necrosis, the outcome of the treatment is considered successful if the tooth remains asymptomatic and a preexisting apical periodontitis heals, respectively, no new apical lesion develops during follow-up. The presence of symptoms and/or a new or enlarging lesion is considered failure of the treatment.

Recently the American Association of Endodontists has proposed the following alternatives to the terms “success” and “failure”:

  • Healed—Functional, asymptomatic teeth with no or minimal radiographic periradicular pathosis.

  • Nonhealed—Nonfunctional, symptomatic teeth with or without radiographic periradicular pathosis.

  • Healing—Teeth with periradicular pathosis that are asymptomatic and functional, or teeth with or without radiographic periradicular pathosis that are symptomatic but for which the intended function is not altered.

  • Functional—A treated tooth or root that is serving its intended purpose in the dentition.

Determination of success or failure may be difficult because of the nature and complexity of the periapical healing process itself and as a result of difficulties in observation. Many asymptomatic endodontically treated teeth demonstrate varying degrees of apical lesions radiographically. The clinician must judge whether a tooth is on a pathway to success or to failure and then decide together with the patient on a proper course of action if indicated.

When to Evaluate

Recommended follow-up periods have ranged from 6 months to 5 years. Six months is a widely accepted and reasonable early follow-up interval for most situations. It is important to determine at what point of a healing process the outcome of treatment will be unlikely to reverse its course, and when treatment can be judged predictably as either success or failure, without a further need for follow-up.

A radiographic lesion that remains unchanged or increased in size after 1 year of follow-up is unlikely to ever resolve, and hence considered to be unsuccessful. If after 6 months a periapical lesion is still present, albeit smaller, it is likely to be in progress of healing, and further follow-up is indicated. Larger periradicular lesions will take longer to heal than smaller lesions. Unfortunately, apparent success may revert to failure later (often as a result of reinfection through coronal leakage), yet, late healing may also occur. Therefore an endodontic evaluation, including a patient history, clinical examination, and radiography of endodontically treated teeth should be part of every comprehensive patient examination.

Methods for Evaluation of Endodontic Outcomes

The evaluation process of successful endodontic therapy is complicated by the lack of direct correlation between measures of the disease process and its clinical manifestation. The clinician must therefore assimilate various metrics of information including patient history, clinical findings, and radiographic examinations to determine endodontic treatment outcomes. Evaluation of endodontic outcomes follows the same diagnostic pathway as for initial treatment (see Chapter 4 ). Biopsy of periradicular tissues during endodontic surgery provides a histologic diagnosis, another method for evaluation of success or failure of root canal treatment. This method is not routinely used and is an impractical approach to determine clinical outcomes of initial nonsurgical root canal treatments.

Patient History

Complaints of new, persistent, or worsening symptoms after root canal treatment has been completed may indicate failure. Persistence of signs (e.g., sinus tract opening) or symptoms long after endodontic therapy had been completed indicate primary and continuing disease. However, emergence of new signs or symptoms months or years after root canal treatment usually result from secondary posttreatment disease such as leakage secondary to absence of suitable coronal restoration. Symptoms related to discomfort or pain on chewing, aching, and so forth are generally an indication of periradicular inflammation or infection regardless of the evidence of radiographic lesion. It must be remembered that bony healing takes time and that a tooth that feels “different” on biting may be en route to healing; this should be confirmed clinically and radiographically. Pain on release may indicate a cracked tooth. A bad taste may indicate a draining abscess. Occasionally a patient reports sensitivity to cold or heat; this is most likely related to an adjacent untreated tooth but could be an indication of a missed vital canal in a treated tooth.

Clinical Examination

Presence of persistent signs or symptoms is usually an indication of disease and failure. However, absence of symptoms does not signify success. Periapical pathosis without significant symptoms is usually present in teeth before and after root canal treatment until healing has occurred. There is little correlation between the presence of pathosis and corresponding symptoms; yet when adverse signs or symptoms are evident, there is a strong likelihood that a pathosis is present. Persistent signs (e.g., swelling, probing defect, or sinus tract) or symptoms usually indicate failure.

Common clinical success criteria include the following :

  • No signs of swelling, infection, or inflammation

  • Disappearance of sinus tract (separate or through periodontal ligament space)

  • No soft tissue defects or pathologic probing depths

As part of the overall assessment of the tooth after endodontic therapy it is crucial to evaluate the current restoration and the periodontal attachment apparatus. A defective/missing restoration as well as active periodontal disease have been significantly associated with loss of an endodontically treated tooth.

Radiographic Findings

Based on the interpretation of radiographs, the outcome of each treatment can be classified as success, failure, or questionable status. To be able to accurately compare radiographs made at different times, it is important that they are made in a reproducible fashion and with minimal distortion. The best way to ensure reproducibility is with paralleling radiographic devices. Teeth with multiple roots or canals should be examined using both straight-on- and off-angle periapical views.

Radiographic success is the absence of an apical radiolucent lesion. This means that a resorptive lesion present at the time of treatment has resolved or, if there was no lesion present at the time of initial treatment, none has developed. Thus radiographic success is evident by the elimination or lack of development of an area of rarefaction for a minimum of 1 year after treatment ( Fig. 22.1 ).

Fig. 22.1
(A) The initial radiograph shows the presence of bone loss from the crest of the ridge around the apex of the distal root. A sinus tract is traced. Periodontal probing demonstrates deep pocketing. There is no response to pulpal vitality tests. (B) Root canal treatment completed. (C) A 12-year recall radiograph shows resolution of the radiolucency, build-up, and post. (D) A 12-year recall radiograph demonstrates healthy apical tissues. The patient wears a removable partial denture.

Radiographic failure is the persistence or development of pathosis radiographically. Specifically, whether this is a radiolucent lesion that has remained the same, has enlarged, or has developed since treatment ( Fig. 22.2 ). Nonfunctional, symptomatic teeth with or without radiographic lesions are considered failure (nonhealed).

Fig. 22.2
(A) Apparently adequate root canal treatment. The tooth was restored later with a post and core and crown. (B) The patient reports persistent discomfort after 2 years. A periradicular radiolucency indicates failure, probably a result of coronal leakage at a defective margin (arrow) .

Radiographically unknown status indicates a state of uncertainty. This classification includes teeth with pathosis that are asymptomatic and functional. The radiolucent lesion in these teeth has neither become larger nor significantly decreased in size. Teeth with radiolucencies that were treated elsewhere and for which there are no prior radiographs for comparison are often assigned to this category ( Fig. 22.3 ).

Fig. 22.3
(A) Obturation demonstrating voids and coronal leakage likely all contributed to failure. The tooth is suitable for nonsurgical retreatment and a new permanent restoration. (B) Postoperative image after retreatment. (C) Three-month recall, the patient reports absence of symptoms. The radiolucent lesion is decreasing in size but has not resolved. (D) Seven-month recall, despite a new restoration, the lesion has remained and stays in within the same proportions.

A shortcoming of radiographic evaluation is that radiographs may not be made or interpreted in standardized ways. As early as 1966, Bender et al. noted that radiographic interpretation is often subject to personal bias and that a change in angulations can often give a completely different appearance to the lesion, making it appear either smaller or larger. Also, different observers may not agree on what they see in a radiograph and the same observer may disagree with himself if asked to review the same radiograph at a different lime period.

Ørstavik et al. suggested the use of the periapical index (PAI) for radiographic evaluation of the outcome of root canal treatment. The PAI relies on the comparison of the radiographs with a set of five radiographic images reported by Brynolf in 1967. These images represent a radiographically healthy periapex (score 1) to a large periapical lesion (score 5). Each of the preoperative and recall radiographs is assigned a score according to its resemblance to one of the five reference images. The outcome of treatment using PAI can be classified as “healing” if the lesion size is reduced, “healed” if the lesion has been eliminated, or “developing” if a new lesion has formed. Although accurate and reproducible, complete healing using the PAI may take up to 4 or 5 years especially after endodontic surgeries evidenced by a larger number of “slow” healers compared with the “late” failures. Others have commonly used the terms healed, healing, and diseased instead of success and failure because of the potential of the latter to confuse patients.

Cone beam computed tomography (CBCT) with high resolution three-dimensional (3D) imaging technique has demonstrable value in diagnosis and outcomes assessment for endodontic patients (see Chapter 3 ). The 3D image allows a precise evaluation without the superimposition of surrounding anatomic structures. Recent studies comparing 2D and 3D images have reported a significant increase in uncertain healing and unsatisfactory healing at the 1-year follow-up period owing to higher and more precise detection of bone lesions that may not be visible with two-dimensional radiology. Currently, the routine use of CBCT is not recommended owing to its higher radiation dosage. However, with constant improvements in hardware and software algorithms CBCT will increasingly become an essential diagnostic and assessment tool for the clinician. The increased sensitivity and resolution may require a reevaluation of criteria for acceptable radiographic periapical healing.

Histologic Examination

The ideal outcome through histologic assessment would necessitate reconstitution of periradicular structures and an absence of inflammation ( Fig. 22.4 ). This is both impractical and impossible without surgery. Additionally, there is uncertainty about the degree of correlation between histologic findings and negative radiographic appearance. Two histologic investigations of teeth treated with root canals in cadavers reached very different conclusions. Brynolf concluded that almost all root canal treated teeth showed some periradicular inflammation despite the appearance of successful treatment on radiographs. In contrast, Green el al. observed that most root canal treated teeth with radiographically normal periapex were indeed free of inflammation histologically. Thus with current technology such as the noninvasive CBCT, the clinical and radiographic evaluation appear to be the more practical means of assessing degree of healing after endodontic treatment.

Fig. 22.4
(A) A periapical radiograph revealed an apical radiolucency on the central incisor. (B) A periapical film taken 6 months later shows resolution of most of the apical radiolucency. Despite radiographic change, the patient remained symptomatic, and surgery had to be performed. (C) Histologic examination of this tooth shows resolution of most of the inflammatory cells near the apex.
Courtesy of Dr. A. Khayat.

Success Rates

As is the case for other dental and medical procedures, unfortunately, not all endodontic treatments are successful. Recognition, acceptance, and management of treatments that do not resolve and heal can be difficult and often involve a complex set of factors. Historically, the popular belief has been that the success and survival rates for root canal treatment are between 80% and 95%. However, general percentages should be taken with caution, and each case should be individually assessed to determine the percentage probability of success.

Torabinejad et al. performed a systematic review of the literature pertaining to success and failure of nonsurgical root canal therapy and assigned levels of evidence (LOE) to the studies. In the previous 40 years, 306 articles have been published related to the outcome of nonsurgical root canal treatment. Fifty-one studies included at least 100 teeth; meta-analysis of these studies suggested an overall radiographic success rate of 81.5% over a period of 5 years. Others who assessed the 4- to 6-year outcomes of initial endodontic treatment have reported similar overall healing rates. In another systematic review, Torabinejad and colleagues compared the outcomes of endodontically treated teeth with those of single implant crowns, fixed dental prostheses (FPD), and no treatment after extraction. Success data in that review consistently ranked implant therapy as superior to endodontic treatment, which in turn was ranked as superior to FPD ( Table 22.1 ). However, very different criteria for success are used in implant dentistry, endodontics, and prosthodontics; therefore such comparisons lack validity. Comparison of survival rates is much more meaningful and were recorded at 97% in same study.

TABLE 22.1
Percentages of Pooled and Weighted Survival and Success Rates of Dental Implants, Root Canal Treatment, and Three- or Four-Unit Bridges Over 2 to 4, 4 To 6, And 6+ Years
Procedure Success (%) Survival (%)
2-4 years
Dental implant (pooled) 98 (95-99) 95 (93-97)
Dental implant (weighted) 99 (96-100) 96 (94-97)
Root canal treatment (pooled) 90 (88-92) 94
Root canal treatment (weighted) 89 (88-91)
Three-unit bridge (pooled) 79 (69-87) 94
Three-unit bridge (weighted) 78 (76-81)
4-6 years
Dental implant (pooled) 97 (96-98) 97 (95-98)
Dental implant (weighted) 98 (97-99) 97 (95-98)
Root canal treatment (pooled) 93 (87-97) 94 (92-96)
Root canal treatment (weighted) 94 (92-96) 94 (91-96)
Three-unit bridge (pooled) 82 (71-91) 93
Three-unit bridge (weighted) 76 (74-79)
6+ years
Dental implant (pooled) 95 (93-96) 97 (95-99)
Dental implant (weighted) 95 (93-97) 97 (96-98)
Root canal treatment (pooled) 84 (82-87) 92 (84-97)
Root canal treatment (weighted) 84 (81-87) 97 (97-97)
Three-unit bridge (pooled) 81 (74-86) 82
Three-unit bridge (weighted) 80 (79-82)

Survival Rates

Long-term survival rates for endodontically treated teeth include tooth retention or survival. Introduced by Friedman and Mor in 2004 the term “functional retention” is frequently used to indicate retention of the tooth in the absence of signs and symptoms regardless of a radiographic lesion. Several very large studies have all reported extremely high long-term survival rates for teeth with root canal treatment: Lazarski et al. reported 94% functional survival for 44,613 cases at 3.5 years in the United States; Salehrabi and Rotstein reported 97% survival for 1.1 million patients at 8 years in the United States; and Chen and colleagues reported 93% survival for 1.5 million teeth at 5 years in Taiwan. Teeth with root canal treatments have remarkably high long-term survival rates.

These rates of survival of endodontically treated teeth allow a better comparison with alternative treatments such as FPD and single implant-supported restorations. The previously mentioned systematic review shows that endodontic and implant treatments resulted in superior ≥6 year survival rates compared with extraction and replacement with an FPD. Torabinejad et al. as well as Iqbal and Kim reported similar findings when they compared the survival rates of restored endodontically treated teeth with those of implant-supported restorations. Doyle and colleagues additionally reported that although similar in failure rates, the implant group showed a longer time to tooth function and a higher incidence of postoperative complications requiring intervention. Furthermore, a recent systematic review reported that implant survival rates do not exceed those of even compromised but adequately root canal treated and maintained teeth. Therefore the importance to maintaining the natural dentition through evidence-based dentistry cannot be overemphasized.

Patient-Based Outcomes

In the current age of patient-centered care, patients’ perspectives of their health status are gaining importance in identifying needs, treatment planning, and ultimately in evaluating outcomes from health care. Today definitions of health include psychologic measures of well-being as well. Anticipation and experience of root canal associated pain are major sources of fear for patients and a very important concern of dentists. A recent systematic review found that the severity of pretreatment root canal associated pain was moderate, dropped substantially within 1 day of treatment, and continued to drop to minimal levels in 7 days. Overall satisfaction ratings for root canal treatment are extremely high, generally above the 90th percentile. Satisfaction is higher when endodontic treatment is provided by specialists, probably a reflection of effective communication and efficient management. Initial costs for root canal treatment and restoration are substantially lower than for replacement with an implant single crown or FDP. ,

Recent studies on patient-based outcomes have focused on the Quality of Life metrics. These instruments have mostly been adapted from medicine for application to dentistry, such as the Oral Health Related Quality of Life instruments (OHQoL). Liu et al. reported a longitudinal study on the OHQoL for 279 patients after endodontic treatment using the Oral Health Impact Profile (OHIP) tool of assessment, which was shown to be both sensitive and responsive to endodontic treatment and useful in understanding patients’ perspectives of outcomes.

A larger study involving over 1250 patients in a practice-based research network suggests that 3 to 5 years after initial root canal therapy a small percentage (5%) of patients experience persistent pain, of which <2% are not attributable to odontogenic causes that may adversely affect their quality of life. Endodontic nonsurgical retreatment has also shown to significantly improve patients’ quality of life and chewing ability over time, with a success rate of 90.4% after 2 years. Future studies from patients’ own perspectives could expand our understanding of the prognostic factors and the consequences of root canal treatment.

Postoperative Complications

As with all dental procedures, complications may occur after root canal treatment. However, the incidence of long-term postoperative complications appears to be lower than for the alternatives, single tooth implants and fixed dental prostheses. , The 10-year complication rate for retained root canal treated teeth is approximately 4%, compared with approximately 18% for retained single tooth implant restorations. Typical complications include symptoms, swelling, and the need for retreatment. In endodontics, complications are recorded as failures according to the criteria described previously; in other disciplines, complications are generally not recorded as failures.

Prognostic Indicators

The classic landmark study published by Larz Strindberg in 1956 related treatment outcomes to biologic and therapeutic factors. Factors now considered to be predictors of success and failure include (1) apical pathosis, (2) bacterial status of the canal, (3) extent and quality of the obturation, and (4) quality of the coronal restoration. The role of these factors should be discussed with the patient before and after treatment.

Several investigations have reported factors that result in a slightly less favorable prognosis: the presence of periradicular lesions and larger lesion size; , the presence of bacteria in the canal before obturation; and obturations that are short, long, contain voids, or lack density. Some evidence suggests that the use of a calcium hydroxide intracanal medicament may improve the prognosis. The quality of the coronal restoration plays a key role in the outcomes of root canal treatment.

Factors such as the tooth type, age and gender of the patient, and obturation technique have minimal if any influence on the prognosis. , Most medical conditions have no significant bearing on the prognosis. However, patients with insulin dependent diabetes mellitus have a significantly lower healing rate after root canal therapy in teeth with apical lesions. Interestingly, diabetes mellitus, hypertension, and coronary artery disease are associated with an increased risk of extraction after root canal treatment. Although this finding does not indicate causality, the systemic disease burden has broad effects on the patient’s welfare, morbidity, and behavior. Obviously, a patient with a complex medical history, serious illness, or disability may present a high degree of difficulty in management and demands high levels of experience and expertise. However, root canal treatment may greatly benefit some patients by preventing the need for high-risk extractions or other surgical procedures; such patients include those with bleeding disorders, those who have undergone head and neck irradiation, and those treated with high-dose bisphosphonates.

Study Questions

  • 1.

    Which of the following criteria WILL NOT be considered part of a truly successful outcome at a 1-year follow-up?

    • a.

      No clinical signs of swelling, infection, or inflammation

    • b.

      Disappearance of a sinus tract

    • c.

      Decrease of a radiolucency in size

    • d.

      No soft tissue defects or pathologic probing depths

    • e.

      No clinical symptoms experienced by the patient

  • 2.

    Which of the following statements about the radiographic detection of periapical pathosis is UNTRUE?

    • a.

      The sensitivity of detecting apical periodontitis with CBCT imaging is higher than with conventional digital radiography

    • b.

      Any apical periodontitis in the mandible will be detectable on radiographs if it exceeds 3 mm in diameter

    • c.

      If radiographs at follow-up are taken at a different angulation than the postoperative control, the actual healing progression may be misjudged

    • d.

      Different observers may disagree on the interpretation of periapical radiolucencies

    • e.

      The same observer may disagree with him/herself on the interpretation of periapical radiolucencies if viewed at different times

  • 3.

    Based on systematic reviews and meta-analyses, which of the following outcome ranges does not reflect the associated procedure?

    • a.

      Success of root canal treatment with a diagnosis of irreversible pulpitis: 90% to 100%

    • b.

      Success of root canal treatment with a diagnosis of apical periodontitis: 75% to 85%

    • c.

      Success of nonsurgical retreatment: 75% to 85%

    • d.

      Success of endodontic microsurgery: 55% to 65%

    • e.

      Survival of single-unit implants: 90% to 100%

  • 4.

    Which of the following factors WOULD NOT be considered to be a predictor of success and failure for endodontic treatment?

    • a.

      Type of root filling material

    • b.

      Presence or absence of apical pathosis

    • c.

      Extent and quality of the root filling

    • d.

      Bacterial status of the root canal system

    • e.

      Quality of the coronal restoration

  • 5.

    Which of the following statements about the PAI is INCORRECT?

    • a.

      The PAI relies on the comparison with a set of five radiographic images reported by Brynolf in 1967

    • b.

      The outcome of treatment using PAI can be classified as “healing” if the lesion size is reduced

    • c.

      The outcome of treatment using PAI can be classified as “healed” if the lesion has been eliminated

    • d.

      The outcome of treatment using PAI can be classified as “developing” if a new lesion has formed

    • e.

      The PAI grades in 4 stages from healthy periapex (score 1) to a large periapical lesion (score 4)

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Feb 23, 2021 | Posted by in Endodontics | Comments Off on Endodontic Treatment Outcomes

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