Abstracts

Introduction

Success is the expected outcome after root canal treatment (RCT), regardless of the clinical conditions. However, predicting success usually requires adopting a referential or criteria, and presupposes that the patient is healthy. It is estimated that RCT should be considered completed when the tooth is permanently restored and in function (¹1. Estrela C, Leles CR, Hollanda ACB, Moura MS, Pécora JD. Prevalence and risk factors of apical periodontitis in endodontically treated teeth in a selected population of Brazilian adults. Braz Dent J 2008;19:34-39.). RCT clinical success can be analyzed based on different points of view, with specific values that involve the dentist, the patient or the tooth itself. References for the dentist are the value of symptom (clinical silence - absence of pain), the value of image (root canal space completely filled with no evidence of periapical inflammation), and the value of clinical condition (a well-restored and functioning tooth). The dentist's skills are crucial to interpret correctly the radiographic features and establish a diagnostic hypothesis. For the patient, the value of symptom (no pain) is essential. Apart from this, RCT success is associated with predictive aspects that eliminate the need of interventions and establishes treatment conclusion. The success for the tooth itself is associated with absence of disease (root canal infection or periapical inflammation).

The life of an endodontically treated tooth implies understanding that biological and mechanical events have a multifactorial nature and cannot be viewed separately. Ideally, it is expected to preserve the largest possible number of teeth until the end of life. Successful RCT prevents pain, apical periodontitis (AP) and tooth loss, but it is a real challenge because several clinical conditions can contribute, alone or in combination, for a poor prognosis, namely root canal perforation, overfilling, endodontic and periodontal lesion, root fracture, periapical biofilm, traumatic dental injury, fracture of instrument, AP, root resorption, etc.

Systemic and periodontal conditions should be carefully examined before RCT. Preoperative diagnosis of dental pulp and/or periapical tissues is an important reference to establish case prognosis. The dentist's health represents a human aspect that is frequently neglected and can also be a risk factor for the occurrence of intraoperative procedural errors. Human error may be associated with stress, working conditions, and lack of attention, adequate planning and sufficient knowledge of new technologies. Renouard and Charrier (²2. Renouard F, Charrier J-G. A la recherche du maillon faible: initiation aux facteurs humans. VC Cultural: São Paulo, 2013. 154 p.) discussed some human factors that could induce accidents and reported that as far as the interactions between the individual and the working environment, errors could be related to other people (life ware), technology (hardware), documentation (software) and environment.

The objective of this review of literature is to discuss relevant factors associated with patient's health, tooth and dentist that could account for a successful RCT. Table 1 enumerates determinant aspects associated with the health of the individual, the tooth and the professional that must be carefully observed for a successful RCT.

The Value of Diagnosis

Establishing a correct diagnosis is essential for planning clinical procedures. A favorable prognosis in RCT relies on the endodontist's scientific experience level and skills. The challenge is to overcome the complex canal morphology, neutralize the microbial pathogenicity regardless of the type and duration of infection, and disrupt the bacterial biofilm. Host's defense (immune response) is fundamental in this process.

Pulpal or periapical inflammatory diseases are usually identified by the consequences of tissue aggressions. The main purpose of canal therapy is the removal of the causative - bacterial, chemical, mechanical and physical etiological - agents. During the diagnosis, it is essential to recognize the clinical conditions that could have led to tissue response, such as dental caries, pain, inflammation, primary infection, secondary infection, symptomatic/ asymptomatic AP, periapical abscess with/without sinus tract, open/closed cavity, history of traumatic dental injury.

Knowing the clinical factors associated with pulpal and periapical pain may provide important information for planing the therapeutic strategies and predicting RCT outcomes. The most frequent diagnosis of pulpal pain has been associated with symptomatic pulpitis and hyper-reactive pulpalgia, and the most frequent periapical pain is symptomatic AP of infectious origin. Endodontic diagnosis and local factors associated with pulpal and periapical pain suggest that the important clinical factor in pulpal pain is closed pulp chamber and caries, and is periapical pain is open pulp chamber (³3. Estrela C, Guedes AO, Silva JA, Leles CR, Estrela CRA, Pécora JD. Diagnostic and clinical factors associated with pulpal and periapical pain. Braz Dent J 2011;22:306-311.).

Understanding the general clinical condition (patient's systemic health) and local (clinical conditions of the tooth) favors the first impression to predict a possible outcome of RCT. The impact of patient's age, smoking status, initial treatment versus retreatment, root canal system exposed to salivary contamination prior to treatment, and the type of instrumentation on RCT outcome were recently evaluated (⁴4. Marending M, Peters OA, Zehnder M. Factors affecting the outcome of orthograde root canal therapy in a general dentistry hospital practice. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:119-124.). The integrity of a patient's nonspecific immune system, which has been neglected in earlier investigations, is a significant predictor for endodontic treatment outcome, and should receive more attention. The immune status of the patient, and the quality of the root filling showed a great influence on RCT outcome in a cohort study (⁴4. Marending M, Peters OA, Zehnder M. Factors affecting the outcome of orthograde root canal therapy in a general dentistry hospital practice. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:119-124.).

Several non-endodontic diseases suggest a typical case of AP. The differential diagnosis of diseases of non-endodontic and endodontic origin should always be made carefully. Radiolucent or radiopaque images in the mandibular or maxillary areas surrounding the root apexes may be a sign of non-endodontic disease, and may be misdiagnosed as AP (⁵5. Bueno MR, Carvalhosa AAC, Castro PHS, Pereira KC, Borges FT, Estrela C. Mesenchymal chondrosarcoma mimicking apical periodontitis. J Endod 2008;34:1415–1419.

6. Faitaroni LA, Bueno MR, Carvalhosa AA, Ale KAB, Estrela C. Ameloblastoma suggesting large apical periodontitis. J Endod 2008;34:216-219.-⁷7. Morais AL, Mendonça EF, de Alencar AHG, Estrela C. Intraosseous lipoma in the periapical region of a maxillary third molar. J Endod 2011;37:554-557.).

Root Canal Infection and its Consequences

The periapical inflammation represents a natural biological defense response, caused by several etiologic agents. The model of the inflammatory response is similar in other parts of the organism. The intensity of periapical inflammation and/or infection can suggest the diagnosis and the treatment option. The traumatic or infectious injury of the dental pulp is able to produce harmful consequences in the periapical region. The infection of the dental pulp mobilizes microorganisms to develop in apical direction, to invade and colonize the periapical tissues. The period of time of an infection process is unpredictable. Microorganisms with different characteristics (structural, metabolic and pathogenic) reaching the periapical region stimulate the inflammatory and immunologic responses. The organic defenses and the degree of virulence of the microorganisms establish several types of periapical alterations and its infection potential (⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.,⁹9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.).

Some signs are solid evidence of the pathogenic potential to be neutralized by therapeutic strategies, like a tooth with root canal that remained open for some time and favored the invasion and colonization by different bacterial species, or the presence of a sinus tract, which collaborates with the invasion and development of a structured bacterial biofilm.

The participation of a bacterial complex in the process of pulp and periapical aggression has been thoroughly discussed in several studies (⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.

9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.

10. Nair PNR. Non-microbial etiology: Foreign body reaction maintaining post-treatment apical periodontitis. Endod Topics 2003;6:96-113.

11. Nair PNR. Non-microbial etiology: Periapical cysts sustain post-treatment apical periodontitis. Endod Topics 2003;6:114-134.

12. Nair PNR, Sjögren U, Figdor D, Sundqvist G. Persistent periapical radiolucencies of root filled human teeth, failed endodontic treatments and periapical scars. Oral Surg Oral Med Oral Pathol 1999;87:617-627.

13. Sundqvist G, Figdor D. Life as an endodontic pathogen: Ecological differences between the untreated and root-filled root canals. Endod Topics 2003;6:3-28.

14. Gomes BPFA, Drucker DB, Lilley JD. Clinical significance of dental root canal microflora. J Endod 1996;24:47-55.

15. Siqueira-Jr JF. Endodontic infections: concepts, paradigms, and perspectives. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:281-293.

16. Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249-281.-¹⁷17. Wilson M, McNab R, Henderson B. Bacterial disease mechanisms: An introduction to cellular microbiology. Cambridge: Cambridge University Press, 2002.).

Sundqvist and Figdor (¹³13. Sundqvist G, Figdor D. Life as an endodontic pathogen: Ecological differences between the untreated and root-filled root canals. Endod Topics 2003;6:3-28.) reported that infection of the root canal is not a random event. The type and mix of the bacterial microbiota develop in response to the surrounding environment. Species that establish a persistent root canal infection are selected by the phenotypic traits that they share and that are suited to the modified environment. Nair (⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.) has defined pathogenicity as the ability of a microbe to produce disease and virulence; it is the relative capacity of a microbe to cause damage in a host (¹⁷17. Wilson M, McNab R, Henderson B. Bacterial disease mechanisms: An introduction to cellular microbiology. Cambridge: Cambridge University Press, 2002.). Any metabolically active microbe living in the root canal has the potential to participate in the inflammation of periapical tissues. Individual species in the endodontic microbiota may be of low virulence, but their survival in the necrotic root canal and pathogenic properties are influenced by a combination of several factors. They include the ability to build biofilms, interact with other microorganisms in the biofilm and develop synergistically beneficial partnerships, the capability to interfere with and evade host defenses, the release of lipopolysaccharides and other microbial modulins, and the synthesis of enzymes that damage host tissues (⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.,¹⁰10. Nair PNR. Non-microbial etiology: Foreign body reaction maintaining post-treatment apical periodontitis. Endod Topics 2003;6:96-113.

11. Nair PNR. Non-microbial etiology: Periapical cysts sustain post-treatment apical periodontitis. Endod Topics 2003;6:114-134.-¹²12. Nair PNR, Sjögren U, Figdor D, Sundqvist G. Persistent periapical radiolucencies of root filled human teeth, failed endodontic treatments and periapical scars. Oral Surg Oral Med Oral Pathol 1999;87:617-627.,¹⁶16. Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249-281.,¹⁷17. Wilson M, McNab R, Henderson B. Bacterial disease mechanisms: An introduction to cellular microbiology. Cambridge: Cambridge University Press, 2002.).

The etiology of disease post-treatment in endodontics has been associated with microbial etiologic factors (intraradicular and extraradicular infection – bacteria, fungi); and nonmicrobial etiologic factors (endogenous – true cysts; exogenous – foreign-body reaction) (⁹9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.

10. Nair PNR. Non-microbial etiology: Foreign body reaction maintaining post-treatment apical periodontitis. Endod Topics 2003;6:96-113.

11. Nair PNR. Non-microbial etiology: Periapical cysts sustain post-treatment apical periodontitis. Endod Topics 2003;6:114-134.-¹²12. Nair PNR, Sjögren U, Figdor D, Sundqvist G. Persistent periapical radiolucencies of root filled human teeth, failed endodontic treatments and periapical scars. Oral Surg Oral Med Oral Pathol 1999;87:617-627.,¹⁶16. Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249-281.). According to Nair (⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.,¹⁰10. Nair PNR. Non-microbial etiology: Foreign body reaction maintaining post-treatment apical periodontitis. Endod Topics 2003;6:96-113.

11. Nair PNR. Non-microbial etiology: Periapical cysts sustain post-treatment apical periodontitis. Endod Topics 2003;6:114-134.-¹²12. Nair PNR, Sjögren U, Figdor D, Sundqvist G. Persistent periapical radiolucencies of root filled human teeth, failed endodontic treatments and periapical scars. Oral Surg Oral Med Oral Pathol 1999;87:617-627.,¹⁶16. Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249-281.), it is important to consider the extraradicular infections occuring by: (a) exacerbating AP lesions, (b) periapical actinomycosis, (c) association with pieces of infected root dentin displaced into the periapex during root canal instrumentation or cut off from the rest of the root by massive apical resorption and (d) infected periapical cysts, particularly in periapical pocket cysts with cavities open to the root canal.

Other etiologic agents should also be correlated as potential periapical aggressors. The periapical inflammation may occur due to a natural defense response against over-instrumentation, over-irrigation or overfilling (¹⁸18. Molven O. The frequency, technical standard and results of endodontic therapy. Bergen, Norway: University of Bergen (PhD Thesis), 1974.

19. Bergenholtz G, Lekholm U, Milthon R, Heden G, Ödesjö B, Engström B. Retreatment of endodontic fillings. Scand J Dent Res 1979;87:217–224.

20. Bergenholtz G, Lekholm U, Milthon R, Engström B. Influence of apical overinstrumentation and overfilling on re-treated root canals. J Endod 1979;5:310–314.

21. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide I: effect of overfilling and refilling. Oral Surg Oral Med Oral Pathol 1979;47:87–92.-²²22. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide II: effect of instrumentation beyond the apices. Oral Surg Oral Med Oral Pathol 1979;47:93–96.). The root canal preparation and obturation should be restricted to the main root canal if there is no evidence contrary to this therapeutic protocol.

Operational Strategies that May Interfere On Success

Apical Limit, Apical Enlargement

The quality of root canal preparation and filling and coronal sealing are essential factors to achieve high rates of success, even in infected root canals. This fact reinforces the concept of eliminating empty spaces that can harbor microorganisms (⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.,⁹9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.,²³23. Ørstavik D. Materials used for root canal obturation: technical, biological and clinical testing. Endod Topics 2005;12: 25-38.,²⁴24. Estrela C, Estrela CRA, Decurcio DA, Hollanda ACB, Silva JA. Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals. Int Endod J 2007;40:85–93.). The RCT excellency is associated with the disinfection process, which involves removing microorganisms from the root canal system by emptying, cleaning and enlarging/shaping, combined with the use of antibacterial therapies (⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.,⁹9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.,¹⁶16. Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249-281.,²³23. Ørstavik D. Materials used for root canal obturation: technical, biological and clinical testing. Endod Topics 2005;12: 25-38.,²⁵25. Estrela CRA, Estrela C, Reis C, Bammann LL, Pécora JD. Control of microorganisms in vitro by endodontic irrigants. Braz Dent J 2003;14:187-192.,²⁶26. Estrela C, Sydney GB, Figueiredo JAP, Estrela CRA. Antibacterial efficacy of intracanal medicaments on bacterial biofilm: a critical review. J Appl Oral Sci 2009;17:1-7.). Based on the need to control the microbiota of infected root canals, some aspects are necessary in a therapeutic protocol. Thus, the apical limit of instrumentation and obturation must be discussed, the determination of apical enlargement level (anatomical diameter) and the antibacterial efficacy of intracanal medicaments in root canal infections.

Several studies reported that root canal preparation and obturation short of the radiographic apex were associated with a better prognosis (¹⁸18. Molven O. The frequency, technical standard and results of endodontic therapy. Bergen, Norway: University of Bergen (PhD Thesis), 1974.

19. Bergenholtz G, Lekholm U, Milthon R, Heden G, Ödesjö B, Engström B. Retreatment of endodontic fillings. Scand J Dent Res 1979;87:217–224.

20. Bergenholtz G, Lekholm U, Milthon R, Engström B. Influence of apical overinstrumentation and overfilling on re-treated root canals. J Endod 1979;5:310–314.

21. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide I: effect of overfilling and refilling. Oral Surg Oral Med Oral Pathol 1979;47:87–92.-²²22. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide II: effect of instrumentation beyond the apices. Oral Surg Oral Med Oral Pathol 1979;47:93–96.). The clinical characterization of apical morphology is extremely complex. The root level of isthmuses and their frequency do not represent as standard (⁹9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.,²⁷27. Moura MS, Guedes OA, Alencar AHG, Azevedo B, Estrela C. Influence of length of root canal obturation on apical periodontitis detected by periapical radiography and cone beam computed tomography. J Endod 2009;35:805-809.). The apical constriction and the apical foramen are not reliable anatomic landmarks for the obturation length at the apical end, and their use to calculate obturation length may result in injury to apical and periapical tissues (²⁸28. Ponce EH, Fernández JAV. The cemento-dentino-canal junction, the apical foramen, and the apical constriction: evaluation by optical microscopy. J Endod 2003;29:214–219.). On the basis of biologic and clinical principles, instrumentation and obturation should not extend beyond the apical foramen (¹⁸18. Molven O. The frequency, technical standard and results of endodontic therapy. Bergen, Norway: University of Bergen (PhD Thesis), 1974.

19. Bergenholtz G, Lekholm U, Milthon R, Heden G, Ödesjö B, Engström B. Retreatment of endodontic fillings. Scand J Dent Res 1979;87:217–224.

20. Bergenholtz G, Lekholm U, Milthon R, Engström B. Influence of apical overinstrumentation and overfilling on re-treated root canals. J Endod 1979;5:310–314.

21. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide I: effect of overfilling and refilling. Oral Surg Oral Med Oral Pathol 1979;47:87–92.-²²22. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide II: effect of instrumentation beyond the apices. Oral Surg Oral Med Oral Pathol 1979;47:93–96.,²⁷27. Moura MS, Guedes OA, Alencar AHG, Azevedo B, Estrela C. Influence of length of root canal obturation on apical periodontitis detected by periapical radiography and cone beam computed tomography. J Endod 2009;35:805-809.

28. Ponce EH, Fernández JAV. The cemento-dentino-canal junction, the apical foramen, and the apical constriction: evaluation by optical microscopy. J Endod 2003;29:214–219.

29. Wu M-K, Wesselink P, Walton R. Apical terminus location of root canal treatment procedures. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:99–103.

30. Ricucci D. Apical limit of root canal instrumentation and obturation, part 1: literature review. Int Endod J 1998;31:384–393.

31. Ricucci D, Langeland K. Apical limit of root canal instrumentation and obturation, part 2: a histologic study. Int Endod J 1998;31:394–409.

32. Kojima K, Inamoto K, Nagamatsu K, et al. Success rate of endodontic treatment of teeth with vital and nonvital pulps: a meta-analysis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;97:95–99.-³³33. Schaeffer MA, White RR, Walton RE. Determining the optimal obturation length: a meta-analysis of literature. J Endod 2005;31:271–274.).

A frequent discussion in endodontic therapy, reported by Ricucci (³⁰30. Ricucci D. Apical limit of root canal instrumentation and obturation, part 1: literature review. Int Endod J 1998;31:384–393.) and Ricucci and Langeland (³¹31. Ricucci D, Langeland K. Apical limit of root canal instrumentation and obturation, part 2: a histologic study. Int Endod J 1998;31:394–409.) concerns the apical limit of instrumentation and obturation. The results of longitudinal studies, basic anatomical knowledge of the apical third of the root canal, and the histological pulp reaction to caries progression, demonstrated the presence of a vital apical pulp remnant, even in the presence of a periapical lesion. Wu et al. (²⁹29. Wu M-K, Wesselink P, Walton R. Apical terminus location of root canal treatment procedures. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:99–103.) reported that the biologic and clinical principles after vital pulpectomy that attained highest success rates were achieved when procedures ended 2–3 mm short of the radiographic apex. When there is pulp necrosis, bacteria and their by-products as well as infected dentin debris may remain in the most apical portion of the root canal, and these irritants jeopardize apical healing. In these cases, highest success rates were achieved when obturation ended at 0–2 mm short of the radiographic apex. When shorter than 2 mm from or beyond the radiographic apex, success rates for infected canals were approximately 20% lower than those found for root filling ending 0-2 mm short of the apex. Systematic reviews (³²32. Kojima K, Inamoto K, Nagamatsu K, et al. Success rate of endodontic treatment of teeth with vital and nonvital pulps: a meta-analysis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;97:95–99.,³³33. Schaeffer MA, White RR, Walton RE. Determining the optimal obturation length: a meta-analysis of literature. J Endod 2005;31:271–274.) also showed that higher success rates are achieved when obturation is short of the apex (root canal obturation 1-2 mm short of apex).

Thus, the filling material should remain confined to the root canal and in no way its presence beyond the apex is justified. It is appropriate to remind that many injuries seem AP, but it does not mean they really are.

The level of enlargement of the root canal and the action potential of disinfection process reflect the effectiveness of antimicrobial strategies. The estimate of the anatomic diameter of the root canal before enlargement should be considered (³⁴34. Wu MK, Roris A, Barkis D, Wesselink PR. Prevalence and extent of long oval shape of canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:739-743.,³⁵35. Pécora JD, Capelli A, Guerisoli DMZ, Spanó JCE, Estrela C. Influence of cervical preflaring on apical file size determination. Int Endod J 2005;38:430-435.). Many instruments do not touch all canal walls (³⁶36. Peters OA, Laib A, Göhring TN, Barbakow F. Changes in root canal geometry after preparation assessed by high-resolution computed tomography. J Endod 2001;27:1-6). Thus, root canal emptying and enlargement represent essential actions for antimicrobial control (³⁵35. Pécora JD, Capelli A, Guerisoli DMZ, Spanó JCE, Estrela C. Influence of cervical preflaring on apical file size determination. Int Endod J 2005;38:430-435.).

Sanitization Process

One of the challenges in RCT is to discover how to sanitize the isthmus areas that harbor microorganisms, which in turn prevents the action of the instruments on bacterial biofilm.

The antimicrobial efficacy of intracanal medicaments on bacterial biofilm is still not confirmed (²⁴24. Estrela C, Estrela CRA, Decurcio DA, Hollanda ACB, Silva JA. Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals. Int Endod J 2007;40:85–93.,²⁶26. Estrela C, Sydney GB, Figueiredo JAP, Estrela CRA. Antibacterial efficacy of intracanal medicaments on bacterial biofilm: a critical review. J Appl Oral Sci 2009;17:1-7.,³⁷37. Nair PNR, Henry S, Cano V, Vera J. Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after ‘one-visit’ endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:231-252.,³⁸38. Sedgley C, Buck G, Appelbe O. Prevalence of Enterococcus faecalis at multiple oral sites in endodontic patients using culture and PCR. J Endod 2006;32:104-109.). Nair et al. (³⁷37. Nair PNR, Henry S, Cano V, Vera J. Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after ‘one-visit’ endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:231-252.) reported the importance and necessity of stringent application of non-antibiotic chemomechanical measures in order to disrupt the biofilm and reduce the intraradicular microbial load to the lowest possible level to ensure the most favorable long-term prognosis for the treatment of infected root canals.

The selection of effective microbial control in infected root canals requires detailed knowledge of the microorganisms responsible for pulp and periapical pathology associated with understanding the action mechanism of the antimicrobial substances (³⁹39. Estrela C, Sydney GB, Bammann LL, Felippe-Jr O. Mechanism of action of calcium and hydroxyl ions of calcium hydroxide on tissue and bacteria. Braz Dent J 1995;6:85-90.,⁴⁰40. Estrela C, Estrela CRA, Barbin EL, Spanó JCE, Marchesan MA, Pécora JD. Mechanism of action of sodium hypochlorite. Braz Dent J 2002;13:113-117.). The success of infected RCT may be influenced by some clinical environments, as the planktonic suspension, presence of biofilm, time and type of infection, host response, and effective antibacterial therapeutic protocol.

Irrigant solutions are necessary during root canal preparation because they help to clean the root canal, lubricate the files, flush out debris, and have an antimicrobial and tissue dissolution effect, without damaging periapical tissues. The selection of an ideal irrigant depends on its action against the root canal microbiota and the biological effect on periapical tissue (²⁴24. Estrela C, Estrela CRA, Decurcio DA, Hollanda ACB, Silva JA. Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals. Int Endod J 2007;40:85–93.,²⁵25. Estrela CRA, Estrela C, Reis C, Bammann LL, Pécora JD. Control of microorganisms in vitro by endodontic irrigants. Braz Dent J 2003;14:187-192.,⁴⁰40. Estrela C, Estrela CRA, Barbin EL, Spanó JCE, Marchesan MA, Pécora JD. Mechanism of action of sodium hypochlorite. Braz Dent J 2002;13:113-117.). Several irrigating solutions have been considered in order to decrease endodontic infection and contribute to canal disinfection, including: halogenated compounds (sodium hypochlorite), chlorhexidine, detergents (anionic, cationic), chelating agents (EDTA, citric acid), MTAD, ozonated water, apple vinegar. However, up to now, sodium hypochlorite and chlorhexidine are the most often indicated antimicrobial agents for treatment protocols against endodontic and periodontal infections (²⁴24. Estrela C, Estrela CRA, Decurcio DA, Hollanda ACB, Silva JA. Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals. Int Endod J 2007;40:85–93.,²⁵25. Estrela CRA, Estrela C, Reis C, Bammann LL, Pécora JD. Control of microorganisms in vitro by endodontic irrigants. Braz Dent J 2003;14:187-192.,⁴⁰40. Estrela C, Estrela CRA, Barbin EL, Spanó JCE, Marchesan MA, Pécora JD. Mechanism of action of sodium hypochlorite. Braz Dent J 2002;13:113-117.).

The antimicrobial effect of sodium hypochlorite by direct contact with E. faecalis occurs after 2 min (²⁵25. Estrela CRA, Estrela C, Reis C, Bammann LL, Pécora JD. Control of microorganisms in vitro by endodontic irrigants. Braz Dent J 2003;14:187-192.). The positive culture of microorganisms following the application of the irrigating solutions (ozonated water, gaseous ozone, 2.5% sodium hypochlorite, 2% chlorhexidine) for 20 min confirmed their inability to sterilize an infected human root canal (²⁴24. Estrela C, Estrela CRA, Decurcio DA, Hollanda ACB, Silva JA. Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals. Int Endod J 2007;40:85–93.). Thus, when a medicament does not reach the target microorganism, its killing potential cannot be recognized. Therefore, it cannot be stated whether the microbial strains were resistant to one or other medication. In this case, it is likely that the microorganisms were able to survive, adapt and tolerate the critical ecological conditions.

In the same direction, the properties of calcium hydroxide stem from its dissociation into calcium and hydroxyl ions and the action of these ions on tissues and bacteria explains biological and antimicrobial properties of this substance (³⁹39. Estrela C, Sydney GB, Bammann LL, Felippe-Jr O. Mechanism of action of calcium and hydroxyl ions of calcium hydroxide on tissue and bacteria. Braz Dent J 1995;6:85-90.). Thus, it was shown that calcium hydroxide induces the deposition of a hard tissue bridge on pulpal and periodontal connective tissue (⁴¹41. Holland R. Histochemical response of amputed pulps to calcium hydroxide. Rev Bras Pesq Med Biol 1971;4:83-95.

42. Holland R, Souza V. Ability of a new calcium hydroxide root canal filling material to induce hard tissue formation. J Endod 1985;11:535-543.

43. Holland R, Otoboni-Filho JA, Souza V, Nery MJ, Bernabé PFE, Dezan-Jr E. A comparison of one versus two appointment endodontic therapy in dogs' teeth with apical periodontitis. J Endod 2003;29:121-125.-⁴⁴44. Holland R, Otoboni-Filho JA, Souza V, Nery MJ, Bernabé PFE, Dezan-Jr E. Tratamiento endodóntico em una o en dos visitas. Estudio histológico en dientes de perros con lesión periapical. Endodoncia 2003;21:20-27.). Its action on connective tissue (pulpal and periodontal tissues) revealed the ability to stimulate mineralization, from the significant involvement of alkaline phosphatase and fibronectin (³⁹39. Estrela C, Sydney GB, Bammann LL, Felippe-Jr O. Mechanism of action of calcium and hydroxyl ions of calcium hydroxide on tissue and bacteria. Braz Dent J 1995;6:85-90.

40. Estrela C, Estrela CRA, Barbin EL, Spanó JCE, Marchesan MA, Pécora JD. Mechanism of action of sodium hypochlorite. Braz Dent J 2002;13:113-117.

41. Holland R. Histochemical response of amputed pulps to calcium hydroxide. Rev Bras Pesq Med Biol 1971;4:83-95.

42. Holland R, Souza V. Ability of a new calcium hydroxide root canal filling material to induce hard tissue formation. J Endod 1985;11:535-543.

43. Holland R, Otoboni-Filho JA, Souza V, Nery MJ, Bernabé PFE, Dezan-Jr E. A comparison of one versus two appointment endodontic therapy in dogs' teeth with apical periodontitis. J Endod 2003;29:121-125.

44. Holland R, Otoboni-Filho JA, Souza V, Nery MJ, Bernabé PFE, Dezan-Jr E. Tratamiento endodóntico em una o en dos visitas. Estudio histológico en dientes de perros con lesión periapical. Endodoncia 2003;21:20-27.

45. Estrela C, Holland R. Calcium hydroxide: study based on scientific evidences. J Appl Oral Sci 2003;14:269-283.-⁴⁶46. Mizuno M, Banzai Y. Calcium ion release from calcium hydroxide stimulated fibronectin gene expression in dental pulp cells and the differentiation of dental pulp cells to mineralized tissue forming cells by fibronectin. Int Endod J 2008;41:933-938.).

There is a great release of hydroxyl ions from calcium hydroxide, which are able of altering the integrity of the bacterial cytoplasmic membrane through the toxic effects generated during the transfer of nutrients or by the destruction of the phospholipids of unsaturated fatty acids. The influence of pH alters the integrity of the cytoplasmic membrane by biochemical injury to organic components (proteins, phospholipids) and transport of nutrients. The maintenance of a high concentration of hydroxyl ions can change the enzymatic activity and provide its inactivation (³⁹39. Estrela C, Sydney GB, Bammann LL, Felippe-Jr O. Mechanism of action of calcium and hydroxyl ions of calcium hydroxide on tissue and bacteria. Braz Dent J 1995;6:85-90.). In addition, the healing process in teeth with AP after RCT in two appointments with the use of calcium hydroxide paste showed a better status of periapical tissue (with mineralized barrier)(⁴³43. Holland R, Otoboni-Filho JA, Souza V, Nery MJ, Bernabé PFE, Dezan-Jr E. A comparison of one versus two appointment endodontic therapy in dogs' teeth with apical periodontitis. J Endod 2003;29:121-125.-⁴⁴44. Holland R, Otoboni-Filho JA, Souza V, Nery MJ, Bernabé PFE, Dezan-Jr E. Tratamiento endodóntico em una o en dos visitas. Estudio histológico en dientes de perros con lesión periapical. Endodoncia 2003;21:20-27.).

The presence of biofilm in the root canal system is a challenge to the outcome of RCT (²⁶26. Estrela C, Sydney GB, Figueiredo JAP, Estrela CRA. Antibacterial efficacy of intracanal medicaments on bacterial biofilm: a critical review. J Appl Oral Sci 2009;17:1-7.,³⁷37. Nair PNR, Henry S, Cano V, Vera J. Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after ‘one-visit’ endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:231-252.). The active participation of mechanical action of endodontic instruments combined with antimicrobial strategies appears to be crucial for decreasing root canal infection.

Criteria for the RCT success

The estimation of the RCT prognosis must be related to criteria for understanding the success. This aspect implies in evaluating results based on longitudinal monitoring, which requires a standard. The RCT success criteria and its prevalence should be routinely reevaluated. Among the clinical and radiographic characteristics of the RCT failure there is often observed the presence of symptoms (pain) and/or the presence of a periapical radiolucent area.

AP is a consequence of root canal system infection, which can involve progressive stages of inflammation and changes of periapical bone structure, resulting in resorptions identified as radiolucencies in radiographs (¹²12. Nair PNR, Sjögren U, Figdor D, Sundqvist G. Persistent periapical radiolucencies of root filled human teeth, failed endodontic treatments and periapical scars. Oral Surg Oral Med Oral Pathol 1999;87:617-627.).

RCT failures may involve microbial and non-microbial factors, as discussed previously (⁹9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.

10. Nair PNR. Non-microbial etiology: Foreign body reaction maintaining post-treatment apical periodontitis. Endod Topics 2003;6:96-113.

11. Nair PNR. Non-microbial etiology: Periapical cysts sustain post-treatment apical periodontitis. Endod Topics 2003;6:114-134.-¹²12. Nair PNR, Sjögren U, Figdor D, Sundqvist G. Persistent periapical radiolucencies of root filled human teeth, failed endodontic treatments and periapical scars. Oral Surg Oral Med Oral Pathol 1999;87:617-627.,¹⁶16. Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249-281.). A high rate of failure is associated with endodontically treated teeth associated with AP, overfilling, and teeth that were not properly restored after RCT (¹⁸18. Molven O. The frequency, technical standard and results of endodontic therapy. Bergen, Norway: University of Bergen (PhD Thesis), 1974.

19. Bergenholtz G, Lekholm U, Milthon R, Heden G, Ödesjö B, Engström B. Retreatment of endodontic fillings. Scand J Dent Res 1979;87:217–224.

20. Bergenholtz G, Lekholm U, Milthon R, Engström B. Influence of apical overinstrumentation and overfilling on re-treated root canals. J Endod 1979;5:310–314.

21. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide I: effect of overfilling and refilling. Oral Surg Oral Med Oral Pathol 1979;47:87–92.-²²22. Holland R, Nery MJ, Mello W, Souza V, Bernabé PFE, Otoboni-Filho JA. Root canal treatment with calcium hydroxide II: effect of instrumentation beyond the apices. Oral Surg Oral Med Oral Pathol 1979;47:93–96.,²⁷27. Moura MS, Guedes OA, Alencar AHG, Azevedo B, Estrela C. Influence of length of root canal obturation on apical periodontitis detected by periapical radiography and cone beam computed tomography. J Endod 2009;35:805-809.,⁴⁷47. Sundqvist G, Figdor D, Persson S, Sjögren U. Microbiologic analysis of teeth with failed endodontic treatment and the outcome of conservative re-treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998; 85:86–93.

48. Ray HA, Trope M. Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. Int Endod J 1995;28:12-18.-⁴⁹49. Tronstad L, Asbjornsen K, Doving L, Pedersen I, Eriksen HM. Influence of coronal restorations on the periapical health of endodontically treated teeth. Endod Dent Traumatol 2000;16:218-221.).

Thus, utmost care must be taken to establish criteria to define success. On this account, the life of a tooth endodontic treatment may be rely on the time and the age of the individual. In a prospective analysis, an endodontically treated tooth is expected to remain throughout the individual's life. The analysis of the RCT success involves reversion of the inflammatory/infectious process, no symptoms, well restored, in function and no evidence of periapical radiolucency. It is important to recognize that along people's life, some diseases may develop and impact their health. Incidentally, an infection or re-infection may arise some time after RCT.

To characterize the outcomes of endodontically treated teeth with vital pulp (healthy or inflamed pulp), infected pulp, AP and periapical abscess, must be considered the time since RCT conclusion and the definite restoration. The previous status of pulp and periapical tissue may aid in the interpretation of actual clinical conditions.

Strindberg (⁵⁰50. Strindberg LZ. The dependence of the results of pulp therapy on certain factors. An analytical study based on radiographic and clinical followup examinations. Acta Odontol Scand 1956;14 (suppl 21):1-174.) described important clinical and radiographic factors associated with RCT success and failure. A considerable number of clinical studies have discussed the causes of failure of endodontically treated teeth and prospects for prognosis in retreatment (⁵⁰50. Strindberg LZ. The dependence of the results of pulp therapy on certain factors. An analytical study based on radiographic and clinical followup examinations. Acta Odontol Scand 1956;14 (suppl 21):1-174.

51. Grossman LI, Shephard LI, Pearson LA. Roentgenologic and clinical evaluation of endodontically treated teeth. Oral Surg Oral Med Oral Pathol 1964;17:368-374.

52. Bender IB, Seltzer S, Soltanoff W. Endodontic success – a reappraisal of criteria. Oral Surg Oral Med Oral Pathol 1966;22:780-801.

53. Seltzer S, Bender IB, Smith J, Freedman I, Nazimor H. Endodontic failures – an analysis based on clinical, roentgenographic and histologic findings. Oral Surg Oral Med Oral Pathol 1967;23:500-530.

54. Holland R, Valle GF, Taintor JF, Ingle JI. Influence of bony resorption on endodontic treatment. Oral Surg Oral Med Oral Pathol 1983;55:191-203.

55. Sjögren U, Hagglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990;16:498-504.

56. Sjögren U, Figdor D, Persson S, Sundqvist G. Influence of infection at the time of root filling on the outcome of endodontic treatment of teeth with apical periodontitis. Int Endod J 1997;30:297-306.

57. Ørstavik D. Time-course and risk analyses of the development and healing of chronic apical periodontitis in man. Int Endod J 1996;29:150-155.

58. Friedman S, Stabholz A. Endodontic retreatment – case selection and technique. Part 1: Criteria for case selection. J Endod 1986;12:28-33.

59. Stabholz A, Friedman S. Endodontic retreatment: case selection and technique, part 2. J Endod 1988;14:607–614.

60. Friedman S, Stabholz A, Tamae A. Endodontic retreatment – case selection and technique. Part 3. Retreatment techniques. J Endod 1990;16:543-549.

61. Kirkevang LL, Orstavik D, Horsted-Bindslev P, Wenzel A. Periapical status and quality of root fillings and coronal restorations in a Danish population. Int Endod J 2000;33:509-515.

62. Mollander A, Reit C, Dahlén G, Kvist T. Microbiological status of root-filled teeth with apical periodontitis. Int Endod J 1998;31:1-7.

63. Wu M-K, Dummer PMH, Wesselink PR. Consequences of and strategies to deal with residual post-treatment root canal infection. Int Endod J 2006;39:343–356.

64. Reit C. Decision strategies in endodontics: on the design of a recall program. Endod Dent Traumatol 1987;3:233-239.

65. Reit C. The influence of observer calibration on radiographic periapical diagnosis. Int Endod J 1987;20:75-81.

66. Reit C, Gröndahl HC. Endodontic decision – making under uncertainty: a decision analytic approach to management of periapical lesions in endodontically treated teeth. Endod Dent Traumatol 1987;3:15-20.

67. Reit C, Hollender L. Evaluation of endodontic therapy and the influence of observer variation. Scand J Dent Res 1983;91:205-212.

68. Brynolf I. A histologic and roentgenological study of the periapical region of human upper incisor. Odontol Rev 1967;18:1-176.

69. Ørstavik D, Kerekes K, Eriksen HM. The periapical index: a scoring system for radiographic assessment of apical periodontitis. Endod Dent Traumatol 1986;2:20-34.

70. Chugal NM, Clive JM, Spångberg LSW. A prognostic model for assessment of the outcome of endodontic treatment: Effect of biologic and diagnostic variables. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:342-352.

71. Chugal NM, Clive JM, Spångberg LSW. Endodontic treatment outcome: effect of the permanent restoration. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:576-582.

72. Eriksen HM, Kirkevang LL, Petersson K. Endodontic epidemiology and treatment outcome: general considerations. Endod Topics 2002;2:1-9.

73. Hollanda ACB, Alencar AHG, Estrela CRA, Bueno MR, Estrela C. Prevalence of endodontically treated teeth in a Brazilian adult population. Braz Dent J 2008;19:313-317.

74. Bender IB. Factors influencing the radiographic appearance of bony lesions. J Endod 1982,8:161-170.-⁷⁵75. Laux M, Abbott PV, Pajarola G, Nair PNR. Apical inflammatory root resorption: a correlative radiographic and histological assessment. Int Endod J 2000;33:483–493.). The correlation of RCT failure with infected root canal was evident in several conditions (¹1. Estrela C, Leles CR, Hollanda ACB, Moura MS, Pécora JD. Prevalence and risk factors of apical periodontitis in endodontically treated teeth in a selected population of Brazilian adults. Braz Dent J 2008;19:34-39.,³3. Estrela C, Guedes AO, Silva JA, Leles CR, Estrela CRA, Pécora JD. Diagnostic and clinical factors associated with pulpal and periapical pain. Braz Dent J 2011;22:306-311.,⁸8. Nair PNR. Biology and pathology of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 285-347.

9. Estrela C, Bueno MR. Epidemiology and therapy of apical periodontitis. In: Estrela C. Endodontic Science. 2 ed. São Paulo-SP, Brasil: Artes Médicas, 2009. p. 349-420.

10. Nair PNR. Non-microbial etiology: Foreign body reaction maintaining post-treatment apical periodontitis. Endod Topics 2003;6:96-113.

11. Nair PNR. Non-microbial etiology: Periapical cysts sustain post-treatment apical periodontitis. Endod Topics 2003;6:114-134.

12. Nair PNR, Sjögren U, Figdor D, Sundqvist G. Persistent periapical radiolucencies of root filled human teeth, failed endodontic treatments and periapical scars. Oral Surg Oral Med Oral Pathol 1999;87:617-627.

13. Sundqvist G, Figdor D. Life as an endodontic pathogen: Ecological differences between the untreated and root-filled root canals. Endod Topics 2003;6:3-28.

14. Gomes BPFA, Drucker DB, Lilley JD. Clinical significance of dental root canal microflora. J Endod 1996;24:47-55.

15. Siqueira-Jr JF. Endodontic infections: concepts, paradigms, and perspectives. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:281-293.

16. Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249-281.

17. Wilson M, McNab R, Henderson B. Bacterial disease mechanisms: An introduction to cellular microbiology. Cambridge: Cambridge University Press, 2002.

18. Molven O. The frequency, technical standard and results of endodontic therapy. Bergen, Norway: University of Bergen (PhD Thesis), 1974.

19. Bergenholtz G, Lekholm U, Milthon R, Heden G, Ödesjö B, Engström B. Retreatment of endodontic fillings. Scand J Dent Res 1979;87:217–224.-²⁰20. Bergenholtz G, Lekholm U, Milthon R, Engström B. Influence of apical overinstrumentation and overfilling on re-treated root canals. J Endod 1979;5:310–314.,²⁴24. Estrela C, Estrela CRA, Decurcio DA, Hollanda ACB, Silva JA. Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals. Int Endod J 2007;40:85–93.

25. Estrela CRA, Estrela C, Reis C, Bammann LL, Pécora JD. Control of microorganisms in vitro by endodontic irrigants. Braz Dent J 2003;14:187-192.

26. Estrela C, Sydney GB, Figueiredo JAP, Estrela CRA. Antibacterial efficacy of intracanal medicaments on bacterial biofilm: a critical review. J Appl Oral Sci 2009;17:1-7.-²⁷27. Moura MS, Guedes OA, Alencar AHG, Azevedo B, Estrela C. Influence of length of root canal obturation on apical periodontitis detected by periapical radiography and cone beam computed tomography. J Endod 2009;35:805-809.,³⁵35. Pécora JD, Capelli A, Guerisoli DMZ, Spanó JCE, Estrela C. Influence of cervical preflaring on apical file size determination. Int Endod J 2005;38:430-435.

36. Peters OA, Laib A, Göhring TN, Barbakow F. Changes in root canal geometry after preparation assessed by high-resolution computed tomography. J Endod 2001;27:1-6

37. Nair PNR, Henry S, Cano V, Vera J. Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after ‘one-visit’ endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:231-252.

38. Sedgley C, Buck G, Appelbe O. Prevalence of Enterococcus faecalis at multiple oral sites in endodontic patients using culture and PCR. J Endod 2006;32:104-109.

39. Estrela C, Sydney GB, Bammann LL, Felippe-Jr O. Mechanism of action of calcium and hydroxyl ions of calcium hydroxide on tissue and bacteria. Braz Dent J 1995;6:85-90.-⁴⁰40. Estrela C, Estrela CRA, Barbin EL, Spanó JCE, Marchesan MA, Pécora JD. Mechanism of action of sodium hypochlorite. Braz Dent J 2002;13:113-117.,⁴⁷47. Sundqvist G, Figdor D, Persson S, Sjögren U. Microbiologic analysis of teeth with failed endodontic treatment and the outcome of conservative re-treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998; 85:86–93.

48. Ray HA, Trope M. Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. Int Endod J 1995;28:12-18.

49. Tronstad L, Asbjornsen K, Doving L, Pedersen I, Eriksen HM. Influence of coronal restorations on the periapical health of endodontically treated teeth. Endod Dent Traumatol 2000;16:218-221.

50. Strindberg LZ. The dependence of the results of pulp therapy on certain factors. An analytical study based on radiographic and clinical followup examinations. Acta Odontol Scand 1956;14 (suppl 21):1-174.

51. Grossman LI, Shephard LI, Pearson LA. Roentgenologic and clinical evaluation of endodontically treated teeth. Oral Surg Oral Med Oral Pathol 1964;17:368-374.

52. Bender IB, Seltzer S, Soltanoff W. Endodontic success – a reappraisal of criteria. Oral Surg Oral Med Oral Pathol 1966;22:780-801.

53. Seltzer S, Bender IB, Smith J, Freedman I, Nazimor H. Endodontic failures – an analysis based on clinical, roentgenographic and histologic findings. Oral Surg Oral Med Oral Pathol 1967;23:500-530.

54. Holland R, Valle GF, Taintor JF, Ingle JI. Influence of bony resorption on endodontic treatment. Oral Surg Oral Med Oral Pathol 1983;55:191-203.

55. Sjögren U, Hagglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990;16:498-504.

56. Sjögren U, Figdor D, Persson S, Sundqvist G. Influence of infection at the time of root filling on the outcome of endodontic treatment of teeth with apical periodontitis. Int Endod J 1997;30:297-306.

57. Ørstavik D. Time-course and risk analyses of the development and healing of chronic apical periodontitis in man. Int Endod J 1996;29:150-155.

58. Friedman S, Stabholz A. Endodontic retreatment – case selection and technique. Part 1: Criteria for case selection. J Endod 1986;12:28-33.

59. Stabholz A, Friedman S. Endodontic retreatment: case selection and technique, part 2. J Endod 1988;14:607–614.

60. Friedman S, Stabholz A, Tamae A. Endodontic retreatment – case selection and technique. Part 3. Retreatment techniques. J Endod 1990;16:543-549.

61. Kirkevang LL, Orstavik D, Horsted-Bindslev P, Wenzel A. Periapical status and quality of root fillings and coronal restorations in a Danish population. Int Endod J 2000;33:509-515.

62. Mollander A, Reit C, Dahlén G, Kvist T. Microbiological status of root-filled teeth with apical periodontitis. Int Endod J 1998;31:1-7.

63. Wu M-K, Dummer PMH, Wesselink PR. Consequences of and strategies to deal with residual post-treatment root canal infection. Int Endod J 2006;39:343–356.

64. Reit C. Decision strategies in endodontics: on the design of a recall program. Endod Dent Traumatol 1987;3:233-239.

65. Reit C. The influence of observer calibration on radiographic periapical diagnosis. Int Endod J 1987;20:75-81.

66. Reit C, Gröndahl HC. Endodontic decision – making under uncertainty: a decision analytic approach to management of periapical lesions in endodontically treated teeth. Endod Dent Traumatol 1987;3:15-20.

67. Reit C, Hollender L. Evaluation of endodontic therapy and the influence of observer variation. Scand J Dent Res 1983;91:205-212.

68. Brynolf I. A histologic and roentgenological study of the periapical region of human upper incisor. Odontol Rev 1967;18:1-176.

69. Ørstavik D, Kerekes K, Eriksen HM. The periapical index: a scoring system for radiographic assessment of apical periodontitis. Endod Dent Traumatol 1986;2:20-34.

70. Chugal NM, Clive JM, Spångberg LSW. A prognostic model for assessment of the outcome of endodontic treatment: Effect of biologic and diagnostic variables. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:342-352.

71. Chugal NM, Clive JM, Spångberg LSW. Endodontic treatment outcome: effect of the permanent restoration. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:576-582.

72. Eriksen HM, Kirkevang LL, Petersson K. Endodontic epidemiology and treatment outcome: general considerations. Endod Topics 2002;2:1-9.

73. Hollanda ACB, Alencar AHG, Estrela CRA, Bueno MR, Estrela C. Prevalence of endodontically treated teeth in a Brazilian adult population. Braz Dent J 2008;19:313-317.

74. Bender IB. Factors influencing the radiographic appearance of bony lesions. J Endod 1982,8:161-170.-⁷⁵75. Laux M, Abbott PV, Pajarola G, Nair PNR. Apical inflammatory root resorption: a correlative radiographic and histological assessment. Int Endod J 2000;33:483–493.).

Traditionally, three aspects are associated in the analysis of RCT success – the clinical, radiographic and microscopic characteristics. In the clinical context, two of these aspects normally guide the decision-making process: clinical history (symptoms – absence; sensitivity, discomfort and/or pain; physical exam – normality; edema, fistula, excessive mobility) and interpretation of images (signs of periapical health; periapical bone radiolucency).

Clinical and radiographic aspects conventionally associated with the RCT failure include pain, AP and/or sinus tract, swelling. The cases of doubt on the success or failure involve a transition phase and definition of criteria may be imposed by the limitations of the used clinical or imaging exams. Clinical success and clinical silence are different aspects to be analyzed. Clinical failure may present or not a symptomatic (pain) condition.

In this sense, AP cannot be correctly identified by periapical radiography only. The experienced professional has many resources to identify the agent responsible for the failure. Notwithstanding the dentist's skills, the diagnosis of odontogenic pain should always follow an accurate protocol, since the pain felt by the patient may not have a direct association with a well or bad endodontically treated tooth.

Various factors may affect tooth survival, such as dental caries, periodontal disease and RCT. The prevalence of endodontically treated teeth associated or not with AP has been examined in several populations (¹1. Estrela C, Leles CR, Hollanda ACB, Moura MS, Pécora JD. Prevalence and risk factors of apical periodontitis in endodontically treated teeth in a selected population of Brazilian adults. Braz Dent J 2008;19:34-39.,⁴⁸48. Ray HA, Trope M. Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. Int Endod J 1995;28:12-18.,⁴⁹49. Tronstad L, Asbjornsen K, Doving L, Pedersen I, Eriksen HM. Influence of coronal restorations on the periapical health of endodontically treated teeth. Endod Dent Traumatol 2000;16:218-221.,⁶¹61. Kirkevang LL, Orstavik D, Horsted-Bindslev P, Wenzel A. Periapical status and quality of root fillings and coronal restorations in a Danish population. Int Endod J 2000;33:509-515.,⁷²72. Eriksen HM, Kirkevang LL, Petersson K. Endodontic epidemiology and treatment outcome: general considerations. Endod Topics 2002;2:1-9.,⁷³73. Hollanda ACB, Alencar AHG, Estrela CRA, Bueno MR, Estrela C. Prevalence of endodontically treated teeth in a Brazilian adult population. Braz Dent J 2008;19:313-317.).

Regarding the prevalence of endodontically treated teeth in Brazilian adults, a previous study showed that in a sample of 29,467 teeth, only 6,313 (21.4%) received treatment (⁷³73. Hollanda ACB, Alencar AHG, Estrela CRA, Bueno MR, Estrela C. Prevalence of endodontically treated teeth in a Brazilian adult population. Braz Dent J 2008;19:313-317.). RCT was most frequent in maxillary premolars and molars, whereas mandibular incisors showed the lowest prevalence. Most endodontically treated teeth were found in people aged 46 to 60 years (47.6%) and the prevalence increased with age in this range. Females (61.9%) showed a higher prevalence of teeth with root fillings than males.

A total of 1,372 periapical radiographs of endodontically treated teeth by postgraduate students were evaluated (¹1. Estrela C, Leles CR, Hollanda ACB, Moura MS, Pécora JD. Prevalence and risk factors of apical periodontitis in endodontically treated teeth in a selected population of Brazilian adults. Braz Dent J 2008;19:34-39.). AP prevalence was significantly higher in teeth with poor endodontic treatment (66.3%) than in teeth with adequate root canal filling (16.5%). Prevalence of AP was also higher in teeth with poor coronal restoration (52.1%) than in teeth with adequate coronal restoration (30.1%). Based on periapical radiographs, the prevalence of AP was low when associated with a high technical quality of RCT.

In health sciences, such as endodontics, various advances were applied to clinical practice. The therapeutic assessment of dental treatment by computed tomography characterizes a sensible advance of information in health (⁷⁶76. Hounsfield GN. Computerized transverse axial scanning (tomography). I. Description of system. Br J Radiol 1973;46:1016-1022.,⁷⁷77. Ambrose J. Computerized transverse axial scanning (tomography). II. Clinical application. Br J Radiol 1973;46:1023-1047.). This contribution may be applied to planning, diagnosis, therapeutic process and prognosis of several diseases. The continuous advance of technology enabled the development of cone beam computed tomography (CBCT) (⁷⁸78. Arai Y, Tammisalo E, Iwai K, Hashimoto K, Shinoda K. Development of a compact computed tomographic apparatus for dental use. DentMaxillofac Radiol 1999;28:245–248.,⁷⁹79. Mozzo P, Procacci C, Taccoci A, Martini PT, Andreis IA. A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results. Eur Radiol 1998;8:1558-1564.), which has widen numerous perspectives for application in different research areas and clinical dentistry (⁸⁰80. Cotton TP, Geisler TM, Holden DT, Schwartz SA, Schindler WG. Endodontic applications of cone beam volumetric tomography. J Endod 2007;33:1121–1132.

81. Patel S, Dawood A, Pitt Ford T, Whaites E. The potential applications of cone beam computed tomography in the management of endodontic problems. Int Endod J 2007;40:818-813.

82. Estrela C, Bueno MR, Leles CR, Azevedo B, Azevedo JR. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod 2008;34:273-279.

83. Estrela C, Bueno MR, Azevedo B, Azevedo JR, Pécora JD. A new periapical index based on cone beam computed tomography. J Endod 2008;34:1325-1331.

84. Bueno MR, Estrela C, Figueiredo JAP, Azevedo BC. Map-reading strategy to diagnose root perforations near metallic intracanal posts by using cone beam computed tomography. J Endod 2011;37:85-90.

85. Wu M-K, Shemesh H, Wesselink PR. Limitations of previously published systematic reviews evaluating the outcome of endodontic treatment. Int Endod J 2009;42:656–66.

86. Alencar AHG, Dummer PMH, Oliveira HCM, Pécora JD, Estrela C. Procedural errors during root canal preparation using rotary NiTi instruments detected by periapical radiography and cone beam computed tomography. Braz Dent J 2010;21:543-549.

87. Alves RAA, Souza JB, Alencar AHG, Pécora JD, Estrela C. Detection of procedural errors with stainless steel and NiTi instruments by undergraduate students using conventional radiograph and cone beam computed tomography. Iran Endod J 2013;8:161-165.

88. Silva JA, Alencar AHG, Rocha SS, Lopes LG, Estrela C. Three-dimensional image contribution for evaluation of operative procedural errors in endodontic therapy and dental implants. Braz Dent J 2012:23:127-134.-⁸⁹89. Estrela C, Valladares Neto J, Bueno MR, Guedes OA, Porto OCL, Pécora JD. Linear measurements of human permanent dental development stages using Cone-Beam Computed Tomography: a preliminary study. Dent Press J Orthod 2010;15:44-78.). Imaging resources have been routinely used before, during and after dental treatment. Conventional radiographic images provide a two-dimensional rendition of a three-dimensional structure, which may lead to interpretation errors. Periapical lesions of endodontic origin may be present but not visible on conventional 2D radiographs (⁸⁰80. Cotton TP, Geisler TM, Holden DT, Schwartz SA, Schindler WG. Endodontic applications of cone beam volumetric tomography. J Endod 2007;33:1121–1132.

81. Patel S, Dawood A, Pitt Ford T, Whaites E. The potential applications of cone beam computed tomography in the management of endodontic problems. Int Endod J 2007;40:818-813.

82. Estrela C, Bueno MR, Leles CR, Azevedo B, Azevedo JR. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod 2008;34:273-279.

83. Estrela C, Bueno MR, Azevedo B, Azevedo JR, Pécora JD. A new periapical index based on cone beam computed tomography. J Endod 2008;34:1325-1331.-⁸⁴84. Bueno MR, Estrela C, Figueiredo JAP, Azevedo BC. Map-reading strategy to diagnose root perforations near metallic intracanal posts by using cone beam computed tomography. J Endod 2011;37:85-90.).

The accuracy of diagnosis is a critical factor for the success. The correct management of CBCT images may reveal abnormalities unable to be detected in periapical radiography and may enhance a more predictable planning and treatment (⁸⁰80. Cotton TP, Geisler TM, Holden DT, Schwartz SA, Schindler WG. Endodontic applications of cone beam volumetric tomography. J Endod 2007;33:1121–1132.

81. Patel S, Dawood A, Pitt Ford T, Whaites E. The potential applications of cone beam computed tomography in the management of endodontic problems. Int Endod J 2007;40:818-813.

82. Estrela C, Bueno MR, Leles CR, Azevedo B, Azevedo JR. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod 2008;34:273-279.

83. Estrela C, Bueno MR, Azevedo B, Azevedo JR, Pécora JD. A new periapical index based on cone beam computed tomography. J Endod 2008;34:1325-1331.-⁸⁴84. Bueno MR, Estrela C, Figueiredo JAP, Azevedo BC. Map-reading strategy to diagnose root perforations near metallic intracanal posts by using cone beam computed tomography. J Endod 2011;37:85-90.). The possibility of a map-reading approach with CBCT images reduces the problems related to difficult evaluation conditions that require special care during diagnosis (⁸⁴84. Bueno MR, Estrela C, Figueiredo JAP, Azevedo BC. Map-reading strategy to diagnose root perforations near metallic intracanal posts by using cone beam computed tomography. J Endod 2011;37:85-90.).

Estrela et al. (⁸²82. Estrela C, Bueno MR, Leles CR, Azevedo B, Azevedo JR. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod 2008;34:273-279.) evaluated the accuracy of CBCT compared with periapical and panoramic radiography in the identification of AP. In view of the limitations of periapical radiography to visualize AP, a review of epidemiologic studies should be undertaken considering the quality of periapical aspects provided by CBCT images. It will certainly reduce the influence of radiographic interpretation, with less possibility for false-negative diagnoses. AP prevalence in endodontically treated teeth, when comparing the panoramic and periapical radiographs and CBCT images, was 17.6%, 35.3% and 63.3%, respectively. A considerable discrepancy can be observed among the imaging methods used to identify AP. AP was correctly identified in 54.5% of the cases with periapical radiographs and in 27.8% of the cases with panoramic radiographs. Minor changes in sensitivity were found for different teeth groups, except for incisors in panoramic radiographs. ROC analysis suggests that AP is correctly identified with conventional methods in an advanced stage. CBCT was proved an accurate diagnostic method to identify AP. Wu et al. (⁸⁵85. Wu M-K, Shemesh H, Wesselink PR. Limitations of previously published systematic reviews evaluating the outcome of endodontic treatment. Int Endod J 2009;42:656–66.) discussed the limitations of previously published systematic reviews assessing the RCT outcomes. A high percentage of cases confirmed as healthy by radiographs revealed AP on CBCT and by histology. In teeth where the small size of the existing radiolucency was diagnosed by radiographs and considered to represent periapical healing, enlargement of the lesion was frequently confirmed by CBCT. In clinical studies, two additional factors may have further contributed to the overestimation of successful outcomes after root canal treatment: (i) extractions and re-treatments were rarely recorded as failures and (ii) the recall rate was often lower than 50%. The outcomes of root canal treatment should be re-evaluated in long-term longitudinal studies using CBCT and stricter evaluation criteria.

Characteristics of the clinical and imaging outcomes from RCT include: success (clinical aspects - absence of pain; tooth with definitive restoration and in masticatory function; imaging aspects - absence of periapical radiolucency); failure (clinical aspects - presence of pain, discomfort; tooth with temporary or definitive restoration; presence of swelling; sinus tract; imaging aspects - presence of periapical radiolucency); doubt (intermediate clinical situations– in these cases may or not present a history involving pain or discomfort, associated with inconclusive image of AP regression).

In case of doubt, it is essential to discuss the clinical case with a more experienced professional, as in some cases it is not easy to determine the differential diagnosis of diseases of non-endodontic and endodontic origin. Various radiolucent images may be associated with the apex, without being diseases of microbial origin and could be misinterpreted as AP (⁵5. Bueno MR, Carvalhosa AAC, Castro PHS, Pereira KC, Borges FT, Estrela C. Mesenchymal chondrosarcoma mimicking apical periodontitis. J Endod 2008;34:1415–1419.

6. Faitaroni LA, Bueno MR, Carvalhosa AA, Ale KAB, Estrela C. Ameloblastoma suggesting large apical periodontitis. J Endod 2008;34:216-219.-⁷7. Morais AL, Mendonça EF, de Alencar AHG, Estrela C. Intraosseous lipoma in the periapical region of a maxillary third molar. J Endod 2011;37:554-557.). The time to start the treatment is also a key factor to determine success or failure. The possibility of map-reading in CBCT images minimizes several problems related to complex diagnosis, particularly in dubious cases. Bueno et al. (⁸⁴84. Bueno MR, Estrela C, Figueiredo JAP, Azevedo BC. Map-reading strategy to diagnose root perforations near metallic intracanal posts by using cone beam computed tomography. J Endod 2011;37:85-90.) suggested a map-reading strategy to diagnose root perforations near metallic intracanal posts by using CBCT. A strategy to minimize metallic artifact in root perforation associated with intracanal post is to obtain sequential axial slices of each root, with an image navigation protocol from coronal to apical (or from apical to coronal), with 0.2 mm/0.2 mm axial slices. This map reading provides valuable information showing dynamic visualization toward the point of communication between the root canals and the periodontal space, associated with radiolucent areas, suggesting root perforation.

Operative procedural errors (OPE) may occur and they represent risk factors able to compromise a tooth (⁸⁶86. Alencar AHG, Dummer PMH, Oliveira HCM, Pécora JD, Estrela C. Procedural errors during root canal preparation using rotary NiTi instruments detected by periapical radiography and cone beam computed tomography. Braz Dent J 2010;21:543-549.,⁸⁷87. Alves RAA, Souza JB, Alencar AHG, Pécora JD, Estrela C. Detection of procedural errors with stainless steel and NiTi instruments by undergraduate students using conventional radiograph and cone beam computed tomography. Iran Endod J 2013;8:161-165.). Errors characterize disability, non-observance of therapeutic protocol and low level of knowledge involving the endodontic principles. Deficient attendance may be responsible for severe consequences and sequels, which impairs the prognosis, and may result in serious judicial questions (⁸⁹89. Estrela C, Valladares Neto J, Bueno MR, Guedes OA, Porto OCL, Pécora JD. Linear measurements of human permanent dental development stages using Cone-Beam Computed Tomography: a preliminary study. Dent Press J Orthod 2010;15:44-78.). Silva et al. (⁸⁹89. Estrela C, Valladares Neto J, Bueno MR, Guedes OA, Porto OCL, Pécora JD. Linear measurements of human permanent dental development stages using Cone-Beam Computed Tomography: a preliminary study. Dent Press J Orthod 2010;15:44-78.) detected the OPE in endodontically treated teeth and dental implants, using CBCT images. In endodontically treated teeth, OPE included underfilling, overfilling, and root perforation; OPE in dental implants were thread exposures, contact with anatomical structures, and contact with adjacent teeth. Underfilling, overfilling, and root perforations were detected in 33.5%, 8% and 4.5% of the teeth, respectively. Dental implants with thread exposures, contact with important anatomical structures and contact with adjacent teeth were seen in 37.5%, 13% and 6.5% of the cases, respectively. OPE were detected in endodontically treated teeth and dental implants, and underfilling and thread exposures were the most frequent occurrences, respectively.

The extension of treatment in a tooth with indication for extraction can be a dental implant. The problem of replacing a biological structure by biocompatible materials requires care and precise indication. Information about criteria and rates of success in endodontically treated teeth and dental implants are of utmost importance.

Torabinejad et al. (⁹⁰90. Torabinejad M, Bahjri K. Essential elements of evidenced-based Endodontics: steps involved in conducting clinical research. J Endod 2005;31:563-569.) analyzed by a systematic review clinical articles addressing success and failure of nonsurgical RCT, and assigned levels of evidence to these studies. It appears that few high-level studies have been published in the past four decades related to the success and failure of nonsurgical root canal therapy. The data generated by this search can be used in future studies to specifically answer questions and test hypotheses relevant to the outcome of nonsurgical root canal treatment.

The current moment of endodontic science is promising in view of all the knowledge acquired over the last few years (⁹¹91. Estrela C, Alencar AHG, Kitten GT, Vencio EF, Gava E. Mesenchymal stem cells in the dental tissues: perspectives for tissue regeneration. Braz Dent J 2011; 22:91-98.). New technologies such as CBCT influenced the quality of diagnosis, planning, therapy and longitudinal control. A wide array of endodontic instruments for safer root canal preparation was introduced in endodontics. Some of these advances contributed to the revision of concepts, and to determine adjustments to the treatment protocol. Estrela et al. (⁸²82. Estrela C, Bueno MR, Leles CR, Azevedo B, Azevedo JR. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod 2008;34:273-279.) suggested a review of epidemiologic studies in view of the limits of periapical radiography and the accuracy to visualize AP by CBCT imaging. Wu et al. (⁸⁵85. Wu M-K, Shemesh H, Wesselink PR. Limitations of previously published systematic reviews evaluating the outcome of endodontic treatment. Int Endod J 2009;42:656–66.) in function of the limitations of previous systematic reviews evaluating the RCT outcomes, considered the need of re-evaluating the outcome in longitudinal studies using CBCT with rigorous evaluation criteria. One concern discussed at meetings in endodontics and in several recent studies (⁸⁰80. Cotton TP, Geisler TM, Holden DT, Schwartz SA, Schindler WG. Endodontic applications of cone beam volumetric tomography. J Endod 2007;33:1121–1132.

81. Patel S, Dawood A, Pitt Ford T, Whaites E. The potential applications of cone beam computed tomography in the management of endodontic problems. Int Endod J 2007;40:818-813.

82. Estrela C, Bueno MR, Leles CR, Azevedo B, Azevedo JR. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod 2008;34:273-279.

83. Estrela C, Bueno MR, Azevedo B, Azevedo JR, Pécora JD. A new periapical index based on cone beam computed tomography. J Endod 2008;34:1325-1331.

84. Bueno MR, Estrela C, Figueiredo JAP, Azevedo BC. Map-reading strategy to diagnose root perforations near metallic intracanal posts by using cone beam computed tomography. J Endod 2011;37:85-90.

85. Wu M-K, Shemesh H, Wesselink PR. Limitations of previously published systematic reviews evaluating the outcome of endodontic treatment. Int Endod J 2009;42:656–66.-⁸⁶86. Alencar AHG, Dummer PMH, Oliveira HCM, Pécora JD, Estrela C. Procedural errors during root canal preparation using rotary NiTi instruments detected by periapical radiography and cone beam computed tomography. Braz Dent J 2010;21:543-549.) relates to overestimated numbers of success in RCT.

Depending on the dentist's knowledge and skills for interpreting CBCT images, higher percentages of errors and failures in RCT may be identified. The possibility of map-reading on the CBCT scans can characterize the reality of a multidimensional structure, aiding with precise information the presence, absence or regression of AP. The life of an endodontically treated tooth implies understanding the biological and mechanical results as a multifactorial event, over the life span of the individual.

The authors deny any conflicts of interest related to this study. This study was supported in part by grants from the National Council for Scientific and Technological Development (CNPq grant 306394/2011-1 to C.E.).

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