Elsevier

Journal of Endodontics

Volume 34, Issue 11, November 2008, Pages 1291-1301.e3
Journal of Endodontics

Review article
Clinical Implications and Microbiology of Bacterial Persistence after Treatment Procedures

https://doi.org/10.1016/j.joen.2008.07.028Get rights and content

Abstract

Apical periodontitis is an infectious disease caused by microorganisms colonizing the root canal system. For an optimal outcome of the endodontic treatment to be achieved, bacterial populations within the root canal should be ideally eliminated or at least significantly reduced to levels that are compatible with periradicular tissue healing. If bacteria persist after chemomechanical preparation supplemented or not with an intracanal medication, there is an increased risk of adverse outcome of the endodontic treatment. Therefore, bacterial presence in the root canal at the time of filling has been shown to be a risk factor for posttreatment apical periodontitis. About 100 species/phylotypes have already been detected in postinstrumentation and/or postmedication samples, and gram-positive bacteria are the most dominant. However, it remains to be determined by longitudinal studies if any species/phylotypes persisting after treatment procedures can influence outcome. This review article discusses diverse aspects of bacterial persistence after treatment, including the microbiology, bacterial strategies to persist, the requisites for persisting bacteria to affect the outcome, and future directions of research in this field.

Section snippets

Understanding Bacterial Persistence

It is important to understand some aspects related to the significance of bacteria found in posttreatment samples. In this context, one should be aware of the time that bacterial “persisters” are detected in treated canals. Studies of the bacteria occurring in the root canal after treatment approaches involve three basic conditions: (1) postinstrumentation samples (collected immediately after completion of chemomechanical procedures), (2) postmedication samples (collected immediately after the

Microbiological Goals of the Endodontic Treatment

Apical periodontitis is an infectious disease caused by microorganisms colonizing the root canal system (20, 21, 22, 23). The endodontic treatment of teeth containing irreversibly inflamed pulps is essentially a prophylactic treatment because the radicular vital pulp is usually free of infection, and the rationale is to treat in order to prevent further infection of the root canal system and consequent emergence of apical periodontitis (24). On the other hand, in cases of infected necrotic

Persistent versus Secondary Infection as the Cause of Failure

It has not been well established whether bacteria present in root canal–treated teeth with posttreatment disease remain from previous treatment (persistent infection) or are a consequence of reinfection (secondary infection). The last 2 decades have witnessed a marked interest on the role of secondary infection resulting of coronal leakage in treated root canals as an important cause of posttreatment apical periodontitis (53, 54). However, indirect evidence seems to point to persistent

Bacterial Persistence as a Risk Factor for Posttreatment Disease

Most intracanal bacteria are sensitive to standard treatment procedures. Nevertheless, some bacteria may survive treatment procedures, and their presence at the time of filling as detected by culture approaches has been recognized as a risk factor for posttreatment apical periodontitis (3, 10, 11, 12, 13, 14). Even though bacterial persistence may jeopardize the treatment outcome, no specific single species has been identified as a risk factor for failure. This is in agreement with the

Strategies to Persist

For bacteria to endure treatment and be detected in posttreatment samples, they must (1) resist intracanal disinfection procedures and (2) adapt to the drastically changed environment (Table 2).

Several strategies may help bacteria to resist treatment. Bacteria can adhere to the root canal walls, accumulate, and form communities organized in biofilms, which can be important for bacterial resistance to and persistence after intracanal antimicrobial procedures (69). Bacteria located in

When Residual Bacteria Influence Treatment Outcome

Bacteria persisting in the root canals after chemomechanical procedures or intracanal medication will not always maintain an infectious process. This statement is supported by the fact that some apical periodontitis lesions can heal even when bacteria were found in the canal at the filling stage (10, 11). The following are explanations for that: (1) residual bacteria may die after filling because of the toxic effects of the filling material, access denied to nutrients, or disruption of

Bacterial Taxa–Persisting Intracanal Procedures

Although several studies have investigated the impact of bacterial persistence on treatment outcome, not so many have consistently identified the species resisting root canal procedures (Table 3). In studies of the effectiveness of intracanal procedures, it is advisable to identify bacterial species at the baseline and after treatment so as to rule out possible contamination during treatment, sampling, or laboratory handling of the sample. Simply detecting growth in broth or counting colonies

Concluding Remarks

Bacteria participating in persistent infections can be identified as those present in the canal at the time of filling, although it must be recognized that many of the species found still had no sufficient time to establish a real infection and will die after filling. However, those that manage to survive in the new drastically modified environment can establish a persistent infection that put the treatment outcome at risk.

Bacterial persistence at the time of root canal filling has been shown

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