Review article
Root Canal Irrigants

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Abstract

Local wound debridement in the diseased pulp space is the main step in root canal treatment to prevent the tooth from being a source of infection. In this review article, the specifics of the pulpal microenvironment and the resulting requirements for irrigating solutions are spelled out. Sodium hypochlorite solutions are recommended as the main irrigants. This is because of their broad antimicrobial spectrum as well as their unique capacity to dissolve necrotic tissue remnants. Chemical and toxicological concerns related to their use are discussed, including different approaches to enhance local efficacy without increasing the caustic potential. In addition, chelating solutions are recommended as adjunct irrigants to prevent the formation of a smear layer and/or remove it before filling the root canal system. Based on the actions and interactions of currently available solutions, a clinical irrigating regimen is proposed. Furthermore, some technical aspects of irrigating the root canal system are discussed, and recent trends are critically inspected.

Section snippets

Facing the Challenge

There can be no doubt today that microorganisms, either remaining in the root canal space after treatment or re-colonizing the filled canal system, are the main cause of endodontic failure (7, 8). The primary endodontic treatment goal must thus be to optimize root canal disinfection and to prevent re-infection.

Infection of the root canal space occurs most frequently as a sequela to a profound carious lesion (9). Cracks in the crown structure extending into the pulp chamber can also be

Root Canal Infection

As the host defense loses its access to the necrotic pulp space, opportunistic microorganisms selected by harsh ecological conditions and the low-oxygen environment aggregate in the root canal system (19). These microbial communities may survive on organic pulp tissue remnants and exudate from the periodontium (20, 21). Consequently, clusters of microorganisms in necrotic teeth and teeth with failed root canal treatments are typically found in the apical root canal area, where they have access

Root Canal Instrumentation

The main purpose of instrumentation is the mechanical debridement of the root canal system and the creation of a space for delivery of antimicrobial substances. Furthermore, a well-shaped root canal system facilitates the proper placement of a tight root canal filling to prevent re-colonization by oral microbiota (38). There have been attempts to perform endodontic treatment without mechanical instrumentation by means of a vacuum device and hypochlorite perfusion of the root canal system (39).

Desired Irrigant Actions

Historically, countless compounds in aqueous solution have been suggested as root canal irrigants, including inert substances such as sodium chloride (saline) or highly toxic and allergenic biocides such as formaldehyde (52). In this review, however, the focus is on currently used irrigating solutions; obsolete substances are not discussed. Based on the above knowledge, it appears evident that root canal irrigants ideally should:

  • Have a broad antimicrobial spectrum and high efficacy against

Choosing the Main Irrigant

Although iodine is less cytotoxic and irritating to vital tissues than sodium hypochlorite and chlorhexidine (53, 54), it bears a much higher risk to cause an allergic reaction (55). The same is true for quaternary ammonium compounds (56, 57). Sensitivities to hypochlorite and chlorhexidine are rare (58, 59). Despite its ubiquitous use, only few cases of allergic reactions to sodium hypochlorite from a root canal irrigant have been reported (60).

Of all the currently used substances, sodium

Chlorhexidine

Chlorhexidine was developed in the late 1940s in the research laboratories of Imperial Chemical Industries Ltd. (Macclesfield, England). Initially, a series of polybisguanides was synthesized to obtain anti-viral substances. However, they had little anti-viral efficacy and were put aside, only to be re-discovered some years later as antibacterial agents. Chlorhexidine was the most potent of the tested bisguanides (74). Chlorhexidine is a strong base and is most stable in the form of its salts.

Natural Occurrence

Chlorine is one of the most widely distributed elements on earth. It is not found in a free state in nature, but exists in combination with sodium, potassium, calcium, and magnesium (86). In the human body, chlorine compounds are part of the nonspecific immune defense. They are generated by neutrophils via the myeloperoxidase-mediated chlorination of a nitrogenous compound or set of compounds (87).

History of Chlorine-Releasing Agents

Potassium hypochlorite was the first chemically produced aqueous chlorine solution, invented in

Chelator Solutions

Although sodium hypochlorite appears to be the most desirable single endodontic irrigant, it cannot dissolve inorganic dentin particles and thus prevent the formation of a smear layer during instrumentation (128). In addition, calcifications hindering mechanical preparation are frequently encountered in the canal system. Demineralizing agents such as ethylenediamine tetraacetic acid (EDTA) (129) and citric acid (130) have therefore been recommended as adjuvants in root canal therapy. These are

Suggested Irrigation Regimen

As indicated above, the chemicals used to clean infected canals should be administered in such manner that they can unleash their full potential on their targets in the root canal rather than act on each other. Hence, a hypochlorite solution should be employed throughout instrumentation, without altering it with EDTA or citric acid. Canals should always be filled with sodium hypochlorite. This will increase the working time of the irrigant. In addition, cutting efficacy of hand instruments is

Technical Aspects of Irrigating Root Canals

Penetration of an irrigant into the instrumented root canal system is a function of irrigating needle diameter in relation to preparation size (160). Hence, while direct evidence is still lacking, the introduction of a slim irrigating needle with a safety tip (Fig. 3, panel A) to working length or 1 mm short of it is a promising approach to improve irrigant efficacy in the infected apical area of nonvital teeth with apical radiolucencies. It should be kept in mind that the solution does not

Alternative Concepts

In this communication it was aimed at presenting a simple and affordable way for the chemical debridement of root canal systems using materials that are currently available to the clinician. This does not mean that there could be no other biologically acceptable possibilities to clean root canal systems. However, the reader should be aware of the fact that new concepts usually are overrated in initial studies when compared to the gold standard (6, 135, 162). Some recent approaches to improve

Acknowledgments

I would like to thank my friends Heather T. Morris, Frank Paqué, and David Sonntag for their help in completing this manuscript.

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