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The Role of Irrigants in Effective Endodontic Care

The removal of pulpal and dentinal debris and the elimination of viable micro-organisms from the root canal system are of paramount importance during endodontic therapy. Bacteria are the main factor in pulpal and periapical inflammation, and failure to effectively eliminate them could result in endodontic compromise.1 Successful cleaning entails physically removing substances, irrigating, and dissolving contents from inaccessible regions.2 It has been reported that viable bacteria can remain within the canal system even after instrumentation.3 

Instrumentation and irrigation can reduce bacterial concentrations, but cannot eliminate bacteriafrom the canal system.4 Irrigation is presently the best method for the removal of tissue remnants and dentin debris. Ideally, an irrigant should be a tissue or debris solvent, have a low toxicity level, have the ability to effectively disinfect the canals, and be able to remove the smear layer.5 Since no irrigant can fulfill all of these criteria alone, a combination of irrigants has been recommended to accomplish these goals.6 

There is no clear consensus as to whether the smear layer should be removed before obturation.7 The smear layer consists of an organic portion (ie, coagulated proteins, necrotic and nonnecrotic pulpa tissue, saliva, microorganisms) and an inorganic portion (ie, minerals from the dentinal structure),8 and its presence along with debris may reduce the efficacy of root canal irrigants and medicaments by blocking access to bacteria residing in the dentinal tubules.9 

 

Sodium Hypochlorite 

 Sodium hypochlorite solutions are the most favored root canal irrigants, based on their antibacterial, vital and nonvital tissue-dissolving, and lubricating properties.10 Their key weakness, however, is the inability to remove the smear layer.11 The choice of concentration of NaOCl is still a matter of debate. At lower concentrations, however, not only is its tissue-dissolving ability reduced, but its antimicrobial effectiveness is as well.12 One approach to improve the effectiveness of hypochlorite irrigants in the root canal system could be to increase the temperature of low-concentration NaOCl solutions. This appears to improve their immediate tissue-dissolution capacity and antibacterial efficacy.11 In endodontic therapy, high concentrations of NaOCl solution for decontamination of gutta-percha cones produce physical alteration of gutta-percha cones, leading to an increase of elasticity,13 which can lead to difficulties during obturation.14  

Previous studies have shown that 5% NaOCl treatment significantly reduced both the bond strength of adhesive resins,15 and the modulus of elasticity and flexural strength of dentin.16 Slutzky-Goldberg et al demonstrated that instrumentation and irrigation with NaOCl changes the biomechanical properties of dentin.17 White et al found that root dentin was weakened after five weeks of exposure to calcium hydroxide, mineral trioxide aggregate, or sodium hypochlorite.18  

 

Ethylenedinitrilotetraacetic Acid (EDTA) 

Disodium salt of EDTA is generally accepted as the most effective chelating agent with prominent lubricant properties, readily removes the smear layer, and prepares the dentin walls for better adhesion of filling materials.19 The effects of EDTA within the canal are known to be self-limiting. Chelating agents react with calcium ions in the hydroxyapatite crystals to produce a metallic chelate. For effective removal of the smear layer, the following methods are also recommended. Gettleman et al showed that a contact time of 3 minutes with 17% EDTA was effective for smear layer removal.20 Calt and Serper demonstrated that a 10 mL irrigation with 17% EDTA for 1 minute was effective in removing the smear layer.19 Crumpton et al demonstrated that 1 mL of EDTA with a contact time of 1 minute was just as effective as 10 mL.

As EDTA solution has a strong demineralizing effect, it causes enlargement of the dentinal tubules, softening of the dentin, and denaturation of the collagen fibers.21 The efficiency of such agents depends on a variety of factors including the root canal length, penetration depth of the material, duration of application, and the concentration of materials.22 EDTA has been shown to be a potent inhibitor of macrophage adherence,23 possibly by preventing the binding of VIP to the macrophage, altering the inflammatory mechanisms involved in periradicular lesions.24  

 

Acid Solutions 

Acid solutions have been recommended for endodontic treatment purposes since 1957. Malheiros et al demonstrated that citric acid (CA), when applied at high concentrations, leads to a delay in cell growth.25 Calcium complexing agents (eg, EDTA, CA) used alternatingly with NaOCl solutions are advocated to remove the smear layer, to clean the dentin wall, and to disinfect the root canal.26 Both agents strongly reduced the available chlorine in NaOCl solutions, possibly rendering them ineffective.27 Among the possible alternatives to EDTA/CA, etidronate disodium (HEBP) appeared to be the most promising. Etidronate disodium is nontoxic and is commonly used to treat bone diseases. Consequently, a less aggressive calcium complexing agent (ie, 7% to 10% HEBP) could be mixed chairside with NaOCl, without any loss of NaOCl activity.28 

Chlorhexidine Gluconate 

Chlorhexidine gluconate (CHX) possesses the ability to sustain antimicrobial activity for up to 21 days,29 and has been shown to be at least as effective an antimicrobial agent as 5.25% NaOCl.30 Used alone, however, CHX does not have the tissue-dissolving ability of NaOCl, nor the ability to remove the smear layer. The antimicrobial mechanism of CHX is related to its cationic bisbiquanide molecular structure. The cationic molecule is absorbed by the negatively charged inner cell membrane and causes leakage of intracelluler components. In the author’s previous studies, the teeth treated with chlorhexidine solution showed the highest bond strength values on the canal wall,31 and the harmless effect on the microhardness and the roughness of root canal dentin when compared to the other irrigants.32 Chlorhexidine gluconate has been reported to cause staining, particularly when combined with NaOCl, which means it needs to be used judiciously, especially in anterior teeth where cosmetic conciderations are greatest. A saline rinse between the NaOCl and the CHX will eliminate the brown pigmentation that develops when these two solutions are mixed in the canal.

Although a relative softening effect exerted by a chemical irrigant on the dentin walls could be of clinical benefit because it permits rapid preparation and facilitates negotiation of small tight root canals, these alterations affect the adhesion and sealing ability of sealers to the treated dentin surfaces.33 Mineral contents of the root canal dentin after treatment with several endodontic irrigation solutions were evaluated in this study. The author found that endodontic irrigation solutions have effects on the mineral contents of root dentin.34 Perfect obturation is required for a successful root canal treatment to inhibit resistance to bacterial ingress and to prevent leakage. A harmless irrigation solution seems to be more appropriate to provide a perfect obturation. Clinicians need to balance the need for optimization of the mechanical efficacy of irrigation provided by the enlargement of canals with negative consequences of reduction in tooth structure and subsequent weakening of the root structure.35 

 

Conclusion 

 Proper cleansing and irrigation of the root canal system to remove debris and eliminate bacteria from the root canal system is a vital step in endodontic therapy. Selection of an effective irrigant is critical for the success of a tooth. Antimicrobial activity is not the only requirement for an endodontic irrigant. Despite the antibacterial properties, any irrigation solution has been shown to dissolve tissue in the root canal system, except for sodium hypochlorite. Following the removal of the smear layer with EDTA and NaOCl, CHX is suggested as a final antimicrobial rinse for canal disinfection.

 

*Associate Professor, Selcuk University Faculty of Dentistry, Department of Endodontics, Konya, Turkey.

 

References

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