Mastering Irrigation in Endodontics: Cleaning and Shaping, or Shaping to Clean?

INTRODUCTION
Endodontic treatment is aimed at chemo-mechanically minimizing microorganisms, inactivating their by-products, and optimally sealing the canal space to prevent future recontamination. If root canals could be thoroughly cleaned using irrigation alone, and then effectively obturated, there would be no need for mechanical instrumentation.¹

The initial cleaning of root canals is commonly performed by mechanical instrumentation, which removes the large bulk of the pulp tissue, the necrotic debris, and bacterial biofilms or a previous root filling. Unless this bulk of material is first removed, no further cleaning is possible. Mechanical instrumentation is performed by using either stainless steel hand files or engine-driven NiTi rotary and/or reciprocation files, neither of which is expected to completely clean the canal when used alone but will create a “space” that will be filled by irrigants to provide the cleaning effect.² A substantial part of the root canal wall is left untouched by contemporary instrumentation techniques,³ and irrigation may be considered the primary method to clean and disinfect these areas of the root canal system. Nevertheless, it is recognized that cleaning and disinfecting the apical part of the canal with irrigants (ie, sodium hypochlorite) is ineffective unless the canal is enlarged to at least a 35.04 size.^4,5

Various irrigation chemicals, techniques, and devices are being used together with mechanical instrumentation to improve the cleaning and disinfection of root canal systems.

Figure 1. Different irrigants and presentations. From left to right, 3% sodium hypochlorite (NaOCl) with surfactant (ChlorCid Surf [Ultradent Products]), EDTA 18% (Ultradent Products), chlorhexidine (CHX) 2% (Consepsis [Ultradent Products]), and 3% NaOCl in viscous presentation (ChlorCid V [Ultradent Products]).

Irrigant Benefits, Limitations, and Interactions
Ideally, a root canal irrigant should provide a broad spectrum of antimicrobial activity while flushing out debris from the root canal. It should be nontoxic and biocompatible in nature and able to disinfect the canal, dissolve organic tissue, and remove the smear layer. The root canal irrigant should have good lubricating action, along with low surface tension, to be able to flow into inaccessible areas. Finally, the irrigant should facilitate dentin removal but not weaken the tooth structure. Figure 1 shows examples of different endodontic irrigants.

Sodium Hypochlorite (NaOCl)
Sodium hypochlorite (NaOCl) is the most common irrigant used in endodontics and is recommended for routine clinical use throughout the instrumentation phase. NaOCl dissolves pulpal remnants and has strong antimicrobial effects, especially against biofilms. However, NaOCl is not able to remove the smear layer by itself as it only dissolves organic material. It has been shown to be extremely caustic when in contact with vital tissue in vitro, even at lower concentrations. Therefore, its use should be restricted within the confines of the root canal system.

Greater contact time and regular replenishing of NaOCl irrigant solution is more important than NaOCl concentration in regard to better tissue-dissolving capability.⁶ The volume of irrigant also correlates with a reduction of micro-organisms and improved canal cleanliness. It is highly recommended to use 15 to 20 mL of irrigant for each canal during instrumentation.⁷

NaOCl Concentration
It is known that NiTi rotary and reciprocation instrumentation techniques have expedited the shaping process. However, decreasing the time the NaOCl was inside the canal forced the use of high-concentrate solutions. Full-strength NaOCl can have a detrimental effect on dentin elasticity and flexural strength due to the proteolytic action of concentrated hypochlorite on the collagen matrix of dentin. Additionally, the higher the concentration, the greater the cytotoxicity. Accidental apical extrusion of high-concentrate NaOCl can create an instant inflammatory reaction, resulting in severe pain, ecchymosis, hematoma, and swelling. Less commonly, some patients have temporary nerve paresthesia.

NaOCl With Surfactant
NaOCl surface tension could affect the ability to penetrate the dentin and, thus, reduce antibacterial effectiveness within dentinal tubules. Surface active and wetting agents can be added to NaOCl to increase its penetration into dentin and inaccessible areas of root canals, improving its overall effect. Additionally, replacement and penetration in the main canal and isthmuses is enhanced in mixtures with lowered surface tension agents. Moreover, as the surfactant is a detergent, it possesses emulsifying properties. These properties facilitate the removal of debris from the dentin surface by maintaining them in suspension, which increases dentin wettability and facilitates instrumentation. Studying the ability of different irrigants in the removal of endotoxins, Valera et al⁸ concluded that the foam formation during instrumentation with NaOCl plus surfactant contributed to a better reduction of bacterial load, particularly against Enterococcus faecalis, as well as to a significant improvement in the removal of endotoxins.

NaOCl Precautions

• Do not use any brand of domestic NaOCl (bleach) and dilute with water. The concentration of “off the shelf” bleach varies from 2.5% to 6%, depending on the conditions and time of storage. Products that are not meant to be used as medical devices don’t receive the same quality control as the medical device predicates.
• The use of closed-ended (side open) irrigation cannulas (NaviTip 31ga Double Sideport Irrigator Tip [Ultradent Products]) (Figure 2) helps to move the irrigant sideways and avoid periapical extrusion. Shaping of the root canal must be at least size #35.04 at the working length (WL) for a 31ga cannula tip to reach the more apical portions of the canal without wedging. The irrigant does not move apically more than 1 mm beyond the side open irrigation tip; therefore, placement needs to be at least 2 mm off the WL during rinsing, and the cannula must be moved up and down freely and constantly to produce agitation and prevent binding or wedging of the cannula.
• A good balance is 3% concentration NaOCl, 12 minutes activity time, and 15 to 20 mL of total volume per canal while replacing the liquid inside the canal between instrument use. A gel formula (Figure 1) of NaOCl (ChlorCid V [Ultradent Products]) can be used during the shaping process to increase lubrication action in intermittent conjunction with NaOCl solution.
• NaOCl is caustic if accidentally extruded into periapical tissue or adjacent anatomical structures, such as the maxillary sinus. Edema and paresthesia may result due to the tissue-dissolving capability of NaOCl. Because the potential for spread of infection is related to tissue destruction, medications such as antibiotics, analgesics, and antihistamines should be prescribed accordingly.
• NaOCl and chlorhexidine (CHX) are not soluble in each other, and they form a brownish-orange precipitate that is a carcinogenic and potentially mutagenic product: parachloroanaline (PCA). It is mandatory to minimize the formation of PCA by washing away the remaining NaOCl with ethylenediaminetetracetic acid (EDTA), saline, or distilled water before using CHX.
• Using NaOCl as the final rinse following EDTA or citric acid should be avoided because it rapidly produces the erosion of dentin.

Ethylenediaminetetracetic Acid (EDTA)
NaOCl is a limited irrigating solution because it cannot dissolve the inorganic component of the smear layer formed during mechanical instrumentation. EDTA, or citric acid, complements the action of NaOCl by chelating the calcium ions in dentin, removing the smear layer. It also exposes the bacteria living in the dentinal tubules, allowing them to be acted upon by the disinfecting irrigants (ie, CHX 2%). Additionally, it allows the endodontic sealer to penetrate the dentinal tubules for a more intimate fit, leading to an enhanced sealing of the canal.

EDTA Precautions

• Concentrations higher than 14% effectively remove the smear layer.
• Time of action and replacement of the liquid are very important to achieve chelating action. One minute of EDTA action, replacing the liquid after the first 30 seconds, is the most popular protocol. Mechanical agitation (sonic or ultrasonic) helps to provide a more efficient smear layer removal.

Chlorhexidine (CHX)
CHX solutions are bactericidal and can adhere to canal dentin, producing a long-lasting effect called substantivity. CHX does not cause the erosion of dentin like NaOCl, making it a good choice for maximizing the antibacterial effect at the end of chemo-mechanical preparation.⁹ The reaction between CHX and EDTA, unlike the reaction between CHX and NaOCl, does not produce significant quantities of PCA, the carcinogenic and potentially mutagenic product of the NaOCl and CHX reaction. To prevent the formation of PCA, use EDTA, saline, or distilled water to flush NaOCl from the canal before the application of CHX.¹⁰

CLOSING COMMENTS
The fundamental goal of endodontic treatment is to remove the contents of the root canal, whether inflamed, necrotic, and/or infected tissue. It seems paradoxical that mechanical instrumentation creates more debris during the action of the instruments, along with not reaching areas of the canal due to the anatomy of the root canal system. The effective cleaning comes from the action of the irrigation liquids, and these must be used properly by respecting their appropriate volumes, times of action, and concentrations. We will discuss proper irrigation techniques and protocols in part 2 of this article, which will be published in a future issue.

References

1. Lussi A, Portmann P, Nussbächer U, et al. Comparison of two devices for root canal cleansing by the noninstrumentation technology. J Endod. 1999;25:9-13.
2. Siqueira JF Jr, Rôças IN, Santos SR, et al. Efficacy of instrumentation techniques and irrigation regimens in reducing the bacterial population within root canals. J Endod. 2002;28:181-184.
3. Siqueira JF Jr, Araújo MC, Garcia PF, et al. Histological evaluation of the effectiveness of five instrumentation techniques for cleaning the apical third of root canals. J Endod. 1997;23:499-502.
4. Baugh D, Wallace J. The role of apical instrumentation in root canal treatment: a review of the literature. J Endod. 2005;31:333-340.
5. Khademi A, Yazdizadeh M, Feizianfard M. Determination of the minimum instrumentation size for penetration of irrigants to the apical third of root canal systems. J Endod. 2006;32:417-420.
6. Baker NA, Eleazer PD, Averbach RE, et al. Scanning electron microscopic study of the efficacy of various irrigating solutions. J Endod. 1975;1:127-135.
7. Sedgley C, Applegate B, Nagel A, et al. Real-time imaging and quantification of bioluminescent bacteria in root canals in vitro. J Endod. 2004;30:893-898.
8. Valera MC, Cardoso FG, Chung A, et al. Comparison of different irrigants in the removal of endotoxins and cultivable microorganisms from infected root canals. ScientificWorldJournal. 2015;2015:125636.
9. White RR, Hays GL, Janer LR. Residual antimicrobial activity after canal irrigation with chlorhexidine. J Endod. 1997;23:229-231.
10. Rasimick BJ, Nekich M, Hladek MM, et al. Interaction between chlorhexidine digluconate and EDTA. J Endod. 2008,34:1521-1523.

Dr. Ramos graduated with a degree in dentistry from the State University of Londrina in Brazil (1987). He is a specialist and PhD in endodontics and a former endodontics sector coordinator at the State University of Londrina. He has had 3 endodontic textbooks published and has written more than a dozen chapters for various endodontic books. He accomplished all of this while working part time exclusively as an endodontic specialist at his private office from 1987 to 2012. Since 2012, he has been the Ultradent Products R&D and clinical affairs senior endodontic advisor. He can be reached via email at carlos.ramos@ultradent.com.

Disclosure: Dr. Ramos is senior endodontic advisor in Ultradent Products Clinical Affairs Department.

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