Is there a rationale for the use of a specific root canal irrigant?

James L. Gutmann, DDS, FACD, FICD, FAD

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Root canal irrigants are necessary to clean the canal of its vital or necrotic infected dental pulp tissue during the enlarging and shaping process. The use of irrigants that possess multiple characteristics, such as tissue-dissolving attributes and bacteriostatic or bactericidal capabilities, is warranted at all times. Other advantages include rinsing away debris created during shaping, lubricating the instruments, demineralizing, and removing the smear layer.

As yet, no one solution possesses all the properties of an ideal irrigant. However, the use of neutral solutions such as water, saline, or anesthetic solutions for the irrigation process serves no useful purpose. The most common irrigant is sodium hypochlorite (NaOCl) in various concentrations. NaOCl is both antimicrobial and capable of dissolving tissue. Additionally, it possesses bleaching and lubricating properties and may inactivate endotoxins.

The effectiveness of NaOCI during cleaning and disinfection depends on the concentration of available chlorine and the pH of the solution. Hypochlorous acid (HOCl) is a weak acid and dissociates to the hypochlorite ion (-OCl) and proton (H+) depending on the solution pH. It is generally believed that HOCl is the active species in the germicidal action, whereas the concentration of -OCl is a key factor determining the cleaning efficiency. Therefore, the optimal pH region of the germicidal activity of sodium hypochlorite differs from that of its cleaning activity.

The concentrations of NaOCl that are used during root canal procedures vary among clinicians and are often chosen empirically. Some bacterial populations are susceptible to percentages as low as 0.5%, but these species may not reflect bacterial populations found in the tooth with a necrotic, infected pulp. However, clinical use for both bacterial control and tissue dissolution favors percentages from 1.0% to 6.0%, with studies claiming various levels of superiority with a particular percentage.

Manipulations that enhance the efficacy of NaOCl include warming the solution to at least 37oC, and the use of agitation (sonic and ultrasonic). Within the bacterial species studied, bacteriocidal rates for NaOCl more than doubled for each 5oC rise in temperature in the range of 5oC to 60oC.Therefore, when heating NaOCl in a laboratory study, the capacity of a 1% solution at 45oC to dissolve human dental pulps was found to be equal to that of a full strength solution at 20oC. Using the NaOCl solutions for periods of five to 30 minutes in the root canal has also been advocated to enhance its effectiveness, although optimal times have not been determined.

NaOCI techniques

While techniques for the agitation of NaOCl are being proffered, meaningful clinical studies are lacking. Even with longer application periods, replenishment may be necessary to increase its effectiveness, especially in the presence of significant amounts of tissue and bacteria encountered in highly irregular canal anatomies in the presence of long-standing necrotic pulp. When used in conjunction with EDTA (ethylenediaminetetraacetic acid) or 10% citric acid, its antibacterial properties are not necessarily enhanced.

When these solutions are used alternately during canal cleaning and shaping, bacterial bioburdens may be efficiently reduced. An ideal second irrigant may be one that combines the functions of smear layer removal with secondary bacteria killing in a single synergistic step.

NaOCl should always be delivered passively to the canal to prevent forceful extrusion beyond the apical foramen. This is best accomplished by avoiding wedging of the delivery needle in the canal, by expressing the solution slowly, and by using specially tipped side-delivery needles that enhance the cleaning of the dentin walls while minimizing potential risks during use.

The movement of small amounts beyond the apical foramen in a passive manner should not create problems for patients. Forceful movement of greater volumes of NaOCl will, however, be deleterious, and the literature is replete with "sodium hypochlorite accidents." Recent developments for irrigant activation within the canal include the EndoActivator® and the ProUltra® PiezoFlow® (DENTSPLY Tulsa Dental Specialties, Tulsa, Okla). These create a dynamic movement of the irrigant during debridement to enhance irrigation efficacy.

Note: References to support this position are available from the author.

James L. Gutmann, DDS, FACD, FICD, FADI, is professor emeritus in restorative sciences, Baylor College of Dentistry, Texas A&M University Health Science Center in Dallas. He is a Diplomate of the American Board of Endodontics and past president of the American Association of Endodontists. Presently, he is in private practice limited to endodontics in Dallas. Reach him via [email protected].