During the past 20 years, Endodontics has begun to appreciate the critically important role that irrigation plays in successful endodontic treatment. Successful treatment demands that we have a protocol that allows us to efficiently clean canals and prepare them to be filled. Irrigation is an important part of this protocol because it assists us in: (a) removing all organic content (a substrate for bacteria) from the root canal system and (b) configuring the system so it can be obturated to eliminate the space where bacteria and its irritants can accumulate again. In order to get maximum efficiency from the irrigant, we must also recognize the need for apical patency and must not be afraid to place instruments to the apex. Getting the irrigant to the apical portions of the canals is crucial.
Our irrigating agent must meet the following criteria:
1. It must have anti-microbial properties
2. It must aid in the debridement of the canal system
3. It should have the ability to dissolve necrotic tissue
4. It should be nontoxic to periapical tissues
These requirements are currently being met with the use of 5.25% Sodium Hypochlorite (aka Clorox or Javex- FULL strength - NOT diluted. "Fresh Scent" additive versions have been found to have no effect on its endodontic action. ). Hypochlorite's anti-bacterial action is based upon its effects on the bacterial cell wall. Once the cell wall is disrupted, the vital contents of the bacteria are released. The bacterial membrane and intracellular associated functions cease. Sodium Hypochlorite is an effective necrotic tissue solvent. The contact of the solution with organic debris helps to eliminate the substrate on which bacteria grows. Clinical investigations have proven that 5.25 % sodium hypochlorite has no greater irritating effect than normal saline solution when properly used as an endodontic irrigant. Because it fulfills all these requirements, NaOCL remains the main irrigating solution of choice in endodontic treatment. Sodium hypochlorite is adversely affected by exposure to high temperature, light, air, and the presence of organic and inorganic contaminants. The tissue-dissolving ability of 5.25% sodium hypochlorite remains stable for at least 10 weeks.
Rotary Ni-Ti instrumentation has allowed many of use to clean and shape canals much faster and easier. But, one negative side-effect of reduced treatment time is that as we get faster, there is less time for the hypochlorite to work in the canals. Unless we make a conscious effort to have patients "soak" their canals for the extra time, we need to find other techniques we can use to enhance its effectiveness without affecting its desirable properties.
HOW CAN WE ENHANCE THE ACTION OF NaOCL ?
TIME - The antimicrobial effectiveness of NaOCl is dependent on its contact time with the canal. The greater the contact time, the greater the antibacterial effectiveness, the tissue solvent action and the cleaner the canal will be. This is especially important in necrotic cases.
HEAT - Warming NaOCL to 60-70 C has shown to increase its solvent properties and enhance digestion of organic tissue. We must be careful not to overheat the solution because this can cause breakdown of the NaOCL constituents and ruin the solution. One of the easiest ( and cheapest!) ways to accomplish this is with the use of a standard coffee cup warmer. These can be purchased from Canadian Tire (Salton is one brand) for as little as $10. The NaOCL can be placed in a pre-sterilized glass container and left on the warmer during treatment.
Specialized Syringes - Most research has shown that unaided irrigation (ie/ irrigation applied passively with a syringe) requires at least a size #25 apex for it to reach the more apical portions of canals. Newer, specialized side venting ( rather than end venting) Endodontic syringes with sizes as small as 32 gauge are now available commercially. They may aid in getting the irrigant closer to the apex. I prefer to use a standard Monoject 413 ED Endo syringe that has been modified. (Bent at a 45 degree angle about ¼ " from the hub. The end is cut off with a disc about 2 inches from the bend and the smoothed. It is a good idea to have several lengths, especially for longer teeth such as cuspids.) Although it is not as small as some of the specialized needles, it clogs less. I also like to use the syringe needle as a "gauge" to determine when I have achieved adequate canal size. Dr. John Stropko has also designed a special set of irrigating and drying syringes that attach to the dental unit. See his web site http://www.microendodoc.com/ref/ref_irrag.html for details.
RC Prep - (Urea Peroxide) - Products containing calcium chelating agents can be alternated with NaOCl. The Urea Peroxide component helps emulsify the organic tissue components and will cause effervescence of the NaOCl. They are a good adjunct to irrigation but should be used very cautiously. RC Prep should never be used for canal negotiation (i.e./ to "find" working length.) They are best used to enlarge canals that have been negotiated with a #. 06 or #. 08 file and are still "tight". Improper use of RC Prep with a stiffer #15 file, with crown down technique or with a rotary instrument can ledge or perforate canals as well as separate instruments.
Surfactants (Surface Tension Reducing Agents) - NaOCL combined with wetting agents allows better penetration of solutions into the canal system by reducing the surface tension of the irrigant. One of the best agents is Zephiran. (Benzalkonium chloride - commonly known as a topical antibacterial agent) It has the advantage of being inexpensive and effective. (In 1986, I assisted one of my Post Graduate classmates at Boston U. who did his Masters Thesis on the use of surfactants in irrigation.) 2 or 3 drops of Zephiran in a 12 oz. of irrigating solution can dramatically reduce the surface tension of the solution and increase the penetration of the NaOCL. It should be applied to the solution just before use. Some recent research has shown that alternating NaOCl with overproof/absolute alcohol (96% by volume) results in more effective flushing of the apical sections of canals by lowering surface tension. You can order Zephiran or overproof alcohol from any pharmacy.
EDTA and Smear Layer Removal - After canals are instrumented, a non-organic layer remains that covers the dentinal tubules. Some controversy still remains as to the benefits or liabilities of removal of the smear layer as it relates to the permeability of dentin. However, there is general agreement that the closest possible adaptation of endodontic filling materials to the canal space is the desirable. That includes trying to adapt gutta percha, sealer or a combination of the two into the dentinal tubules. Therefore, to remove this layer a final rinse with 17-20 % EDTA is now recommended. I prefer to rinse the EDTA again with NaOCL before drying with 95% alcohol, suction and paper points. EDTA solutions are available from dental suppliers but are most economically obtained through your pharmacist.
Overproof Alcohol - Giving the canal a final rinse with highly volatile overproof alcohol (96%) allows for better drying of the canal spaces and results in fewer paper points being required to dry the canals. Dry canals allow for the best seal during obturation.
Ultrasonic Activation - Research has shown that the acoustic streaming caused by ultrasonic activation of the irrigating solutions can create cleaner canals. This is especially helpful in necrotic cases. Rather than use ultrasonically activated files, some endodontists are using small, activated tips (shaped like an small endo explorer) in specially designed piezoelectric instruments (similar to a Cavitron). The device has many uses - Post removal, instrument removal, and retropreparation. The tip essentially becomes an ultrasonic swizzle stick. This is done to enhance final irrigation, once the canal has been cleaned and shaped. Recommended time of action with EDTA is 30 secs to 3 mins per canal (depending on which research you read) followed by a final flush with NaOCL.
Dangers of NaOCL Use - It is important to remember that although NaOCL is non toxic during intra-canal use, 5.25% Sodium Hypochlorite can cause serious consequences if injected periapically. Irrigation with this solution should always be performed passively. Treating canals by using apical patency demands that we are cautious while irrigating. The syringe should NEVER be locked in the canal. This is especially important in cases with larger apical diameters and when using smaller commercial needles that can be placed within the last few mms of the canal space. If inadvertent periapical injection occurs, the consequences can be quite alarming and painful. There generally is an immediate severe burning sensation often accompanied by very rapid gross swelling. The condition is best treated with oral analgesics antibiotics and by reassuring the patient.
Other agents - Some clinicians are also recommending a 2% chlorhexidine rinse before the final EDTA rinse, in order to further eliminate any canal bacteria. At ROOTS SUMMIT 1 (Toronto June 2001) other agents such as "electrolyzed neutral superoxide water", Oxoferin (a tetracholordecaoxygen), Sterilox and enzyme based treatments were also mentioned as current avenues of research .
For a great overview with references) of "Biomechanical Cleansing" by Endodontists - Drs. Glassman and Serota click this Link.