Barry Musikant

ATELY I have gotten onto the theme of analyzing a variety of approaches to endodontic procedures using a set of criteria to attempt to objectively evaluate the effectivenss of the tools and their utilization to accomplish their tasks. On the Endo-Mail Message Board I have already discussed useful criteria by which to judge varying methods of instrumentation and obturation. To avoid being redundant, let’s see if we can apply criteria for the effectiveness of irrigation. For starters, let’s determine what the criteria should be.

1. the dissolution of organic debris
2. the killing of bacteria
3. the ability to penetrate into the dentinal tubules
4. the ability to breakdown the biofilm
5. the ability to keep the solutions contained within the walls of the canal

     One recognized sequence of irrigation uses NaOCl (3–6 percent) because it is the only solution we have that will actively digest organic debris. It is most rapidly effective when the tissue in the canal is already necrotic. In fact, one school of thought says that NaOCl should not be the first irrigant in teeth with vital tissue because of its tendency to coagulate that tissue prior to digesting it. Coagulated tissue can hamper the initial negotiation of the canals because it is tougher to negotiate through. Consequently, at the onset of irrigation in teeth with vital tissue 17 percent EDTA, a mild acid that chelates while removing the smear layer that is extruded from the tubules, is recommended rather than NaOCl. Using EDTA prevents the coagulation of the soft gelatinous vital tissue occupying the canal spaces, thereby aiding the mechanical negotiation of the canals. Once the bulk of the tissue is removed, the NaOCl and the EDTA can be used sequentially throughout the shaping procedure.
     When it comes to killing bacteria and breaking down the biofilm that coats the walls of highly infected canals, nothing surpasses the effectivenss of NaOCl, and this should be the first irrigant used. When the biofilm has been penetrated and degraded by the NaOCl, the EDTA can reach the walls of infected teeth and effectively remove the smear layer, opening the dentinal tubules in the process, thereby aiding in the deeper penetration of the NaOCl that kills the bacteria that are residing there.
     Endodontic treatment of non-vital teeth has a better prognosis when the teeth are also irrigated with 2 percent chlorhexidine (CHX). However, CHX must never be placed where either NaOCl or EDTA is already present. A precipitate will form on contact with either irrigant, complicating further cleansing and obturation of the canals. To avoid either precipitate, any residue of NaOCl or EDTA must be removed with a sterile water or saline rinse. Only after all the residue material has been removed can CHX be introduced. Its purpose is to kill the few bacteria that are resistant to NaOCl.
     So far, we have limited our discussion to the most effective irrigants and the sequence in which they should be used in vital and non-vital teeth. In addition to using the correct irrigants, it is also important to use them in the right way. According to the literature, the minimum canal preparation for adequate irrigation is a 30; a 35 preparation is even better. We cannot escape the relationship between the final dimensions of the canal space and the effectiveness of the irrigants when they are placed.
     Ample research has shown that activated irrigants work more effectively than passively placed irrigants. There are two forms of activation, sonic and ultrasonic. Ultrasonic is the more powerful of the two, but it can be easily dampened when the instrument touches the canal walls. If the power setting on ultrasonic is so high that it overrides the dampening effect, there is a high likelihood that it will start removing tooth structure in unpredictable ways. Sonic irrigation is less powerful, but cannot be dampened. This feature allows the instruments to plane all the walls of the canals as the irrigants are being activated. Although direct contact with the instrument produces ineffective results with ultrasonics, direct contact is a distinct plus with sonic systems. The most effective irrigation results when the canals have been opened sufficiently and the irritants within them have been activated by means that also plane all the walls of the canal. The use of a relieved reamer in a reciprocating engine oscillating between 3000 and 4000 cycles per minute with a manually applied up-and-down stroke just short of the apical foramen breaks up any air bubbles that might be present to prevent the thorough flow of the irrigants, ensuring that organic debis is chemically removed throughout the entire length of the canal.
     In summary, irrigation is optimized by preparing canals sufficiently, using the proper irrigants in the correct sequence, and activating irrigants after the final canal shaping is done. Extrapolating backwards, we don’t want to shape canals that don’t routinely produce apical preparations of less than 30, with 35 being even more desirable. Extrapolating forward, we want a canal prepared free of organic debris with open tubules so that the cement can penetrate them easily. You don’t want to limit yourself to passive irrigation because it is less effective than active irrigation in digesting organic debris, removing the smear layer, and opening the dentinal tubules. Shaping has an impact on irrigation, which in  turn has an impact on obturation. Only when we think of these three steps as part of a continuum can we appreciate their total interdependence.