Allan Deutsch
 
 
 
 
 
 
 

OR MOST OF MY endodontic career there was only one irrigant, and that was sodium hypochlorite. It was and still is the workhorse of endodontic treatment the world over. It dissolves tissue and kills most of the bacteria present in the root canal—but not all of it. The one bug that it does not kill too well is E. faecalis. This bacteria is becoming increasingly associated with failed root canal treatment. So, if your instrumentation doesn’t remove E. faecalis, you may have a doomed root canal treatment from the very beginning (Figure 1). Luckily for us, over the last ten years a lot of research has been done on chlorhexidine and its antibacterial properties. Most of you are probably familiar with chlorhexidine as the active ingredient in the mouthwash “Peridex.” Peridex is a 0.12 percent solution of chlorhexidine. Unfortunately the 0.12 percent solution is not strong enough for use as an endodontic irrigant. At this low concentration, the chlorhexidine would take several hours to kill the bacteria in the canal. This length of time is not a practical option when treating patients. The research has shown, however, that a 2 percent solution of aqueous chlorhexidine will kill the bacteria in one to two minutes. This length of time is certainly acceptable for practical endodontic treatment.
    However, it is not as easy as that. When we instrument the canal, we create a smear layer of dentinal debris. This smear layer covers the dentinal tubules and protects the bacteria and biofilm that are located in the tubules and along the canal walls. If the smear layer is intact, chlorhexidine will not kill the infecting bacteria even if we use it all day long, because it never comes in contact with them. Therefore, before we use 2 percent chlorhexidine we must remove the smear layer. Luckily, there is much literature that demonstrates that rinsing the canal for one to three minutes with 17 percent aqueous EDTA will remove the smear layer and open the dentinal tubules (Figure 2). We prefer an aqueous solution of 17 percent EDTA because it is easy to get into the canal and easy to get out of the canal. Gel-bassed preparations of EDTA (RC-Prep™for example) are difficult to get into the canal, and you never know whether you are covering all the walls. Once in the canal, the gel-based EDTA is difficult to remove entirely. The liquid EDTA is also extremely good as a lubricating agent while you are instrumenting the canal. It will help remove the debris created by the instrumentation and will facilitate easier cleaning, especially when you are using an engine-driven instrumentation system.
    We also use a 17 percent EDTA aqueous solution to condition the canal walls in preparation for cementing Flexi-Post® Fiber and Flexi-Flange® Fiber posts with EDS’s titanium-reinforced self-curing composite cement, Flexi-Flow®. The EDTA opens up the tubules and micro-etches the intratubular dentin for maximum retention of the cement to the dentin. The Flexi family of fiber posts are the only threaded fiber posts on the market. They give maximum retention through the combination of thread and bonding of the cement to the canal at all levels (Figure 3).
    There is only one minor precaution to be taken when using these irrigants together. Chlorhexidine 2 percent is a very reactive compound and will form precipitates with both sodium hypochlorite and EDTA (Figure 4). Always use a wash of either sterile water, or anesthetic solution between EDTA and Chlorhexidine and between Sodium Hypochlorite and Chlorhexidine. The wash will eliminate the formation of a percipitate with Chlorhexidine. Happy irrigating.

FIGURE 1: Bacterial biofilm coating the walls of the canal and inside the dentinal tubules.

FIGURE 2: CHX and EDTA made by EDS (201-487-9090, www.edsdental.com).

FIGURE 3: After post-hole preparation for the Flexi family of fiber posts, use EDTA to condition the dentin for maximum retention.

FIGURE 4: CHX forms a white precipitate with EDTA and a brownish precipitate with sodium hypochlorite.