DOs and DONTs in CHLORHEXIDINE

ONE OF THE largest causes of endodontic failure is infection. Infection can be the reason for the tooth’s needing endodontics in the first place, or it can be the cause of retreating an already endodontically treated tooth. The causes of infection include caries, fracture, excessive trauma from operative or prosthetic preparation, leakage of restorations, missed canals or anatomy when doing the endodontics initially, inadequate instrumentation of the canal, and calcified canals. Endodontic infections are generally caused by multiple species of bacteria living on the canal walls or in the dentinal tubules.Many times, the bacteria can be found in biofilms attached to the walls and entering into the tubules. The biofilm coats the bacteria in a film that makes it much harder to kill the bacteria—in other words, much more difficult to get rid of the infection. 

       Luckily for us, the primary way to cure an endodontic infection is through instrumentation and enlargement of the canal. The longer the infection has been around, the farther up the dentinal tubules the bacteria will have gone. In badly infected teeth, I recommend instrumenting to a number 45 or 50 if possible to the apex. In straight canals, such as incisors and canines, we can even go to wider-diameter instruments if necessary. However, research has shown that instrumentation alone does not remove all the debris in the canal. A substantial amount of debris is left in the canal even after thorough instrumentation. In order to remove more debris we must irrigate the canal. The best irrigant to date is sodium hypochlorite, or Clorox. It will dissolve the debris and kill most of the bacteria. However, it does not kill all the bacteria. Therefore it needs a little help. Over the last ten to twelve years there has been more and more literature showing the bacterial killing ability of 2 percent chlorhexidine (CHX). It actually kills E. faecalis, a bacteria shown to be prevalent in failed and infected root canals, better than sodium hypochlorite. Therefore, in order to increase my endodontic success rate in non-vital cases, I irrigate every non-vital case with 2 percent CHX . This practice has especially helped get rid of infections from failed root canal treatments. 

        To use CHX successfully, we must be aware of several facts and put them into practice clinically. First, for endodontic infections CHX works effectively only at the 2 percent strength. Peridex, which is a 0.12 percent solution of CHX, is not strong enough and will take more than six hours to kill the bacteria in the canal. This length of time is not acceptable for an in-office procedure. The 2 percent CHX will kill the bugs in two minutes. Therefore, when using CHX, I leave it in the canals for two minutes. However, before placing it in the canal we must remove the smear layer .

     The smear layer, produced by instrumentation, obliterates the openings of the dentinal tubules into the canal and covers the bacteria that are on the walls of the canals. If the smear layer is not removed, the CHX will not penetrate into the tubules. If the CHX does not get into the tubules and against the canal wall, it cannot kill the bacteria. It must be in contact with the bacteria in order to kill them. Therefore, we must remove the smear layer and expose the canal walls and tubules. This can be done using 17 percent EDTA in water . The 17 percent EDTA must be in contact with the smear layer for a minimum of one minute for it to work. 

      Once the smear layer is gone, the 2 percent CHX can readily contact any bacteria that remain in the canal or in the tubules. 

    Chlorhexidine is a very reactive chemical; that is why it works so well in killing bacteria. However, because it is so reactive it reacts with both sodium hypochlorite and EDTA. It forms a precipitate with both of them . These precipitates should be avoided.

    Therefore, if there is any residue of EDTA or sodium hypochlorite in the canal it should be rinsed out. You can use either water or anesthetic solution to accomplish this step. Do not go directly from EDTA or NaOCl to CHX; you will get a precipitate in the canal. Currently, no one is quite sure what these precipitates are, but they do clog the canal and perhaps may interfere with obturation

To summarize the most important features:

1. Use 2 percent CHX only.
2. Leave it in the canal for a minimum of two minutes to work.
3. Use 17 percent EDTA in water to remove the smear layer before using CHX.
4. Do not allow CHX to come directly in contact with EDTA or sodium hypochlorite; use a rinse between the reagents.