Allan Deutsch
 
 

FIGURE 1: Two percent CHX solution was more effective than 2.5 percent NaOCl against E. faecalis.

    It turns out that the percentage of CHX is crucial! Sassone et al. in their article “The influence of organic load on the antimicrobial activity of different concentrations of NaOCl and chlorhexidine in vitro,” International Endodontic Journal, 2003,36;848-852 concluded that a 0.12 percent CHX solution did not eliminate E. faecalis at any time interval. One percent CHX eliminated all strains. The 0.12 percent is equivalent to “Peridex” mouthwash. Many other articles point to a 2 percent solution for clinical use in endodontics. At a 2 percent level the antimicrobial effect of CHX can be achieved in 1?2 minutes of contact. 
    At this point you may be saying to yourself, “This is very nice, but I still like to put calcium hydroxide in the canal in between visits to kill the bacteria.” Really amazing research has just been published concerning calcium hydroxide. Kayaoglu et al. in their article “Growth at high pH increases Enterococcus faecalis adhesion to collagen,” International Endodontic Journal, 2005,38;389-396, conclude that a minor increase in pH up to 8.5, which may be a consequence of insufficient treatment with alkaline medicaments such as calcium hydroxide, increases the collagen-binding ability of E. faecalis, in vitro. This can be a critical mechanism by which E. feacalis predominates in persistent endodontic infections. Wow! Taken clinically, if you don’t get enough calcium hydroxide into the canal to raise the pH enough, you make the infection worse (harder to get rid of). An additional two articles (Lin et al. JOE, 2003,29;565-566 and Basrani, OOO, 2003,96;618-624) showed that CHX was effective against E. faecalis and Ca(OH)2 was not. So for me, no more calcium hydroxide antibacterial therapy; it may make matters worse, not better!
     The article “Effect of root canal dressings on the regeneration of inflamed periapical tissue,” by Dammaschke et al. in Acta Odontologica Scandinavica, 2005, 63;143-152, concluded that chlorhexidine used as an intracanal medicament showed good periapical regeneration, suggesting that this may be an alternative to calcium hydroxide root canal dressing. OK, now we know that the tissue heals with this stuff!
    There is a bonus effect with chlorhexidine use. Rosenthal et al. in “Chlorhexidine substantivity in root canal dentin,” OOO, 2004;98:488-492, concluded that the results of their study indicate that CHX is retained in root canal dentin in antimicrobially effective amounts for up to 12 weeks. A fabulous property for an antimicrobial agent! They also said, “CHX is known to be particularly effective against many strains of bacteria found in infected root canals, including E. faecalis.” In a study comparing common endodontic disinfectants, 0.5 percent CHX was also significantly more effective at killing C. albicans than Ca(OH)2, 5 percent and 0.5 percent NaOCl and 2 percent IKI. While these substantive and antimicrobial properties of CHX found here are promising, it does not have the tissue-dissolving properties of NaOCl. Although NaOCl is still considered the irrigant of choice, the use of CHX may be considered advantageous as a treatment prior to obturation, an alternative irrigant during retreatments, or even incorporated into antimicrobial dressings.
     The take-home lesson is that CHX is good stuff, but how should we use it clinically? It appears that the key is the use of 15?17 percent aqueous solution of EDTA before the use of CHX. A large percentage of the bacteria causing the problem reside in the dentinal tubules. After instrumentation, the bacteria are covered by the smear layer of dentin. If we do not remove this layer, our 2 percent CHX cannot get to the bacteria and consequently will not kill them. Conversely, as shown by Clark-Holke et al. in “Bacterial penetration through canals of endodontically treated teeth in the presence or absence of the smear layer,” Journal of Dentistry, 2003, 31;275-281, when the smear layer is removed and the canal is obturated with gutta percha and an epoxy resin cement (like EZ-Fill®), there was no leakage of bacteria through the apical foramen. The presence of the smear layer resulted in leaking in 60 percent of the model systems over the experimental time period. So it is a good thing to remove the smear layer: 

1. before CHX application 
2. before obturation with an epoxy cement.

1. While instrumenting from #08 to #40 Stainless steel SafeSiders, use NaOCl 5 percent as the irrigant
2. While instrumenting with the 30/.04 and 25/.08 NiTis, use 17 percent aqueous EDTA (removes the smear layer)
3. Rinse out EDTA with water or anesthetic. Both EDTA and NaOCl form a precipitate and inactivate CHX! Therefore, do not let the CHX contact either EDTA or NaOCl.
4. Irrigate with 2 percent CHX and let sit in the canals for at least two minutes.
5. You can leave the canal slightly damp with CHX if obturating with EZ-Fill sealer. The epoxy EZ-Fill will set even under water. This will ensure prolonged maximum antibacterial activity.
6. Obturate the canals.