The dentin mud or “smear layer” forms as a result of the action of endodontic instruments during root canal therapy. The debris (inorganic materials along with the pulpal tissues, bacteria, blood cells, etc.) that is formed is smeared against the canal surface during the cutting and planing actions of the endodontic files and instruments. This layer harbors surviving micro-organisms and interferes with the penetration of irrigation solutions, medication and obturation materials into the dentinal tubules.
Removal of this layer not only allows the irrigants to better penetrate and kill the micro-organisms that have invaded the dentinal tubules, but it also improves the contact and adaptability between the obturation material and the canal walls and ultimately the seal.
The most commonly used endodontic irrigants are: sodium hypochlorite (NaOCl) and EDTA. They effectively remove both organic and inorganic components of the smear layer. Alternate use of NaOCl and EDTA solutions during irrigation provides the most cost-effective method of disinfecting the root canal system.
Other all-in-one irrigation solutions such as SMEAROFF 2-IN-1 (Proprietary EDTA / CHX mix formulated with wetting agents and surface modifiers) or QMix (EDTA, CHX and a detergent) have also been shown to be very effective in removing the smear layer and killing the micro-organisms while respecting the dentinal structure.
Dr. Mahmoud Ektefaie @ vanendo
What is your opinion of using 2% chlorhexidine at the end prior to obturation?
Dentin medicated with chlorhexidine (in QMix or as 2% solution) as well as tetracyclines (in BioPure MTAD) shows antimicrobial substantivity. It is certainly beneficial to use multiple irrigants in order to reduce or possibly eliminate the micro-organisms from the root canal system. However, for any irrigant to be effective it has to physically reach the micro-organisms. If we mechanically allow the irrigants to reach deep into the irregularities and dentinal tubules (by means of complete shaping, removing the smear layer, using sonic or ultrasonic agitation techniques, etc.), any irrigant will do the job. And on top of all, full-strength NaOCl is the most effective.