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 BioPure MTAD (Tetracycline, citric acid and a detergent) 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.