Residual canal debris is organic and/or inorganic material that remains on the dentinal wall after conventional endodontic chemomechanical canal preparation is completed.35 This residual canal debris is also referred to as the smear layer. The organic and/or inorganic substance is derived from ground dentin; pulpal remnants; and, in cases of infected root-canal systems, bacteria.36
A possible explanation for the residual canal debris after chemomechanical canal preparation is that NiTi rotary files remain centered in the canal and therefore will not make contact with all the dentinal walls due to various invaginations and irregularities.37 An in vitro study by Chuste-Guillot demonstrated that regardless of which NiTi rotary-file system a clinician used to prepare an infected root-canal system, the root dentin that remained was infected and not bacteria-free.38 Lin et al reported that the major factors associated with endodontic failures were the persistence of bacterial infection in the canal space and/or the periradicular area.39
Another explanation for the presence of residual canal debris after canal instrumentation and irrigation may be that a clinician is not being vigilant in using EDTA and sodium hypochlorite.40 Lastly, canal morphology can be complex, making it difficult for the chemomechanical canal preparation to be effective in removing all the canal debris.41
The three main factors in removing residual canal debris are irrigation activation, mechanical debridement, and chemical debridement. Irrigation activation with ultrasonic, a polymer finishing file, polymer ultrasonic tip, positive pressure syringe, and negative pressure device have all demonstrated various abilities in removing residual canal debris.41,42
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