An update on smear layer in endodontics - ROS - 2001 - Tome 30 - N°4

During root canal processing, formation of smear layer is unavoidable. The dentin chips detached from the canal walls by the endodontic tools combine with the pulp residue to form a mud which adheres to the dentinal surface. This may be prevented by using nickel-titanium instruments in continuous rotation, according to the crown-down method. Canal preparation is most often performed under continuously renewed irrigation by a sodium hypochlorite solution. This dissolves organic debris and has an antibacterial effect but the penetrating power of the irrigation solution is limited by the use of a syringe and the very presence of smear layer which prevents contact between the active principale and the bacteria.
Many instruments support this smear layer elimination at the end of preparation, notably its impact on : canal disinfection, the efficacy of calcium hydroxyde temporary treatment, the sustainability and seal of final gutta-percha obturation.
These objectives may be achieved by a final two-stage irrigation procedure : the smear layer is eliminated by a solution of EDTA or liquid citric acid in synergy with ultrasounds ; a combination of sodium hypochlorite and ultrasounds is then used to neutralise the chelating agent disinfect beyond the eliminated smear layer.