An ultrastructural study of the smear layer: comparative aspects using secondary electron image and backscattered electron image.

The aim of this investigation was to study the influence of three irrigation procedures on the composition, structure, and aspect of the smear layer within root canals. Three homogeneous groups were prepared without irrigation, with physiological serum, or with Dakin (dilute, neutral solution of sodium hypochlorite). Root canals were instrumented with Rispi Reamers mounted on a counterangle Giromatic. The irrigating solution was delivered with an endodontic irrigation needle. Modifications were observed by scanning electron microscope using secondary electron imaging and backscattered electron imaging. Instrumentation without irrigation produced a very thick smear layer that appeared in backscattered electron imaging as a compact assembly or organic and inorganic components. Instrumentation using Dakin produced canal walls that were less smeared, and the pockets of debris remaining were smaller in size than when using physiological serum. When the root canals were irrigated, the smear layer appeared as a double layer, one superficial and the other deep. The layers were predominantly inorganic with Dakin.