Sodium hypochlorite (NaOCI) has been recommended for irrigation during root canal preparation. This investigation used scanning electron microscopy to examine instrumented and uninstrumented surfaces in the middle third of root canals following the use of several concentrations of NaOCI (5.25%, 2.5%, 1.0%, and 0.5%). NaOCI was delivered with either an endodontic irrigation needle or an ultrasonic device. All of the concentrations of NaOCI with either delivery system were very effective in flushing out losse debris from the root canals. A smear layer with some exposed dentinal tubules was seen on all instrumented surfaces regardless of concentration of NaOCI or irrigation device. NaOCI in concentrations of 5.25%, 2.5%, and 1% completely removed pulpal remnants and predentin from the uninstrumented surfaces. Although 0.5% NaOCI removed the majority of pulpal remnants and predentin from the uninstrumented surfaces, it left some fibrils on the surface.
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