A scanning electron microscopic evaluation of the effectiveness of the F-file versus ultrasonic activation of a K-file to remove smear layer.

The objective of this study was to compare the effectiveness of F-files and ultrasonics to remove the smear layer from instrumented root canals when irrigated with sodium hypochlorite and EDTA. Sixty healthy human premolar teeth were instrumented with ProTaper file series to F3, and the canals were enlarged with Profiles 35/.06, 40/.06, and 45/.06. The canals were then instrumented with either the F-file or an ultrasonically activated #20 K-file with or without EDTA. The removal of smear layer was visualized using blind scanning electron microscopic micrographs. There appeared to be little difference between the F-file and the ultrasonically activated #20 K-file in removal of the smear layer with or without EDTA. The effect of ultrasonic activation appeared to be self-limiting with high-volume flushes of irrigant. It appears the F-file was not any more beneficial in removing smear layer. Conversely, smear layer removal appears to be mostly influenced by the introduction of an EDTA rinse.