SEM evaluation of root canal dentin morphology after Ni-Ti instrumentation

The aim of this study was to compare, through scanning electron microscope (SEM), the ability of four Ni-Ti rotary instrument systems in shaping root canal walls and their ability in removing smear layer and dentin debris. Forty-six extracted single-rooted human teeth were divided into four groups and prepared to size 35 (Alpha System, FlexMaster, MFile) or 30 (NRT files). Irrigation was carried out with NaOCl and EDTA. Three parameters were evaluated in the coronal, middle, and apical thirds of the root canals: smear layer morphology, pulpal-inorganic debris presence and surface profile morphology. Data were statistically analyzed using the Kruskal-Wallis test (ANOVA). None of the Ni-Ti rotary instrument systems resulted in being able to obtain constantly regular shaped surfaces in apical thirds, where smear layer, pulpal and inorganic debris were often present. NRT file specimens resulted in being relatively free from debris and smear layer and gained better results and scores at any canal level.