Shaping ability of ProFile rotary nickel-titanium instruments with ISO sized tips in simulated root canals: Part 2.

The aim of this study was to determine the shaping ability of ProFile 0.04 taper rotary nickel-titanium instruments with ISO sized tips in simulated canals. A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by ProFile instruments using the 'crown down' approach recommended by the manufacturer. Part 2 of this two-part report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and the overall post-operative shape. Out of 37 completed specimens 9 zips (24%) and one ledge (3%) were created, but no perforations or danger zones were found. There were significant differences (P < 0.01) between canal shapes for the incidence of zips and elbows but not for their distance from the end-point of preparation. At specific positions along the canal length there were significant differences between the canal types in terms of their mean total width; overall, at the end-point of preparation and along the curved portion of the canals those specimens with 40 degrees curves were widest. This trend continued for the width of material removed from the outer aspect of the canal curves, whereas along the inner aspect of curves more material was removed in the 20 degrees canals. Overall, transportation was towards the outer aspect of the curve at the end-point of preparation and along the curved portion of canals but more balanced along the straight coronal section. Absolute transportation was small and below 0.1 mm at every position including the zips. Under the conditions of this study, ProFile nickel-titanium rotary instruments with ISO sized tips produced a larger number of zips than expected; however, the degree of zipping was limited and relatively minor.