SummaryForty‐five acrylic blocks with simulated curved canals were divided into three groups of 15 blocks each. In group 1 the canals were instrumented with ultrasoni‐cally energized K‐files (UEF) using a piezoelectric ultrasonic device. In group 2 the canals were prepared with ProFile 0.04 Taper Series 29 Rotary Instruments (PRI) in conjunction with a low‐speed high torque handpiece. In group 3 (control) the canals were hand instrumented (HI) with conventional K‐type files using a standard push‐pull circumferential technique. The efficiency of these techniques for preparing the simulated canals were compared by measuring the amount of transportation of the prepared canals at different levels from the working length using a double exposure photographic technique. A statistical analysis was used to indicate any significant difference among groups. The results showed that the use of PRI provided well‐centred and more tapered preparations. Conversely, the use of UEF and HI resulted in frequent alteration of the original curvature, showing transportation at different levels from the w
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