Effect of rotational speed on root canal preparation with Hero 642 rotary Ni-Ti instruments.

The purpose of this study was to evaluate the influence of Hero 642 rotary Ni-Ti instruments driven at 300, 400, or 600 rpm on root canal straightening, loss of working length, and instrument breakage. Sixty mesial root canals from extracted human mandibular molars were divided into 3 groups of 20 each and were instrumented at the aforementioned rotational speeds with a crown-down technique. Using a digital intraoral radiography system directly on the images of pre- and postoperative radiographs, degrees of canal curvatures were measured and recorded. Statistical analysis showed that final canal curvatures and working lengths were significantly reduced compared with those of original values in each group (p < 0.001). However, using Hero 642 rotary Ni-Ti system at different rotational speeds had no effect on canal curvature and working length alterations (p > 0.05). No file breakage was observed in any of the groups.