A comparative study of the effects of two nickel-titanium preparation techniques on root canal geometry assessed by microcomputed tomography.

The present study was conducted with the aim of evaluating and comparing the effects of a new Hero group (Endoflare, Hero-shaper, and Hero-apical; Micro-Mega, Besancon, France) and Protaper Ni-Ti rotary instruments (Dentsply/Maillefer, Ballaigues, Switzerland) on root canal geometry in extracted human teeth using microcomputed tomography (muCT). Twenty-two mesial root canals of mandibular first molars were randomly divided into two groups. Canals were scanned before and after preparation with both systems. Cross-sectional images of each canal were obtained at 2-mm intervals. Differences in canal roundness, cross-sectional area, perimeter of each canal before and after instrumentation, and the extent of root canal transportation were calculated using image analysis software. There was no difference between the two rotary systems in regards to working time. Both systems create a similar round shape after instrumentation regardless of the initial root canal's shape. The Hero instruments showed a greater cutting efficiency compared with the ProTaper at the levels of 8 mm, 6 mm, and 4 mm but not at the level of 2 mm. On the other hand, the ProTaper seems to have a similar cutting efficiency at all levels. However, the ProTaper showed a tendency toward apical transportation. Under the conditions of the present study, both preparation techniques prepared the canals rapidly with a sufficient round shape. Despite that, it seems that there is a great potential for the improvement of shaping ability of rotary instruments. Hybrid instrumentation techniques should be evaluated by future studies in order to provide better results regarding the shaping ability of rotary instruments.