Shaping ability of Hero 642 rotary nickel-titanium instruments and stainless steel hand K-Flexofiles in simulated curved root canals

Objective. The purpose of this study was to compare the shaping ability of Hero 642 rotary nickel-titanium instruments with that of stainless steel hand K-Flexofiles. Study design. Simulated 28 degrees and 35 degrees curved canals were prepared with Hero 642 instruments by using a crown-down preparation and with K-Flexofiles by using a reaming working motion (n = 24 canals in each case). All canals were sequentially prepared up to size 35. Preinstrumental and postinstrumental images were taken, and assessment of the canal shapes was completed with a computer image analysis program. Material removal was measured at 20 measuring points, beginning 1 mm away from the apex. In addition, preparation time, changes of working length, and instrument failures were recorded. Results. In comparison with stainless steel K-Flexofiles, rotary Hero 642 instruments achieved better canal geometry and showed less canal transportation, both in canals with 28 degrees curves and in canals with 35 curves. Three Hero instruments separated, whereas none of the K-Flexofiles separated. In 28 degrees curved canals, Hero instruments were significantly faster (P < .01) and maintained working distance significantly better (P < .05) than K-Flexofiles. These differences were insignificant in 35 degrees curved canals. Conclusion. Hero 642 instruments prepared curved canals rapidly, without change in working length and with only minimal transportation toward the outer aspect of the curve.