Aim To determine the cleaning effectiveness and the shaping ability of FlexMaster nickel-titanium rotary instruments and stainless steel hand K-Flexofiles during the preparation of curved root canals in extracted human teeth.Methodology A total of 48 root canals with curvatures ranging between 25degrees and 35degrees were divided into two groups of 24 canals. Based on radiographs taken prior to the instrumentation with the initial instrument inserted into the canal, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared by FlexMaster instruments using a crown-down preparation technique or by K-Flexofiles using a reaming working motion up to size 35. After each instrument, the root canals were flushed with 5 mL of a 2.5% NaOCl solution and at the end of instrumentation with 5 mL of NaCl. Using the pre- and post-instrumentation radiographs, straightening of the canal curvatures was determined with a computer image analysis program. After splitting the roots longitudinally, the amount of debris and smear layer were quantified on the basis of a numerical evaluation scale, using a scanning electron microscope.Results Completely cleaned root canals were not found with any of the two instruments. In general, K-Flexofiles resulted in significantly less debris (P < 0.001) and less smear layer (P < 0.05) than FlexMaster instruments, but these differences were not significant in the apical third of the canals (P > 0.05). FlexMaster instruments maintained the original canal curvature significantly better (P < 0.0001) than K-Flexofiles. No significant differences were detected between the instruments (P > 0.05) for the time taken to prepare the canals.Conclusions Under the conditions of this study, K-Flexofiles allowed significantly better canal cleaning than FlexMaster instruments. FlexMaster instruments maintained the original curvature significantly better.

Aim The purpose of this study was to compare the shaping ability of FlexMaster rotary nickel-titanium instruments with stainless steel hand K-Flexofiles. This part of the two-part report describes the efficiency of these two instruments in simulated curved root canals.Methodology Simulated 28degrees- and 35degrees-curved canals were prepared by the FlexMaster instruments with a rotational speed of 250 rpm using a crown-down preparation technique, and by the K-Flexofiles using a reaming motion (n = 24 canals in each case). All canals were prepared up to size 35. The pre- and post-instrumentation images were recorded and assessment of the canal shape was completed with a computer image analysis program. The material removal was measured at 20 measuring points, beginning 1 mm away from the apex. Incidence of canal aberrations, preparation time, changes of working length and instrument failures were also recorded.Results In comparison with stainless steel K-Flexofiles, the rotary FlexMaster instruments achieved better canal geometry, showed less canal transportation and created fewer canal aberrations in both the canal types. Two FlexMaster instruments were separated, and 15 FlexMaster instruments and 11 K-Flexofiles were permanently deformed during preparation. However, these differences were not significant (P > 0.05). Between both the canal types, FlexMaster was significantly faster (P < 0.001) than K-Flexofiles. Both instruments maintained a good working distance.Conclusions FlexMaster instruments prepared curved canals rapidly, and with minimal transportation towards the outer aspect of the curve.