The effect of preflaring on the rates of separation for 0.04 taper nickel titanium rotary instruments.

The purpose of this study was to compare the rates of separation of 0.04 taper nickel titanium (NiTi) rotary instruments using two different instrumentation techniques. Twenty sets of 0.04 taper Profile Series 29 rotary instruments, sizes 2 to 6 were used in the mesial (mandibular) or buccal (maxillary) canals of extracted human molars with a 20 to 30 degree root curvature according to the Schneider classification. The rotary instruments were used up to 20 times either with the crown-down technique recommended by the manufacturer or with a combination of preflaring with hand files in a passive step-back technique followed by rotary instrumentation. Statistical analysis of the data showed that the combination technique allowed more uses before separation compared with the crown-down technique recommended by the manufacturer p < 0.0001.