The Effect of Preflaring on the Rates of Separation for 0.04 Taper Nickel Titanium Rotary Instruments.

By Roland D, Andelin W, Browning D, Hsu G, Torabinejad M,

Date: 01/2002
Journal: JOE


Purpose: to compare the separation rates of 0.04 taper NiTi instruments, using the manufacturer’s recommended technique, with a combination of passive step-back technique and rotary NiTi instrumentation.

N= 20 sets of 0.04 taper Profile Series 29 sizes 2 to 6 rotary NiTi instruments

inclusion criteria for the teeth: mesial roots of mandibular molars and buccal roots of maxillary molars with fully formed apices, curvatures between 20 to 30 degrees according to the method of Schneider and no previous RCT.  


•Standard access preparations were made & WL determined visually by seeing the patency file emerging through the apex.

•The 20 stets of the rotary instruments were divided into 2 groups. (A and B). Two operators were assigned to each group and given 5 sets of instruments.

•G A – the canals were instrumented by crown down technique recommended by the manufacture up to apical preparation with #4.

•G B – canals were preflared with hand files in passive step-back technique followed by rotary instrumentation in step-back enlargement to size#4. •The rotary instruments were used until they completely separated or to a maximum of 20 uses.

Most highlighted Results:

  • Separations occurred in 19 instances in group A ( crown down technique) and 3 instances in group B (combination of passive step back and rotary instrumentation) (p <0.0001).

Clinical significance: 

The importance of preflaring to reduce the chance of instruments separation.