Abstract:

Objective

To evaluate the shaping effect of two different rotary nickeltitanium instruments in simulated resin curved canals performed by abecedarian.

Methods

Thirty simulated canals in resin blocks were divided into two experimental groups， and prepared with Protaper and Hero642 by fifteen beginners by crown-down technique. Another two resin blocks were reserved as negative control. Preoperative and postoperative photographs， recorded using a digital camera， were superimposed， and aberrations were recorded. The amounts of apically extruded debris were recorded， the curvature degrees and the apical transportation indexes （ATI）pre- and post instrumentation were compared in order to test the shaping ability of these two instruments. All the data were analyzed with SPSS using t test.

Results

The result showed that there was no statistically difference in the curvature of the canal reduced by both groups （P ＞0.05）， nevertheless， the curvature was significantly reduced by Protaper than that reduced by Hero642， which was -6.77° with Protaper and -5.48° with Hero642. Three pieces of Protaper with broken， whereas one piece of Hero642 was broken. The mean widths of the root canal prepared by Protaper are larger than Hero642， moreover， the differences of the mean widths in the middle and coronal aspects of the canal are statistically significant.

Conclusions

Protaper instruments show better shaping ability， however， Hero642 instruments are easier， safer and more efficient to use. Therefore， Hero642 instruments are easier for rotary nickel-titanium instruments beginners to master.

Key words: Abecedarian experiment, Rotary nickel-titanium instruments, Root canal preparation, Simulated curved canals in resin blocks