Torsional profiles of new and used 20/.06 GT series X and GT rotary endodontic instruments with a quantitative analysis of both alloys

The purpose of this study was to investigate the torsional profiles of new and used 20/0.06 GTRTM series X(TM) (GTX) and GTRTM (GT) instruments and to determine their elemental components. Eight groups of 30 instruments were used 2, 6, or 10 times in simulated canals or remained as unused controls. Testing of torque (TF) and angle at fracture (AF) was conducted according to ANSI/ADA specification No. 28. Data analyses were performed using one- and two-way ANOVA with HSD post-hoc comparison, with alpha =0.05. Surface analysis was conducted for each instrument type. GTX showed a significant initial increase in TF with 2 and 6 uses (p<0.001), while GT which showed a linear reduction in TF with increased use (p<0.004). GTX and GT showed a significant decrease in AF in all uses-groups except the GT 2 uses-group (p<0.021). GTX instruments had a higher resistance to torsional failure after use as compared to GT. Both instruments have the same elemental components.