The effect of autoclaving on torsional moment of two nickel-titanium endodontic files

Aim To evaluate the effects of repeated autoclaving on torsional strength of two nickel-titanium (NiTi) rotary endodontic files: Twisted Files (SybronEndo, Orange, CA, USA) and GT Series X files (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA). Methodology Four groups of 20 GT Series X (size 20, .06 taper) and four groups of 20 Twisted Files (size 25, .06 taper) were subjected to 0, 1, 3 or 7 autoclave cycles. The nonautoclaved files served as controls. Failure in torsion was recorded using a torsiometer according to ANSI/ADA 58 and ISO 3630-1 standards. Mean results were analysed using analysis of variance (anova) at a 95% confidence level. Dunnett's procedure was used for post hoc analysis. Results There was no significant difference in torsional moment between the number of autoclave cycles for Twisted Files. However, the mean torque at failure was significantly lower for GT Series X files after three (P<0.001) and seven (P<0.001) autoclave cycles. For Twisted Files, there was a significant increase (P<0.001) in mean number of degrees of rotation to failure with more autoclave cycles compared to nonautoclaved files. For GT Series X files, there was no significant association (P=0.527) between the number of autoclave cycles and the degrees of rotation to failure. Conclusions Repeat autoclaving of unused GT Series X files between three and seven times resulted in a significant reduction in torsional strength, whilst there was no effect observed for Twisted Files.