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.
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.