Effects of simulated clinical conditions on nickel-titanium rotary files

When rotary nickel-titanium files are used in highly curved canals, there is a significant risk of separation. This study exposed files to saline or 5.25% NaOCI, while freely rotating in axial motion with a range of ≅6 mm at 150 rpm for 30 s in a 1.5 mm inner diameter, thin-walled metal tube of 15 mm length with a 90° curve and a 5 mm radius of curvature. Files of 0.04 taper; 25 mm length; and in ISO sizes 25, 30, and 35 were each used three times. Groups were sterilized in a Chemiclave at 132°C for 30 min after each use or tested without sterilization. Controls were not subjected to simulated use. Torsional moment (N-cm) and angular deflection (degrees) at failure was determined on a Torsiometer/Memocouple. Data (n = 5) were analyzed by analysis of variance. Tukey-Kramer intervals at the 0.05 significance level were determined. Exposure to cyclic fatigue, irrigants, and sterilization did not consistently affect torsional moment or angular deflection, compared with controls. Torsional moment significantly increased with an increase in size, regardless of condition (unsterilized vs. sterilized) or solution (saline vs. NaOCl).