title: Effect of immersion in sodium hypochlorite on torque and fatigue resistance of nickel-titanium instruments.
abstract: This study investigated the effect of immersion in sodium hypochlorite (NaOCl) on torque and fatigue resistance of two nickel-titanium files. Size 25 .04 ProFile and RaCe files were immersed in 5.25% NaOCl for 1 or 2 hours at temperatures of 21 degrees C and 60 degrees C. Torque and angle at failure were measured according to ISO 3630-1. Resistance to cyclic fatigue was determined by counting rotations to breakage in a 90 degrees curve with a 5-mm radius. Data were analyzed by 2-way analysis of variance. Torsional resistance of both rotaries was not significantly affected by immersion in NaOCl, except after 2 hours of immersion at 60 degrees C. Resistance to cyclic fatigue decreased significantly for ProFile and RaCe instruments after immersion in NaOCl. Spontaneous fractures occurred in 28 of 160 files during immersion in NaOCl. In conclusion, nickel-titanium rotaries have reduced resistance to cyclic fatigue after contact with heated NaOCl and may then be considered single-use instruments.
authors: Division of Endodontics, Preventive and Restorative Dental Sciences, UCSF School of Dentistry, 707 Parnassus Ave, San Francisco, CA 94143, USA. ove.peters@ucsf.edu
authors: Ove A
authors: OA
authors: Peters
authors: Jan O
authors: JO
authors: Roehlike
authors: Michael A
authors: MA
authors: Baumann
mesh_terms: D000704:Analysis of Variance; D009532:Nickel; D012388:Root Canal Irrigants / Q000009:adverse effects*; D018915:Root Canal Preparation / Q000295:instrumentation*; D012973:Sodium Hypochlorite / Q000009:adverse effects*; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium; D019415:Torque
chemical_list: D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite