Cyclic fatigue and torsional resistance evaluation of Reciproc R25 instruments after simulated clinical use.

BACKGROUND To assess the influence of multiple uses on the cyclic flexural fatigue and torsional resistance of Reciproc R25 (REC) instruments. METHODS 256 canals (2 for each mandibular molar) were prepared using Reciproc R25 instruments. A total of 96 25-mm-long Reciproc R25 instruments were divided in six groups (n=8) on the basis of different number of canal shaped: new instruments (control group), 1, 2, 3, 4 or 6 canals shaped during simulated clinical use for other groups respectively. Sixteen files were used for each of the six groups (8 instruments for cyclic fatigue test and 8 ones for torsional test). Times to fracture (TtF) for cyclic fatigue and ultimate torsional strength and angle of rotation to fracture for torsional resistance were recorded. Data were statistically evaluated by the analysis of variance (ANOVA) with P .05). REC used in four and six canals showed significant lower times to fracture when compared with other groups (P .05). CONCLUSIONS REC25 files showed a significant decrease in cyclic fatigue resistance only when used in four or more molar canals while their torsional behavior was not affected by multiple uses.