Comparison of the Cyclic Fatigue Resistance of Reciproc and Reciproc Blue Nickel-Titanium Instruments in Artificial Canals with Single and Double (S-shaped) Curvatures

The aim of this study was to compare the cyclic fatigue resistance of Reciproc (VDW, Munich, Germany) and Reciproc Blue (VDW) in artificial canals with both single and double (s-shaped) curvatures. Methods: In total, 80 instruments were tested in this study. Reciproc R40 and Reciproc Blue R40 instruments were selected for the cyclic fatigue resistance test (n=20 in each test). Each instrument was rotated in canals with a single curvature (60° curvature, 5-mm radius) and a double curvature (first coronal curve: 60° curvature and 5-mm radius; second apical curve: 70° and 2-mm radius) until fracture. The time to fracture was calculated, and the length of each fractured fragment was recorded. A one-way analysis of variance (ANOVA) and Tukey’s post hoc tests were used to analyse the time to failure. Results: All the instruments had significantly higher fatigue resistance in the single simulated curvature canal than in the double curvature canal (P<0.05). In both curvature groups, the time to fracture of the Reciproc Blue was longer than that of the Reciproc instruments (P<0.05). In the double curvature canal, the instruments tended to fracture more often in the apical curvature than in the coronal curvature. There was no significant difference in the length of the broken fragments between the two groups in either the single or double canal curvatures (P>0.05). Conclusion: The Reciproc Blue instruments showed higher cyclic fatigue resistance than the Reciproc instruments in both single and double canal curvatures.