Influence of Different Distances of Pecking Motion on Cyclic Fatigue Resistance of Reciproc Blue Files

The aim of the present study was to evaluate the influence of different distances of pecking motion (in-and-out axial movement) on the cyclic fatigue of Reciproc Blue files (VDW, Munich, Germany). Forty-two instruments were subjected to a dynamic cyclic fatigue test using a stainless-steel artificial canal with a 69° angle and 2.5-mm radius of curvature in a custom-made device that allowed the instruments to rotate freely inside the simulated curved canal in a reciprocating movement with different distances of pecking motion until fracture occurred. Fourteen instruments were tested in each group at three different pecking depths at a constant pecking speed of 2.5 mm/s: G(2.5): 2.5-mm depth, G(5.0): 5-mm depth, and G(7.5): 7.5-mm depth. The time to fracture and the number of cycles to fracture (NCF) were recorded. Data were analyzed using analysis of variance (ANOVA) followed by the post hoc Tukey test, with a significance level of 5%. The fracture surface of the fragments was examined by scanning electron microscopy. The results demonstrated that the time to failure and NCF significantly increased as the pecking distance increased. The mean time to fracture and NCF were significantly lower in G(2.5) compared to the G(5.0) and G(7.5) groups (P < 0.001). There were no statistically significant differences in the parameters between G(5.0) and G(7.5) (P > .05). The results show that different distances of pecking motion can significantly extend the life span of rotary files. Appropriate pecking motions in the root canals are recommended to prevent the breakage of nickel-titanium rotary instruments.