2020 Volume 63 Issue 6 Pages 512-518
Purpose: This study examined the effect of taper on the dynamic cyclic fatigue resistance of nickel-titanium (NiTi) rotary instruments.
Methods: This study examined three NiTi instruments with a tip size of 0.25 mm and 25 mm in length; i. e., Vortex Blue (Dentsply Sirona; size #25/0.04 taper and #25/0.06 taper; Group VB 0.04 and Group VB 0.06, respectively), and ProTaper Gold F2 (Dentsply Sirona; size #25/0.08 taper; Group PTG 0.08) (n=10 in each group). An artificial stainless steel canal with a 60° angle and 3 mm radius of curvature was used. The instruments were rotated in the artificial canal using a custom-made dynamic cyclic fatigue test device operated at an up-and-down speed of 50 mm/min and an axial amplitude of 1 mm. Rotational speeds were set according to the manufacturer’s recommendation. The canal was filled with a silicone oil to reduce the generation of frictional heat during the rotation of instruments. The time to fracture was measured using a digital stopwatch, and the number of cycles to fracture (NCF) was determined by multiplying the time by the number of rotations per minute. The length of the fractured tip was measured with an electronic digital caliper. NCF and the length of the fractured fragment in the three groups were statistically analyzed using the Kruskal-Wallis test followed by multiple comparisons with the Steel-Dwass test, with 5% set as the level of significance.
Results: NCF of Group VB 0.04 showed significantly higher values compared with that of Groups VB 0.06 and PTG 0.08 (p<0.05). There was no statistically significant difference between NCF of Groups VB 0.06 and PTG 0.08 (p>0.05). The length of the fractured fragment of Group VB 0.04 was significantly shorter compared with that of Group VB 0.06 (p<0.05). None of the other intergroup comparisons were statistically significant (p>0.05).
Conclusion: Under the present experimental conditions, the 0.04 taper Vortex Blue instrument showed a significantly higher dynamic cyclic fatigue resistance compared with the 0.06 taper Vortex Blue instrument. The dynamic cyclic fatigue resistance of the ProTaper Gold F2 instrument was similar to that of the 0.06 taper Vortex Blue instrument.
