Cyclic fatigue of different nickel-titanium endodontic rotary instruments.

Objective: A comparative study of the fatigue resistance of rotary nickel-titanium endodontic instruments was performed with the aim of assessing the influence of both instrument design and surface treatment on flexural fracture.

Study Design: To evaluate fatigue resistance of different rotary instruments, a total of 120 instruments were tested; these came from different sources: ProFile, RaCe, K3, Hero, and Mtwo. To compare the effect of electro-polishing procedures on fatigue resistance, a group of RaCe instruments (which are normally electro-polished) without surface treatment was used. A scanning electron microscope (SEM) study for each instrument was performed before and after fatigue study to determine the mode of fracture and the aspect of tips and cross-sectional surface areas.

Results: ProFile instruments gave the best values for fatigue resistance. It was seen that for RaCe instruments the surface treatment reduces the presence of micro-cracks, surface debris, and machining damage.

Conclusions: This study shows that the instrument design often proves to be an important factor in the fatigue resistance of NiTi rotary instruments. In RaCe instruments the electro-polishing surface treatment increases the fracture-related fatigue resistance.