Cyclic Fatigue Resistance and Force Generated by OneShape Instruments During Curved Canal Preparation

Objectives: To evaluate the cyclic
fatigue resistance and the force generated by OneShape files during preparation
of simulated curved canals. Methods:
Six OneShape files (the test) and six ProTaper F2 files (the control) were
subject to the bending ability test. Another thirty files of each type were
used to prepare artificial canals (n=60), which were divided into 3 groups
according to respective curvatures of the canals (30°, 60°, and 90°). The
numbers of cycles to fatigue (NCF) as well as the positive and negative forces
that were generated by files during canal preparation were recorded. The
scanning electron microscopy was applied to detect the fracture surfaces. Results: Compared with ProTaper F2
files, the bending loads of OneShape files were significantly lower at
deflections of 45°(P < .05), 60° (P < .05) and 75° (P < .01). No significant difference
was found at 30°. OneShape files presented a higher NCF in both 60° and 90°
canals than the control (P < .01).
No significant difference of NCF was found between OneShape and ProTaper files
in 30° canals. During the preparation of 30° canals by both files, the negative
forces were dominant. With the increase of the curvature, more positive forces
were observed. When the OneShape Files were compared with the control, significant
different forces were found at D3 and D2 (P < .05) in 30° canals, at
D2 (P < .05), D1 (P < .01) and D0 (P < .01) in 60°
canals, and at D4 and D3 (P < .01) in 90° canals. Conclusions：OneShape files possessed a reliable flexibility and cyclic fatigue
resistance. According to the assessments of the forces generated by files,
OneShape instruments performed in a more fatigue-resistant way during curved
canal preparation, compared with the ProTaper F2 files.