Abstract
ObjectivesTo evaluate the cyclic fatigue resistance and the force generated by OneShape files during preparation of simulated curved canals.MethodsSix 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.ResultsCompared 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.ConclusionsOneShape 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.
Highlights
Nickel-titanium (NiTi) instruments, essentially owning to their superelastic characters, have become an elementary implement in root canal preparation [1, 2]
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)
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
Summary
Nickel-titanium (NiTi) instruments, essentially owning to their superelastic characters, have become an elementary implement in root canal preparation [1, 2]. In spite of the increased flexibility compared to the stainless steel instruments, NiTi instruments are still exposed to the risk of fracture in clinical situations, which was caused by torsional and cyclic fatigues [3, 4]. The cyclic fatigue typically happens in preparing curved root canals where the instruments are subjected to alternating tensile and compressive stresses [5,6,7]. The longitudinal axial stress subject to files during canal preparation was considered as resistance resulting from the apical compressive force, which was named as the positive force (PF) [9, 10]. The characterization of both PF and NF generated during preparation of curved canals is not fully understood
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