Abstract
The aim of this study was to investigate the role of the flat-designed surface in improving the resistance to cyclic fatigue by comparing heat-treated F-One (Fanta Dental, Shanghai, China) nickel–titanium (NiTi) rotary instruments and similar prototypes, differing only by the absence of the flat side. The null hypothesis was that there were no differences between the two tested instruments in terms of cyclic fatigue lifespan. A total of 40 new NiTi instruments (20 F-One and 20 prototypes) were tested in the present study. The instruments were rotated with the same speed (500 rpm) and torque (2 N) using an endodontic motor (Elements Motor, Kerr, Orange, CA, USA) in the same stainless steel, artificial canal (90° angle of curvature and 5 mm radius). A Wilcoxon–Mann–Whitney test was performed to assess the differences in terms of time to fracture and the length of the fractured segment between the flat- and non-flat-sided instruments. Significance was set at p = 0.05. The differences in terms of time to fracture between non-flat and flat were statistically significant (p < 0.001). In addition, the differences in terms of fractured segment length were statistically significant (p = 0.034). The results of this study highlight the importance of flat-sided design in increasing the cyclic fatigue lifespan of NiTi rotary instruments.
Highlights
The development of endodontic nickel–titanium (NiTi) rotary instruments have improved root canal shaping, making the treatment more feasible, repeatable, and faster [1,2,3]
Despite the superior mechanical properties of the NiTi alloy, the risk of intracanal separation of the nickel–titanium rotary instruments has been shown to increase when compared with the traditional stainless steel files [1]
Published studies have shown that mechanical motion plays an important role in improving cyclic fatigue resistance by reducing the stress applied to the instrument [12,13,14]
Summary
The development of endodontic nickel–titanium (NiTi) rotary instruments have improved root canal shaping, making the treatment more feasible, repeatable, and faster [1,2,3]. Despite the superior mechanical properties of the NiTi alloy, the risk of intracanal separation of the nickel–titanium rotary instruments has been shown to increase when compared with the traditional stainless steel files [1]. Published studies have shown that mechanical motion plays an important role in improving cyclic fatigue resistance by reducing the stress applied to the instrument [12,13,14]. A new thermally treated NiTi rotary instrument, F-One (Fanta Dental, Shanghai, China), characterized by an S-shaped, flat-sided cross-section has been developed. The manufacturer claims that the S-shape and flat design confers advantages in terms of reducing blade engagement and increasing fatigue lifespan. It is claimed that the flat design reduces stress by sweeping the Materials 2019, 12, 2523; doi:10.3390/ma12162523 www.mdpi.com/journal/materials x FOR PEER REVIEW
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