Abstract
The aim of the present study is to evaluate operative torque, torque at failure and the difference between these two values—the “torque range”—of two different NiTi files. We also sought to evaluate and compare these parameters for new and used files. Forty S-One 20.06 and forty M-Two 20.06 were tested, divided in four equal groups (n = 10) for each brand. Ten instruments from each brand performed three root canal treatments each on standardized extracted single-rooted teeth. Afterwards, each group was subjected to the following two tests: operative torque and torsional resistance. Mean values for all the tested groups were calculated. The results for new instruments showed that S-One developed significantly higher operative torque, but higher torsional resistance. The results for used instruments showed that the S-One 20.06 developed less operative torque and higher mean torsional resistance value compared to the M-Two. Moreover, the percentage reduction of both values was significantly higher for M-Two. The results of the present study showed a safer torsional behavior of the S-One. These results could be related to the heat treatment and the manufacturing process.
Highlights
During root canal treatments (RCT) instruments undergo flexural and torsional stresses that could eventually result in the instrument separation [1,2,3]
This type of test do not take into account the multitude of stresses, since nickel titanium (NiTi) rotary instruments are used dynamically [15]
The present article investigated the role of the torque range over the torsional resistance of an instrument, both in a static and dynamic way
Summary
During root canal treatments (RCT) instruments undergo flexural and torsional stresses that could eventually result in the instrument separation [1,2,3]. According to Sattapan et al [4], torsional failure is the most common cause of intracanal failure. This fracture occurs when the tip or another apical part of the instrument binds into the canal while the upper part continues to rotate. To date in literature several studies investigate the parameters that could influence the torsional resistance. These factors are the cross section, the metal mass of the instrument, the heat treatments and the metallurgical properties of the nickel titanium rotary (NTR) instruments [5]
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