WOG Primary (25, 0.07) variable taper with a parallelogram cross section with two cutting edges in contact with the canal wall, alternating with an off-centered cross section. Starting at 6%, the X2 file has ten increasing percentage tapers from D1–D11, whereas from D12–D16, there are decreasing percentage tapers. It has a centered mass and axis of rotation from D1–D3 (diameter), whereas from D4–D16 has an offset mass of rotation. Two NiTi instruments with similar cross-sectional geometry but different alloys were selected for this study PTN X2 (25, 0.06) variable taper with a rectangular cross section. Therefore, the aim of this study was to compare the mechanical properties of the PTN files with WOG. Interpreting all the mechanical properties of those recent NiTi rotary files and how it affect their performance in the canal is very important in order to select the adequate file according to each clinical situation. Counter-clockwise which is greater than the clockwise allows the file to progress apically while the latter disengages the file and eliminates file binding (Webber 2016 Adıgüzel and Capar 2017). It rotates in a reciprocal motion, with preset values set by the manufacturer of clockwise/counter clockwise angles. Its parallelogram-shaped cross-section has two cutting edges which are in contact with the canal wall, alternating with an off-centered cross section where only one cutting edge contacts the canal wall. The gold process is a post-manufacturing procedure in which the ground NiTi files are heat-treated and slowly cooled. WaveOne Gold (Dentsply Maillefer) when introduced was claimed to have an increased elasticity owing to its metallurgical developments in gold-wire heat treatment. Moreover, this asymmetric cross section improves canal shaping effectiveness as assumed by manufacturer (Elnaghy 2014). M-wire has resulted in an increased resistance of the file to cyclic fatigue of up to 400% compared to other files (Dentsply Maillefer n.d. ProTaper Next ( Dentsply Sirona, Ballaigues, Switzerland) is made of M-wire premanufacturing heat treatment technology with a rectangular asymmetric cross section, variable taper and is run by a clockwise (CW) continuous rotation. Thermal modification of the alloy results in alteration of the physical properties (Ha et al. Heat treatment and composition of the alloy, in addition to instrument geometry, influence the flexibility of NiTi rotary files. Flexible files will decrease iatrogenic errors as canal transportation and will lead to a more centered and safer preparation. Torsional failure is prevalent in narrow straight canals where the tip of the file is locked in the canal while the shank continues to rotate (Park et al. Cyclic fatigue is common in curved canals where the file is exposed to repetitive compression and tension (Al-Hadlaq et al. Many factors may relate to file separation, but cyclic fatigue and torsional stress are the two main causes (Al-Hadlaq et al. Several studies revealed that the rate of fracture of NiTi is seven times more than stainless steel files while others reported that NiTi rotary files fractured at a rate of approximately 5 times clinically (Alapati et al. Inspite of the increased flexibility in comparison with the stainless steel files, NiTi rotary instruments are more prone to fracture (Iqbal et al. Recently, there have been significant enhancements in the design and alloy of NiTi rotary files by improving the process of manufacturing, properties of the materials, and its microstructures (Gao et al. Hence, being aware of these behavioral differences, each clinician will be able to use the adequate file according to the clinical situation in addition to the manufacturer’s instructions. The geometry of the instrument, thermomechanical treatment of the alloy, and its composition affect the mechanical behavior (bending and torsion) of nickel titanium rotary files. In terms of torsional resistance, PTN also revealed higher torsional resistance than WOG. ProTaper Next® revealed higher flexibility than WaveOne Gold® when exposed to cantilever bending but showed higher stress accumulation than WOG. Instrument behavior under bending or torsional conditions was numerically analyzed in SolidWorks software package. Two-dimensional models of the two files PTN and WOG were created using computer tomography scanning and stereomicroscope to produce a three-dimensional digital model. The objective of this study was to assess the bending and torsional properties of two nickel-titanium endodontic files with equivalent sizes and various designs and alloys using finite element analysis, ProTaper Next®X2 (PTN) size 25 with 0.06 taper and WaveOne Gold® (WOG) primary size 25 with 0.07 taper.
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