###### Abstract
The starting content for M-Wire thermal processing was a Nitinol formulation containing approximately 55.8 \(\pm\) 1.5% nickel, 44.2 \(\pm\) 1.5% titanium, and less than 1% trace elements [16]. Several papers have shown that M-Wire is more flexible than conventionally-treated NiTi alloys [17; 18; 19]. ProTaper Next (Dentsply-Maillefer), WaveOne (Dentsply-Maillefer), and Reciproc (VDW) are examples of systems manufactured by M-Wire. Shortly after the launch of M-Wire in 2008, SybronEndo (Orange, CA, USA) created another manufacturing method to produce Twisted File, a revolutionary rotary NiTi system (TF). Three new technologies were used in the production of TF: R-phase heat treatment, metal wire spinning, and a special surface treatment [20]. The twisting method is carried out by converting a raw NiTi wire in an austenitic state into R-phase using a patented thermal process. R-phase has a lower shear modulus and a transition strain that is one-tenth that of martensite transformation [21]. As a result, less stress is required to induce plastic deformation in R-phase, allowing the twisting mechanism to occur. To retain its new shape [22], TF is transformed back to austenite through additional thermal procedures after twisting. K3 XF and TF Adaptive are two other systems that use R-phase technology (TFA, SybronEndo, Orange, CA, USA). Unlike the instruments of the TF and TFA systems, K3 XF files are created using conventional grinding processes and R-phase heat treatment after the fact. TFA instruments are used with a new adaptive motion technology that allows for either rotary or reciprocating file kinematics based on the strain exerted by the root canal walls [14]. The Self-Adjusting File system (SAF; ReDent-Nova, Ra'anana, Israel) differs from other systems for two key reasons. First, the SAF is a hollow and adjustable file that adheres to the outline of the root canal in three dimensions, with the ability to fit to its cross-section. The SAF vibrates and eliminates a uniform dentin layer from the canal walls, also in oval, flat oval, and in any irregularly-shaped root canal while in use. Rather than machining a central part of the root canal into a circular cross-section, the SAF causes a flat canal to remain flat with slightly wider dimensions. Second, the hollow file allows for continual irrigation of the root canal during the process, with the irrigant being activated further by the vibrating motion of the file, which induces turbulence in the root canal. Irrigation is delivered by a special rinsing unit that delivers the irrigant at a flow rate of 5 mL/min (VATEA, ReDent-Nova) [23; 24]. The advancement of NiTi instruments has made endodontic care even more convenient for both patients and practitioners. However, clinicians and experts continue to be concerned with root canal anomalies [25; 26], radicular perforations [25; 26], instrument fracture [25; 26], and dental microcracks. Dentinal microcracks are complete or incomplete thickness cracks that occur on the root canal walls as a result of endodontic file operation. These defects result in vertical root fracture [27] and tooth extraction [28; 29; 30]. Regardless of the NiTi file system used during chemo-mechanical preparation, dental microcracks have been observed. The goal of the study is to analyze the effect of different file systems with respect to their different composition of NiTi alloys and cross-sectional shapes in dental crack formation during root canal instrumentation.