## 4 Discussion  
The main aim of endodontic therapy is to clean and fill the RCS in order to preserve or regain the integrity of the periapical tissues [45]. Despite continuous developments in instruments to improve RCS cleaning [46], dentin microcracks continue to be a source of concern for clinicians and researchers [47; 48] as they often contribute to the instrumented tooth fracturing and extraction [49; 50; 51]. Although, there are multiple factors that contribute to dental crack formation like the design of the file, flexibility of file, and stress on the tooth surface used during instrumentation. Files considered in the study are ProTaper Universal file and Mtwo which belong to the conventional NiTi file system group. The cross-sectional design of ProTaper Universal resembles that of a reamer, with three machined cutting edges and convex core [52]. The Mtwo files cross-sectional design resembles that of the S-file [53]. It has no radial lands, progressive blade pitch from tip to shaft, positive rake angles, and a non-cutting tip. Mtwo files have two cutting edges with minimal radial contact providing maximum space for dentin removal. It is advised by the manufacture to use all files in the instrumentation sequence to the full length of the root canal [54]. ProTaper Next is fabricated utilizing M-wire technology which helps to increase file flexibility. The off-centered rectangular cross section and the unique design of the file generate enlarged space for debris [55]. WaveOne made of M-wire metallurgy have a reverse helix and 2 distinct cross-sections along the length of their active portions. From D1-D8, the WaveOne files have a modified convex triangular cross-section, whereas from D9-D16, these files have a convex triangular cross-section [56]. Reciproc also made of M-wire technology consist of s-shaped cross section, the variable taper, the cutting angles and the thermally improved raw material provides high efficiency and cutting performance. The file's tip is non-cutting for a gentle treatment near the apex [57]. Twisted File Adaptive (TFA) is made up of R-phase heat treatment, twisting of the metal wire, and a special surface conditioning [58]. As a result of this it is consider superior to traditional NiTi instruments respect to their flexibility; cyclic fatigue resistance, cutting efficiency, and their ability maintain the original canal shape with minimal transportation [59; 60]. K3 XF consists of modified triple and developed by R-phase heat treatment [61]. Self-adjusting files system (SAF) file system is a hollow-file system that adapts to wall of the root canal according to anatomy of the canal [62]. Although there are different design and cross sections of the files developed there is still development on dentinal cracks during root canal instrumentation. Another important factor that contributes to dentinal cracks is improper tooth preparation. It is often seen that rough dehydration leads to fracturing, cracking and volumetric shrinkage [63]. It recommended to prepare the tooth with lubricants to replace water before root canal instrumentation for desired results to avoids necessary factors affecting the desired results [64]. Although the step of tooth preparation is an important step in root canal instrumentation it is described in detail in the studies included in the systematic review. The aim of this systematic analysis was to assess the prevalence of dentin microcracks after using instruments made with conventional, R-Phase, and M-Wire NiTi alloys and the SAF system. A systematic review of the literature is a coordinated review focused on a pre-established approach to classify, pick, and critically examine important studies regarding a topic or doubt. The aim of systematization is to reduce the significant amounts of prejudices that are typically present in a traditional or non-systematic analysis of the literature [65]. Critically, studies that involved the use of mandibular teeth with a maximum curvature of 40 degrees and no prior dentinal microcracks were included.