12/3/2023 0 Comments Endodontic filesIn this step of the review were found 412 research papers. Table 1 summarizes the search strings, databases, and the number of articles found in the review process. Therefore, the words “fatigue” (involving the most complex failure phenomenon) and “endodontic file” (object of study) were used to construct the search equation applied for filtering titles, abstracts, and keywords. It was found that the answer to the question about the failure mechanism is summarized in the phenomenon of fatigue, which involves failure considerations related to torsional and bending loads. ![]() ai were reviewed to define which one provides more information and establish a general overview of the topics of interest. The following databases Scopus, Web of Science (WOS), Science Direct, and Dimensions. The following questions were formulated to guide the information search: What are the failure mechanisms identified for NiTi files? What tests are performed to determine the mechanical behavior of NiTi files, and what type of equipment is used? Who are the most active authors? How has the study of the failure of NiTi files evolved? Search for publications (including search strings, databases selection, and inclusion and exclusion criteria). This scoping review focuses on identifying the different endodontic files studies related to fatigue behavior as well as gathering relevant information about the tests, types of studies, authors, and gaps in the area. The operator does not perceive any deterioration until the file is fractured. The biggest drawback is that the shape memory and superelasticity properties of the NiTi alloy imply that the files do not exhibit deformation or signs of the proximity of failure detectable with the human eye during endodontic treatment 13, 14. NCF (number of cycles for fracture) values for NiTi rotary files have been recorded depending on this design 12, demonstrating variability and randomness in fatigue failures due to the limited information collected during their operation. There is a wide variety of cross-sectional geometries. time behaviors is illustrated in Figure 1D. ![]() The alternating direction of these friction forces causes fatigue failure. In this case, the file is not trapped, but in the reciprocating motion, the friction between the root canal walls generates torsional opposition loads to the file, as shown in Figure 1C. A third failure mechanism known as the torsional fatigue can be identified for reciprocating instruments. At the same time, the driven motor continues rotating this mechanism is illustrated in Figure 1B. Another mechanism is the torsional failure caused when a part of the NiTi instrument becomes trapped in the root canal (by friction and/or adhesion). Tension and compression stresses occur when the file rotates inside the canals, causing fatigue failure ( Figure 1A). 11įigure 1 shows the primary failure process of the file when it is used inside the root canal. In this case, one of the file surfaces acts in tension, and the other works in compression. Some experimental approaches have been developed to identify that the failure mechanism for rotatory files is flexural fatigue caused by the bending of the file when it is placed in the root canal. Others are focused on the use of Finite Element Analysis 10. However, few studies are related to completely understanding the fatigue failure mechanism 1, 6 - 9. 5 Fatigue failure resistance of NiTi files has been widely studied, mainly by comparing brands. From the beginning, studies have been conducted to minimize or eliminate the intrinsic defects of the material, increasing its hardness and flexibility, improving resistance to fatigue life, and prolonging its cutting efficiency. About ten years ago, the reciprocating motion (rotation changes direction at some point of the revolution) was introduced. NiTi instruments are driven by an electric motor initially used with a continuous rotary motion. In addition, this failure generates subsequent medical inconveniences if it is not possible its immediate removal. 3 A failure during the procedure implies a significant reduction in its effectiveness since the separated fragment can become an element that stands in the way of the successful eradication of the infection. ![]() However, these instruments are susceptible to fracture by fatigue 2, which is considered harmful for the prognosis and treatment. Due to the hyperelastic material behavior of NiTi, this alloy enables elastic deformations that are useful to follow the random geometry of the root canal 1. Fracture forms an integral part of fatigue cracking mechanisms in NiTi endodontic files.
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