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Cyclic fatigue resistance of nickel titanium rotary files in the martensitic state: a systematic review.Cowling, Steve; Harrison, Trisalda (University of Chester, 2020-04-16)Background: There are many factors which effect the cyclic fatigue resistance of Nickel titanium or NiTi files. The metal can exist in a soft martensitic state which is thought to improve the resistance to cyclic fatigue. The NiTi alloy transforms from one state to the other at a certain temperature and various factors can modify this transition temperature. Temperature effects the state of the metal so the way the file acts at intracanal temperature is significant. Most cyclic fatigue tests have been carried out at room temperature. Objectives: Identifying martensitic files and whether the resistance to cyclic fatigue is greater in these files at intracanal temperature. Methods: A PICOS is used to formulate the review question. It provides a framework to develop inclusion and exclusion criteria. Search terms are used on the databases Science Direct, Wiley, PubMed and Google Scholar. A single reviewer screened the results, applying inclusion and exclusion criteria. The results are analysed and a descriptive analysis carried out. A Joanna Briggs checklist for cohort studies is used to assess the quality of the studies. An assessment of bias in the primary studies and bias in the review process is carried out. Keywords: cyclic fatigue, martensitic, intracanal temperature, CM files, Gold files, Blue files, EDM files. Results: The overall quality of the included studies was judged as moderate. However, cyclic fatigue testing methods have no standardisation, so it is difficult to compare studies. Many studies did not show evidence of sample size calculation and this was not taken into consideration by the scoring system for quality assessment. Within the limitations of the study it is found that at intracanal temperature, Hyflex EDMTM is potentially martensitic, existing in the R-phase which is considered to be a martensitic phase. It is also found that a wide range of 30.8 °C – 36 °C exists for intracanal temperature. Conclusions: Within the limitations of the study it is found that the Hyflex EDM file is martensitic at intracanal temperature and has a higher cyclic fatigue resistance than the other martensitic phase files. Most of the martensitic phase files identified possessed a greater cyclic fatigue resistance than the other files tested.