The use of nickel-titanium instruments during endodontic treatment ensures high-quality treatment of root canals. However, during instrumentation in the curved root canals of nickel-titanium instruments experience cyclic loading, which leads to their breakage. The splinter of the tool in the root canal makes it difficult for high-quality processing and obturation of the root canal, which is a very urgent problem. To carry out instrumental processing in canals with various anatomical and topographic features, the files must have phenomenal flexibility, lack of straightening of the canal, and have a safe non-aggressive tip. And for this reason, one of the most popular nickel-titanium COXO SC PRO tools was selected as a study, which, according to the manufacturer, have all the listed properties. The aim of the study is to determine the limit of resistance to cyclic loading and signs of breakage of the nickel-titanium endodontic instrument COXO SC PRO. Sterilization treatment, which is based on autoclaving, significantly reduces the strength characteristics of COXO SC PRO nickel-titanium files, which limits the use of these tools to one-time use without the risk of their breakage.