Introduction. One of the most important steps in endodontic treatment is the preparation of a uniform space, the use of endodontic irrigant and creating space for the endodontic filling. The success and effectiveness of endodontic treatment is largely determined by the quality of chemo-mechanical root canal treatment. In recent years there has been a major emphasis on the use of rotary mechanical instrumentation systems, namely the use of Nickel-Titanium alloys, which due to their properties represent a favorable flexibility in the instrumentation of difficult anatomies. The objective of this study is to analyze the properties of different varieties of rotary systems used in the mechanical preparation of the endodontic space. Material and methods. The study was conducted on 20 subjects that were divided into 2 groups. Group 1-6 patients received treatment with the Protaper Universal rotary system, group 2- 14 patients to whom mechanical instrumentation was applied, 7 of which received treatment with the Protaper Next and the other 7 with Dc Taper. Results. Mechanical instrumentation was performed on different nosological entities, the prevalence being acute pulpitis. Among instrumented teeth, the prevalence was on the side of multirooted teeth. Conclusions. The clinical application of different NiTi rotary systems has to be determined individually, as each clinical case has its own particularities. The success of an endodontic treatment depends not only on the selection of rotary instruments used and their method of use, but also on the practitioner's experience and stepbystep instrumentation protocols.