Introduction. Modern endodontic procedure implies the use of rotary Ni-Ti instruments during chemomechanical treatment of root canals. The aim of this study is to analyze the surfaces of new (unused) rotary endodontic instruments using the SEM-EDS method and determine how frequently manufacture defects or impurities appear on their working surfaces. Material and method. Five new different sets of rotary endodontic Ni-Ti instruments were included in this study: K3, Mtwo, ProTaper Universal, HyFlex and BioRaCe. The working part of endodontic instrument was analyzed using SEMEDS method (magnifications ?150 to ?2000), which determined the morphological characteristics of the instrument surface and chemical composition of the found impurities. Statistical analysis was performed using the Fisher?s test (p < 0.05). Results. The results of SEM-EDS analysis showed that there is no new instrument without defects on its surface. The most common defects were observed in K3 (27.43%) and ProTaper Universal group (27.21%) and the least were in BioRaCe instruments (7.67%). The most common type of defect in tested instruments was fretting. In addition, the presence of debris and metal strips was found on all instruments, while corrosion of the working part was observed only in K3, ProTaper Universal and Mtwo systems in a small percentage. Conclusion. Based on the results of this research, it can be concluded that manufacturing defects were noticed in all examined instruments. The most common defect is pitting. Impurities such as debris and metal strips have also been registered. No organic debris was observed on electropolished surface of BioRaCe instruments, but a small percentage of other types of defects were registered.

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Introduction. Deformations and fractures of Ni-Ti instruments during chemomechanical instrumentation of root canals occur due to the action of cyclic and torsional forces. The aim of this research was to analyze the surfaces of the working parts of Mtwo instruments after preparation of root canals with different curvatures using SEM and determine possible changes and deformations after instrumentation. Materials and methods. The study included 3 sets of Mtwo (VDW, Munich, Germany) instruments. Each set was used to instrument 10 canals in three experimental groups (straight, slightly curved, and highly curved canals). Instrumentation was carried out using crown-down technique with the following irrigation solutions, 2% NaOCl (CHLORAXID 2%, Cerkamed, Polska) and Distilled water (Iva, Serbia) in the amount of 5 cm3. The apical and middle third of the instruments were scanned in two directions using SEM at different magnifications (150-2000X). The SEM images were analyzed using qualitative analysis for the presence of different irregularities according to Eggert et al. Statistical analysis of obtained data was performed using Fisher test at a confidence level of 5% (? = 0.05). Results. Most defects (37.3%) were observed in instruments used in highly curved canals, followed by the instruments of the second group (35.6%), and the least defects were (27.1%) observed in the group with straight canals. Higher prevalence of defects was observed in the apical thirds of instruments (54.2%), especially in the experimental group of curved canals where the highest presence was observed (20.3%). The presence of production grooves was observed in all instruments, and the most common types of defects after instrumentation were the appearance of corrosion and changes in the cutting edges. In the group with extremely curved canals fractures were observed in two instruments (10/0.04 and 15/0.05). Conclusion. Root canal curvature significantly affects the occurrence of deformations and fractures of Ni-Ti rotating instruments. The most common types of defects were grooves, corrosion and changes in the blade edges. Mtwo instruments showed deformations in terms of thread changes, microfractures and two complete fractures.