Amaç: Çeşitli döner nikel-titanyum enstrümantasyon sistemlerinin kullanımı sonrası kök dentini eğilme dayanımının değerlendirilmesi.

Aim: To assess the flexural strength of root dentin after using various rotary nickel-titanium instrumentation systems.Method: Eighty extracted single-rooted human mandibular premolar teeth were used. Initially, access cavities were prepared and a size 10 K-file was placed into the canal until it was visible at the apical foramen, and the working length (WL) was established 1 mm short of this length. The root canals, which standardized in the same length and thicknesses, were prepared using One Shape New Generation (OSNG), K3XF, Twisted File Adaptive (TFA) and ProTaper Next (PTN) instruments. The samples were exposed a three-point bending test. The data obtained were analyzed using the one-way analysis of variance (ANOVA) and Tukey post-hoc tests.Results: The TFA group provided statistical higher values compared to all other groups (p<0.05). The flexural strength of root dentin formed after PTN group was significantly lower than TFA group (p<0.05). Although the lowest flexural strength values were detected in OSNG and K3XFgroups, there was no significant difference between the OSNG and K3XF (p>0.05).Conclusions: Under the conditions of this study, all instrumentation systems caused the weakening of root dentin and thus reduction of the flexural strength. Specially, OSNG and K3XF instruments caused the least flexural strength value on root dentin.