The aim of this study is to evaluate and compare dentinal microcracks formation during root canal preparation by different commercially available nickel-titanium (NiTi) file systems. Materials and Method: Ninety freshly extracted permanent single-rooted teeth were selected. All specimens were decoronated and divided into six groups of 15 each. Teeth were mounted in the acrylic block to simulate periodontal ligaments. Fifteen teeth served as a control in which no treatment was performed. Experimental groups were instrumented with TruNatomy rotary files, ProTaper rotary files, WaveOne Gold in rotary motion, WaveOne Gold in reciprocating files, Reciproc Blue file systems. Roots were then sectioned 3 and 6 mm from the apex, and the cut surface was observed under a stereomicroscope and checked for the presence or absence of dentinal microcracks.