Introduction: The aim of this study was to compare the incidence of root cracks after root canal instrumentation with the IF Adaptive, WaveOne, ProTaper Next, and ProTaper Universal systems. Methods: Seventy-five extracted mandibular central incisors with mature apices and straight root canals (<5 degrees) were selected and kept in distilled water. The root canals were instrumented by using the ProTaper Universal, ProTaper Next, WaveOne, and TF Adaptive systems. All the roots were horizontally sectioned 3, 6, and 9 mm from the apex with a low-speed saw underwater cooling. The slices were then viewed through a stereomicroscope at x25 magnification. The samples were photographed with a camera to determine the presence of dentinal cracks. Results: The control group had no cracks, and the difference between the control group and the experimental groups was statistically significant (P < .001). The ProTaper Next and IF Adaptive systems produced significantly less cracks than the ProTaper Universal and WaveOne systems in the apical section (3 mm) (P < .05). Conclusions: Under the study conditions and within the limitations of this study, it can be concluded that the ProTaper Universal, ProTaper Next, WaveOne, and IF Adaptive instruments can result in dentinal cracks.