Aim and objective: Evaluating dentinal cracks in root canal surface after biomechanical preparation using rotary file systems such as ProTaper Next, 2 Shape, and RaCe. Materials and methods: Forty extracted human single canal mandibular premolars were decoronated perpendicular to the long axis of the tooth leaving roots (12 ± 1 mm) and then positioned centrally in a mold using acrylic resin. Roots were randomly divided into four main groups (n = 10) according to the nickel-titanium (Ni–Ti) rotary file system used in preparation as follows: Group I: Control group roots were left unprepared. Group II: Canals were prepared using Ni–Ti 2 Shape system up to TS2 file (#25/0.06). Group III: Canals were prepared using Ni–Ti ProTaper Next system up to X2 file (#25/0.06). Group IV: Canals were prepared using Ni–Ti RaCe system up to file (#25/0.06). Each root was sectioned horizontally using IsoMet saw into three sections as coronal, middle, and apical with a total of 120 sections and observed by stereomicroscope and scanning electron microscope to detect dentinal cracks. Results: There are more dentinal cracks in the ProTaper Next group than in the 2 Shape, RaCe, and control groups as there was a statistically significant difference present (p < 0.05). There was no statistically significant difference between the apical, middle, and coronal sections (p = 0.536). Conclusion: ProTaper Next group showed a high percentage of dentinal crack incidence followed by RaCe, 2 Shape, and control groups regardless of the root canal cross-section, and the highest percentage of dentinal crack incidence was in the apical third followed by middle and coronal thirds regardless of the Ni–Ti system. Clinical significance: To evaluate Ni–Ti rotary system effect on dentinal crack incidence.