Aim: The aim of this invitro study was to evaluate and compare the dentinal crack formation after root canal preparation using protaper gold, protaper next and trunatomy file systems. Material and Methods: The study was conducted on 50 extracted single- rooted mandibular premolar teeth. Access cavity preparation was done and working length was established with 15k type file. Biomechanical preparation was done according to manufacturer’s instructions using three file systems, Protaper gold (Dentsply), Protaper next (Dentsply) and Trunatomy (Dentsply) grouped as A, B and C respectively. Teeth in group D were instrumented and serve as a Control group. Canals were irrigated with 12 mL of 1% sodium hypochlorite solution and rinsed with 5mL of distilled water. Then the roots of all teeth will be cut at apical third,middle third and coronal third from apex.The sections were observed under a stereomicroscope for dentinal cracks.