Background: This study was done to compare the dentinal damage caused by several rotary files and how it appeared under a stereomicroscope during root canal treatment. Material and methods:100 newly extracted mandibular premolars were divided into 5 groups, each with 20 teeth, and each group underwent biomechanical preparation. Group 1 included teeth that had not been prepped; Group 2 included hand files; Group 3 included ProTaper rotary instruments; Group 4 included K3 rotary instruments; and Group 5 included Easy RaCe rotary instruments. Then, roots were cut horizontally at 3, 6, and 9 mm intervals from the apex, and they were viewed under a stereomicroscope. The dentin had flaws, it was found. Groups were investigated using chi-square analysis