Background: The purpose of this study was to evaluate themorphological alterations of the ProTaper next rotary file (PTN)under scanning electron microscopy (SEM).Materials and Methods: A total of 18 simulated root canals wereallocated to three groups. Six new sets of PTN instruments were used3 times. A #10 K-file was inserted into the working length, followedby ProGlider to create a glide path. Ensuring the manufacturersinstructions with 99% ethyl alcohol for irrigation, all canals wereprepared. Files were photographed in the same position before andafter three canals preparations using a high-resolution SEM.Result: A metal strip appeared on one X1 instrument surfacepreoperatively. Microcrack defects were observed on two X2 filespostoperatively, and the blunt cutting edge was observed on threeX1 files before and after use and one file fractured.Conclusion: Small number of changes appeared on PTN surfaces,yet same PTN file can be used safely 3 times to prepare multi-rootedteeth within the same patient
