The aim of this study was to evaluate and compare the surface topography, distortion and fracture of titanium nitride-coated and titanium nitride- non coated nickel titanium rotary endodontic instruments utilized in the preparation of curved root canals on using different irrigants.Materials and Methods: a total of one hundred and twenty freshly-extracted, human mandibular molars (mesio-buccal root canals) selected free from obvious defects or abnormal morphology. The digitized preoperative images were analyzed using the Digora software package to determine pre-instrumentation canal curvature measuring within a range of (15◦- 45◦) according to Schneider's technique.Teeth were divided into two equal main groups. Sixty were prepared with ProTaper system and sixty were prepared with Alpha system. Each group was further divided into three subgroups according to irrigant type: ethylene diaminetetraacetic acid (17 % EDTA) , Sodium hypochlorite (5.25 % NaOCl ), and Saline( 0.9 % NaCl). Root canal preparation was carried out according to the manufacturer's instructions of both systems. Two files from each system were examined under scanning electron microscope (SEM). In Alpha system yellow sequence for narrow canals, the AF04 file (tip size 20) and AF06 file (tip size 20) were examined. In ProTaper system, F1 (tip size 20) and F2 (tip size 25) were examined. All these selected files were examined when they were new and after preparation of 1, 3 and 5 root canals, at the following sites: 1) At tip ; 2) At 5mm -6mm from the tip; 3) Top view for the fractured surface.The files were examined for the presence of signs of wear, spiral distortion, or fracture. All data were tabulated for each system according to the score system of then statistical analysis was done.Results: ProTaper system instruments showed statistically significantly higher spiral distortion and wear scores than the alpha system instruments (p< 0.05).o Sodium hypochlorite and saline showed statistically significantly higher spiral distortion and wear scores than EDTA (p< 0.05).o The instruments significantly more spirally distorted 5mm from the tip than at the tip (p< 0.05). However, the two sites showed similar wear signs ( p> 0.05).o Both spiral distortion and wear significantly increased by the increase in the number of uses (p< 0.05).Conclusion:Under the conditions of this study, it may be concluded that:•The surface topography (Wear) and spiral distortion of both systems (Alpha system and ProTaper system) are adversely affected by repeated usage times. This was more evident with the ProTaper system.•Sodium hypochlorite and saline had an adverse effect on wear and spiral distortion instruments.•Surface engineering techniques like physical vapor deposition (PVD), electro polishing, ionic implantation of boron) can enhance surface wear resistance of the NiTi instruments.