ObjectiveThe aim was to compare the canal straightening ofM-wire [Reciproc (VDW, Munich, Germany)] andblue-wire heat-treated [Reciproc Blue (VDW)] instruments in simulated resin L-shaped curved root canals.Materials and MethodsA total of 26 simulated L-shaped root canals with curvature of 45° and length of 17 mm (#15-0.02 taper)endo training blocks were divided into two groups (n= 13). All canals were prepared to an apical size 25according to the manufacturers’ instructions. Preand post-instrumentation digital photography weresuperimposed and canal straightening was analysedusing a computer imaging programme. Shapiro-Wilktest was used to determine the normal distribution ofthe data. For comparing two groups according to canal straightening independent t-test was used.ResultsDuring preparation no instrument fractured. All instruments maintained the original canal curvature wellwith no significant differences between the instruments. Regarding preparation time, no significant differences between the two instruments were obtained(P > 0.05).ConclusionUnder the conditions of this study, instruments weresafe to use and all instruments respected the originalcanal curvature well. It was concluded that reciprocal motion files with or without blue-heat treated hadsimilar preparation time and similar shaping abilitiesat intracanal temperature and maintained root canalcurves equally well.