Aim: To evaluate the shaping and cleaning abilities of SafeSider rotary instruments and compare them with those of ProTaper Universal rotary nickel-titanium instruments in curved root canal preparation. Methodology Part I: Forty extracted human mandibular first molars were selected with curvature ranging between 20-40 degrees, distal roots were resected and mesiobuccal canal orifices were located. The working length of the samples was standardized at 15 mm by flattening the mesiobuccal cusps. These samples were placed in polyester blocks. The samples were arranged in a specially fabricated cartoon box with their buccal sides oriented in the same direction. Then, the teeth were scanned using CBCT to evaluate the shaping abilities of both rotary instruments in curved root canals preparations, in terms of: change in canal curvature (Degree of straightening), degree and direction of canal transportation and centering ratio. Canals were instrumented using the two systems according to manufacturer's instructions and scanned again. Part II: Twenty extracted maxillary molars were collected from which palatal roots were separated and prepared using the two systems. Each root was splitted into two halves and equally marked into three thirds to be examined under Stereomicroscope (30X) and Environmental Scanning Electron Microscope (2500X) to evaluate the distribution and amount of debris and smear layer. Results Part I: showed that both rotary systems had decreased in canal curvature, with no statistically significant difference between them. There was no statistically significant difference between the two systems regarding the degree of canal transportation. ProTaper showed higher prevalence of mesial transportation while SafeSider showed higher prevalence of distal transportation at middle and apical thirds in the mesio-distal views. There was no statistically significant difference in the centering ratio between the two systems in bucco-lingual view while ProTaper showed statistically significantly higher mean centering ratio than SafeSider in middle third at mesio-distal view. Part II: Completely clean root canals were never observed. No statistically significant difference was detected in debris percentage between the two systems. All three segments of the canal wall showed smear layer free areas that disappear gradually towards the apical third. Conclusion Under the conditions of this study, both rotary systems caused significant straightening of canal curvatures and were able to remain centered within the canals with a degree of transportation. Both instruments produced almost clean and debris free dentine surfaces with no or minimal smear layer in the middle and coronal thirds. While, they showed limited efficiency in cleaning the apical thirds of the root canals.