Aim of the study: First: to evaluate and compare the effect of a continuous rotation full- sequence (NiTi) systems-BioRace (KFG), and reciprocating (NiTi) single-file system-Reciproc R25 (VDW) on the shaping of curved root canals using Cone Beam Computed Tomography (CBCT). Second: to assess quantitatively the effect of reciprocation and continuous rotation instrumentation on apical debris extrusion. Methodology: Forty extracted mandibular first molars with severely curved mesial roots (25°-40°) and length of curved part ranging from 5-9mm were selected for the study. Teeth were classified into two main groups (1 and 2) according to the instrumentation movement kinematics. Groups were further subdivided into two equal subgroups (A and B) for the shaping ability and the debris extrusion study parts. Canals preparations were done to a standard apical size of #25 in both groups using the same motor- VDW and following manufacturer’s directions. CBCT iCAT was used for pre and post-operative image acquisition and three-dimensional canal volume rendering using the Mimics and Invivo-5 software. Subsequently, canal curvature, length of curved part, volume, and surface area were deliberated. Transportation and centering ratio were calculated at 2, 4, 6, and 9mm sections from root apex. Extruded debris resulted from the two instrumentation kinematics were collected in pre-weighed Eppendorf tubes. Electronic balance was used for debris weighing. Results: Canal curvature angles showed a statistically insignificant decrease in both groups while length of curved part showed small insignificant increase in the two groups with no significant differences between them (P value =0.5 and 0.07 respectively). Canal volume increased significantly in both studied groups after instrumentation (P value= 0.001 and 0.000 for group groups 1 and 2 respectively) and Reciproc outweigh Bio-Race in this respect (P value= 0.001). Same trend was found in the surface area in both studied groups (P value= 0.001 and 0.000 respectively) with a statistically significant difference between Reciproc outweigh Bio-Race (P value = 0.012). Small and similar absolute canals transportation values were generally found in both instrumentation techniques at all studied levels. The differences between all studied levels were statistically insignificant (P value =0.157 and 0.687 for Reciproc and Bio-Race respectively). Both tested kinematics showed centering ratio of less than1. Mean centering ratio was 0.62 in Reciproc and 0.61 in the Bio-Race group. This difference was statistically insignificant. However, a significantly better centering ability was found at L2 in Reciproc group as compared to the Bio-Race group at the same level (P= 0.05). A lower mean debris extrusion was found in the reciprocation group as compared to the continuous rotation group (0.0008gm and 0.0009gm respectively). This difference was found to be of no statistical significance (P value=0.243). Conclusions: Both Reciprocation and continuous rotation instrumentation techniques resulted in a significant increase in canal volume and surface area. Reciproc R25 caused a significantly higher increase in both parameters. Reciproc and Bio-Race instrumentation produced small and similar canal transportation values mostly toward the distal side in the apical half of the canals. The two tested instrumentation kinematics showed centering ratio of less than 1with an insignificant better centering in the Reciproc group. Both techniques did not prevent debris extrusion although small in amount.