Although rotary instrumentation has been widely studied in permanent dentition, it is a rather new field of study concerning primary teeth. Purpose: We aimed to evaluate apical displacement and time needed for instrumentation of root canals of primary molars by manual and rotary techniques. Materials and Methods: Root canals of 144 extracted first and second primary maxillary molars were randomly divided into 2 groups: I- manual instrumentation (K-files); II- rotary instrumentation (K3 Rotary

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... stem®). The canals were radiographed with pathfinding files in place, prepared by both techniques, and instrumentation time was recorded. After preparation, root canals were radiographed again with pathfinding files in place. To analyze the degree of apical displacement, digital images were superimposed using the Adobe Photoshop® software. Results: Mean apical displacement (0.70 mm) in the manual instrumentation group was not statistically different from that in the rotary instrumentation group (0.79 mm). However, mean time for root canal preparation was significantly shorter using the rotary system (128.0 s) than using the manual system (174.0 s) (p<0.05). Conclusions: The use of rotary instrumentation in pediatric dentistry is feasible, offering time-saving advantages in root canal preparation.