This study was designed to determine the efficiency of hand and rotary instruments in shaping oval root canals. Seventy-five oval canals were equally divided into three groups. The apical third was prepared with rotary LightSpeed instruments either to size 52.5 (mandibular incisors) or to size 57.5 (distal root of mandibular molars). The middle third with an oval cross-section was shaped with Hedström hand files using circumferential technique, with 6% taper rotary Hero files in a circumferential filing movement or with rotary LightSpeed instruments in a step-back technique. Instrumentation was performed under clinical conditions in a phantom head. The teeth were sectioned at two levels in the middle third of the root. An assembly technique allowed comparing the canal outline before and after instrumentation. The photographed root sections were superimposed and traced under a stereomicroscope. The ratio of prepared to unprepared canal outline was calculated for each section. The lowest values were observed in the LightSpeed group (mean: 0.42; 95% confidence interval (CI): 0.37; 0.47). Significantly higher values were recorded in the Hero group (mean: 0.58; 95% CI: 0.53; 0.64) and in the Hedström group (mean: 0.56; 95% CI: 0.49; 0.62). No instrumentation technique was capable of completely preparing dentin walls of oval root canals. Circumferential filing of the middle third of oval root canals with either 6% taper Hero files or conventional Hedström hand files gave comparable results.