Introduction: The aim of this study was to use micro-computed tomography to evaluate the amount of remaining root filling material in oval canals filled by using 2 obturation techniques after retreatment with the ProTaper Universal Retreatment with or without solvent. Methods: Forty mandibular incisor teeth with oval canals were prepared to the ProTaper Universal F3 and filled with gutta-percha and iRoot SP sealer by using continuous wave of condensation or cold lateral condensation techniques. The root fillings were removed with the ProTaper Universal Retreatment system, and the canals were prepared further with ProTaper F4. The operating time was measured. Preoperative and postoperative micro-computed tomography imaging was used to assess the percentage of volume of residual filling material in the canals. Results: Remaining filling material was observed in all specimens. The mean volume of remaining material was higher in the continuous wave of condensation groups than in the cold lateral condensation groups, especially in the apical portions of the root canals (P < .05). The time required to reach a working length was significantly less in the solvent groups than in the nonsolvent groups (P < .05). However, in the nonsolvent groups, less time was required to achieve satisfactory gutta-percha removal and root canal refinement than in the solvent groups (P < .05). Conclusions: None of the retreatment techniques were able to completely remove all gutta-percha/sealer from the oval canals. More root filling material was left in the root canals filled by using the continuous wave condensation technique than those filled by using the cold lateral condensation technique after retreatment. In the nonsolvent groups, less time was needed to achieve satisfactory gutta-percha removal and root canal refinement than in the solvent groups. (J Endod 2012;38:1516-1520)