Evaluation of the Effectiveness of MicroMega Remover, ProTaper Universal Retreatment, Reciproc, and Hedstrom Files in the Retreatment of Curved Root Canals Obturated with Different Techniques: A Micro-Computed Tomography Study

<i>Background and Objectives</i>: The anatomically demanding structure of curved root canals increases the technical difficulty of retreatment procedures. This study aimed to evaluate the retreatment efficacy of various rotary and reciprocating instruments in curved root canals obturated with cold and warm techniques regarding root canal filling material removal, apical transportation, and retreatment time. <i>Materials and Methods</i>: Sixty-four curved mesial root canals of mandibular molars with Vertucci type IV morphology were prepared using the ProTaper Gold system and obturated with AH Plus sealer using either the single-cone (SC) (n = 32) or continuous wave vertical compaction (CWC) (n = 32) technique. Each group was divided into four subgroups (n = 8) and retreated using MicroMega Remover (MM Remover), ProTaper Universal Retreatment (PTUR), Reciproc (Rec), and Hedstrom file systems. Micro-computed tomography was used to assess residual filling material volume and apical transportation. The time required for retreatment was recorded. The level of statistical significance was set at <i>p</i> < 0.05. <i>Results</i>: Across both obturation techniques, the MM Remover and PTUR groups demonstrated shorter retreatment times compared with the CWC-Hedstrom group (<i>p</i> < 0.05). No statistically significant differences were observed among the file systems in terms of filling material removal and apical transportation (<i>p</i> > 0.05). <i>Conclusions</i>: All tested instruments effectively preserved root canal anatomy within clinically acceptable apical transportation limits. The MM Remover and PTUR systems achieved significantly shorter retreatment times, indicating clinical advantages in efficiency. None of the evaluated systems achieved complete removal of the filling materials in either obturation technique. This study provides one of the first comparative evaluations of the MM Remover system, supporting its applicability in complex canal configurations.