Minimally invasive versus conventional apical enlargement during retreatment of severely curved mesial canals: A micro–CT study

OBJECTIVES: This study used micro-computed tomography (micro-CT) to compare a minimally invasive retreatment approach (reinstrumentation 30/0.04) with a conventional retreatment protocol (reinstrumentation 40/0.04) during different stages of filling removal in curved mesial roots of mandibular molars. MATERIALS AND METHODS: Fourteen extracted mandibular first molars with Vertucci type IV and severe curvature (25°-40°) were selected, endodontically prepared (25/0.04), and obturated. A paired intra-root design compared minimally invasive retreatment (D-Race + iRace to 30/0.04) with a conventional protocol (Mtwo to 40/0.04). Retreatments were performed without solvents, and micro-CT scans were taken at three stages. Residual filling material was quantified and analyzed at a 5% significance level. RESULTS: Initial filling volumes were similar between protocols (P > .05). After desobstruction, the minimally invasive protocol removed more material (P .05), with both protocols achieving high removal rates (98% vs. 95%). CONCLUSION: The minimally invasive protocol showed greater efficiency in the initial removal of obturation material. After final reinstrumentation, both approaches achieved similar outcomes, with < 5% residual material. These findings suggest that conservative enlargement to 30/0.04 may be as effective as 40/0.04 while better preserving radicular dentin. CLINICAL RELEVANCE: Extensive apical enlargement (40/0.04) is not essential for effective removal of obturation material in severely curved canals. A conservative approach (30/0.04) achieves similar cleanliness while better preserving radicular dentin and structural integrity.