Effect of Kinematics and Speed on Filling Material Removal, Canal Transportation, and Apical Extrusion During Retreatment of Curved Canals.

This study evaluated the effects of kinematics (reciprocating vs. continuous rotation) and rotational speed (350 vs. 1200 rpm) on filling removal, canal transportation, and apical extrusion during retreatment of curved root canals. Vertucci type II mesial roots of mandibular molars were prepared, filled, and scanned by micro-computed tomography (micro-CT). After 30 days, specimens were assigned to four groups (n = 15): WOrec, WOctn, PF350, and PF1200. Retreatment time was recorded, and micro-CT was used to assess filling removal, canal transportation, and apical extrusion. Data were statistically evaluated and revealed that all systems significantly reduced the amount of filling material (p < 0.05). PF1200 and WOctn showed superior removal compared with PF350 and WOrec, respectively (p < 0.05). No differences were observed in extrusion (p > 0.05). Increased canal transportation occurred only in the mesiolingual canal with WOctn and PF1200 (p < 0.05). Higher speed and continuous rotation improved efficiency without increasing extrusion but resulted in greater transportation.