Evaluation of filling material remnants after basic preparation, apical enlargement and final irrigation in retreatment of severely curved root canals in extracted teeth

Aim To compare the retreatment ability of several rotary and reciprocating file systems in curved root canals of extracted teeth and to evaluate the influence of additional apical enlargement performed after a basic retreatment on the amount of remaining filling material. Methodology A total of 65 round curved root canals were used. The root canals were prepared with the ProTaper Next rotary system to size 25, .06 taper and filled with an epoxy resin‐based sealer and gutta‐percha using continuous wave vertical compaction and warm injection back‐filling. The canals were randomly divided into four groups according to the retreatment system used: Group I. ProTaper Universal Retreatment system + ProTaper Gold (PTG) instrumentation system up to PTG F2; Group II. Reciproc Blue system up to the instrument RB25; Group III. Reciproc system up to the instrument R25; Group IV. Wave One Gold (WOG) system up to the instrument WOG25. After the basic retreatment, additional apical enlargement was performed in each group with an instrument that was one size larger: in Group I, II and III up to apical size 40, and in Group IV up to 35. The final irrigation protocol included the following: 15% ethylenediaminotetraacetic acid followed by NaOCl irrigation. The volume of filling material was measured using an industrial micro‐CT four times: after root canal filling (Volume I), after basic retreatment with size 25 files (Volume II), after additional root canal enlargement with larger instruments (Volume III), and after the final irrigation protocol (Volume IV). The decrease in the amount of filling material after each retreatment protocol was analysed using a Kruskal–Wallis test. Intergroup analyses were performed with a Kruskal–Wallis test and between‐group differences were further analysed with Mann–Whitney U test. Results There were no significant differences amongst the systems tested in the amount of remaining filling material, or the reduction rates after each phase of the retreatment procedures (P > 0.05). Intragroup analysis indicated that the use of a larger final instrument removed significantly more filling material in all groups (P