Micro-computed tomographic evaluation of the effect of the final apical size prepared by rotary nickel-titanium files on the removal efficacy of hard-tissue debris

OBJECTIVE: This study was performed to compare the removal efficacy of hard-tissue debris in mandibular first molars prepared to various apical sizes. METHODS: The mesial root canals of 40 extracted mandibular first molars were prepared by rotary nickel-titanium files to an apical size of #25/0.04 (Group #2504), #30/0.04 (Group #3004), #35/0.04 (Group #3504), and #40/0.04 (Group #4004). Irrigation was performed with 5.25% NaOCl and 17% EDTA. Micro-computed tomography was used to scan the samples before and after root canal preparation. Remnant hard-tissue debris was identified, quantified, and visualized three-dimensionally using shape recognition and image superimposition analysis, and the debris was mapped to its location. RESULTS: After preparation, 11.67%±2.99% of the root canals contained hard-tissue debris in Group #2504, 8.00%±2.71% in Group #3004, 7.17%±2.88% in Group #3504, and 4.51%±1.61% in Group #4004. The amount of accumulated hard-tissue debris was significantly less in Group #4004 than in the other groups. However, there were no significant differences between Groups #3004 and #3504. CONCLUSIONS: An increased final apical size resulted in significantly lower debris accumulation. However, no root canal in any group was completely free from hard-tissue debris, and debris was mostly found in the isthmus of the mesial root canals.