To evaluate the efficiency and amount of apically extruded debris when preparing curved root canal to different apical working width using ProTaper Next (PTN) , K3XF and HyFlex CM (HF) .

Extracted molars meeting the following criteria were collected: without root canal treatment, mature apex, without root resorption and calcification. Seventy-two canals with the curvature between 20 and 45 degrees and apical patency with a size 10 K-file were recruited in this study. The canals were randomly assigned to 3 groups according to the instruments (PTN, K3XF, HF) . Each group were divided into 3 subgroups based on the apical working width (size 25, 30, 40) . The apically extruded debris of each group were collected and dried in preweighted centrifugal tubes, and then assessed with an electronic balance. The total time required to complete root canal preparation was also recorded. The level of significance was determined by One-Way ANOVA followed by Tukey post hoc test for a multiple comparison procedure.

The amount of apical debris of PTN in three subgroups (size 25, 30, 40) were (0.37 ± 0.09) , (0.43 ± 0.14) , (0.42 ± 0.15) mg respectively. As for K3XF, the debris weight of three subgroups were (0.47 ± 0.13) , (0.50 ± 0.16) , (0.47 ± 0.15) mg respectively. And about HF, the debris weight of three subgroups were (0.88 ± 0.19) , (0.91 ± 0.20) , (0.80 ± 0.15) mg respectively. HF extruded significantly more debris than PTN and K3XF at the same apical working width (F₂₅= 28.700, P₂₅<0.001; F₃₀= 19.292, P₃₀<0.001; F₄₀= 15.190, P₄₀<0.001) . No significant differences were found related to the apical working width (P>0.05) . The instrumentation time with PTN which was (173.1 ± 18.0) s showed significantly shorter time than K3XF with (220.5 ± 29.7) s and HF with (227.6 ± 22.3) s at apical working width of size 40 (F= 12.369, P= 0.001) . But no significant differences were found among three rotary systems at apical working width of size 25 and 30 (P>0.05) .

In the preparation of curved root canals, HF extruded significantly more debris than PTN and K3XF. PTN was faster than K3XF and HF when canals were prepared to a large apical size.