2020 Volume 63 Issue 4 Pages 305-311
Purpose: This study aimed to evaluate the canal-centering ability, working time and frequency of procedural errors of nickel-titanium (NiTi) rotary and hand stainless-steel root canal instrumentation performed by undergraduate students who were inexperienced in NiTi rotary instrumentation.
Methods: Fifty-nine undergraduate students with no experience of NiTi rotary instrumentation participated in this study. Simulated J-shaped resin canals that had been preflared with ProTaper SX were instrumented by the students using either ProTaper NEXT (NiTi-file Group) or K files (K-file Group) (n=1, each). In the NiTi-file Group, after glide path preparation with #10-20 K files, the canals were instrumented with ProTaper NEXT X1, X2 and X3 to the full working length using an endodontic motor (X-Smart Plus). In the K-file Group, the canals were instrumented manually to the full working length with #15-30 K files and then step-back prepared in 1-mm increments up to #55. The working time was measured with a stopwatch by the instructor. The frequency of instrument fracture and ledge formation was recorded. Pre- and post-instrumentation images were superimposed with image processing software (Photoshop 7.0) and the centering ratio was calculated at 0, 0.5, 1, 2 and 3 mm from the apex by the following formula: [(amount of resin removed from outer side) − (amount of resin removed from inner side)] / (post-instrumentation canal diameter). Data were statistically analyzed with the paired t-test for the centering ratio and working time and with the McNemer test for the frequency of ledge formation (σ=0.05).
Results: At 0, 0.5, 1, and 2 mm from the apex, the NiTi-file Group showed significantly lower canal-centering ratio (i.e., less deviation) than the K-file Group (p<0.05). The working time of the NiTi-file Group was shorter than that of the K-file Group (p<0.05). Ledge formation occurred in 5 and 43 canals in the NiTi-file Group and K-file Group, respectively (p<0.05). No instrument fracture occurred in either group.
Conclusion: Within the limitations of this study, instrumentation with ProTaper NEXT showed better canal centering ability, shortened working time and decreased frequency of ledge formation compared with manual K-file instrumentation, when curved canals were instrumented by operators who had no experience of NiTi rotary instrumentation.
