2021 年 42 巻 2 号 p. 91-97
Abstract : Purpose : The aim of this study was, firstly, to evaluate the canal-centering ability, working time and frequency of procedural errors of different nickel-titanium (NiTi) rotary instruments used by novice undergraduate dental students in curved canals. The second aim was to assess the usability of the instruments for the students.
Materials and Methods : Simulated J-shaped resin canals were instrumented by undergraduate students (n=13) using JIZAI (MANI) in a single-length technique, WaveOne Gold (Dentsply Sirona ; WOG) in a single-length technique with a reciprocating motion, EndoWave (FKG ; EW) in a crown-down technique, or stainless-steel K-files (Zipperer ; SS) in a manual step-back technique. Canal-centering ratios at 0, 0.5, 1, 2 and 3mm from the apex were calculated after superimposition of pre- and post-instrumentation images. Working time was measured and ledge formation was recorded. After completion of all instrumentation, each student was asked to rank the relative usability of the four instruments using scores 1 (highest) to 4.
Results and Discussion : All NiTi instruments at all levels, except for EW at 1, 2 and 3mm and JIZAI at 3mm, showed significantly lower centering ratio (i.e., less deviation) than SS (p<0.05). EW showed significantly higher centering ratio than JIZAI at 2 and 3mm and WOG at 3mm (p<0.05). The working time was significantly shorter with the three NiTi instruments than with SS (p<0.05), but similar among the NiTi instruments (p>0.05). Ledge formation occurred in three canals each in EW and SS, and no instrument fractured. The usability scores of NiTi instruments were lower (i.e., higher usability) than SS.
Conclusion : Under the present experimental conditions where curved resin canals were instrumented by novice undergraduate students, JIZAI, WOG and EW exhibited superior canal-centering ability and shorter working time, and were rated by the students as easier to use, compared with SS. JIZAI and WOG tended to create less canal transportation than EW.
