Bidirectional evaluation of canal transportation, centering ability and curvature changes of three NiTi rotary systems using cone beam computed tomography (invitro study)

The main aim of root canal treatment is to clean and shape root canals while preserving the original canal anatomy. Even with improvements in the manufacturing of NiTi files, maintaining the original canal anatomy in curved root canals is a challenge. This study aimed to compare the shaping ability of three different NiTi files via CBCT to assess mesiodistal and buccolingual canal transportation, canal centering ability, and canal straightening in severely curved canals. Thirty-six human extracted mandibular molars were used in this study, and the samples were randomly divided into three equal groups (n = 12) according to the files used for root canal instrumentation. Preoperative CBCT scans were performed to evaluate the canal position at three different levels: apical, middle, and coronal. Group I: mesiobuccal (MB) canals of each molar were instrumented with Zarc BlueShaper files (Zarc4Endo, Gijon, Spain) up to Z4 file (25/~), Group II: MB canals were instrumented with RCS Rainbow One file (RAMO MEDICAL, Suzhou, China) of size (25/0.06), and Group III: MB canals were instrumented with HyFlex EDM One file (25/~) (Coltene/Whaledent AG, Alstätten, Switzerland). Measurements were performed on Postoperative CBCT scans of instrumented canals to evaluate the canal transportation, centering ability and straightening at the apical, middle and coronal levels. HyFlex EDM One demonstrated the most favorable shaping performance, showing minimal transportation, high centering, and least curvature alteration. These outcomes were followed by Zarc BlueShaper and subsequently by RCS Rainbow One. A statistically significant difference was observed in mesiodistal overall centering ability, where RCS Rainbow One exhibited less centering ability than HyFlex EDM One (P = 0.048). However, no statistically significant differences were detected among the three groups regarding mesiodistal canal transportation (P = 0.14), buccolingual canal transportation (P = 0.39), buccolingual centering ability (P = 0.6), or curvature change (P = 0.42). Within the limitations of this in vitro study, all the tested rotary systems demonstrated clinically acceptable performance in shaping curved root canals, despite minor differences in canal transportation, centering ability, and canal straightening.