Evaluation of the shaping ability of different rotary file systems in severely and abruptly curved root canals using cone beam computed tomography.

Background: When selecting an instrument for canal preparation, it is important to consider several parameters that influence the shaping efficiency, including instrument design, metallurgy, and operating motion. This study aimed to evaluate the shaping ability of the ProTaper Next (PTN), WaveOne Gold (WOG), and XP-endo Rise Shaper (XPRS) rotary systems in severely and abruptly curved root canals using cone beam computed tomography (CBCT) and ImageJ software. Materials and Methods: Forty-eight mesial root canals of the mandibular first molars were assigned equally to three groups: PTN, WOG, and XPRS. Using ImageJ software, CBCT images were acquired pre- and post-instrumentation to assess dentin removal, remaining dentin thickness (RDT), canal transportation, and centering ratio at the coronal, middle, and apical levels. Statistical analyses were conducted on all numerical data. Results: All rotary systems removed significantly more distocoronal dentin in the danger zone (DZ), than the mesiocoronal area. PTN removed significantly more dentin and caused less RDT than XPRS (p < 0.05). However, there were no significant differences between PTN-WOG and WOG-XPRS. In the DZ, the highest percentage of specimens with an RDT < 0.5 mm was observed when using PTN (50%), followed by WOG (31.3%), and XPRS (6.3%). Compared with PTN and WOG, XPRS demonstrated less coronal transportation. Among all rotary systems, there was no significant difference in apical transportation or centering ratio. Conclusions: Based on our observations, all rotary instruments exhibited a tendency to remove dentin in the DZ, but to different degrees. XPRS demonstrated better results in terms of coronal transportation and dentin thickness in the DZ. Comparable centering abilities and minimal apical transportation were demonstrated using all rotary instruments.