Objectives: This study aimed to assess geometric characteristics in canal preparation using nickel-titanium (NiTi) files used for minimal invasiveness. Methods: Thirty J-shaped simulated canals in resin blocks were instrumented with either TruNatomy (TR; Dentsply Sirona), EndoRoad (ER; Maruchi), or ProTaper Ultimate (PTU; Dentsply Sirona). The simulated canal blocks were scanned using microcomputed tomography before and after instrumentation. The scanned images were reconstructed, and the canal surface area was measured from 0.5 to 6.5 mm from the apex. Three-dimensional representative models of each group were rendered. The data were statistically analyzed using one-way analysis of variance and Kruskal-Wallis test at 95% significance level. Results: TR showed a superior ability to maintain the canal's center. TR demonstrated comparable apical preparation to PTU. ER showed a smaller and limited apical preparation than other systems, with a tendency for canal preparation toward the inner side of the curvature. PTU featured the largest prepared apical size among the file groups and tended to straighten the curvature by preparing the canal more towards the outward side. The surface area instrumented using each NiTi file showed statistically significant differences among the three groups at all levels except 0.5, 2.0, and 3.5 mm from the apex (p 0.05). Conclusions: While PTU is suitable for general canal preparation to facilitate irrigation and intracanal medication, TR and ER excel in preserving canal centering with minimal concern for canal transportation by minimally invasive preparation.
Jang et al. (2026) studied this question.