Background: Minimally invasive endodontics (MI Endo) with minimal dentin shaping prevents root canal fracture in endodontically treated teeth. Alternatively, reduction of the surgical field and limitation of the visual field by MI Endo make root canal shaping difficult. The purpose of this study is to analyze the effect of minimally invasive (MI) shaping of canal orifice dentin by evaluating the shaping characteristics of TruNatomy (TN), a Ni–Ti file developed for MI Endo.Methods: A J-shaped canal model was used to compare the final canal morphology formed using a MI shaping TN or conventional shaping ProTaper NEXT (PTN) file. The TN files were used in two experimental groups: no straight-line access (A) and straight-line access (B). The PTN files of the control were similarly classified: no straight-line access (C) and straight-line access (D). The increase in canal width and the median displacement (transportation) among the groups were compared.Results: The analysis of the canal width prepared with the TN file showed that the displacement of the inner canal curve increased at the point 5 mm from the apex in Groups A and B; however, the displacement of the outer width increased at the other measurement sites. In Groups C and D using PTN, the displacement of the inner canal curve increased at points 3–5 mm from the apex. Alternatively, the displacement on the outer width increased at 8 mm, and the displacement in Group D increased significantly. The canal transportation in the case with a TN file was 0.1 mm or smaller for Groups A and B, although the PTN preparation showed significant transport 3–5 mm from the apex on the inner curve of Group D compared with Groups A and B.Conclusions: TN shaping preserves the tooth structure and canal geometry without straight-line access. The TN file developed based on the concept of MI Endo facilitates accurate root canal shaping and reduces transportation.
