The TRUShape 3D Conforming File (TRUShape), a novel, S-shaped nickel-titanium (NiTi) rotary file, was developed to facilitate cleaning and shaping of irregular-shaped root canals. The purpose of this study was to evaluate the shaping ability of TRUShape compared to Vortex Blue (VB) when used in non-round, oval-shaped root canals by micro-computed tomography (MCT). Thirty single-rooted human mandibular premolar teeth with radiographically similar root canal size and curvature were randomly allocated to two groups (N=15), and mechanically prepared with TRUShape or VB. Each tooth was submitted to MCT at 20 μm resolution at three time intervals: before shaping, and after shaping to an intermediate apical size 30 and a final apical size 40. Three-dimensional data sets were superimposed and evaluated for root canal volume, surface area, and treated surface. Matched axial slices in the apical, middle, and coronal root thirds were evaluated for area, roundness, and canal transportation expressed as center of mass shift (CMS). Data were statistically analyzed using parametric and non-parametric tests. Root canal volumes increased similarly and significantly overall (p< 0.001; from an initial volume of 7.3±3.5 mm3 to an intermediate volume of 8.7±3.1 mm3 and a final volume of 9.9±3.0 mm3). Treated canal surface was significantly larger in the TRUShape group at both apical sizes 30 and 40 with 72±15% vs. 55±23% and 85±12% vs. 71±20% non-static voxels for TRUShape and VB, respectively (p< 0.05). Canal transportation was less than 100 μm in all but 8 out of 90 cross sections and was not significantly different between groups. This MCT study demonstrated the TRUShape 3D Conforming File to be effective in the mechanical preparation, specifically, the surface treatment, of single-rooted premolars with non-round, oval-shaped root canals. Funding was provided by the American Association of Endodontists (AAE) Foundation and the Department of Endodontics at the University of Iowa, College of Dentistry.