Skyscan 1174v2

Originally, each tooth was slightly dried, mounted on a custom attachment, and
scanned in a micro-CT scanner (SkyScan 1174v2; BrukermicroCT, Kontich, Belgium) at an
isotropic resolution of 18 µm. The X-ray tube was operated at 50 kV and 800 mA, and
the scanning was performed by 180° rotation around the vertical axis with a rotation
step of 1.0, using a 1.0-mm thick aluminum filter. Images of each specimen were
reconstructed with dedicated software (NRecon v.1.6.3; Bruker-microCT, Kontich,
Belgium), providing axial cross sections of the inner structure of the samples.
Three-dimensional models of the teeth in a stereolitographic format
(.stl) adjusted to 600,000 triangles resolution, from the apex to
1 mm above the pulp chamber level, were generated by the binarization process using
CTAn v.1.12 software (Brucker-microCT, Kontich, Belgium). An analysis of the internal
anatomy of the teeth revealed a Vertucci Type I configuration in both mesial roots
with a ribbon-shaped canal at the cervical and middle third of the root (Figures 1A and 1B).

After the Ethics Committee Protocol Approval (Protocol #703.054), 88 extracted mandibular second molars with fused roots from a Brazilian population were selected. All teeth were scanned in a micro-CT system (SkyScan 1174 v2; Bruker-microCT, Kontich, Belgium) with 19.6 μm of voxel size, 50 kV, 800 mA, and 360° of rotation. The system includes a charge-coupled device camera (1304 × 1024 pixels). Radiographic images of each tooth were reconstructed with dedicated software (NRecon v. 1.6.3; Bruker-microCT) providing axial cross-sections of the inner structure of the samples.
Following the reconstruction, the cross-sections of all samples were analyzed on the DataViewer v1.5 (Bruker-microCT, SkyScan, Belgium) software. Only fused molars without C-shaped roots and presenting a shallow radicular groove that continued to less than half of root length as classified by Kotoku[8 (link)] were chosen [Figure 1]. The shallow groove was selected according to the groove/thickness ratio.[7 (link)] Following these criteria, a total of 30 molars were chosen for further analysis.

A total of 10 instruments of each brand were scanned by Micro-CT (Skyscan 1174v2; Bruker-micro-CT, Kontich, Belgium) to evaluate the metal mass volume (mm³) and cross-section area of each instrument (mm²). The methodology used was previously described (16 (link)). The Micro-CT parameters used were 50 kV, 800 mA, 360° of rotation, an isotropic resolution of 14.1 μm, and 0.5 mm-thick aluminum filter. The images of each specimen were reconstructed into cross-section slices perpendicular to the long axis of the instruments with dedicated software (NRecon v. 1.6.3, Bruker-micro-CT), which enabled two and three-dimensional analysis. The three-dimensional evaluation measured the metal mass volume from the instrument tip until the 3^rd and 5^th mm from this initial point (Fig. 1a). Also, the two-dimensional analysis was based on reconstructed cross-section slices, which allowed a topographic view at 3 and 5 mm from the tip of the instruments (Fig. 1b). Then, the cross-section area (mm²) was measured at these levels.

The sample was scanned using a micro-CT device (SkyScan 1174v2, Bruker microCT, Kontich, Belgium) after root canal filling and retreatment procedures using the following parameters: 50 kV, 800 mA, isotropic resolution of 21.8 μm, 360° rotation around the vertical axis, rotation step of 0.5°, and frame averaging of 3, using a 1-mm thick aluminum filter. Then, the NRecon v.1.6.9 software (Bruker microCT) was used to reconstruct the acquired images into cross-sectional slices, and the volume of interest was selected to extend from the cemento-enamel junction to the apex of the root, resulting in the acquisition of 700–800 transverse cross sections per tooth. CTAn v.1.16.1 software (Bruker microCT) was used for measuring initial and residual volumes of filling materials (mm³). The percentage of residual volume relative to the initial volume of the filling material was calculated.