Ct 50 scanner

Human teeth were scanned in a µCT 50 scanner (Scanco Medical, Bassersdorf, Switzerland) at 70 kVp, 76 µA, 0.5 Al filter, 900 ms integration time, and 10 µm voxel dimension. Mouse hemi‐mandibles were scanned under the same parameters except for 6 µm voxel dimension. DICOM files were created from raw data, exported, and calibrated to five known densities of hydroxyapatite (mg/cm³ HA), as previously described (Shin, Chavez, Ikeda, Foster, & Bartlett, 2018). Reconstructed images were analyzed using AnalyzePro (version 1.0; AnalyzeDirect, Overland Park, KS). For both human teeth and mouse first mandibular molars, enamel was segmented semi‐automatically (with manual corrections where necessary) at 1,600 mg/cm³ HA, and dentin/cementum was segmented at 650 mg/cm³ HA, as previously described (Shin et al., 2018). Average dentin thickness was determined for regions of interest (ROIs) by adapting algorithms defined for cortical bone analysis (Bouxsein et al., 2010). The crown dentin ROI initiated 60 µm coronal to the CEJ and extended 150 µm coronally, while the root dentin ROI initiated 300 µm apical to the CEJ and extended 150 µm apically. Mouse crown dentin thickness was measured in the 150 µm of dentin coronal to the CEJ, and root dentin thickness was measured in the central 150 µm of the mesial root.