2.2. Micro-CT image acquisition and 3D model generation

The majority of the sample was scanned using conventional micro-CT systems at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany (a BIR ARCTIS 225/300 industrial micro-CT scanner and a Skyscan 1172 micro-CT scanner) with an isotropic voxel size ranging from 13.7 to 31.67 μm. Details on the scanning parameters are further described in Le Cabec et al. (2013). Synchrotron micro-CT data for the La Quina H18 upper canine (voxel size: 31.12 μm) were obtained from the ESRF (European Synchrotron Radiation Facility, Grenoble, France) paleontological microtomographic database (http://paleo.esrf.eu/picture.php?/378/category/1509, Smith et al., 2010). Data for Equus Cave 9 (EQ 9; Grine and Klein, 1985) were acquired at the ESRF on the ID19 beamline (voxel size: 30.12 μm). The RMH sample from Italy was scanned at the Institute of Clinical Physiology - CNR in Pisa using Xalt, an in-house designed micro-CT scanner, using the following scan parameters: 50 kVp, a 2 mm-thick Al filter, 720 projections over 360°, 0.8 mAs/projection (see further technical details in Panetta et al., 2012). Volumetric data for this latter sample were reconstructed using Feldkamp-type cone-beam filtered backprojection (FBP; Feldkamp et al., 1984) with cubic voxel size of 18.4 μm.

The reconstructed micro-CT images were processed using a semiautomatic threshold-based approach in Avizo 7 (Visualization Sciences Group Inc.) and Seg3D (v2.1.4; http://www.sci.utah.edu/cibc-software/seg3d.html). The segmented enamel cap and virtually filled dentine were converted to meshes using the Windged-Edge Mesh tool of the MeVisLab software (http://www.mevislab.de).

The 3D digital models of the canines were imported in Rapidform XOR2 (INUS Technology, Seoul, Korea; now Geomagic design X: http://www.geomagic.com/it/) for cleaning processes (e.g., removal of triangles not connected to the surface or those that projected beyond the outer surface of the mesh) and correction of defects (e.g., filling of small holes) to create fully closed surfaces necessary for further 3D digital analysis. Following procedures described in Benazzi et al. (2014a), a spline curve was digitized at the cervical line to isolate the coronal dentine, which was then closed by interpolating the curve with a smooth surface (Fig. 1).

Illustration of the protocol (Benazzi et al., 2014a) used to isolate a standardized volume of coronal dentine in the Neandertal specimen Le Moustier 1 (lower right canine). a) A spline curve (blue) was digitized at the cemento-enamel junction which was then used to isolate the enamel–dentine junction (EDJ) surface. b) The cervical line was identified to interpolate a smooth non-planar surface from the uneven contour of the crown, thus c) closing the inferior surface of the coronal dentine core. M: mesial, Li: lingual, D: distal, La: labial. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)