Nuove prospettive di indagine tassonomica di denti decidui usurati attraverso analisi di immagine e tecnologie tridimensionali

Despite the general increase in digital techniques for dental morphometric analyses, only a few methods are available to study worn teeth. Moreover, permanent dentitions are studied much more frequently than deciduous teeth. In this study we address both issues by providing a taxonomic classification of Neanderthal and modern human lower second deciduous molars (dm2s) through the analysis of crown and cervical outlines. Crown and cervical outlines were obtained from a three-dimensional (3D) digital sample of uniformly oriented dm2s. Both outlines were centered on the centroid of their area and represented by 16 pseudolandmarks obtained by equiangularly spaced radial vectors out of the centroid. We removed size information from the oriented and centered outlines with a uniform scaling of the pseudolandmark configurations to unit Centroid Size. Group shape variation was evaluated separately for the dm2 crown and cervical outlines through a shape – space principal component analysis (PCA). Finally, quadratic discriminant analysis (QDA) of a subset of principal components was used to classify the specimens. In addition, we selected a further sample of modern dm2s and we compared both crown outlines detected from occlusal photographic images and the same profile obtained by 3D digital models in order to assess whether the two procedures provide consistent results. Our results demonstrate that both cervical and crown outline successfully separate the two groups. Crown Outline properly discriminates the 92% of individuals while cervical outline allows 96% of correct attribution. Neanderthals showed a buccodistal expansion and convex lingual outline shape, whilst modern humans have buccodistal reduction and straight lingual outline shape. Therefore, we confirmed that the cervical outline represents an effective parameter for distinguishing between the two taxa when dealing with worn or damaged dm2s. Finally, the results achieved with the outlines digitized on photographic images are consistent with those obtained by using 3D models, which stands up for the reproducibility of the photographic protocol, faster and cheaper than the one based on the 3D digital models.