Laser scanner versus stereophotogrammetry : a three-dimensional quantitative approach for morphological analysis of pubic aymphysis

The reconstruction of biological profile is a crucial step for personal identification of unknown decedents, both in forensic and archaeological context. At this purpose, determination of age at death is a very important issue. Among the skeletal regions used for estimating it, the analysis of pubic symphysis by Suchey-Brooks method remains the most reliable aging technique. In the last years, technologies involving 3D image acquisition have acquired a growing importance in anthropology and may provide a relevant help in diffusion and sharing of skeletal specimens. In particular, among all the new available instruments, laser scanners and stereophotogrammetric systems are particularly useful to obtain 3D reconstructions of the pubic symphyseal surface. Furthermore, the possibility to create digital models of these bony structures allows researchers to easily and fast share their datasets worldwide, avoiding any possible damage to the real sample. This study aims at verifying the technical reproducibility of 3D acquisitions, performed by laser scanner and stereophotogrammetry, as a preliminary study to possible assessment of differences in age at death estimation. Since accuracy and reproducibility of these two instruments have already been evaluated, the study aims at comparing them in order to verify if there are some differences on relevant measurements obtained from the analysis of the 24 commercial casts (by Diane France). These 24 symphyseal casts (12 female and 12 male) were scanned by a dental laser scanner (Dental Wings series 3, Dental Wings Inc., Montreal, Canada) and a stereophotogrammetric system (Vectra 3D, Canfield Scientific, Fairfield, NJ). For each sample two scans were performed by the same tool and some measurements (symphyseal surface length, symphyseal surface area and billowing area) were taken twice on digitized surfaces, by the same operator. The second assessment was performed 15 days after the first one. Repeatability of operator measurements on different scans was assessed by paired Student t-test, or Mann-Whitney test, depending on data distribution. Linear regression was performed as well. To compare the two instruments, Bland-Altman analysis was carried out for billowing measurements. Results show no significant difference (p>0.05) in identification of the same parameter on different scans through both instruments and no significant difference between billowing areas, measured through laser scanner or stereophotogrammetry. In conclusion, data suggest that both 3D image acquisition systems may provide a technically reliable reproduction of pubic symphysis. However, the technical reproduction of skeletal specimens does not mean that the 3D scans are suitable for age estimation, which remains, in anthropological practice, a morphological procedure and requires a specific experience of the operator. Further studies are required to validate the opportunity to use this approach for anthropological age at death estimation.