Forensic age estimation: comparison and validation of the Iscan method in 3D reconstructions using a surface scanner in a Spanish population

When investigating a death, post-mortem identification provides with results of great legal and humanitarian significance. The effectiveness of the methods used to estimate age depends on the reference population, considering variables such as sex and ancestry. The aim of this study was to validate the Iscan method to estimate age in a Spanish forensic population, comparing the estimates obtained in dry bones and 3D reconstructions created with a surface scanner. We carried out a cross-sectional study on 109 autopsied corpses (67% male), scanning the sternal end of the right fourth rib in a 3D mesh, using an EinScan-Pro® surface scanner (precision: 0.05 mm). Two observers estimated the phases in dry bones and 3D images according to the Iscan method and to the sex of the subject. The mean age was 57.73 years (SD = 19.12 years;18–93 years). The intra-observer agreement was almost perfect in bones (κ = 0.877–0.960) and 3D images (κ = 0.954), while the inter-observer agreement was almost perfect in bones (κ = 0.813) and substantial in 3D images (κ = 0.727). The correlation with the Iscan phases was very strong in bones (Rho = 0.794–0.820; p < 0.001) and strong in 3D images (Rho = 0.690–0.691; p < 0.001). Both sex-adjusted linear regression models were significant (dry bones: R(2) = 0.65; SEE = ± 11.264 years; 3D images: R(2) = 0.50; SEE = ± 13.537 years) from phase 4 onwards. An overestimation of age was observed in the first phases, and an underestimation in the later ones. Virtual analysis using a surface scanner in the fourth rib is a valid means of estimating age. However, the error values and confidence intervals were considerable, so the joint use of different methods and anatomical sites is recommended.