A 3D vector-based approach to facial soft tissue–cranial relationships for forensic identification in the Spanish population

Facial soft tissue thickness is a key parameter in forensic craniofacial identification, reflecting the anatomical relationship between the skull and the overlying soft tissues. This study characterizes the spatial correspondence between cranial (craniometric) and facial (cephalometric) landmarks in a Spanish adult population through a three-dimensional vector-based approach applied to computed tomography data. CT scans from 459 healthy individuals (264 males, 195 females; aged 18-60 years) were analyzed. A total set of 12 cephalometric and craniometric landmarks were selected. For each pair of landmarks, the spatial coordinates (X, Y, Z) were extracted and used to compute vectors describing both the orientation and direction in space, as well as the distance corresponding to soft tissue thickness between bone and skin. Statistically significant sex differences were found for most landmarks, but only four exceeded the measurement error threshold. The 3D vectorial approach provides a comprehensive representation of craniofacial spatial relationships beyond linear measurements, allowing a more precise understanding of tissue distribution and landmark orientation. This study presents the first vector-based facial soft tissue thickness reference dataset for the Spanish population, enhancing the accuracy of craniofacial identification and its integration into computational and AI-based forensic applications.