Soft-tissue facial anthropometry in three dimensions : from anatomical landmarks to digital morphology in research, clinics and forensic anthropology

The quantitative assessment of the dimensions of human facial soft-tissue structures (eyes, nose, mouth and lips, chin, ears), their reciprocal spatial positions and relative proportions, has an interdisciplinary perspective: anatomical and anthropometric descriptions, medical evaluations (clinical genetics, orthodontics, maxillo-facial and plastic surgery), forensic medicine, they all need reference three-dimensional data collected on healthy, normal individuals selected for sex, age, ethnic group, to be compared to those obtained on the single individual. The data collection technique should be non-invasive, fast, as simple as possible, performed directly on the subjects using low-cost instruments. Data should be collected in digital format, so to allow the creation of computerized data bases, and the use of the computerized techniques of visualization and simulation of treatment. Independent of classic direct anthropometry, various three-dimensional image analyzers are increasingly being used in clinical investigations and research. The instruments can be divided into two main categories: optical, non contact digitizers, and contact instruments. The first kind of instruments (mainly, laser scanners and stereophotogrammetric devices) perform a fast digitization of the face, providing a detailed analysis of the soft-tissue surface. Contact instruments (electromagnetic and electromechanic digitizers) use a landmark representation of the soft-tissue facial surface. Landmark coordinates are coupled to a mathematical and geometric model of the face, and angles, distances and ratios similar to those measured in conventional anthropometry can be obtained. Additionally, multivariate methods of analysis, obtained either from geometric morphometry or from other analytical methods, could be used. Optical instruments provide a larger amount of information but they cannot assess all the actual anatomical landmarks obtained by contact instruments. Motion artifacts are more common with contact instruments, but they can be easily transported, and they are less expensive. Overall, contact instruments seem sufficiently reliable, simple and fast to be used also in a clinical context, thus providing useful quantitative information to allow a better patient care, without submitting the subjects to potentially harmful procedures.