In the last years, 3D technologies have acquired an increasingly central role in medical practice to improve diagnosis and imaging procedures. One of the fields in which 3D methodologies have found an important application is the support to maxillo-facial surgery where they seem to be an effective tool to plan more accurately operations and to predict the possible outcomes of the surgery, even the undesired ones. The aim of this thesis, carried out in collaboration with the maxillofacial department of the San Giovanni Battista Hospital in Turin, was to investigate the soft tissue variations in patients who underwent orthognathic surgeries and factors that influenced these variations.