12/4 Facial simulation

		Facial simulation of an advancement of the lower jaw. Comparison of face profile before (left) and after (right) of the simulated operation.

Since the human face plays a key role in interpersonal relationships, prediction of post-surgical morphology and appearance of human faces for patients with facial deformities is a critical issue in facial surgery. Even very subtle malformations of facial proportions can strongly affect the appearance of a face and determine on aesthetic aspects such as individual beauty. Therefore, surgeons often face the problem of predicting a fair facial surface before the actual surgery is carried out.

Typically, the maxillofacial surgeon (sometimes with the help of a medical artist) draws the patient's predicted profile to give at least a 2D appearance of the future face. It is clear that both surgeons and their patients have a strong demand for a method which enables them to compute highly realistic 3D pictures of the post surgical shape. With the development of advanced range scanners the idea was born to combine both volume and surface data to build a physically based facial model. This model has to capture the most important anatomical and mechanical parameters of the face, and it should also allow interactive manipulations and the prediction of resulting facial shape.

Facial simulation aims at approximating the results from maxillofacial surgery as closely as possible. The standard computational approach to accurate simulation of deformations is the use of a non-linear, globally continuous finite element model of the facial surface. This can be combined with triangular polynomial shape functions, such that increasing the number of finite elements results in a facial surface that tends to be highly smooth. Finally, patient-specific data can be incorporated by adding boundary conditions from CT data of the skull.