Methods of three dimensional analysis of patients with asymmetry of the face.

One of the problems of patients with facial asymmetry is that two dimensional analysis of such patients does not give a satisfactory picture of the underlying problem. Various methods have been suggested to overcome this problem, such as stereophotogrammetry (Burke et al. 1983) and Moire fringes (Takasaki 1970, Xenofos and Jones 1979). These methods are time consuming and are not fully automated. At present no 3D method is available which provides a readily analysable, global description of change in the face due to the limitations of the techniques which have been used. The 3D changes in shape of the face which occur during growth and with surgical intervention remain undetermined, either qualitatively or quantitatively. Although the importance of such a development has been pointed out, no method of 3D analysis has been developed. (Cutting et al. 1986). Attempts at three dimensional (3D) measurement of the face for monitoring the growth of children with facial deformities usually use hazardous and invasive techniques of ionizing radiation and metallic implants to assess the growth of the skull. Over the past 10 years the Departments of Orthodontics and Medical Physics and Bio-Engineering at University College London have collaborated in the development of a computer graphics based 3D system for the simulation, planning and prediction of maxillo-facial surgery. The laser scanning system developed measures over 20,000 points over the surface of the face in 10 seconds using a non-invasive and completely non-hazardous technique (Arridge et al. 1985, Moss et al. 1987, Moss et al. 1988). The data acquired is accurate to approximately 0.5 mm. Analytical programmes have been developed to handle the enormous quantity of data produced. These programs form the basis of a practical, user-friendly, clinical system whose performance has been evaluated and is now in routine use (Moss et al. 1989).