A method, apparatus, media and signals for applying a shape transformation to at least a portion of a three dimensional representation of an appliance for a living body is disclosed. The representation is defined by an input plurality of coordinates representing a general shape of the appliance. The method involves identifying a coordinate location of a datum plane with respect to the representation of the appliance, the datum plane defining a transform volume within which the shape transformation is to be applied, the transform volume extending outwardly from and normal to a first surface of the datum plane. The method also involves identifying input coordinates in the plurality of input coordinates that are located within the transform volume. The method further involves modifying the identified input coordinates in accordance with the shape transformation to produce a modified representation of the appliance, and storing the modified representation of the appliance in a computer memory.