1. A method for applying a shape transformation to at least a portion of a three dimensional representation of an appliance for a living body, the representation being defined by an input plurality of coordinates representing a general shape of the appliance, the method comprising: identifying a location of a datum plane with respect to the representation of the appliance, said datum plane defining a transform volume within which the shape transformation is to be applied, said transform volume extending outwardly from said datum plane in a normal direction to a first surface of said datum plane, said normal direction defining a direction for applying said shape transformation; identifying input coordinates in the plurality of input coordinates that are located within said transform volume; identifying a location of at least one constraint plane, said at least one constraint plane being perpendicular to said datum plane and operable to limit an extent of said transform volume in a direction normal to said constraint plane; identifying a blending region in said transform volume proximate said constraint plane; modifying said identified input coordinates in accordance with the shape transformation to produce a modified representation of the appliance, wherein identifying said location of said constraint plane comprises identifying a coordinate location to cause said constraint plane to intersect the representation of the appliance such that said modified representation of the appliance includes a modified portion within the transform volume and an unmodified portion outside the transform volume; altering a shape transform magnitude in said blending region to cause continuity of shape between said modified portion and said unmodified portion of the modified representation of the appliance; wherein modifying said identified input coordinates in accordance with the shape transformation comprises scaling said identified input coordinates in a direction normal to said first surface of said datum plane and wherein altering said shape transform magnitude comprises applying a plurality of different scaling magnitudes to identified input coordinates in the blending region such that input coordinates in the blending region located proximate the constraint plane are scaled less than input coordinates in the blending region that are located distal to the constraint plane; displaying the representation of the appliance and the datum plane on a computer display; and storing said modified representation of the appliance in a computer memory.