R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Case studies 265
and sharp radii required to represent anatomical forms and textures. In fact,
in applications such as automotive and aerospace design it is highly desirable
to avoid unwanted creases in the surfaces being created. Software
aimed towards three-dimensional computer gaming and animation, such as
3dsMax ® (Discreet-AutoDesk Inc., 10 Duke Street, Montreal, Quebec,
H3C 2L7, Canada) exhibits many of the same limitations as engineering
CAD, but typically allows a greater freedom for surface manipulation. As
these objects are not actually physically produced, as long as the visual
effect on the screen is convincing there is no need to go further in terms of
detail. The textures that appear on these animations and games are normally
represented by two-dimensional images that are ‘wrapped’ around
the object. This creates an illusion of texture rather than true threedimensional
relief. Therefore, for the purposes of prosthesis manufacture,
this wrapped texture cannot be used, because it cannot be physically reproduced
using RP techniques.
Recently, methods of true three-dimensional texture creation have been
explored (18). The application of textures has been applied in the jewellery
industry and software such as ArtCAM TM (Delcam plc, Small Heath
Business Park, Birmingham, B10 0HJ, UK) incorporate tools to map
three-dimensional textures around a CAD model (18). However, ArtCAM TM
and other jewellery design software construct their shapes in the same
manner as engineering CAD and are, therefore, not suited to the representation
and manipulation of anatomical forms. Recent developments in
CAD software have led to design packages that offer a more intuitive and
freehand interface to the design process. Software such as ZBrush ®
(Pixologic Inc., 320 West 31st Street, Los Angeles, CA 90007, USA) and
FreeForm ® (SensAble Technologies Inc., 15 Constitution Way, Woburn,
MA 01801, USA) may provide a CAD environment that is more analogous
to sculpting by hand which clearly is more appropriate to the design and
manufacture of a facial prosthesis. Both FreeForm ® and ZBrush ® allow
complex three-dimensional forms to be manipulated and given highresolution
textures in a freehand manner. FreeForm ® has been shown to
be suitable for facial prosthesis design in previous research (8, 11, 12). In
addition, the haptic interface between the user and FreeForm ® software
allows shapes to be manipulated in ways that more closely mimic the hand
carving techniques used in conventional prosthesis sculpting. Also,
FreeForm ® has a number of functions that can create relief on a model
surface derived from a two-dimensional image.
RP reproduction of skin textures
RP offers the most suitable solution to the production of a prosthesis or
pattern from CAD data (11, 12). Computer numerically controlled (CNC)