R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

198 Medical modelling
Finishing
The anatomical buck model was then removed, acting as a Boolean cutting
tool to leave just the prosthesis pattern. Unwanted clay was also removed
from behind the eye with the ‘paint on mask’ tool used to protect important
visible detail from accidental carving.
Up until this point, the clay was defi ned relatively coarsely in order to
minimise the use of computer memory. The clay was refi ned, which had the
effect of smoothing edges and refi ning detail, but also increased the fi le size.
The results can be seen in Figs. 6.63(a–c). The prosthesis pattern was then
exported as an STL fi le for preparation and building.
Manufacture
6.62 The blended in prosthesis.
The pattern was produced using a ThermoJet ® printer in the ‘TJ88’ grade
material, (3D Systems Inc., 26081 Avenue Hall, Valencia, CA 91355, USA).
This process selectively deposits wax layer-by-layer, building the part on a
scaffold of supports, and is capable of building thin edges and fi ne detail.
The down-facing surfaces are rougher due to the support structure that
attaches the objects to the build platform. The difference between up- and
down-facing surfaces is shown in Fig. 6.64. Given that the fi tting surface of
the prosthesis was likely to require modifi cation, it was decided to orientate
it downwards using the preparation software. The entire preparation took
approximately 15 minutes.