R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Case studies 203
grating the technology with existing techniques. Previous research has
also considered the manufacture of patterns using other methods such as
stereolithography (SLA ® , 3D Systems Inc.), Fused Deposition Modelling
(FDM TM , Stratasys Inc., 14950 Martin Drive, Eden Prairie, MN 55344-2020,
USA), Laminated Object Manufacture (LOM TM , see Section 5.8), Selective
Laser Sintering (SLS ® , 3D Systems Inc.) and Solid Ground Curing (SGC)
(5, 7). Numerically controlled machining and vacuum casting have also
been explored (8). The techniques discussed in this previous research all
require additional steps in the pattern fabrication process or the extensive
use of expensive RP materials and processes since the materials used are
not directly compatible with laboratory techniques. Any additional steps in
the process add both time and, therefore, cost that direct manufacture in
wax eliminates. Mould manufacture is also more complicated (possibly
requiring more than two parts to create undercuts in the pattern) and
requires more material, thereby increasing build times and costs further (6).
Direct mould manufacture also removes the ability to test fi t a pattern on
the patient and modify the design by creating fi ne, feathered edges and
the best possible fi tting surface in order to improve the marginal integrity
(10, 11).
Disadvantages of the ThermoJet ® technique include the poor quality
down-facing surfaces and the delicate nature of the wax parts produced.
However, this did not cause a problem in this research. ThermoJet ® printing
is relatively fast (short preparation and build times: approximately two
and a half hours to manufacture a single pattern), clean (safe material,
requires no solvents for cleaning), quiet and cheaper than most alternative
methods. High levels of surface detail with only a minor stepping effect
were also achieved, thereby minimising the need for hand fi nishing.
6.11.5 Conclusions
Due to the complex production of a facial prosthesis it is diffi cult to ascertain
accurately the time saved by integrating these new methods into the
prosthetists’ procedures. However, a prosthesis of this nature would normally
take around ten hours of patient consultation through the various
stages of impression, carving and ‘try on’. The same procedure was carried
out in four hours with three hours manufacture using reported techniques,
a great saving. It is expected that with practice and the establishment of
FreeForm ® design protocols, the design time could be further reduced.
Although the authors recognise that an experienced prosthetist can hand
carve close mirror images of the anatomy, such as an ear, in quite a short
time, this technology could really become of benefi t when dealing with
large orbital cases or those involving multiple facial structures. These not
only take a great deal of time to construct but the patients are often too ill