R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

234 Medical modelling
Jean-Talon Blvd North, Suite 310, Sainte-Foy, Quebec, Canada, G1N 4N6).
Spider software (Alias-Wavefront Inc., 210 King Street East, Toronto,
Ontario, Canada, M5A 1J7) was used to produce a polygon surface in the
STL fi le format (8).
Step 2: design of the RPD framework
The CAD package used in this study, called FreeForm ® (SensAble
Technologies Inc., 15 Constitution Way, Woburn, MA 01801, USA), was
selected for its capability in the design of complex, arbitrary but welldefi
ned shapes that are required when designing custom appliances and
devices that must fi t human anatomy. The software has tools analogous to
those used in physical sculpting and enables a manner of working that
mimics that of the dental technician working in the laboratory. The software
utilises a haptic interface (PHANTOM ® Desktop TM haptic interface;
SensAble Technologies Inc.) that incorporates positioning in three-dimensional
space and allows rotation and translation in all axes, transferring
hand movements into the virtual environment. It also allows the operator
to feel the object being worked on in the software. The combination of tools
and force feedback sensations mimic working on a physical object and allow
shapes to be designed and modifi ed in a natural manner. The software also
allows the import of scan data to create reference objects or ‘bucks’ onto
which fi tting objects may be designed. The RPD metal frameworks used in
this study were designed according to established principles in dental technology
using this CAD software and based on a three-dimensional scan of
a patient’s cast (9). The computer-aided design of RPD frameworks using
this software has been described previously (5, 6, 7). The fi nished design
used in this case is shown in the screen capture shown in Fig. 6.86.
Step 3: rapid manufacture
In a previous study, the application of RP methods was investigated for the
production of sacrifi cial patterns that were used to investment cast RPD
frameworks in cobalt-chrome alloy (7). Four RP methods were compared:
stereolithography (SLA ® ) (3D Systems Inc., 26081 Avenue Hall, Valencia,
CA 91355, USA), ThermoJet ® (3D Systems Inc.), Solidscape ® T66
(Solidscape Inc., 316 Daniel Webster Highway, Merrimack, NH 03054-
4115, USA) and Perfactory ® (EnvisionTEC GmbH, Elbestrasse 10, D-
45768 Marl, Germany). These various RP processes are described more
fully in Chapter 5.
In this study, direct manufacture was attempted with the aim of eliminating
the time and material consuming investment-casting process. The development
of Selective Laser Melting (SLM TM ) technology showed potential