R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

208 Medical modelling
Engineering CAD software packages typically work with geometric shapes
and provide methods of aligning components. However, engineering software
is poorly suited to handling complex and individual anatomical forms.
CAD software such as FreeForm ® provides a more intuitive solution to
handling anatomical forms (more akin to a digital sculpting package)
yet doesn’t provide suitable tools for aligning the various components.
A suitable CAD software package must provide tools for precisely aligning
geometric shapes as well as the manipulation of complex anatomical
forms.
Manufacture
Material requirements for maxillofacial prostheses are varied according to
the separate components. For the soft tissue elements that are currently
made from colour-matched silicone, no technology exists that is able to
build the fi nal prosthesis form directly from CAD data. Therefore, a pattern
must be produced instead. The review of previous research and experiments
carried out at PDR and Morriston Hospital has shown that producing
the pattern in a material compatible with conventional sculpting
techniques is highly desirable. Building the pattern in wax allows the prosthetist
to easily adjust the pattern using their existing techniques and skills,
particularly during test fi tting on the patient (9, 10, 11). The substructures
need to be accurate and rigid enough to contain the retentive elements and
the forces experienced during attachment and removal. The retentive components
that remain attached to the patient via the implants must be noncorrosive
and un-reactive (similar to jewellery) and also rigid enough to
withstand the retentive forces. The materials for all of the components must
also not react with each other and resist the effects of being included in the
manufacture of the fi nal prosthesis from the pattern, such as mould heating.
Finally they must also provide adequate wear resistance, resist permanent
distortion and provide adequate retention for the service life of the
prosthesis.
6.12.5 Case study 1
In order to accurately assess the capabilities of current advanced technologies
in the design and manufacture of an entire implant-retained prosthesis,
an exploratory study was undertaken. The study would not only evaluate
the ability of current technologies but measurements and observations
made would inform future research. A bar and clip, implant-retained auricular
prosthesis case was selected. A three-dimensional computed tomography
(CT) scan had already been undertaken and the data used to plan the