R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

206 Medical modelling
current position and, where they fall short, direct further research that will
identify the direction and magnitude of the developments required.
6.12.3 Existing facial prosthetics technique
Facial prosthesis design and construction techniques have changed little in
40 years and are described well in textbooks (12, 13) and papers (14, 15).
By their nature, prostheses are one-off, patient-specifi c devices that cannot
benefi t from batch or mass manufacture. Hand crafting techniques are
therefore used to fabricate the prosthesis form and retentive components
and, in some cases, join them to pre-fabricated components that enable the
prosthesis to be attached to the implants.
Various retention methods may be used to secure a facial prosthesis such
as magnets, bar and clip, adhesives or engaging anatomical undercuts.
However, in many cases implant-retained prostheses are now considered
to be the optimum solution. In implant-retained cases, the prosthesis typically
consists of three components; the soft tissue prosthesis itself, a rigid
substructure incorporating the retention parts and the corresponding retention
parts that remain attached to the patient. The attachment between the
two retention components can be by bar and clip or by magnets. Bar and
clip gives the highest retention force, and the strength may be altered by
crimping the metal clips. Magnets can provide a range or retentive forces
(around 500–1000 g) depending on the number and type used. Magnets may
either be screwed directly on to the abutments or located on a framework.
The prosthesis-mounted components may be bonded directly into the silicone
if the prosthesis is small or a substructure is not necessary.
Prosthesis design is typically undertaken by shaping wax on a plaster
replica of the patient’s anatomy. Realism is predominantly achieved through
the prosthetist’s ability to interpret the correct location and physically recreate
the anatomical shape and detail. Colour matching of the silicone also
helps to complete a good blend into the surrounding anatomy.
Although these existing techniques are time consuming, they can be
applied to a wide range of situations. Previous studies have shown that to
be effective digital technologies must be sympathetically integrated into
these existing techniques so that the skills and fl exibility of the prosthetist
are not hampered (9, 10, 11).
6.12.4 Review of advanced technologies in
facial prosthetics
A review of previous research highlights a range of advanced technologies
that may be used to design and manufacture a facial prosthesis (1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11).