R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

266 Medical modelling
machining has also been used to create textures (18), but is not as well
adapted to create fi tting and undercut surfaces and is also limited by suitable
material choice (machining of soft fl exible materials is diffi cult). CNC
becomes very slow when creating intricate or small scale detail such as
textures and requires a cutting tool with a very small diameter. A review
of the currently available RP technologies highlights a number of technologies
that are capable of creating the level of detail required to reproduce
realistic skin textures. A critical parameter in order to achieve the level of
detail required is the layer thickness that the RP system uses. To achieve
the level of detail identifi ed above, a layer thickness of below 0.1 mm is
necessary. Currently available RP technologies that can achieve a layer
thickness of below 0.1 mm include:
• ThermoJet ® wax printing (3D Systems Inc., 26081 Avenue Hall,
Valencia, CA 91355, USA);
• Perfactory ® digital light processing (EnvisionTEC GmbH, Elbestrasse
10, D-45768 Marl, Germany);
• Solidscape wax printing (Solidscape Inc., 316 Daniel Webster Highway,
Merrimack, NH 03054-4115, USA);
• Objet PolyJet TM modelling (Objet Geometries Ltd, 2 Holzman St,
Science Park, PO Box 2496, Rehovot 76124, Israel);
• Stereolithography (SLA ® , 3D Systems Inc.).
Of these, only the ThermoJet ® and Solidscape printing technologies are
capable of producing parts in a material directly compatible with current
prosthetic construction techniques. Therefore, it was decided that these
would provide the focus of the study. The Solidscape process utilizes a
single jetting head to deposit a wax material and another one to deposit a
supporting material, which can be dissolved from the fi nished model using
a solvent. This process produces very accurate, high-resolution parts but,
due to its single jetting head, is extremely slow. Therefore, the process is
highly appropriate for small, intricate items such as jewellery or dentures
but proves unnecessarily slow for facial prosthetic work. Like the Solidscape
process, the ThermoJet ® process deposits a wax material through inkjetstyle
printing heads, building a solid part layer by layer. The object being
built requires supports, which are built concurrently as a lattice, which can
be manually removed when the part is completed. The ThermoJet ® process
uses an array of jetting heads to deposit the material and is, therefore, much
faster. The material is also softer than that used by Solidscape, making it
more akin to the wax already used by MPTs and, therefore, more appropriate
for manipulation using conventional sculpting techniques. Although no
accuracy specifi cations are given for ThermoJet ® , it is advertised as having
a very high resolution (300 × 400 × 600 dots per inch in x-, y- and z-axes)
and is aimed at producing fi nely detailed parts (a drop of wax approximately
every 0.085 mm by 0.064 mm in layers 0.042 mm thick).