R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

196 Medical modelling
refi ned in order to produce the higher levels of detail required in the fi nishing
stages. Shapes can be viewed from any angle, clay added to the model
and measurements in any direction established in precise ways. A protective
‘mask’ or ‘buck’ setting may also be used to protect a model from
inadvertent carving. The user interface with the software is provided by a
stylus (PHANTOM ® Desktop TM haptic interface, SensAble Technologies
Inc.) that incorporates positioning in three-dimensional space and allows
rotation in all axes. In essence, the stylus translates hand movement to the
virtual sculpting environment. Force feedback sensations (for example,
when the virtual tool contacts the model) in relation to the tool position
within the sculpting environment are fed through to the user with the result
closely mimicking the tactile sensations of handcrafting.
Creation of the basic form
The STL fi le generated by Mimics was imported into FreeForm ® as a protected
buck model that could not be accidentally carved. The patient’s
defect was on their left side, so an area based on the required extents surrounding
the unaffected right orbit was fi rst selected. The selected clay was
copied and then recreated as a separate model that could be worked on
independently from the facial buck model. Fig. 6.60 shows the copied piece
being mirrored around the mid-sagittal plane (midline of the body) to form
the basis of the prosthesis pattern design. The original right side copied
piece was then deleted, leaving the anatomy buck model and prosthesis
pattern clay.
6.60 Mirroring the selected, unaffected area to the affected side.