R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Case studies 211
technique that has also been reported in the digital design of other
prostheses (9, 10, 11).
Manufacture
The fi nal design of the prosthesis pattern was physically manufactured using
the ThermoJet ® printing process in a wax material. The use of wax allowed
modifi cations to include the retentive components to be made using conventional
methods. A colour-matched, silicone prosthetic ear was then
fabricated for the patient using conventional methods.
Initial fi ndings from Case study 1
This initial trial highlighted the limitations of non-contact scanning to
capture anatomy and fi nely detailed abutments with suffi cient resolution.
6.12.6 Case study 2
Data capture
The fi rst case study showed that the data captured was insuffi cient to be
used in the design of the retentive components. Therefore, the same case
was repeated using a higher-resolution structured white light scanner
(Steinbichler Optotechnik GmbH, Am Bauhof 4, D-83115 Neubeuern,
Germany). This type of scanner is typically used for engineering and has a
much longer capture time. Therefore, it was used to digitise the dental stone
replica of the patient produced using conventional impression methods.
This scanner captures approximately nine points per mm 2 (three per mm
in the x, y plane) and around 140 000 points per scan over an area of
approximately 250 mm × 250 mm and a working range of approximately
180 mm. In order to make the abutment locations easier to scan, magnetic
keepers (Technovent Ltd, Headingley House, 39 St Michael Lane, Leeds,
LS26 3SR, UK) were screwed on to the abutments to provide a fl at surface
and the model was coated in a fi ne matt white powder to reduce refl ectivity.
A total of six overlapping scans covering the entire model were taken and
the data aligned using Polyworks ® software (InnovMetric Software Inc.,
2014 Jean-Talon North, Suite 310, Quebec, QC Canada, GIN 4N6). STL
fi le data was created from the point cloud information using Spider (Alias-
Wavefront Inc., 210 King Street East Toronto, Canada, M5A1J7) and the
data imported into Magics. Magics provides alignment and modifi cation
tools for STL fi le data and was used to digitally remove the abutment caps.
The fl at surfaces of each abutment cap in turn were aligned by selecting
a triangle on the top surface and using a Magics function to make it