R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Case studies 209
placement of two implants in a single-stage operation. A healing period of
six weeks was allowed before prosthesis construction.
Data capture
An impression and dental stone replica that recorded the implant abutment
locations and the surrounding anatomy was made using conventional
methods. In addition, the patient was digitally scanned using a pair of laser
scanners (Konica-Minolta Vivid 900 laser scanners, Osaka, Japan) to allow
for subsequent digital prosthesis design. Previous work has shown that
these scanners had a relatively fast capture time and an accuracy level
appropriate to the scanning of faces (17, 18). The actual number of points
captured per mm 2 is determined by scanner’s fi eld of view. At a distance
of 1.35 m, the scanners each captured an area of 445 × 333 mm, resulting in
a point density of one point per 0.69 mm 2 . A paired set-up was used in order
to capture a wider fi eld of view without having to move the patient. In
this confi guration the scanners are triggered consecutively (simultaneous
capture would lead to the scanners interfering with each other). The patient
was seated with their head positioned 1.35 m away from the scanners and
a 14 mm focal length lens used. Although the specifi ed capture time is 0.6
seconds for each camera, a short pause between scans meant that the
patient had to remain motionless and with the same facial expression for
approximately eight seconds. The point cloud scan data was aligned and
converted to an STL fi le using Rapidform TM software (INUS Technology
Inc., SBC, Ludwig-Erhard-Strasse, 30–34, D-65760, Eschborn, Germany).
Shadow areas behind the ears were not captured. However, the threedimensional
CT data that had been acquired for the implant planning was
also available to be used as the basis for the prosthesis design.
Design
The scan data was imported into the sculpting CAD package FreeForm ®
using the ‘thickness’ option to make a solid model. Whilst the scanners have
been shown to be able to capture anatomical detail well, this study demonstrated
that the data resolution was insuffi cient to describe the implant
abutments accurately (see Fig. 6.70). However, the data was good enough
to allow the abutment locations to be identifi ed, which allowed the overall
prosthesis form to be designed around them with suffi cient accuracy. The
patient’s opposite healthy ear was obtained from the CT data, imported
into FreeForm ® and mirrored to the defect site (see Fig. 6.71). The tools in
FreeForm ® were then used to blend this ear into the surrounding anatomy
and fi nally subtracted from it to leave an accurate fi tting surface using a