R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

134 Medical modelling
patient contact in theatre meant that the stereolithography template could
be used directly in surgery after sterilisation. Sterilisation presents no
practical problems and appropriate methods include ethylene oxide (55 ºC),
formaldehyde, low temperature steam (75 ºC) and gamma irradiation. The
template locates onto the anatomical features on the surface of the skull at
the implant site and indicates the drilling sites to the surgeon. The mastoid
and zygomatic process are exploited to provide positive anatomical features
so that the template locates accurately and fi rmly.
6.3.7 Results
In surgery, the template was found to fi t very accurately and securely to
the area of the skull as shown in Fig. 6.20. The drilling was carried out and
the bone thickness and quality was found to be as indicated by the data.
The positions indicated by the template were found to be much more accurate
than those indicated by marks transferred from the soft tissue with ink
and needle, by as much as 5 mm in one case. The team have now successfully
carried out many similar cases using this approach with equally positive
results and a considerable saving of time and money. If we consider
the typical procedure for the traditional method being as follows; carve a
planning ear (30 minutes), take impression of defect site (15 minutes),
6.20 The template in position during theatre, located in the centre of
the surgical incision.