Page 50 - Craniomaxillofacial Implant Surgery - Jeroen P.J. Dings

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Chapter 3
Furthermore, it was expected that the use of bone-fixated pins improved the accuracy of the guided implant placement procedure.
MATERIAL AND METHODS
2.1. Procedures
Ten fresh frozen cadaver heads were collected by the Anatomy Department Radboud University Medical Centre Nijmegen and used in the present study.
The cadaver skulls were stabilized to prevent movement artefacts in an upright position for the CBCT scan and in a supine position for the MDCT scan like in real patients. CBCT images were obtained using the KaVo 3D eXam Imaging System (KaVo Dental GmbH, Biberach, Germany). 3D imaging data were acquired at 120 kV and pulses of 1.2 mA. The scan time was 40 seconds. The field of view was 22 cm with a voxel size of 0.300 mm. Data were converted into DICOM format (Digital Imaging and Communications in Medicine). MDCT examination was carried out with a commercially available 320-detector row CT-system (Toshiba Aquilion ONE; Toshiba Medical Systems Corporation, Tochigi, Japan) with the following scan parameters kept identical for all specimens: tube voltage 120 kV, slice thickness 0,5 millimetre with a radiation exposure per slide of 61.8 mGy and a total exposure of 1619.1 mGy with a field of view of 26.2 cm.
Subsequently, 3D-models of the entire cadaver heads were created from the DICOM files using Maxilim software (Medicim NV, Mechelen, Belgium). The 3D digital model of the skin surface was obtained by setting a suitable threshold value. Both models were achieved semi-automatically by threshold based segmentation, contour extraction, and surface reconstruction.
Branemark MK III TiU implants with regular platforms (RP; ∅3.75 mm; Nobel Biocare, Zürich, Switzerland) were virtually planned by an oral maxillofacial surgeon (JD) using the Procera System (NobelGuide; Nobel Biocare, Göteborg, Sweden) in optimal positions with respect to both the available bone volume and prosthetic demands. By including the exported 3D-computer models of the planned implants, a full surgical template was created with the aid of Autodesk 3ds Max Design software (version 2012; Autodesk Inc., San Rafael, CA, USA). Templates were exported as STL-files, transferred to the rapid prototyping system and 3D-printed from biocompatible resin with an