Marker-free registration for intraoperative navigation using the transverse palatal rugae.

Background: Registration is most important in navigation-assisted-surgery including the matching between the coordinates of the actual patient space and the medical image. Marker-based techniques mostly include marker application with subsequent radiography. In the edentulous patient, maker-free methods are generally less accurate and reproducible. This new method of a marker-free registration uses the transverse palatal rugae as registration structures.

Methods: (1) Segmentation of bone and hard palatal mucosa from initial 3D imaging (DICOM), (2) Maxillary intraoral-scan with transfer to the 3D imaging using an Iterative-Closest-Point-Algorithm (ICP), (3) Marking digital registration points with holes within IOS-stl, (4) Transformation of the spatially aligned IOS-stl to LabelMap and storage in DICOM (IOS-DICOM), (5) Alignment of DICOM and IOS-DICOM, (6) Controlled positioning of digital reg. points and clinical correlation.

Results: Fiducial localization error (0.48 mm) and Target registration error (0.65 mm) is comparable to those of tooth-supported registration methods.

Conclusion: This approach of marker-free registration for navigation-assisted-surgery could improve the treatment in edentulous patients avoiding additional imaging and invasive marker insertion.