CAD/CAM-based referencing aids to reduce preoperative radiation exposure for intraoperative navigation

Intraoral Scanning Enables Virtual-Splint-Based Non-Invasive Registration Protocol for Maxillofacial Surgical Navigation

Background/Objectives: Surgical navigation has advanced maxillofacial surgery since the 1990s, bringing benefits for various indications. Traditional registration methods use fiducial markers that are either invasively bone-anchored or attached to a dental vacuum splint and offer high accuracy but necessitate additional imaging with increased radiation exposure. We propose a novel, non-invasive registration protocol using a CAD/CAM dental splint based on high-resolution intraoral scans. Methods: The effectiveness of this method was experimentally evaluated with an ex vivo 3D-printed skull measuring the target registration error (TRE). Surgical application is demonstrated in two clinical cases. Results: In the ex vivo model, the new CAD/CAM-splint-based method achieved a mean TRE across the whole facial skull of 0.97 ± 0.29 mm, which was comparable to traditional techniques like using bone-anchored screws (1.02 ± 0.23 mm) and dental vacuum splints (1.01 ± 0.33 mm), while dental anatomical landmarks showed a lower accuracy with a mean TRE of 1.84 ± 0.44 mm. Multifactorial ANOVA confirmed significant differences in TRE based on the registration method and the navigated level of the facial skull (p < 0.001). In clinical applications, the presented method demonstrated high accuracy for both midfacial and mandibular surgeries. Conclusions: Our results suggest that this non-invasive CAD/CAM-splint-based method is a viable alternative to traditional fiducial marker techniques, with the potential for broad application in maxillofacial surgery. This approach retains high accuracy while eliminating the need for supplementary imaging and reduces patient radiation exposure. Further clinical trials are necessary to confirm these findings and optimize splint design for enhanced navigational accuracy.

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 (IOS) 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 (0.48mm) and target registration error (0.65mm) is comparable to those of tooth-supported registration methods.

CONCLUSION

This methodology is a promising approach to marker-free navigation-assisted-surgery in the edentulous patient. This approach of marker-free registration for navigation-assisted-surgery could improve the treatment in edentulous patients avoiding additional imaging and invasive marker insertion. This article is protected by copyright. All rights reserved.