Journal of Cranio-MaxilloJk~cialSurgery (1999)27, 77-81 © 1999 EuropeanAssociation for Cranio-Maxillofacial Surgery Positioning of dental implants using computer-aided navigation and an optical tracking system: case report and presentation of a new method Franz Watzinger, 1Wolfgang Birkfellner, 2 Felix Wanschitz, 1Werner Millesi, 1Christian Schopper, 1 Klaus Sinko, 1Klaus Huber, 2 Helmar Bergmanny Rolf Ewers 1 1Clinic of Oral and Maxillofacial Surgery (Head." Prof. Dr. Dr. Rolf Ewers, MD, DMD), :Department of Biomedical Engineering and Physics (Head." Prof. Dr. Helrnar Bergmann, PhD), 3Ludwig-Boltzmann Institute of Nuclear Medicine, Medical School, University of Vienna, Vienna General Hospital Waehringer Guerte118 20, A-1090, Vienna SUMMARY A navigation system for computer-aided surgery (Virtual Patient System, VPS) has been described in previous studies for different indications in oral and maxillofacial surgery. The aim of the system is the intraoperative transfer of preoperative planning on radiographs or CT scans on the patient, in real-time, and independent of the position of the patient's head. Until now an electromagnetic tracking system has been used for intra-operative position measurement. For placement of dental implants, the electromagnetic tracking system is not suitable since the motor of the implant drill leads to a considerable distortion of the magnetic field, thus direct visualization of drilling the implant socket was not possible. To overcome this problem, an optical tracking system which is not disturbed by conductive materials was integrated in the VPS system. The first patient operated on with this system had a posttraumatic loss of the upper incisors; three implants have been placed according to the prosthetic axis previously planned on radiographs and CT scans. The experience gained in this intervention led to the conclusion that computer-aided surgery provides a valuable tool in implant dentistry. INTRODUCTION Several studies confirm the importance of proper implant positioning concerning the prosthetic axis and the information gained by radiographic images (Jeffcoat et al., 1991; Weinberg, 1993; Horiuchi et al., 1995; Bianchi et al., 1997; Mayfield-Donahoo et al., 1997). Computer-assisted methods have been devel- oped to correlate the prosthetic axis with the patient's anatomy when performing dental implants (Fortin et al., 1995; Ploder et al., 1995; Verstreken et al., 1996). Nevertheless, it has turned out that the direct transfer of the preoperative planning data to the intra-opera- tive site is difficult. A widespread technique utilizes resin splints with guideholes directing the implant bur to the planned position (Fortin et al., 1995). A new method is presented which allows direct visu- alization of the implant burr on radiographs on a com- puter monitor with a computer-guided intra-operative navigation system based on an optical tracker. This permits the real time transfer of the preoperative plan- ning results on the patient, and the interactive control of proper implant positioning is possible. USA) and custom-made light emitting diode (LED) assemblies especially designed for implant dentistry (Fig. 1). The fiducial markers necessary for registration of CT-scans and cephalograms to the patient in the operating theatre are attached to an acrylic frame (3D-splint) which is mounted on an occlusal splint (Figs 2 and 3). Care has to be taken that the position of the splint is exactly reproducible. An accurate superimposition of X-ray and patient data requires that the fiducial markers are in the same position relative to the facial structures during the X-ray and MATERIAL AND METHODS Hard- and software, registration protocol: The navigation system consists of the navigation software (Virtual Patient System, ARTMA Medizin- technik, Vienna), an optical tracking system (Flash- point 5000, Image Guided Technologies, Boulder, 77 Fig. 1 - Instruments for optical navigation: reference LED assembly for registration of patient's data (small arrow). LED assembly on the handpiece for registration of position data of the implant drill (arrowhead). 5 degree-of-freedom probe (broad arrow).