A precise and useful method for coordinating computed tomography and jaw movement frames of reference.

PURPOSE The aim of this study was to develop a means of coordinating helical computed tomography (CT)- based morphological data in 3 dimensions (3-D) with that pertaining to jaw movement as recorded by a device that measures jaw movement in six-degrees-of-freedom (6-DOF), thus producing multi-point movement analysis of the condyle. METHODS The study sample was two volunteers. One of the subjects had erosive bony changes in both condyles, while the other had healthy condyles. We employed a customized facebow, which enabled us to coordinate jaw movement data and morphological volume data from CT. Total uncertainty of the coordination was computed, according to International Organization for Standardization (ISO). In order to demonstrate the effects of multi-point analysis for complex condylar movement, we tried to visualize the trajectory of the working condyle in lateral excursion. RESULTS The overall uncertainty at a condylar center chosen as an example to illustrate the method was 0.38 mm, 0.19 mm, and 0.50 mm in antero-posterior, lateromedial, and supero-inferior directions, respectively, in terms of 95% coverage as defined by the ISO. CONCLUSION We developed facebow-based X-ray markers with high clinical operability, which could correlate the helical CT's coordinate system with our 6-DOF jaw movement measuring system for precise analysis of 3-D condylar movements. In motion analysis of rotational condyle, even a small amount of measurement error cannot necessarily be neglected. Then, a multi-point approach such as that realized by our system presents the best option.