Evaluation of soft-tissue artifacts when using anatomical and technical markers to measure mandibular motion

Background/purpose: Skin marker-based systems are used to accurately measure the three-dimensional motion of the temporomandibular joint. Since skin markers move relative to the underlying bone during jaw movements, the measured temporomandibular joint kinematics is subject to soft-tissue artifacts. A complete evaluation of soft-tissue artifacts for markers on the facial anatomical landmarks and on an optical frame during jaw opening/closing movements is not available. The purpose of this study was to further our knowledge using a commercial opto-electronic movement tracking system to measure marker movements, that were then compared to true values defined by a transoral rigid device attached to the incisors. Materials and methods: Twenty healthy subjects performed jaw opening/closing movements at a self-selected pace while the 3D trajectories of 17 facial skin markers, three markers on an optical frame, and 4 markers on a transoral device were measured using a six-camera opto-electronic motion tracking system. Movements of the skin and optical frame markers relative to the head coordinate system defined by the transoral device (gold standard) were calculated. The movements of the head coordinate systems defined using different groups of skin markers relative to the gold standard were also analyzed. Results: The results showed that nose-bridge markers had minimal displacements but the middle- and side-face markers had large displacements. Conclusions: It appears that markers on the frontal nose bridge are good alternatives to transoral rigid devices for measuring mandibular motion, compared to optical frame markers and other skin markers on the face. The results of the current study will be helpful for establishing guidelines for marker placement when measuring mandibular movements in patients with potential temporomandibular disorders. Copyright (C) 2011, Association for Dental Sciences of the Republic of China. Published by Elsevier Taiwan LLC. All rights reserved.