A technique to investigate the three-dimensional kinesiology of the human temporomandibular joint S. Siegler, PhD.,* R. Hayes, D.D.S.,** D. Nicolella, M.S.C.,*** and A. Fielding, D.M.D.**** Drexel University, and Temple University, School of Dentistry, Philadelphia, Pa. Previous kinesiological studies of the temporomandibular joint (TMJ) were based on the motion of only one or two selected points on the mandible (such as the lower central incisor, the mandibular condyle). In the present study, a technique was developed to measure, analyze, and describe the full three-dimensional kinematic characteristics of the TMJ during any mandibular activity. The technique was based on determination of the relative position between the mandible and the temporal bone from measurement of the location of points on light-weight frames rigidly attached through splints to the maxillary and mandibular teeth. An opto- electric kinematic data acquisition system has been used to record the location of these points. The results of the study indicate the following major advantages of this technique over previously reported kinesiological methods: (1) the technique provides a full description of the motion of the mandible with respect to the temporal bone, including all the six degrees of freedom associated with this motion; (2) the description of motion in terms of joint parameters enhances interpretation of the data by clinicians; (3) the motion of any point of interest on the mandible can be easily derived from the data and; (4) the system provides only negligible interference with the natural jaw motion of the subject. It does not require head fixation, does not alter or interfere with the natural occlusion, and its light weight causes only minimal (and negligible) loading of the mandible. (J PROSTHET DENT 1991;65:833-9.) For more than a century, researchers have devel- oped techniques to monitor and analyze the kinesiology of the temporomandibular joint (TMJ) and applied these techniques to study the kinematics of both the normal and the dysfunctional TMJ. 11° Recent advances in electronic and computer technology facilitated the development of electronic techniques to record the motion of the mandible. The main advantages of these techniques over previous ones were that they could accurately record the dynamic motion of the mandible. In addition, because of their reduced size, these devices pro- vided little interference with the natural motion of the mandible. The goal of this study was to develop a method to mea- sure, analyze, and describe the three-dimensional kine- matic characteristics of the human TMJ. This method was based on studies that had used a similar technique to in- *Associate Professor, Department of Mechanical Engineering, Drexel University. **Professor, Department of Orofacial Growth and Development, Temple University, School of Dentistry. ***Graduate student, Department of Mechanical Engineering, Drexel University. ****Professor, Department of Oral and Maxillofacial Surgery, Temple University, School of Dentistry. vestigate the three-dimensional kinematic characteristics of the ankle and subtalar jointsJ 1,12 According to this technique, the complex movements of the mandible during a variety of functional activities can be described in terms of six independent variables that can be easily interpreted by clinicians. These variables include three independent rotations and three independent translations) 3 MATERIAL AND METHODS Measuring system and testing procedure This study of the kinematics of the human TMJ was based on the measurement of the relative position between the mandible and the temporal bone. To obtain this mea- surement, a three-dimensional kinematic data acquisition system was used. This system had the capability of measuring the position of points located on the mandible and the position of points located on the temporal bone. Because these bones are not directly accessible in vivo, the actual points measured were located on lightweight frames that were rigidly attached to the upper and lower teeth. The kinematic system used in this study was an opto- electric system that measured the location in space of min- iature light-emitting diodes (LEDs). This system had the capability of recording the motion of up to 32 LEDs with a spatial error of less than 0.1 mm and a sampling rate of up to 4000 samples per second. The experimental system is shown schematically in Fig. 1. The system consisted of the light-emitting diodes (LEDs) corresponding to the THE JOURNAL OF PROSTHETIC DENTISTRY 833