Abstract
The purpose of this research is to develop a magnetic sensing device for measuring the three dimensional mandibular movement around the intercuspal position of the mandible with high accuracy. Four chip coils are assembled in this device. One of them (a primary coil) is used as a target and is fixed on the buccal surface of the lower first molar, and the other three coils (secondary coils) act as sensors and are fixed on the buccal surface of the opposite upper posterior teeth. A chip coil is a small and light coil; 2.5mm in diameter, 2.0mm in height and 60 mgr in weight. The measuring range of this device is 6×6×8mm and the average of the measurement error after correcting three dimensional distortion is 62μm. From the preliminary experiments, when chip coils were placed into the mouth the output values from the device were influenced by three factors; oral temperature, dental materials (Au-Ag alloy, Au-Pd-Ag alloy) and tilt of the primary coil and secondary ones. As regard to the temperature, the output values at each subject's oral temperature was transformed to the values at room temperature (23.5°C). The influence of dental materials could be eliminated if the distance between coils and dental materials were separated more than 2mm. A small amount of tilt between the primary coil and the secondary coil will occur because the mandibular movement is an ingenious combination of translation and rotation. The measurement error resulting from this tilt was approximately 40μm at the maximum tilt angle 5.9° and this is not substantial enough to disturb the measurement of the physiological movements such as mastication and swallowing. The magnetic sensing device was proven to be capable of measuring the mandibular movements more physiologically than the other measuring tools. It will be possible to make less invasive measurement of jaw movements, especially in the case of children.
