An intra-oral telemetry system for the continuous recording of vertical jaw movement

Continuous measurement of the separation between upper and lower dental arches, the so-called interocclusal distance (10D), is of interest in dentistry. Criteria for making such measurements by radio telemetry are discussed. It is concluded that a transmitter small enough to fit in a molar tooth gap is necessary in order to minimize interference with normal function; other design factors are related to obtaining adequate frequency stability, on which measurement accuracy depends. A transmitter fulfilling these requirements is described which sensed the instantaneous value of 10D by the frequency change produced when a metallic object (dental filling, gold crown, shorted turn of wire or piece of ferrite) in one dental arch moved relative to the transmitter in the other. Errors due to lateral and protrusive jaw movements were measured. Careful design and the use of high grade ceramic chip capacitors resulted in a transmitter of good frequency stability (+/- 0.03% in 10 h, +/- 0.02%/degrees c) and small size (10 X 7 X 5 mm). An example is given illustrating 10D movements due to swallowing, speech and respiration.