[Development of a new device for continuous measurement of vertical dimension using Magneto-Impedance (MI) sensors]

The purpose of this study was to develop a new device to measure continuously the vertical dimension of the human jaw relation using magnetic sensors.

A sensor unit was made of six MI (Magneto-Impedance) sensors (AMI302 4.0 x 3.5 x 1.4 mm, Aichi Steel Corp.) placed in a line at intervals of 4 mm. The unit was positioned to the head by a glasses-type sensor holder. A target magnet (3 mm in diameter, 12 mm in length) was set in a resin board positioned on the mentum with adhesive tape. 1) In vitro experiments using a precision-movement stage were conducted. 2) One healthy volunteer (age: 25 years) was instructed to perform a jaw opening-closing task with 10 mm range of motion. Before and after the task his jaw position in the intercuspal position was measured for five minutes. The jaw movements were recorded simultaneously using a 6-degree-of-freedom jaw-tracking device.

The mean square error of the in vitro experiment was 0.06 mm under the worst conditions. The mean square error of the positional accuracy was 0.35 mm. The reproducibility of the intercuspal position was 0.33 mm. These values correspond to about 16% of the value of the shift phenomenon of the resting position (approximately 2.2 mm).

Our new device using an MI sensor enables the vertical dimension to be recorded continuously with sufficient accuracy.