AN ELECTRONIC STRAIN GAUGE FOR MEASURING ORAL FORCES

¹ Department of Electrical Engineering and Dental School, Tufts College, Boston, Mass.

An electronic strain gauge has been devised for measuring oral forces, which makes use of the principle of change in inductance of a coil as a silver plated spring is brought near the coil. The deflection of this spring is proportional to the force applied and the deflection produces a change in inductance. The coil is part of a tuned circuit which is coupled to a radio-frequency oscillator. Force applied to the spring changes the inductance and tunes the coupled circuit away from the oscillator frequency. This permits the amplitude of oscillation to increase and the magnitude of the grid current in the oscillator is used as a measurement of biting force.

A set of four elements are employed to cover the ranges of forces involved. The ranges are 100 to 300 pounds, 30 to 100, 5 to 30, and 1 to 5 pounds.

The bite element is narrow enough to permit maximum force readings on any tooth in the mouth with a bite opening of 7 to 10 millimeters. The bite element is small, light, unaffected by temperature and moisture, and capable of withstanding sterilization.