An Electronic Strain Gauge for Measuring Oral Forces

N UMEROUS instruments have been devised for measuring the maximum biting force. The literature prior to 1938 has been adequately covered by Brawley and Sedgwick 2 who found thirty-one references to different instruments for measuring biting force. The principles involved in construction of these devices included use of simple levers, springs, manometers or combinations of these principles, and steel ball impressions. Since that date, instruments have been developed by Worner,3 Boos,4 and Losch,' and a technic was suggested by Baker, Brekhus, and Dowell.6 In Worner 's device, the biting force was transmitted from a plunger to a liquid and registered on a pressure gauge. The equipment employed by Losch consisted of a Sylphon bellows through which pressure was applied to a liquid and registered on a manometer. It was similar to the equipment used by Brekhus and Armstrong7 and by Waugh.8 The device prepared by Boos was applicable only for measuring forces between dentures. The technic suggested by Baker, Brekhus, and Dowell are similar in principle to that recommended by Koehler and Etling.9 It seems evident that the most suitable instrument for measuring biting force will be one with the minimum size for the part on which the force is exerted. During actual chewing the teeth are very nearly in contact when the maximum forces are being exerted. For this reason the bite element should be thin enough to permit observations to be made when there are only a few millimeters of bite opening. Of course, a thin basic element can be adapted to experiments where greater bite opening is desired. The element should also be narrow enough to permit measurements to be made on any tooth in the mouth. Furthermore, it would be desirable to have the bite element not connected to heavy or bulky equipment and to have it capable of withstanding sterilization. The completed instrument should have adequate precision. It is interesting that essentially these requirements were set forth by the Rotterdam Dental Society in 1911 in an effort to stimulate development of a suitable instrument.10 Their size requirement was that the bite element should be small enough to enter an aperture 1 cm. square. Regarding precision, they stipulate an error not over six pounds below 120 pounds, and not over twelve pounds between 120 and 330 pounds. There is no record that these requirements were ever met. Many of the instruments which have been reported for measuring oral forces could not be applied to measurements on a single tooth without modification. Those designed by Friel, Black,'2 Johnson and Hatfield,13 Brawley and