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Abstract

There is disclosed a device for detecting the position of an apical foramen of a tooth's root by measuring a change in the impedance between a measuring needle inserted into a tooth's root canal and an electrode abutting on oral mucosa. This device includes a circuit for generating two kinds of different frequency signals, detection circuits for detecting a change in the impedance in response to the respective frequencies and a 'difference' detection circuit for successively comparing outputs of the detection circuits and for producing a 'difference' signal, and a feed back circuit for feeding an output of the 'difference' detection circuit to one of the input terminals of the 'difference' detection circuit so as to equalize its two inputs by addition or by subtraction and thereby to make its output equal to zero. Furthermore, the device is provided with a means for announcing that the output of the 'difference' detection circuit is set to zero, and an indicating means for informing that the output of the 'difference' detection circuit has reached the specified value when the measuring needle is inserted further into the tooth' s root canal after the above-mentioned zero setting. The position of the apical foramen is considered to be the location of the measuring needle's tip when the output of the 'different' detection circuit reaches the specified value.

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First Claim