PROBLEM TO BE SOLVED: To facilitate a zero adjustment operation for adjusting an output voltage for each frequency at the same voltage in root canal length measurement in which two kinds of voltages different in frequency are applied between a measurement needle inserted in the root canal and an opposite electrode connected to a lip, an impedance in the root canal is measured from the difference in output voltage between the frequencies and the position of root apex is determined.SOLUTION: At least two kinds of frequency signals different in frequency are applied between the measurement needle 1 inserted in the root canal 3 and the opposite electrode connected to the lip 5, a voltage caused by a change in impedance between the measurement needle 1 and the opposite electrode 7 in response to each of the frequencies is detected, the output voltages are each adjusted to the same voltage, a difference in the voltage after adjustment is detected, and the root apex position ap is determined based on the difference in voltage. In adjusting both the output voltages by a switch 39 prior to detection of the difference in voltage, a switch 41 acting in the same way as the switch 39 is provided on a file holder 40. Thus, the zero adjustment operation by an operator is facilitated.COPYRIGHT: (C)2013,JPO&INPIT【課題】根管内に挿入される測定針と口唇に接続される対向電極との間に周波数の異なる2種類の電圧を印加し、各周波数に対する出力電圧の差から根管内インピーダンスを測定し、根尖位置を決定する根管長測定において、各周波別の出力電圧を同一電圧に調整するためのゼロアジャスト操作を容易にする。【解決手段】根管3内に挿入される測定針1と口唇5に接続される対向電極との間に周波数の異なる少なくとも2種類の周波数信号を印加し、各周波数に応答して測定針1と対向電極7との間のインピーダンス変化による電圧を検出し、各出力電圧を同電圧に調整し、調整後の前記電圧の差を検出し、該差電圧より根尖位置apを決定する。差電圧を検出するに先立って両出力電圧をスイッチ39によって同一電圧が調整するが、このスイッチ39と同じ作用をするスイッチ41をファイルホルダー40に設け、術者によるゼロアジャスト操作を容易にした。【選択図】図1
