A study on electric method for measuring root canal length.

As a fundamental study on the electric method for measuring root canal length, the various factors which affect the measured impedance were investigated using a wide range of frequencies. 1) The impedance between two saliva ejectors in contact with the oral mucosa near the bilateral premolars in the lower arch generally showed low values. The difference between the maximum and minimum measured impedance was reduced and eventually approached zero as the frequency increased. 2) When a 1.0-mm length of the reamer tip was inserted into 2% agar containing 0.90% or 0.45% NaCl solution, the impedance in the former solution was lower than that in the latter. 3) When the impedance of a reamer covered with insulating tape except at the tip, and exposed in a glass tube containing 0.90% NaCl solution was compared, the former showed a higher value than the latter. The smaller the inner diameter of the glass tube into which the reamer was inserted, the higher was the impedance of the reamer. In every case, the measured impedance and the difference between them decreased as frequency increased. With regard to the electric method for measuring root canal length, the application of high frequency of more than 30 kHz was considered to keep the influence of such factors to a minimum and contribute to the improvement of this method.