Sensitivity of the Root Canal Impedance to Electrode Displacement – in vivo and in vitro Measurement

Root canal impedance measurement was carried out in vivo on a series of patients and in vitro on a model (tooth dipped into a saline solution). Impedance was measured for several file tip displacements from apical foramen in the frequency range from 100 Hz to 1 MHz. Comparison between in vivo and in vitro results was performed for the measured value of impedance and for the components (Rp, Cp) of two element parallel equivalent circuit. It has been shown that normalized values obtained on apex have very similar frequency dependence, but the sensitivity to electrode displacement differs great in magnitude and its frequency dependence when measured in vitro from the one obtained in vivo. It is possible to use model – based measurements to draw some conclusions or test apex locator devices if the measurement is conducted on apex, when the file is displaced from apex difference towards in vivo measurement becomes significant.