Electrochemical impedance characterization of human and bovine enamel

The alternating current impedance characteristics of human and bovine enamel slices were measured in vitro. An electrochemical cell containing two platinum gauze electrodes and 0.01 mol/L KCl buffered to pH 7.4 at 20 degrees C was used. The electrodes were attached to a potentiostat that was connected to a microcomputer-controlled frequency-response analyzer. Measurements were made at discrete frequencies between 1 Hz and 65 kHz by application of a sinusoidal potential of 50 mV (rms) across the assembled cell. The impedance was calculated from the input potential and the resulting measured flow of current. For quantitative evaluation of these measurements, an equivalent circuit was postulated. It contained five passive electronic components and accurately modeled the different specimens. Values for individual electrical components in the equivalent circuit were estimated by complex non-linear least-squares regression analysis. This study demonstrated that it is possible to measure and quantitatively distinguish between the impedance characteristics of: permanent human, deciduous human, and bovine enamel, as well as the enamel from a variety of sites from human teeth, some of which had been extracted prior to being fully erupted. Proposals are made as to which physical properties in the specimens are modeled by individual components in the equivalent circuit.