IMPEDANCE SPECTROSCOPY OF TEETH WITH AND WITHOUT APPROXIMAL CARIES LESIONS - AN IN-VITRO STUDY

Caries diagnosis by the measurement of electrical resistance is hamper ed by polarization effects when de or single-low-frequency ac currents are used. Electrical impedance spectroscopy, measuring impedance over a large range of frequencies, will provide more detailed information about the electrical characteristics of teeth. It was the aim of this study (a) to characterize the complex impedance behavior of whole extr acted teeth, measured at the approximal surface, and (b) to identify p arameters of the complex impedance behavior of the teeth which would b e useful in distinguishing between degrees of carious involvement. Thi rty-nine extracted premolar teeth with 59 unrestored and undamaged (ex cepting caries) approximal surfaces were selected. The tooth surfaces were divided into three groups according to their macroscopic appearan ce: sound (group S, n = 16), white- or brown-spot lesion present (grou p L, n = 33), or cavitated (group C, n = 10). The teeth were inserted into a jig which allowed for counter-electrode contact via a conductin g gel. The working electrode consisted of a carbonated fiber material. Electrical impedance measurements were performed over a maximum range of about 1 MHz to 0.1 Hz. We analyzed electrical impedance data by fi tting equivalent circuits. Fit was evaluated numerically and visually. The complex impedance spectra divided naturally into three groups whi ch corresponded almost perfectly with the classifications of S, L, and C. The groups differed most in the de resistance (R(dc)), as calculat ed from the impedance parameters. Mean R(dc) for groups S, L, and C we re 68 M Omega, 5.9 Mn, and 321 k Omega, respectively. These means were significantly different from each other (log-transformed data, ANOVA, p < 0.001; Tukey multiple comparisons, p < 0.001). It is concluded th at the in vitro performance of electrical impedance spectroscopy in di fferentiating among sound, non-cavitated carious, and cavitated approx imal tooth surfaces is excellent.