Objective: The aim of the study was to develop a new method of ac impedance spectra analysis to improve the resolution of early caries lesion diagnosis. Methods: Material of the study consisted of 20 unrestored premolars extracted for orthodontic or periodontal reasons obtained from subjects aged 18 - 35. The buccal (SB) and approximal (SD) surfaces of the samples were assigned to one of two groups: sound - SB, SD (N = 10) and with spot lesion - C (N = 10). Histological examination of tooth sections was carried out. Ac impedance measurements were realised using a two-electrode system with small radius working electrode. The impedance measurements were done in conditions similar to oral cavity. Results: Reproducibility of the method is characterized by the errors of the average of the capacitance parameters, T and phase angles j, which are not higher than 3% and 0.4%. A Student's t – test for the differences between the means was used to statistical analysis and assumed null hypothesis is the absence of differences between the means in the compared groups. The values at which the null hypothesis should be rejected at the assumed level of confidence (<0.05) are in bold type (Table). Conclusions: These results prove high precision and accuracy of the capacitance parameters T and j. On the basis of the obtained results it can be concluded that with the measuring procedure consisting of the use of multiple small radius electrodes and sophisticated ac impedance results analysis it is possible to diagnose caries C in comparison with sound SD and SB without a statistical error.

TABLE

Compared surfaces:

SB-C; SD-C; SD-SB;

Probability of the absence of differences between the means of T parameters:

0.0044; 0.0000; 0.0486

Probability of the absence of differences between the means of j parameters:

0.0000; 0.0000; 0.6550

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