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On the applicability of electrical impedance indices to characterize the condition of the oral mucosa

In recent years efforts have been put on the development of objective, noninvasive and inexpensive method to evaluate the condition of the oral mucosa. It was demonstrated in some special cases (experimental conditions, induced irritation reactions) that electrical impedance techniques have the potential of fulfilling these requirements. The aim of our study was to compare the information contained in baseline impedance values with the information extracted by impedance indices proposed by Ollmar et al. [10], and to evaluate these indices as a data reduction technique. Therefore, we measured impedance magnitude and phase in the range of 30 Hz to 1 MHz at ten different points of the oral mucosa. Measurements were performed on a group of 20 subjects. From impedance data at 20 kHz and 500 kHz we calculated impedance indices MIX, PIX, RIX and IMIX, and performed statistical analysis. We have demonstrated mathematically that MIX, RIX and IMIX form a redundant set of indices i.e. any of them can be calculated from other two. This disagrees with the essence of data reduction. Experimental results have shown that indices RIX and IMIX behave as downscaled index MIX, which indeed is the most valuable, intuitively well defined, and from the instrumentation point of view easiest to measure. We have also found that, due to its extremely high variability, index PIX has no practical value (except maybe in cases when direct reference from the same subject is available). The main conclusion of our study is that the proposed set of indices is not fully satisfactory nor could be generally accepted as data reduction technique. Their applicability for characterization of the mucosal tissue is limited. The probe being used for impedance measurement plays an important role and indices should be defined anew for every probe design.

electrical impedance; impedance measurement; impedance indices; oral mucosa; data reduction; modeling

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