In the endodontic treatment of the root canal, one of the most important procedures is the root canal length determination. Apex-locators are commercial electronic devices used to determine canal length by measuring the electrical impedance. The verification of such instruments in-vivo is hard to perform because the only accurate way of measurement is by extracting the tooth and then measuring the canal length. For this reason, testing of apex-locators and their comparison as well as new measuring method evaluation are often performed by model-based in-vitro measurements on extracted teeth. In this paper we demonstrate that significant differences between electrical properties of the model and the vital tooth exist. Frequently used physical models in current studies consist of a tooth immersed either in saline solution or in freshly mixed alginate. In order to investigate the electrical properties of these physical models, we have measured the value of root canal impedance |Z| and the elements of two-element parallel equivalent circuit (R p , C p ) in both physical models and compared the results with in-vivo root canal impedance measurements. We have shown that the results of the measurements of electrical impedance on the physical models significantly differ from in-vivo measurements. Therefore, due caution is required when drawing conclusions about apex-locator accuracy or performing method evaluation based on model measurements.

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