Verification of physical models used for root canal measurement by impedance comparison

Abstract

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.

Comparison of In Vivo and In Vitro Readings When Testing the Accuracy of the Root ZX Apex Locator

“…However, some of these materials might give greater accuracy than can be accomplished in vivo (26). Moreover, Marjanovic et al (27) observed that there are significant differences in electrical properties between in vitro and in vivo models. In light of these findings, extrapolation from in vitro studies to the clinical setting might not be appropriate.…”

Comparison of Electrical Equivalent Circuits of Human Tooth used for Measuring the Root Canal Length

“…After that, the tooth has been immersed in freshly mixed alginate prior to the hardening of the material. The alginate material is widely used as a physical model for in vitro measurements [2,4,12,15] since it has adequate physical and electrical properties. We have used Fast Set alginate dental impression material by GC Europe n.v. (Leuven, Belgium) prepared according to manufacturer's instructions using tap water.…”

“…Prior to this study we have used equivalent circuits with two or three linear elements (resistors and capacitors) to model the tooth [8,10,[12][13][14][15]. They could represent impedance behavior in a narrow frequency range, but their elements had to be frequency dependent in order to describe impedance in wider frequency range.…”

“…In our previous work possibilities of using two-element and three-element equivalent circuits that include linear frequency-independent components were examined [8,10,[12][13][14][15]. Some authors have also proposed a few simpler [16] and more complex [17] equivalent circuits.…”