Restor Dent Endod.  2015 May;40(2):113-122. 10.5395/rde.2015.40.2.113.

Evaluation of electrical impedance ratio measurements in accuracy of electronic apex locators

• Kim PJ
• Kim HG
• Cho BH

• KMID: 2148860
• DOI: http://doi.org/10.5395/rde.2015.40.2.113

Abstract

OBJECTIVES
The aim of this paper was evaluating the ratios of electrical impedance measurements reported in previous studies through a correlation analysis in order to explicit it as the contributing factor to the accuracy of electronic apex locator (EAL).
MATERIALS AND METHODS
The literature regarding electrical property measurements of EALs was screened using Medline and Embase. All data acquired were plotted to identify correlations between impedance and log-scaled frequency. The accuracy of the impedance ratio method used to detect the apical constriction (APC) in most EALs was evaluated using linear ramp function fitting. Changes of impedance ratios for various frequencies were evaluated for a variety of file positions.
RESULTS
Among the ten papers selected in the search process, the first-order equations between log-scaled frequency and impedance were in the negative direction. When the model for the ratios was assumed to be a linear ramp function, the ratio values decreased if the file went deeper and the average ratio values of the left and right horizontal zones were significantly different in 8 out of 9 studies. The APC was located within the interval of linear relation between the left and right horizontal zones of the linear ramp model.
CONCLUSIONS
Using the ratio method, the APC was located within a linear interval. Therefore, using the impedance ratio between electrical impedance measurements at different frequencies was a robust method for detection of the APC.

Keyword

Canal length; Electrical impedance; Electronic apex locator; Endodontics; Impedance ratio

MeSH Terms

Architectural Accessibility
Constriction
Electric Impedance*
Endodontics

Figure

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  Figure 1 Selection process for the articles evaluated in this study.

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  Figure 2 Sample plots for data obtained from the studies included in the correlation analysis. (a) Three-dimensional plot of a grouped data set from Pilot and Pitts, in which the inputs were the distance from the apical constriction and the frequency, and the outputs were the absolute impedance values (Zabs);19 (b) Plot of the log-scaled frequency and the Zabs from a sample data set from Krizaj et al.15

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  Figure 3 Plots of the distance from the apical constriction (APC) and the impedance ratio (Yratio), and the method used to find a simple linear ramp function model. (a) Plots of the distance from the APC and the Yratio between 400 and 8,000 Hz for all groups; (b) Model between the distance from the APC and the Yratio between 400 and 8,000 Hz; (c) - (e) Point selection algorithm for the simple linear ramp function model between the distance from the APC and the Yratio values. Move the discriminating points (1). (d) In odd trials, the last point at the end of the left horizontal section (2A) was changed to the next right point (2B); (e) In even trials, the first point at the start of the right horizontal section (3A) was changed to the next left point (3B).

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  Figure 4 Plots of the distance from the apical constriction and the relative value from Distance 0. Approximate resistance values (β) obtained at 1 Hz from Equation 1 were substituted for the resistance at frequency f = 0 and calibrated using the approximate resistance value at point 0.

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