Apical Constriction Diameter Influence on Endodontic Impedance Using Spectroscopy Analysis

Objectives: electronic apex locators measure endodontic impedances. Control of extrinsic parameters such as irrigation liquid (IADR 00), or range of frequencies (IADR 01), improve their accuracy. Among intrinsic parameters, variation of dentin resistivity along root canal does not interfere with measurement of working length (IADR 02). The aim of this study was to determine, in vitro, the influence of Apical Constriction (AC) diameter. Methods: seven resin models teeth with canal, AC diameter from 10/100 to 40/100e (5/100 e step) and foramen, were manufactured. Each one was inserted in a CuSO4 gel, catheterized from 1mm above the AC, down to 2mm beyond (5/100 e step), using a 15/100e K file conducted by a micrometric displacement table (Mitutoyo). For every value of AC diameter, 3 spectroscopic analysis were performed from 0.1 kHz up to 100 kHz (1260 endodontic impedances). For every frequency, average values of these 3 measures were computed and compared, using a Kruskal-Wallis test (p=5%). Results: taking in account every frequency, it appeared, on one hand, that around the AC there was a significant difference between impedances obtained with diameters 10 and 15/100e (1 to 37kOhms) versus the others (0.8 to 20kOhms) and on the other hand, that if there was no significant decrease of impedance 0.5mm beyond the AC, so its diameter was between 20 and 30/100e. Conclusion: during the catheterism, the value and the evolution of endodontic impedance depends on the AC diameter.