In vivo assessment of the impedance ratio method used in electronic foramen locators

Abstract

BackgroundThe results of an in vivo study on the "ratio method" used in electronic foramen locators (EFL) are presented. EFLs are becoming widely used in the determination of the working length (WL) during the root canal treatment. The WL is the distance from a coronal reference point to the point at which canal preparation and filling should terminate. The "ratio method" was assessed by many clinicians with the aim of determining its ability to locate the apical foramen (AF). Nevertheless, in vivo studies to assess the method itself and to explain why the "ratio method" is able to locate the apical foramen and is unable to determine intermediate distances were not published so far.MethodsA developed apparatus applies an electrical current signal with constant amplitude of 10 μARMS through the endodontic file within the root canal. The applied current signal is composed by summing six sine waves, from 250 Hz to 8 kHz. Data were acquired with the endodontic file tip at 7 different positions within root canals. In the frequency domain the quotients between the amplitude of a reference frequency and the amplitudes of the other frequencies components were calculated. Twenty one root canals were analyzed in vivo, during the endodontic treatment of twelve teeth of different patients, with age between 20 to 55 years.ResultsFor the range of frequencies used in the commercial EFLs and for distances ranging from -3 mm to -1 mm of the AF, the impedance of the root canal is mainly resistive. However, when the file tip gets closer to AF, the root canal electrical impedance starts to change from a mainly resistive to a complex impedance. This change in the measured root canal impedance starts when the file tip is near -1.0 mm from the AF, getting stronger as the file tip gets closer to the AF. This change in the impedance behavior affects the ratio (quotient) of the impedance measured at different frequencies. Through graphic analysis it is demonstrated why EFLs based on the ratio method are unable to accurately measure any distances between - 3.0 and -0.5 mm from the apical foramen. The only reliable measurement is the 0 mm distance, which is when the file tip is at the AF.ConclusionsThe electrical impedance values of 21 root canals were in vivo studied. The results confirm the ability of EFLs that are based on the ratio method to accurately locate the AF position and explain why they are unable to determine the file tip position along the root canal.

Accuracy of Root ZXII, E-PEX and FIND apex locators in teeth with vital pulp: an in vivo study

“…Errors related to working length can lead to overinstrumentation and consequent overfilling, inducing the formation of granulomas, impairing the outcome of endodontic treatment, since cytotoxic effects of obturating materials can induce postoperative pain and even persistence of the inflammatory process. 6,7,8 In biopulpectomy, the biological philosophy preserves the vitality of the invaginated periodontal tissue inside the cemental canal (periodontal stump) aiming a periapical repair process. 9,10 Endodont ic l iterat u re suggest s t h at t he consistency and accuracy of the electronic apex locators (EALs) function may vary in the apical foramen and the apical constriction.…”

An In Vivo Study of Working Length Determination with a New Apex Locator

“…In the sequence, the endodontic file that better fitted into the root canal walls at that limit was fixed. Several important researchers ensure that AF represents an anatomic structure more reliable to carry out the eletronical measurements (11,12,15,21,23).…”

“…Although several studies (11)(12)(13)(14)(15) have shown the reliability of new-generation EALs, some models have not been assessed in vivo yet. This is the specific case of the Quill Apex Locator® (Ultradent Products, South Jordan, UT, USA), a third-generation EAL.…”