In Vitro Measurement Accuracy of an Electronic Apex Locator in Teeth with Simulated Apical Root Resorption Fernando Goldberg, DDS, Ana C. De Silvio, DDS, Susana Manfre ´ , DDS, and Natalia Nastri, DDS The purpose of this in vitro study was to evaluate the accuracy of Root ZX apex locator to determine the working length in teeth with simulated apical root resorption. Fifty extracted, single-rooted, hu- man teeth with mature apices were used in this study. An irregular cavity defect was drilled at the apex of each tooth simulating an apical root re- sorption. Three operators used the Root ZX to measure the working lengths, comparing the elec- tronic readings with the direct visual measure- ments. The Root ZX was 62.7%, 94.0%, and 100.0% accurate to within 0.5 mm, 1 mm, and 1.5 mm of the direct visual measurements, respectively. Statisti- cally significant differences were observed be- tween operator A and B and A and C (p < 0.01), but no significant differences were detected between operator B and C (p > 0.01). The determination of the working length and its maintenance during cleaning and shaping procedures is a key factor for suc- cessful endodontic treatment. Root canal instrumentation should ideally terminate at the apical constriction. This statement is supported by Kuttler (1), who showed that the average apical constriction is 0.524- to 0.659-mm coronal to the apical foramen. The determination of the apical constriction has traditionally been made by digital-tactile sense and radiography (2). When a tooth has been involved in a traumatic episode and chronic inflammation of the pulp or periodontal tissue or both results in apical root resorption, it may be difficult to establish the working length if the apical constriction has been pathologically altered. In these cases, the combination of digital-tactile sense and radiography have important limitations to estimate the ideal work- ing length. Since Sunada (3) reported his findings, many electronic apex locators (EAL) have been introduced into the market. Currently, accurate readings can generally be obtained in the presence of vital pulp tissue, intracanal irrigants, and fluids, such as serous, puru- lent, or hemorrhagic exudates. Although different papers point out that EALs don’t give correct results in teeth with open apices (4, 5), only a few papers report the use of an EAL in teeth with apical root resorption (6, 7). Kobayashi and Suda (8) introduced an EAL called the Root ZX (J. Morita Corp., Kyoto, Japan). This EAL simultaneously calcu- lates the ratio of two different frequencies, and reportedly, the accuracy of the measurement is not affected by vital pulp tissue, sodium hypochlorite, or the various clinically encountered exudates. According to Nguyen et al. (9), the Root ZX was able to identify the location of the apical constriction even when this anatomic landmark was eliminated. The purpose of this in vitro study was to evaluate the accuracy of Root ZX to determine the working length in teeth with simulated apical root resorptions. MATERIALS AND METHODS Fifty extracted, single-rooted, human teeth with mature apices were used for this study. Radiographs in buccolingual and mesio- distal directions were taken to evaluate the root canal anatomy. Conventional endodontic access cavities were prepared using diamond round burs. The coronal and middle portions were shaped using #1 and #2 Peeso reamers (Dentsply-Maillefer, Ballaigues, Switzerland). Irrigation was performed using 3 ml of 2.5% sodium hypochlorite solution. An irregular defect was drilled at the apex of each tooth with a #3 carbide-round bur to simulate an apical root resorption. The roots of the teeth were placed up to the CEJ into a plastic tube containing a sponge soaked with normal saline solution. The lip clip was then placed between the sponge and the plastic tube. The root canal was irrigated with normal saline solution. Depend- ing on the canal size, a K-file was attached to the file holder and slowly inserted into the root canal until the signal on the display flashed “APEX.” The file was then retracted until the EALs digital display read 0.5 mm, which generally confirms that the instrument is at the apical constriction. The silicone stop on the inserted file was set to a flat anatomical reference point on the crown. The file was removed and measured with an endodontic ruler. Each tooth was measured separately by three operators using the same Root ZX device, the same end- JOURNAL OF ENDODONTICS Printed in U.S.A. Copyright © 2002 by The American Association of Endodontists VOL. 28, NO. 6, JUNE 2002 461