Influence of Apical Constriction Diameter on Root ZX Apex Locator Precision Manuela Herrera, DDS, MD, PhD,* Camilo Ábalos, DDS, MD, PhD, † Amparo Jimenez Planas, DDS, MD, PhD, † and Rafael Llamas, DDS, MD, PhD* Abstract Small-diameter hand files are systematically used to deter- mine the initial working length and to establish patency of the root canal. In wide canals, electronic apex locator accuracy might be influenced by file size. This article reports on a study to assess the influence of apical constriction diameter on the precision of the Root ZX apex locator by using files of varying diameter on teeth with 3 different degrees of apical widening: 0.37, 0.62, and 1.02 mm. Ten extracted single-root teeth, stored in saline solution at 37°C, were sectioned at the enamel-cement junction and embedded in an alginate mold. Initial working length (L 0 ) was determined with a #10 Kerr file, and canals were irrigated with either 50% citric acid or 5.25% sodium hypochlorite. To assess the ability of the locator to identify the narrowest area of the root canal as constriction diameter increased, the canal was progressively widened by insertion of files of increasing diameter (10 –100) at a point L 0 + 1 mm. After each enlargement, the working length (L) was redetermined, with files from #10 (L 10 ) up to the file used for widening. Comparison of statistical results was based on the difference between final working length and initial length (L 10 ) for each apical width. Statistical anal- ysis was carried out with analysis of variance test for com- parison of means. Results showed that at apical constriction widths of 0.37 and 0.62 mm, there was no significant differ- ence between initial working lengths as determined by a Kerr #10 file and final working lengths after widening with files of up to #60. In those teeth whose apical width had been increased to 1.02 mm, there was no statistically significant difference between initial and final working lengths as mea- sured by files from #10 –#25; however, significant differences were apparent between #10 and #30, #35, or #40 ( P  .05), and the degree of significance increased considerably ( P  .001) for files #45 or greater. These results suggest that Root ZX apex locator precision varies as a function of apical con- striction diameter. (J Endod 2007;33:995–998) Key Words Apex locator, apical constriction, apical widening P roper endodontic treatment involves thorough cleaning and hermetic sealing of the root canal. These procedures have to be confined to the canal to prevent damage and iatrogenic irritation of periapical tissue and to minimize the extrusion of filling materials into the periapex. The apical constriction is widely considered to be the ideal anatomic limit for root canal instrumentation and obturation (1–4); locating the apical constriction is there- fore a key stage in endodontic treatment. Radiography has traditionally been used to establish the apical limit; unfortunately, however, the apical constriction varies considerably in shape and is not detectable by radiography. In 1962 Sunada (5) reported a new method for measuring the length of the root canal, giving rise to the development and marketing of the first electronic apex locators (EALs), on the basis of the electrical resistance theories of Suzuki (6). These first- generation locators provided rather inaccurate measurements as a result of the pres- ence of vital pulp tissue, excessive blood, exudates, or moisture within the canal. Other devices based on electrical impedance were subsequently developed to overcome these drawbacks (7). In the 1990s a new dual-frequency technique was designed to locate the apical constriction by measuring the maximum difference in the impedance generated by a dual-frequency alternating current (8). The major advantage of this apparatus is that it provides precise measurements even in the presence of blood, pus, or pulp tissue, with a reliability ranging between 80%–95% (9 –16). Although they are largely reliable, dual-frequency locators might yield erroneous measurements in certain clinical situations, including subgingival caries, root fracture (17), and teeth with a widened apical foramen or an immature apex (12, 18 –20). A number of studies reported that as apical foramen diameter increases, EAL accuracy decreases (12, 21, 22). Small-diameter hand files are systematically used to determine the initial working length and to establish patency of the root canal. In wide canals, EAL accuracy might be influenced by file size, because a slim file is likely to leave space within the canal, whereas a larger-diameter file will yield a tighter fit. This article reports on a study to assess the influence of apical constriction diam- eter on the precision of the Root ZX (J. Morita USA, Irvine, CA) apex locator by using files of varying diameter on teeth with varying degrees of apical width. Material and Methods Ten single-root teeth were extracted and stored in saline solution at 37°C until use. Crowns were sectioned at the enamel-cement junction to gain standard root canal access and obtain a fixed, stable point of reference, with a view to minimizing errors in working length measurements caused by variations in the coronal refer- ence point. Teeth were then embedded in an alginate mold that was kept moistened in saline solution throughout the study to model a locator operation in a clinical context (23– 25). Initial working length (L 0 ) was routinely determined with the Root ZX apex locator by using a #10 Kerr file, following manufacturer’s instructions. The file was advanced into the canal until the reading on the apex locator dial flashed “apex.” The file was then retracted until the device signaled that the constriction was reached. This procedure was repeated as necessary for each measurement. Three measurements were made for From the *Department of Dental Pathology and Therapeu- tics and † Department of Dental Materials, School of Dentistry, University of Sevilla, Sevilla, Spain. Address requests for reprints to Dr Manuela Herrera Mar- tinez, Departamento de Patología y Terapéutica Dental, Fac- ultad de Odontología, Universidad de Sevilla, C/Avicena, s/n, 41009 Sevilla, Spain. E-mail address: manuelah@us.es. 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2007.05.009 Basic Research—Technology JOE — Volume 33, Number 8, August 2007 Apical Constriction Diameter and Root ZX Apex Locator Precision 995