The Use of Micro–Computed Tomography to Determine the Accuracy of 2 Electronic Apex Locators and Anatomic Variations Affecting Their Precision

• The root canal length and working length were determined by means of micro-CT imaging, visual method, and 2 EALS.
• The exact location of the apical constriction (AC) was determined using micro-CT imaging.
• There was no statistically significant difference in the accuracy of the tested devices (Root ZX and Apex ID) and between the tested marks (APEX/0.0 and 0.5).
• Lateral positioning of the apical foramen (AF) affected the accuracy of EAL to determine the RCL.
• The “0.5” mark of EALs is a reliable mark to determine the WL, and it can be affected by the increased AF–AC distance (<0.5 mm).

IntroductionThe aim of this study was to compare the accuracy of 2 electronic apex locators (EALs), Apex ID (SybronEndo, Glendora, CA) and Root ZX (J. Morita, Tokyo, Japan), by means of micro–computed tomographic (micro-CT) imaging and to determine anatomic variations that may affect their accuracy.MethodsThe root canal length (RCL) and working length (WL) of 33 single-rooted premolars were measured using a visual method, 3-dimensional micro-CT reconstructions, and 2 different EALs. Two different measurements were recorded for each EAL: at the “APEX/0.0” mark and at the “0.5” mark. The WL was determined using 2 different methods: method 1: at the “0.5 mark” of the apex locator and method 2: subtracting 0.5 mm from the “APEX/0.0” mark. The precision of measurements was compared with those recorded by micro-CT imaging. Apical foramen (AF) position and diameter, apical constriction (AC) diameter, distance between the AC and the AF, and the presence/absence of accessory canals were recorded from the micro-CT scans, and their correlation to the accuracy of EALs was determined.ResultsThere was no statistically significant difference in the RCL measurements by any of the different methods. There was a statistically significant difference in the WL recorded by micro-CT imaging compared with those by the visual method and at the “APEX/0.0 mark” − 0.5 mm (P = .031). There was no difference in the measurements acquired by any of the EALs. The “APEX/0.0 mark” − 0.5 mm was less accurate than the “0.5” mark. However, the results were not statistically significant (P > .05). The position of the AF and the AC–AF distance affected the accuracy of the RCL (P = .003) and the “0.5” mark (P = .013).ConclusionsRoot ZX and Apex ID are equally precise in determining the RCL and WL. The “0.5” mark can be used to determine the WL with high precision. Some anatomic variations may influence the accuracy of EALs.