A comparison between two electronic apex locators: an ex vivo investigation

Aim To compare ex vivo the performance of the Apex Finder and the Root ZX apex locators, with and without irrigant, in canals having different diameters. Methodology Sixty canals in 60 teeth were prepared using stainless steel hand files and 0.04 taper NiTi rotary instruments. During preparation the narrowest diameter of the canal was transported to the apical root surface. The canals were irrigated with RC-Prep and 5% NaOCl solution. Six groups were obtained, each with 10 canals having the same diameter of foramen, either 0.15, 0.20, 0.25, 0.40, 0.60 and 0.80 mm. A size 15 K-file was advanced into each canal until its tip was observed under x10 magnification to reach the foramen and the corresponding length recorded. The measurements were performed to an accuracy of 0.25 mm as a base unit of length. The teeth were then fixed to a plastic bar suspended over a glass container filled with 0.9% NaCl solution. Each apex locator was tested when the K-file was at the foramen, or 0.5, 1.0, 1.5 and 2.0 mm short; with the root apex immersed into the solution; with the canal dry or irrigated with NaCl. To evaluate the accuracy of both electronic apex locators (EALs) each electronically determined distance was compared with the actual length and the data analysed using the General Linear Model and the Student t-test. Results Out of 2400 measurements 100 were electrically unstable, all with the Root ZX. In total, 521 measurements located the position of the file tip beyond the apex, in general, in high conductive conditions with the Root ZX and in low conductive conditions with the Apex Finder. No significant difference in terms of accuracy was found between the two EALs when the file tip was at the foramen (Root ZX mean +0.12 mm, SD 1.22 mm; Apex Finder mean +0.57 mm, SD 1.16 mm). Comparing all the measurements performed with the file tip within 2 mm of the foramen, in all the different conditions tested, the accuracy was affected (P < 0.025) by diameter of the foramen, type of EAL, distance to the apex, and by several interactions. Conclusions Under the different ex vivo conditions both EALs provided accurate measurements when the file tip was at the foramen. The accuracy of the Apex Finder was negatively influenced by high conductive conditions, whilst the Root ZX provided inaccurate and unstable measurements mostly in low conductive conditions.