Accuracy of the Justy II Apex locator in determining working length in simulated horizontal and vertical fractures

Aim  To study the effectiveness of an electronic apex locator (EAL; Justy II; Yoshida Dentcraft, Tokyo, Japan) in locating simulated horizontal and vertical fractures in single roots. Methodology  An EAL was used to measure the distance within the canal of horizontal ( n  = 31) and vertical ( n  = 31) fractures, created with a disk in single‐rooted teeth. Accuracy of the EAL was evaluated by comparing the measurements with those made using a size 10 file. Data were analysed with the non‐parametric Passing and Bablok method. Results  For simulated horizontal fractures, the EAL measured exactly the same length as a size 10 file, without constant or proportional errors. In vertical simulated fractures, the EAL measured (on average) with a constant error of 7.5 mm shorter than the size 10 file; the difference had a wide confidence interval (−72.3 to 2.6 mm). Conclusions  In this laboratory study, the Justy II EAL was able to determine accurately the position of simulated horizontal fractures, but was unreliable when measuring simulated vertical fractures.