They can save time in determining initial working length, and can be particularly helpful when the periapex is unclear on radiographs or when there is a question about whether a perforation has occurred. EALs have gone through at least three generations of development. Early versions used a direct current which was rather unreliable. The next generation was improved by use of alternating currents, and the most recent EALs use multiple alternating currents of different frequencies. Each of these changes have made them more accurate and reliable.
Apex locators function by using the body to complete an electrical circuit.
The EAL is connected by wires to the lower lip and to a file which is placed in the root canal. When the PDL is contacted by the file tip, an audio alert is sounded and it is indicated visually on the screen. Since the file is contacting the PDL it is slightly past the apical constriction. This information can then be used in length determination. Like any new technology, there is a learning curve for EALs.