Impedance-Type Apex Locators.
Operates on the principle that there is electrical impedance across the walls of the root
canal due to the presence of the transparent dentin. The tooth exhibits an increasing electrical
impedance across the walls of the root canal, which is greater apically than coronally. At the
DCJ, the level of impedance drops dramatically. The unit detects the sudden change and
indicates it on the analogue meter. To overcome the problem of a wet environment, insulated
probes are utilized.
Apex locator A d v a