Abstract: A device for locating an apex of a root canal of a tooth comprises a first electrode having a conductive probe with a tip adapted for insertion into the root canal, and a second electrode configured to electrically contact a patient's body. The device includes a voltage generator which provides AC test voltage signal, a AC voltage driver with an internal output impedance, and a voltage detector coupled to the electrodes to detect an AC voltage across the first and second electrodes. An electronic controller coupled to the voltage detector calculates the test scores, determines the position of the probe tip on the basis of the test score values, and informs the user of the position of the probe tip in the canal. The position of the probe tip in the root canal is indicated on a display by a marker.