An important part of canal preparation is the accurate detection of the canal terminus. This measurement helps determine how far instruments should advance within the root canal and at what point the preparation and filling should stop.
The clinician must also maintain precise control of working length during the root canal procedure to avoid root perforation. A root perforation can lead to short- and long-term complications for the patient, including infection, additional surgery, and a more painful recovery.
An apex locator has a pair of electrodes, one typically clipped to a patient’s lip and the other connected to an endodontic file. When the tip of the file contacts the periodontal tissue, the three components form a complete electric circuit. Resistance then decreases and a current begins to flow, which triggers the device to sound or register a digital readout.
An Apex Locator measures the impedance, frequency, and resistance of surrounding material – different devices using different principles to determine lengths. These electronic devices have been shown to be more accurate than radiography when determining the position of the apical foramen.