Accurate length determination of root canal is essential in root canal therapy. Radiography has been the conventional method for this measurement but recently several in-vitro studies have shown that new generations of Electronic Apex locators are as accurate as radiography in length determination. It is hypothesized that the latest generation of Electronic Apex locator can produce acceptable results as radiography when used for length determination.
See also apex location An electronic apex locator is an electronic device used in endodontics determine the position of the apical foramen and thus determine the length of the root canal space. The apex of the root has a specific resistance to electrical current, and this is measured using a pair of electrodes typically hooked into the lip and attached to an endodontic file. The electronic principle is relatively simple and is based on electrical resistance; when a circuit is complete (tissue is contacted by the tip of the file), resistance decreases markedly and current suddenly begins to flow. According to the device, this event is signaled by a beep, a buzz, a flashing light, digital readouts, or a pointer on a dial.
The original electronic apex locators operated on the direct current principle. A problem with these devices was that conductive fluids such as hemorrhage, exudate, or irrigant in the canal would permit current flow and therefore a false reading. Newer devices are impedance-based, using alternating current of two frequencies;these measure and compare two electrical impedances that change as the file moves apically. The benefit is that these devices are much less affected by fluid conductive media in the canal. The impedance type apex locators have been demonstrated to be 80 to 95% accurate in identifying the apical foramen. Therefore after obtaining a reading, 1 to 2 mm is subtracted as the corrected working length.
Introduction:A method of electronically locating the apical foramen of a root canal was first introduced nearly forty years ago. Although it had the advantage of locating the apical foramen by electronic means rather than using the radiographic apex to estimate its location, it was technique sensitive and therefore unpredictable. It was not until the 1990's that a reliable, easy to use electronic apex locator gained popularity. The Root ZX (J. Morita, MFG. Corp.) has been shown to locate the apical foramen within .5mm in 96.2% of teeth tested.
