Apex location is a method of determining the length of the root canal of a tooth - manually or with a mechanical canal instrument that passes a low intensity electrical current through the tooth.
The electrical characteristics of the tooth structure are measured and the exact position of the instrument in the tooth is determined. When the tool tip touches the top of the tooth, the instrument signals that the apical foramen is reached. Whenever the channel instrument is pulled out its length can be measured to determine the depth of the root canal and all other dental tools can be adjusted to this length.
The Adaptive method of measurement is implemented by the so-called electronic apex locator. In the process of penetrating the instrument makes continuous measurements and selects a suitable method of measurement. In case of dry canal the device uses the method of Prof. Sonada. In case of wet canal the device automatically adjusts the measurement method of Professor Kobayashi. The adaptive method is highly accurate and does not require moistening or drying the canal.
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.
Electronic apex locators have been shown to be more accurate than radiography when determining the position of the apical foramen.
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[clarification needed], this event is signaled by a beep, a buzz, a flashing light, digital readouts, or a pointer on a dial.
Adaptive Apex Locator overcomes as the disadvantages of the popular apex locators 4th generation – low accuracy on working in wet canals, as well the disadvantages of devices V th generation – difficulty on working in dry canals and necessarily of compulsory, additional wetting. Adaptive Apex Locatorcontinuously defines humidity of the canal and immediately adapts for dry or wet canal. On this way is possible to be measured as in dry and in additional wetted canals as well, canals with blood or exudates, canals with still not-extirpated pulp.