Apex locator

From Wikipedia, the free encyclopedia

An Apex locator is an electronic device used in endodontics to determine the length of the root canal space.

Successful endodontic therapy requires accurate location of the apical foramen and proper working length determination. The traditional method of apex location consists of exposing a radiograph with an endodontic file strategically placed near the apical foramen.

Electronic apex location is an alternative method of apex location. Electronic apex locators use an electrical circuit, traversing through the endodontic canal and the patient’s oral tissues, to determine the location of the apical foramen. The earliest models of electronic apex locators were unreliable and caused patient discomfort. It wasn’t until the late 1980s that reliable units were introduced which did not cause patient discomfort.

Today, electronic apex locators are commonly used in conjunction with radiographic apex location. Some studies have questioned the accuracy of electronic apex locators1, but most have shown electronic apex location to be comparable in accuracy to radiographic apex location.2,3 Other studies have shown electronic apex location to be more accurate.4,5 Comparisons of different electronic apex locators on the market have demonstrated varying degrees of accuracy.2,3,4

An electronic apex location system consists of a console, a lead that attaches to a file placed into the canal, and another lead that attaches to the patient’s lip. With the two leads in place, and with the file at the apex, an electrical circuit can be created, running from one lead to the file, out the apex to the periodontal ligament, through the patient’s mucosa to the lip-clip, and back to the console. Since hard tooth structure is a poor electrical conductor the circuit cannot be completed until the file tip reaches the patient’s electrolytic tissues at the apical foramen. When the advancing file tip finally reaches the apical foramen the electrical circuit is maximized and recognized by the system, which then notifies the provider through visual means on an LCD or LED screen, and usually with an audio signal.

The earlier single-frequency electronic apex locators were often unreliable when the canal contained fluid, since this allowed generation of a weak electrical current before the apical foramen was reached. The newest generation of apex locators uses technology that is purportedly much less affected by the presence of fluid. A simplified explanation of this technology is that it uses two frequencies and monitors the changes in both as the apex is approached, allowing calculation of the location of the apical foramen. Today’s dual frequency electronic apex locators are heavily promoted as no longer being affected by the presence of tissue, blood, electrolytes, etc. Studies seem to indicate this to be true. 6,7

Electronic apex locators are small, light-weight, equipment items that can easily be transported from room to room. Most are battery-operated and most have an automatic shut-off function. They all have a display or screen to show the practitioner the approximate distance of the file tip from the apex and to show when the apical foramen is reached. All electronic apex locators in this synopsis have an audio signal to indicate when the foramen is reached. The current trend is to make the units small enough to be placed close to the oral cavity for easy viewing and enhanced ergonomics.

With a variety of electronic apex locators on the market this synopsis (HTML version, PDF version) should assist federal dental service customers in comparing, contrasting, and purchasing an electronic apex locator.

References:

1. Hoer D, Attin T. The accuracy of electronic working length determination. Int Endod J 2004; 37(2):125-131.

2. DeMoor RJ, Hommez GM, Martens LC, De Boever JG. Accuracy of four electronic apex locators: an in vitro evaluation. Endod Dent Traumatol 1999;15(2):77-82.

3. Lucena-Martin C, Robles-Gijon V, Ferrer-Luque CM, De Mondelo JM. In vitro evaluation of the accuracy of three electronic apex locators. J Endod 2004;30(4):231-233.

4. Kaufman AY, Keila S, Yoshpe M. Accuracy of a new apex locator: an in vitro study. Int Endod J 2002;35(2):186-192.

5. Ounsi HF, Haddad G. In vitro evaluation of the reliability of the Endex electronic apex locator. J Endod 1998;24(2):120-121.

6. Kobayashi C, Suda H. New electronic canal measuring device based on the ratio method. J Endod 1994;20(3):111-114.

7. Meares W, Steiman H. The Influence of Sodium Hypochlorite Irrigation on the Accuracy of the Root ZX Electronic Apex Locator. J Endod 2002;28(8):595-598.

(Col Strampe)