Apex locators

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The establishment of a correct working length is one of the fundamental parameters for endodontic success. Traditionally this has been determined using radiography, but electronic apex locators are increasingly being used. Electronic apex locators reduce the number of radiographs required and assist where radiographic methods create difficulty. The use of an electronic apex locator in combination with the radiograph is greater precision in the determination of root canal length. The aim of this paper is to review the electronic determination of the length of the root canal.

The success rate of conventional root canal treatment is predictably high, as long as the basic principles of endodontic treatment are followed. Accurate determination of root canal length is particularly important to the success of root canal treatment: cleaning, adequate

shaping and complete filling of the root canal system

cannot be accomplished unless the correct working length is established, and if the canal length is known,damage to the periapical tissues and procedural accidents such as ledging can be avoided by confining instruments and root filling materials within the root canal system.

The radiograph is one from the traditional method for the determination of the root canal length, but it is difficult to achieve accuracy of canal length because the

apical constriction (AC) cannot be identified, and variables

in technique, angulations and exposure distort this image and lead to error1-2. Thus, in addition to radiographic measurements, electronic root canal working length determination has become increasingly important.


Electronic apex locators (EALs) have been used clinically for more than 40 years as an aid to determine the

file position in the canal. These devices, when connected

to a file, are able to detect the point at which the

file leaves the tooth and enters the periodontium. An

electronic method for root canal length determination

was first investigated by Custer.
Although the term “apex locator” is commonly used and has become accepted terminology17, it is a misnomer . Some authors have used other terms to be more precise such as electronic root canal length measuring instruments or electronic canal length measuring device.

These devices all attempt to locate the AC, CDJ, or the AF. They are not capable of routinely locating the radiographic apex.In 1918, Custer3 was the first to report the use of electric current to determine working length. In 1962, Sunada reported that there is a constant value (6.5 k) of the electrical resistance between the mucous membrane and the periodontium, and he stated that it is possible to use this value of resistance in the estimation of the root length. Additionally, he showed that if an endodontic instrument that is connected to an ohmmeter is introduced into the canal and advanced until the ohmmeter shows the value of 40 microA, the tip of the instrument has reached the periodontal ligament at the AF . The device by Sunada in his research became the basis for most EALs.
In 1962, Sunada constructed the first EAL. Since then, different generations of Electronic Apex Locators have been developed to measure root canal length.

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