See also apex location

Apex location

Apex location is a method of determining the length of the root canal of the tooth - manuallyor by mechanical canal instrument . Thus...

An electronic apex locator is an electronic device used in endodontics

Endodontics

Endodontics is one of the dental specialties recognized by the American Dental Association, Royal College of Dentists of Canada, and Royal Australasian College of Dental Surgeons, and deals with the tooth pulp and the tissues surrounding the root of a tooth...

 determine the position of the apical foramen

Apical foramen

In anatomy the apical foramen is the opening at the apex of the root of a tooth, through which the nerve and blood vessels that supply the dental pulp pass...

 and thus determine the length of the root canal

Root canal

A root canal is the space within the root of a tooth. It is part of a naturally occurring space within a tooth that consists of the pulp chamber , the main canal, and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.-Root canal anatomy:...

 space. The apex of the root has a specific resistance

Electrical resistance

The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

 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.

History and uses

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

Radiography

Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....

when determining the position of the apical foramen.

Adaptive Apex Locators

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 Locator continuously 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.

External links

• The use of apex locators in the diagnosis of perforations, Dr. Yosef Nahmias, Endodontic Magazine