Apex location is a method of determining the length of the

root canal A root canal is the naturally occurring anatomic space within the root of a tooth. It consists of the pulp chamber (within the coronal part of the tooth), the main canal(s), and more intricate anatomical branches that may connect the root c ...

of a

tooth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

- manually or with a mechanical canal instrument that passes a low intensity electric 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 In dental anatomy, the apical foramen, literally translated "small opening of the apex," is the tooth's natural opening, found at the root's very tip—that is, the root's apex—whereby an artery, vein, and nerve enter the tooth and commingle w ...

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.

Methods of measurement

Method of Sonada

The method of Sonada measures the canal's impedance using one or more electric frequencies. The method tracks the penetration of the instrument in the canal. It is unreliable though in the presence of fluid in the canal which requires additional drying.

Method of Kobayashi

The method of Kobayashi performs a calculation of the ratio of the measured impedance of two or more electric frequencies. The method is highly accurate in the presence of fluid in the root canal. The method does not provide good monitoring of the penetration before reaching the apex. This method faces difficulties when working in a dry canal. Therefore the canal should be moistened. After measurement the canal should be dried.

Adaptive method

The Adaptive method of measurement is implemented by the so-called

electronic apex locator An electronic apex locator is an electronic device used in endodontics to determine the position of the apical constriction and thus determine the length of the root canal space. The apex of the root has a specific resistance to electrical current ...

. 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 Sonada. In case of wet canal the device automatically adjusts the measurement method of Kobayashi. The adaptive method is highly accurate and does not require moistening or drying the canal.

External sources

Adaptive methods for apex location
*''Color Atlas and Textbook of Oral Anatomy, Histology, and Embryology'' by B. K. Berkovitz, G. R. Holland, B. J. Moxham Hardcover, {{Endodontology Dentistry