Apex location is a method of determining the length of the root canal of the tooth - manually or by mechanical canal instrument (by passing low intensity electrical current). Thus 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 apex, the instrument signals that the apical foramen is reached. Whenever the channel instrument is pulled out its length could be measured to determine the depth of the root canal and all other dental tools could be adjusted to this length.
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Method of Prof. Sonada measures canal's impedance using one or more electric frequencies. The method thoroughly 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 Professor Kobayashi performs mathematical 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.
The Adaptive method of measurement is implemented by the so-called Adaptive 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 channels.
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