Source:http://linkedlifedata.com/resource/umls/id/C0179099
UMD: Electronic devices designed to accurately locate the apex (i.e., apical foramen) of a tooth root. Operation of these instruments is based on the constant relationship of electrical resistance (impedance) between the periodontium and the oral mucosa. Several accurate methods are used, including measuring the voltage gradient, measuring the ratio of impedance at different frequencies, as well as a completely automatic method known as Root ZX. Some devices can display the length of the root canal. Apex locators are used in endodontic procedures to determine the length of the root canal that is needed and to determine perforations and their communication with the periodontal membrane. Some devices are a component of a dental handpiece, used to stop its rotation upon reaching the apex.