Clinical accuracy of a new apex locator with an automatic compensation circuit

A new circuit was designed to automatically compensate for measurement errors of an electronic apex locator in various electrolytes. Thirty-one root canals were clinically tested for accuracy. A file was inserted into the canal until the apex signal was obtained, at which point the file was immobilized with glass-ionomer cement. After extraction, the apical area was exposed and the position of the file tip was examined under an operating microscope. Distances from the major foramen and cemento dentinal junction (CDJ) were recorded. The average distance from the major foramen was -0.13 mm with a range of -1.28 mm and +0.46 mm. The average distance in 26 detectable CDJ samples was +0.18 mm with a range of -0.98 mm and +0.65 mm. The measurements, which were within +/- 0.5 mm, were 94% (29/31) from the major foramen and 92% (24/26) from the CDJ. Measurement consistencies within one SD were 81% for the major foramen and 65% for the CDJ, respectively. Measurements within two SD were 97% for the major foramen and 92% for the CDJ. There were no differences between the smaller (< # 25) and larger apical foramens (< or = 25) or vital and nonvital pulps.