The Effect of an Apex Locator on Exposure to Radiation During Endodontic Therapy Paul A. Brunton, PhD, MSc, BChD, FDS (Rest Dent), FDSRCS (Edin), Dilshan Abdeen, BDS, and Tatiana V. Macfarlane, BSc, PhD The objective of this study was to investigate whether the use of an electronic apex locator re- sults in a reduction in X-ray exposure during end- odontic therapy. Fifty, sound, extracted, single- rooted canine and incisor teeth were selected and randomly divided into two groups (A and B) of 25 teeth. The working length was determined radio- graphically with (group B) and without (group A) adjunctive use of an apex locator by one operator. After working length determination, the teeth were sectioned and the actual working length measured for comparison. For group A, 14 retake radio- graphs were required to determine the working length, whereas group B required no retake radio- graphs; this difference was highly significant (p < 0.001). The electronic apex locator was extremely accurate in locating the apical foramen with all teeth tested within 0.5 mm of the anatomical apex and 11 (44%) teeth at the apical foramen. In con- trast, 15 (60%) teeth tested using radiographs alone were within 0.5 mm of the anatomical apex and only 4 (16%) teeth were actually at the ana- tomical apex. It was concluded that using an elec- tronic apex locator as an aid to endodontic therapy could potentially reduce the number of diagnostic radiographs required for working length determi- nation. Location of the apical foramen using a combination of an electronic apex locator and ra- diographs to determine working length is more accurate than using radiographs alone. The concept of measuring root canal length electrically as part of endodontic treatment was first reported over 30 yr ago (1). Electronic apex locator devices, which rely on the ratio of two electrical imped- ances between an electrode in contact with the oral mucosa and one passed through a root canal in contact with the periodontal ligament, are being used to a greater extent (2). The accuracy of electronic apex locators has been studied in depth, and they have been proven to locate the apical foramen effectively and reproducibly (3–5). Even in the presence of canal irrigants, such as ethanol, local anesthetic solution, and sodium hypochlorite, as well as pus and necrotic tissue, apex locators are still able to maintain their high level of accuracy (4, 6). The current generation of electronic apex locators have reported accuracy of up to 93.4% (7). To achieve this degree of accuracy, however, the operator must have a good working knowledge of root canal anatomy as well as being aware of possible variations in morphology (2). Experience with electronic apex locators is also essential for good and consistent results (2). The relative accuracy of electronic apex locators compared with radiographic methods to reliably locate the apical foramen has also been investigated (8). It was concluded that the apex locator was marginally more reliable than the radiographic method when lo- cating apical foramina. Indeed, it has been shown that when electronic apex locators are used the probability of being within 0.76 mm of the cementodentinal junction, and therefore the apical foramen, is 68% (9). As a consequence it has been suggested, that when electronic apex locators are used radiographs need not be taken for working length determination. It is still recommended, however, that a radiograph be taken at this stage so as to exclude the possibility that a lateral canal has been negotiated in error (3). During endodontic treatment a number of radiographs are re- quired (10): 1. Preoperative assessment supplemented with parallax views if required 2. Working length determination at different angles in the case of teeth with multiple roots 3. Post obturation 4. For review and monitoring purposes It is at the working length determination stage where the greatest potential variation in X-ray exposure to patients occurs. This is mostly due to repeat radiographs being taken, particularly by inexperienced practitioners, which potentially leads to increased X-ray exposure to the patient. The aim of this study was to investigate whether the use of an electronic apex locator as an adjunct to the radiographic determination of working length could potentially result in a reduction of X-ray exposure to patients during endodontic therapy. MATERIALS AND METHODS Fifty, sound, extracted, single-rooted canine and incisor teeth were selected and randomly divided into two groups (A and B) of JOURNAL OF ENDODONTICS Printed in U.S.A. Copyright © 2002 by The American Association of Endodontists VOL. 28, NO. 7, JULY 2002 524