Length Determination

2TheApex Electronic apex locators the most accurate method of determining canal length.


Accurate length determination is essential for adequate root canal treatment.  Root canal space that has not been adequately cleaned is a potential nidus of bacteria which may lead to future periapical pathosis.  On the other hand, over extended obturation material will create an inflammatory reaction that can cause pain and impede healing. (1)  The two most common methods of length determination are radiographs and electronic apex locators (EALs).  Radiographs are an indispensable tool that will yield much more anatomical and diagnostic information than just the length of the canal, however, in vivo studies directly comparing the accuracy of the two techniques have shown that EALs are more accurate in locating the apical foramen. (2) This is due to the apical foramen being located an unknown distance from the radiographic apex, a difference which will not always be evident on a periapical radiograph.  A recent meta-analysis by Schaeffer showed that the best prognosis is obtained when the canal is adequately obturated between 0 and 2 mm from the radiographic apex, highlighting the need for accurate length determination for successful outcomes. (3)  In addition to length measurement, EALs will aid in the diagnosis of perforations and resorption. (4, 5) Modern apex locators operate on a principal of relative ratios of impedance which allows them work in the presence of any common irrigating solution, and are accurate in both vital and necrotic teeth. (6,7) EALs are technique sensitive, but when used in conjunction with necessary radiographs will yield the most reliable and accurate results.


1: Ricucci, D., and K. Langeland. “Apical limit of root-canal instrumentation and obturation, part 2. A histological study.” International Endodontic Journal 31 (1998): 394-409.

2: Williams, Clayton B., Anthony P. Joyce, and Steven Roberts. “A comparison between in vivo radiographic working length determination and measurement after extraction.” Journal of endodontics 32.7 (2006): 624-627.

3: Schaeffer, Michelle A., Robert R. White, and Richard E. Walton. “Determining the optimal obturation length: a meta-analysis of literature.” Journal of endodontics 31.4 (2005): 271-274.

4: Kaufman, A. Y., et al. “Reliability of different electronic apex locators to detect root perforations in vitro.” International endodontic journal 30.6 (1997): 403-407.

5: Goldberg, Fernando, et al. “In vitro measurement accuracy of an electronic apex locator in teeth with simulated apical root resorption.” Journal of endodontics 28.6 (2002): 461-463.

6: Shabahang, Shahrokh, William WY Goon, and Alan H. Gluskin. “An in vivo evaluation of Root ZX electronic apex locator.” Journal of Endodontics 22.11 (1996): 616-618.

7: Dunlap, Craig A., et al. “An in vivo evaluation of an electronic apex locator that uses the ratio method in vital and necrotic canals.” Journal of Endodontics 24.1 (1998): 48-50.