The removal of all pulp tissue, necrotic material and
microorganisms from the root canal is essential for
endodontic success. This can only be achieved if the
length of the tooth and the root canal is determined
with accuracy. The outcome of treatment of roots with
necrotic pulps and periapical lesions is influenced
significantly by the apical level of the root filling
(Sjo¨gren et al. 1990). Traditionally, the point of termination
for endodontic instrumentation and obturation
has been determined by taking radiographs. The
development of the electronic apex locator has helped
make the assessment of working length more accurate
and predictable (Fouad & Reid 2000). The aim of this
review is to examine the variety of apex locators
available and overview their development. Contemporary
endodontic texts were consulted and a database
search performed using Medline to identify general
studies on electronic apex locators. This resulted in 70
published articles in English. As apex locators have
evolved over more than 60 years a number of older
texts were consulted. Data from manufacturers was also
studied, especially where identical instruments
appeared to be marketed under different names around
the world. A list of electronic apex locators was
compiled and Medline searches were created for information
on current electronic apex locators and accuracy
studies for first, second and third generation apex
locators based on the units name. This search resulted
in a further 43 published articles in English.
Study results were standardized in the comparison
tables by using accuracy data for plus or minus
0.5 mm from the apical foramen. Some studies used
the apical constriction as a measure of accuracy but
also included the apical foramen data.