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Apex Locators Buyers Guide

10 January 2015

Buyers Guide of Apex Locators [A comprehensive review of Electronic apex locator (EAL)]


Ideal root canal treatment consists of the removal of the infected pulp tissue and cleaning

and shaping of the root canal system till the apex followed by a three-dimensional root

filling. To achieve this we need to asses the correct length of the root canals.

measuring the Working length of the root canal plays a major role in the success of the root

canal therapy. Commonly the minor apical foramen  is demarcation between the dental pulp and the periodontal area, This is about 0.5 to 1 mm short of the anatomical apex. If the apical foramen is not properly determined it will lead to either over instrumentation that is

working beyond the apical foramen causing damage to the peri apical tissues or under

instrumentation leading to inadequate removal of the pulp debris leading to the root canal


Usually we follow 3 methods in determining the working length.

1.Depending on the tactile sensation felt by inserting the paper points or a reamer. But

this method may not give accurate result due to either the curvature of the root or open


2.By taking an Intra Oral Peri Apical radiograph after inserting a file or a reamer 1.0 to

.5 mm short of the radiographic apex.

3.By totally depending on the Electronic Apex Locators [EAL] in determining the working



History: The early apex locator was developed experimentally by Suzuki (1942) by using the

electrical resistance between the oral mucosa and the periodontal ligament in the dogs.

This feature was introduced into clinical practice by Sunada (1962) by measuring the

electrical resistance.

Over the last few decades 5 generations of the apex locators were introduced.


First Generation : Measurement done by electrical resistance offered by periodontal ligament and oral mucosa. They gave false readings in the presence of Blood, Pus endodontic irrigants etc.They were best operated in the dry fields. Disadvantages: Pain and discomfort are often observed while using this type.

Eg: Endodontic meters, Root canal meters.


Second Generation :  Here the measurement is done by the electrical impedance.,they work by measuring the opposition to flow of alternating current (AC).Disadvantages: Here the presence of electro conducive irrigants leads to inaccurate readings.

Eg:  Sono explorer, Digipex, Endodontic meter etc


Third Generation :  They work on using two different frequencies at the same time the difference of impedance is least in the coronal part and as the canal narrows the impedance also increases. Highest impedance is measured at the CEJ. These require a clip.Disadvantages: This is sensitive to canal fluids and needs fully charged battery .

Eg:  Foramatron (Parkell), Root ZX (J Morita), Mini Apex Locator (Sybron Endo), Dentaport ZX (J Morita)


Fourth Generation:  They work on the principle of two or more non-simultaneous continuous frequencies in order to measure the difference ratio between two currents.Disadvantages: This requires relatively dry canals for accurate results.

Eg : Raypex4 (VDW), Propex (Dentsply), Apex NRG XFR (Medic NRG Ltd), iPex (NSK)


Fifth Generation: These are developed in the year 2003.It measures the capacitance and resistance of the circuit separately

Eg: Raypex 5 (VDW), I-ROOT (S-Denti), Propex II (Dentsply)


Many eminent endodontists across the world have tested the abilities of Electronic Apex locators of different generations to measure the accurate length of the root canal. Most of the results were identical, these tests revealed that almost all the EALs are accurate to an acceptable range of + or – 0.5 mm. The recent generation of EALs fared better in terms of accuracy than their predecessors. These offered better patient comfort and more user friendly to the dentists. But few other studies state that some EALs of third generation are better  than the fourth generation EALs.

All the results indicate that all EALs provide definite and accurate readings but they should be used in conjunction with the IOPA radiographs for working length determination.