Electronic Apex Locator

An electronic apex locator is an electronic device used in endodontics determine the position of the apical foramen and thus determine the length of the root canal space. The apex of the root has a specific resistance to electrical current, and this is measured using a pair of electrodes typically hooked into the lip and attached to an endodontic file. The electronic principle is relatively simple and is based on electrical resistance; when a circuit is complete (tissue is contacted by the tip of the file), resistance decreases markedly and current suddenly begins to flow. According to the device, this event is signaled by a beep, a buzz, a flashing light, digital readouts, or a pointer on a dial.1

History:

1942- Suzuki discovered that the electrical resistance between an instrument inserted into a root canal and an electrode attached to the oral mucosa registered a consistent value. There are tow type:

1-The Resistance Method- detects a change in the resistance of the canal with a single current source.

(1969- Root Canal Meter (1^st generation.), Sono-Explorer (second generation), Endocater (second generation)

2-Voltage Gradient Method- a concentric bipolar electrode measures the current density evoked in a limited area of the canal. The maximum potential is obtained when the electrode is at the apical constriction.

The Apit (frequency difference), Root ZX(3^rd generation )2

Electronic apex locator are highly sensitive devices that can be used to accurately determine the location of apical construction within a narrow interval in both vital and necrotic permanent teeth .although the use of EALs can reduce radiographic exposure for the patient ,as the operator may need fewer radiographs to correctly determine the working length. It is important to note that EALs are not an absolute substitute for radiographs and should be used as an adjunct .The range of sensitivity varied depending on the particular generation of EALs used in the study. For second generation the sensitivity range was 51.5 -93.4% and for third generation it was 75-90.7% .forth generation EALs exhibited sensitivity ranging from 34.4-80%. Overall ,the Root ZX a third generation EALs provided the greatest sensitivity in working length determination with arrange of 75-90.7% within 0.5 mm of the apical construction.3

Root ZX & Bingo 1020

*In all parameters tested, a significant statistical difference was found between Bingo 1020 and the Root ZX. Measurements obtained using the Bingo 1020 were consistently closer to the AL (0.08 mm) than those obtained using the Root ZX. Both EALs measured the tooth length with great accuracy and a positive correlation of 0.76 (P = 0.00) existed between the two devices. No significant difference was found between the two apex locators when measurements were taken with the different irrigants (P = 0.34) and the content of the root canal did not affect the accuracy of the measurements. Lengths obtained by calculations from the radiographs were longer than the AL as well as the length obtained by both EALs (P = 0.00).The Bingo 1020 proved to be as reliable as Root ZX and was user friendly. Under the experimental conditions, electronic measurements were more reliable than radiographs in the process of root length determination.4

Using An Electronic Apex Locator:

General Instructions

1. Electrical Connection- insure good to electrode at mucus membrane (lip clip) and file holder/file

2. Cervical Leakage- may cause inaccurate reading. Causes include tooth decay, electrode (file) in contact with metal restoration or presence of electro-conductive irritant in the pulp chamber

3. Dry Canals- may result in low readings (long working length), keep the canal wet and the chamber dry

4. Long Root- beware of high readings (short working lengths)

5. Lateral Canal- may give a false Apex reading if the lateral canal is large

6. Open Apex- electronic apex location is contraindicated

Using The Root ZX

The Root ZX is a fully automatic apex locator, which allows for accurate measurement of the apical constriction in the presence of sodium hypochlorite, hydrogen peroxide, blood or pulp.

1. Turn on the unit before plugging in the attachments and probe. The Root ZX automatically calibrates. A flashing indicator bar appears when the unit is done calibrating, a few seconds.

2. Dry the pulp chamber and the coronal portion of the tooth. The canal may be wet but the coronal part of the chamber needs to be dry.

3. Always advance the file until an APEX reading is obtained. The apical constriction should be approximately .5mm shy of this point.

4. Take readings before instrumenting the canal. If you are having trouble getting a consistent reading, try removing more tissue. If you get no reading try using a larger file.

Trouble-shooting

First check that batteries are installed correctly. Make sure the low battery indicator is not displayed. Check all connections and volume adjustment. Make sure the metal part of the file holder is clean and free of corrosion.

Advanced Trouble-shooting

1. The meter in the display does not move.

Canal may be calcified
Canal may be obstructed (dentin shavings)
Canal is too dry
Root has a sharp angle which has not been negotiated
Apex is surrounded by a pustule (measurement some times impossible in this case)

1. Meter overreacts as soon as the file touches the inside of the root canal

Canal has a large foramen, self correcting as the file advances toward the apex
Pulp chamber is wet
Perforation may be present
File is too small, use a snug-fitting file
Too much pulp in the canal
File is touching a metal restoration
Restoration is leaking oral fluids into pulp chamber

1. Meter may give erroneous readings for the following reasons

Retreatment of canals with silver points
Large lateral canals present
Incomplete apex

To test that your unit is working properly moisten your finger with water and place the file holder and lip clip about 1cm apart on it. This should give you a consistent meter reading.5

Root ZX® II Low Speed Handpiece Module

Root ZX II can easily be upgraded to a low speed handpiece offering speeds from 150 - 800 rpms. The low speed handpiece module is interchangeable and snaps easily into the back of the unit. This new versatility allows the clinician to choose between apex locator, low speed handpiece, or a combination of both. Designed for enhanced performance, the tailor-made handpiece is lightweight (70 g) and has a compact head height (12.5 mm). Proven Root ZX II technology delivers extreme accuracy and reliability, while the display screen allows the clinician to visualize file movement during instrumentation.

The Root ZX II low speed handpiece is loaded with automatic safety functions. A new feature, Auto Torque Slow Down, offers added protection when preparing the canal. The file automatically slows down as the torque load approaches its set limit helping to reduce file breakage.

ability of the ROOT ZX II to locate the apical foramen and to control the apical extent of rotary canal instrumentation.

he ROOT ZX II reliably located the major apical foramen, but was not an accurate method for controlling the apical extent of rotary instrumentation. Rotary instrumentation with the automatic apical reverse feature was always closer to the foramen than expected. 6