Endo-Eze® FIND™ Apex Locator

Accurate working-length determination has a profound influence on ideal canal preparation, microbial disinfection, and hermetic sealing of the root canal system. However, the location of the appropriate apical position has constituted a persistent challenge in clinical endodontics, largely because different opinions exist regarding the ideal apical limit of the root canal instrumentation and obturation.

 

Radiographs have been commonly used to determine the working length. However, radiographic assessments of the working length may prove inaccurate, depending on the direction and the extent of the root curvature and the position of the apical foramen in association with the anatomic apex.

By measuring the electrical properties of the apical part of the root canal, such as resistance and impedance, it should be possible to detect the canal terminus. The root canal system is surrounded by dentin and cementum, both insulators to electrical current. At the apical foramen, however, there is a small isolation interruption in which conductive materials within the canal space (tissue, fluid) are electrically connected to the periodontal ligament that is itself a conductor of electric current.

Therefore, various electronic methods have been developed that use a variety of other principles to detect the canal terminus. While the simplest devices measure resistance, other devices measure impedance using high frequency or multiple frequencies.

Endo-Eze® FIND™ Apex Locator
Endo-Eze FIND (Figure 1) is a battery-operated portable device designed for foramen localization, using a multifrequency-dependent impedance method. With features like a full-color screen, compact design, fully automatic measurements, audio feedback with volume control, and automatic turn off, FIND caters to the user. It offers highly accurate apical foramen localization in wet and dry canals, and it displays numerical values to indicate the file progression, making it easy to identify the position of the foramen and any time the file extends beyond the foramen.  

Operative step-by-step sequence

• Turn on the device.
• Ensure that the measuring cable is properly connected. The cable symbol  should appear after the connection is made (Figure 2).
• Before placing the instrument inside the canal:

Perform contact between the electrodes (file clip and lip clip). The “connection test” symbol  should appear on the status bar of the display, indicating proper connection (Figure 2).

After access, verify that the tooth is well isolated and that there are no metal restorations projecting into the canal entrances. Metal restorations divert the circuit, diminish impedance, and give a false-positive result.
A partial pulpectomy before electronic measurements should be performed. This must be limited to approximately 5 mm short of the tooth length on the X-ray image (Figure 3).

Place the lip clip in the corner of the patient’s mouth. It is important that the canal contain an irrigation solution; the pulp chamber should not contain an excess of it. The endodontic instrument selected to explore the undebrided apical portion of the canal, and the associated electronic working length, must be 5 mm longer than the temporary working length, which was measured on the initial radiograph. This is due to the need for available space to place the file clip between the rubber stop and the instrument handle.

Insert the selected instrument to the temporary working length. Ensure that the tip of the instrument is in contact with the internal walls. Very thin instruments may give a false-positive result. Use instruments of a diameter close to the anatomic diameter.

Connect the file clip to the file. The Endo-Eze FIND will automatically detect that root canal measurement has started. If the electrical contact is good, and the conductivity of the root canal is sufficient, the file icon inside the small tooth image will stop blinking, and a double-beep audio signal will sound.

Introduce the file apically in the direction of the apical foramen, turning it gently in a clockwise direction, perceiving the start of movement on the monitor. The monitor of Endo-Eze FIND is shown in Figures 4 to 6.

When coming closer to the final reading, an intermittent alarm sounds. Continue with the instrument in an apical direction until the alarm sound is continuous, which will place the readout in the position of the foramen exit (0.0).
At this time, the operator must proceed to mark the working length, sliding the rubber stop to the chosen occlusal or incisal reference point and subtracting 1 millimeter (or 0.5 mm) of the pointed measurement using an endodontic ruler.

Precautions during electronic measurements
Some points must be observed during electronic measuring, irrespective of the model used:
Acquire a reliable diagnostic radiograph, preferably with the parallel technique, using an XCP System locator (in which the cone is lined up with a ring outside the mouth of the patient, while biting down on the X-ray holder). The real temporary working length, measured from a proper initial radiograph normally differs from 0% to 15% from the definitive working length measurement.

In case of vital pulp, perform a partial pulpectomy removing at least two-thirds of the pulp tissue volume. Clinically, it has been noticed that in cases of irreversible pulpitis, placement of an instrument in the cervical third can result in a measurement that indicates a point close to the foramen. When partially removing tissues, abundant irrigation followed by aspirating excess fluid helps the measurement return to normal.  
The number of the instrument used for measurement must match the anatomic diameter of the canal. Larger-size instruments will not reach the apical third. Thin instruments make apical placement and reading difficult, due to the lack of control over penetration.

The electrodes (file clip and lip clips) must be free of oxidation products, which may have developed as a result of contact with irrigation solutions.

The irrigation solution in the root canal cannot be beyond the canal entrance(s). The canals must be moist when measurements are made, preferably using a sodium hypochlorite solution.

When the bar indicator on the display screen starts to oscillate up and down, remove the instrument from the canal. Irrigate, aspirate excess irrigation solution, and start the procedure again. Verify that the tip of the file is well adapted to the dentin walls. Verify the presence of contact between the file and metal restorations (if present). Verify the presence of excess pulp tissue in case of an irreversible inflamed pulp. Verify that the battery is fully charged.
This information was provided by Ultradent.