The reciprocal effect of electronic apex locators and implantable cardiac defibrillator

Drs. Roy Gadassi, David Keinan, Ritz Shlomi, and Iris Slutzky-Goldberg evaluate the potential electromagnetic interference from electronic apex locators on the function of an implantable cardioverter defibrillator (ICD).

Drs. Roy Gadassi, David Keinan, Ritz Shlomi, and Iris Slutzky-Goldberg study the impact of electronic dental devices on the function of pacemakers and ICD


Introduction: The purpose of this ex vivo study was to evaluate the potential electromagnetic interference from an electronic apex locator (EAL) on the function of an implantable cardioverter defibrillator (ICD). In addition, we evaluated the effect of the ICD on EAL reading accuracy.

Method: We tested two EALs ex vivo to assess their potential interference with the function of an ICD as determined using a Medtronic Programmer. We also assessed the accuracy of each EAL during the delivery of ICD pacing electrical shocks.

Results: None of the EAL devices (BingoPro and MedicNRG XFR) interfered with pacemaker activity. However, the accuracy of the EALs was impaired during ICD pacing; the changes measured were between -1 mm (BingoPro) and -2.5 mm (MedicNRG XFR). We found no effect on EAL function at any of the energy levels tested during the delivery of a series of electric shocks by the defibrillator.

Conclusions: In view of the results, the potential risk of overinstrumentation during the use of EALs for length determination in patients with an ICD must be considered.


Cardiac arrhythmias are relatively common. A cohort of 10,000 dental patients showed that 17.2% had cardiac arrhythmias, and that over 4% of those arrhythmias were life-threatening.1 Pacemakers treat symptomatic cardiac arrhythmias, specifically in patients who do not respond to medication.2 A pacemaker, implanted subcutaneously below the left clavicle, can mechanically replace cardiac cells that are nonfunctioning or poorly functioning.3 An implantable cardioverter-defibrillator (ICD) is a small battery-powered electrical impulse generator implanted in patients at risk of sudden cardiac death due to ventricular fibrillation or ventricular tachycardia. The device is programmed to detect any cardiac arrhythmias and to correct them by delivering a jolt of electricity.4

Both pacemakers and ICDs may be sensitive to electromagnetic radiation from dental devices. This risk may be increased by proximating the pacemaker and the dental electrical devices.5-7 Furthermore, older pacemakers are more susceptible to electrical interference than modern devices that are hermetically sealed in a metal case with cables that efficiently filter electromagnetic signals.8-10 Therefore, it may be prudent to consult with the patient’s cardiologist to determine whether a dental electrical device can be safely used.

Studies have suggested that electronic apex locators (EALs) may cause minor or major interferences with pacemaker function.11-12 In an in vitro study on the effect of different types of EALs on pacemaker function, four of the five EALs tested caused no interference with pacemaker function.13 However, the Bingo-1020 device interfered with the electrical functions of the pacemaker.13 In another study, researchers monitored 27 patients with either an ICD or pacemaker using an ECG during EAL or pulp tester use, and found normal ECGs during use of either of the two devices.14 Similar results were found in a study of 66 patients with different types of pacemakers while using a Root ZX mini; some noise was recorded in the ECG in two of the patients, but pacemaker’s function was not affected.11

The influence of EALs on pacemaker function has been studied in detail in various studies, but the effect of the defibrillator on the accuracy of EAL measurements has not been tested. Since modern defibrillators serve as both a defibrillator and a pacemaker, they constantly regulate the patient’s heart rate throughout the day. We aimed to check the reciprocal effects between two EALs and a defibrillator in an ex vivo model.

Materials and methods

We used 10 randomly chosen single-root extracted teeth that were kept in tap water and stored at 4°C for this study. The teeth had been extracted for orthodontic or periodontal reasons unrelated to the study. Patients subjected to extraction signed an informed consent to allow use of the teeth for research purposes. We serially marked the teeth to enable comparisons of the results for experiments with both apex locators and the defibrillator. 

Preparation of teeth for measurement: The crowns were grinded to establish a flat surface to serve as a reproducible reference point for all measurements. Cavity access was achieved using A3 diamond burs (Straus & Co., Ra’anana, Israel). Next, Gates Glidden burs Nos. 1-3 (Dentsply Maillefer, Ballaigues, Switzerland) were used to prepare the coronal third of each canal. During access cavity preparation, the canals were irrigated with a saline solution, and the patency of the apical foramen was verified with a size 10-K file (Dentsply Maillefer Ballaigues, Switzerland).

Canal length measurements: Canal length was established by passively introducing a 15 K-File (Dentsply Maillefer) in each canal until its tip was visible at the apical foramen. This procedure was conducted under 2.6× magnification using surgical loupes (Orascoptic, Madison, Wisconsin). After adjusting a silicone stop at the incisal surface, we removed the file from the canal and measured the distance between the tip of the file and the rubber stop with the aid of an endodontic ruler (Dentsply Maillefer). This measurement was repeated three times, and the mean value for each tooth was calculated and recorded as the “actual length” (AL).

Electronic length measurements: The next step involved mounting all the roots in alginate (Plastalgin, Septodont, Lancaster, Pennsylvania) in a plastic container. Prior to the experiment, we measured the impedance of the alginate to verify the resemblance between the alginate model and cardiac tissue. We placed each root through a hole in the container and fixed it with acrylic resin to avoid movement during instrumentation. We made a second smaller hole in the top of the container to stabilize the electrode (lip-clip) and allow it to be in contact with the alginate to simulate the conductivity conditions of the periodontium. Our ex vivo model was adapted with modifications of that by Kaufman, et al.15  For each tooth, an electronic length measurement was carried out using a No. 15 K-file (Dentsply Maillefer) attached to the EAL until the 0.5 marking, in order to ensure that the EAL reading was consistent with the manual length determination. The choice of the 0.5 marking was based on the EAL’s manual, and does not necessarily represent a 0.5 mm distance short of the working length.

The Medtronic Virtuoso™ device (Medtronic USA, Inc., Minneapolis Minnesota), is a multi-programmable, implantable cardioverter defibrillator (ICD). This device monitors and regulates a patient’s heart rate by providing ventricular tachyarrhythmia therapies and rate-responsive bradycardia pacing.

Defibrillator position: To simulate realistic clinical circumstances of distance between the mouth and the defibrillator, the ICD was placed 15 cm from the first row of teeth, and the defibrillator leads were placed 10 cm away from the pacemaker (Figure 1).

Measurements of effects of apex locaters on functions of the defibrillator: Two EALs were used to test reciprocal effects between EALs and the cardiac defibrillator (BingoPro, Forum Technologies, Rishon Lezion, Israel) and Medic ApexNRG-XFR™ (Afik, Afikim, Israel).

The EALs are usually operated by a 7–9 V battery releasing low-intensity electric signs that decrease within the square of the distance.16 According to recommendations, the EAL should be placed at least 15–20 cm from the free edges of the defibrillator electrodes.17 Thus, we placed the defibrillator and electrodes separated from the teeth and from the EAL (Figure 1).

Figure 1: Experimental settings — The defibrillator leads were placed 10 cm away from the defibrillator, located at a distance of 15 cm from the teeth

The measurements were made with the defibrillator set at maximum sensitivity (unipolar AAI mode, 0.1 mV). Pace monitoring was carried out using a Medtronic CareLink Programmer (Medtronic).

First, the effect of the defibrillator was measured on the action of the EAL while the defibrillator was set at maximum sensitivity (unipolar AAI mode, 0.1 mV) without pacing. After obtaining a stable EAL (maintained for 30 s), we programmed the defibrillator to pacing from a low to a high amplitude (1.5/0.4 V to 8/1.5 V) and recorded EAL readings during the pacing.

During the second stage, the effect of defibrillator shock administration was assessed on the accuracy of EAL measurements. After pacing, the defibrillator was set to deliver a series of electric shocks starting from the lowest to highest energy level (1 J to 35 J). We recorded EAL readings during shock administration.


The impedance of the alginate was measured prior to conducting the experiments. The values accepted were on average 7.30 ± 0.072 Ω.

Normal pacing patterns of the defibrillator were observed while testing the effect of apex locators on defibrillator function. None of the EAL devices (BingoPro or MedicNRGXFR) interfered with defibrillator activity.

Next, the effect of the defibrillator on the readings of the two types of EALs was examined. Inaccurate readings for BingoPro were demonstrated in as many as seven teeth during pacing especially at high voltages, whereas inaccurate readings for NRGXFR were produced in only three teeth during pacing.

BingoPro: In three teeth, the readings were not affected by defibrillator function; in four teeth, the readings were +1 mm longer than the actual length; and in three other teeth, the readings were 1 mm shorter than the actual length

Thus, the pacing affected measurements in seven teeth with reading changes for each tooth at different pacing voltages. The change in readings was ±1 mm. For example, the reading for tooth No. 4 was shorter by 1 mm at 2 V.

Medic ApexNRG-XFR: EAL readings remained unchanged in six teeth during defibrillator function. In two teeth, the readings were 2.5 mm longer than the actual length, and in one tooth, the length was 2.5 mm shorter than the actual length. We failed to obtain readings in one tooth (Figure 2).

Figure 2: Medic ApexNRG-XFR — Reading accuracy vs. pacing voltage. The readings on six teeth were normal during the pacing. However, we observed changes within a range of 2.5 mm. In two teeth, we observed a 2.5 mm increase in EAL readings; and in one tooth, the EAL reading was reduced by 2.5 mm. Tooth No. 2 showed a long reading only at pacings above 4.5 mV

Increasing the pacing voltage caused interference with the EAL readings. This was more prominent for the BingoPro than for the Medic ApexNRG-XFR EAL. When the BingoPro EAL was tested, an increase in voltage to 2.5 V resulted in inaccuracies in as many as five teeth; even more inaccurate readings were obtained with further voltage increases. When defibrillator function was tested with the Medic ApexNRG-XFR, we observed inaccurate results at the lower function voltages, and voltage elevations resulted in overestimated readings in an additional tooth. The number of inaccurate readings increased with pacing voltage increments. While pacing at 1.5 V, we observed inaccurate readings in two teeth with both apex locators. Pacing voltage increments resulted in more inaccurate readings, especially for the BingoPro EAL (observed at pacing voltages above 4.5 V).


This study evaluated interferences during EAL use in patients with ICDs, including the effect of the defibrillator on the accuracy of EAL readings.

Data regarding the effect of EALs on the function of pacemakers or defibrillators is abundant in the literature. Some studies have shown absence of interference of EALs with ICD function, in accordance with our study,18-20 while other studies have reported minor11,12 and severe effects.12 An in vivo study examining the effect of electronic dental devices on pacemaker function21 found that pacemaker function was not affected by any of the electronic dental devices tested, including an air scaler, ultrasonic curettes, electric pulp tester, and an electrotome. However, the researchers recommended increased caution in patients with old pacemakers or with standardized dental devices.21

In the present study, the accuracy of both apex locators was interrupted during pacing. Inaccurate readings were obtained for both EALs, although the BingoPro readings were more often interrupted than those of the Medic ApexNRG-XFR. This difference may be attributed to the mode of action of both devices. The function of BingoPro is based on two alternating currents of -500 Hz and 8 kHz. On the other hand, Medic ApexNRG- XFR uses square multifrequency currents, which undergo digital processing. According to its manufacturers, the device takes the basic analog signals emanating from the file, before it is exposed to any distortion, and converts it into a digital signal configuration, which is then analyzed. The available reading is an average of the majority of the signals. The multiple currents might compensate for the distortion caused by the ICD by canceling the effects of eccentric results.

Most pacemaker power sources deliver approximately 2.5 to 3 V, while ICDs deliver higher energies at 700 to 800 V within 10 to 15 ms.22 Modern ICD designs have been improved with better shapes, more reliability, and more efficient capacitors to produce high voltages than older designs. The higher voltages produced by ICDs as compared to those by EALs may explain the interference of the ICD with adjacent electronic devices (similar to the interferences found with the EALs assessed in this study).

The results of this study demonstrate that the EALs tested did not affect ICD function, whereas the ICD had an effect on the accuracy of EAL readings. One explanation for this difference can be related to the difference in the impedance of the tissues involved. The average impedance value of normal sheep myocardium was found to be 158 ± 26 Ω,23 whereas the impedance of the oral mucosa was found to be 6.5 Ω.24 Therefore, lower currents are required to provoke a change in a device connected to the oral mucosa (e.g., EAL) compared with a device implanted in the myocardium (e.g., ICD).

The importance of a precise working length during root canal treatment is well recognized in the endodontic literature.25 The apical extent of canal filling was found to be a significant prognostic factor for the root canal treatment outcome.25-27 Furthermore, apical extrusion of debris may lead to a higher risk of flare-ups28 and even persistent periapical radiolucency.29,30 Although a tolerance of ± 0.5 to 1 mm seems to exist for accuracy of the EAL as reported in the endodontic literature,31 longer readings in excess of 1 mm to 2.5 mm (BingoPro and Medic ApexNRG-XFR, respectively) may lead to substantial clinical implications, especially when treating patients with ICDs. These patients are at higher risk for bacterial endocarditis.32 Therefore, overinstrumentation in patients with ICDs should be avoided to prevent invasion of bacteria into the bloodstream.33


The potential impact of electronic dental devices on the function of pacemakers and ICDs has been widely studied.34-36 Although this influence has been reduced with the development of modern pacemakers and ICDs, the prudent dentist should consult with the patient’s cardiologist. Clinical precautions include keeping a distance of at least 10 to 20 cm from the pacemaker or ICD.17 To our knowledge, this is the first study to assess the impact of ICDs on the accuracy of EAL readings. We have shown that some of the length measurements for both EAL devices were longer than the actual lengths, especially under high ICD voltages. Therefore, the potential risk of overinstrumentation during the use of EALs for length determination in patients with an ICD must be considered.

Read this CE by Dr. Keinan and colleagues that studies the effect of chloroform on the performance of electronic apex locators. Subscribers who pass the 10 question quiz, receive 2 CE credits!

Drs. Roy Gadassi and Ritz Shlomi are from the Medical Corps, Israel Defense Forces (IDF).
Dr Iris Slutzky-Goldberg is from the Department of Endodontics, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel.
Dr. David Keinan is Head, Department of Endodontics, School of Postgraduate Dentistry, Rambam HCC, Haifa, Israel.
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