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 Table of Contents  
Year : 2016  |  Volume : 28  |  Issue : 1  |  Page : 18-22

A comparative clinical study on the correlation of working length determined using three different electronic apex locators with radiographic working length: An in vivo study

1 Department of Conservative Dentistry, Sri Sankara Dental College, Varkala, Thiruvananthapuram, Kerala, India
2 Department of Restorative Dental Science, College of Dentistry, King Khalid University, Abha, Saudi Arabia

Date of Web Publication21-Jun-2016

Correspondence Address:
Devi S Lekshmy
Department of Conservative Dentistry and Endodontics, Sri Sankara Dental College, Varkala, Thiruvananthapuram, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-7212.184325

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Aim: This in vivo study was done to correlate the values of three different electronic apex locators: Root ZX, iPex, and Apex ID, with the radiographic working length (WL).
Materials and Methods: Nineteen maxillary incisors with completely formed root apices indicated for endodontic treatment were chosen. After access preparation, coronal flaring and pulp extirpation, electronic measurement of WL was done with a No: 15 K file using the three devices on each tooth. A WL radiograph was then taken with the file placed within the canal and the length determined by following Ingle's method. The data were then analyzed using the correlation coefficient and Z-test.
Results: Root ZX showed the maximum correlation (r = 0.9881) with radiographic WL followed by Apex ID (R = 0.9731) and iPex (R = 0.9508). Root ZX had a statistically significant higher correlation with radiographic WL in comparison with iPex (P < 0.05).
Conclusion: Maximum correlation of readings with the radiographic length was shown by Root ZX followed by Apex ID and then by iPex.

Keywords: Electronic apex locators; endodontic treatment; working length.

How to cite this article:
Lekshmy DS, Deepthi P R, Ganesh C, Chacko G, Abhilash A, Satheesh S L, Aravind L, Nair SV, Sreedhar S. A comparative clinical study on the correlation of working length determined using three different electronic apex locators with radiographic working length: An in vivo study. Endodontology 2016;28:18-22

How to cite this URL:
Lekshmy DS, Deepthi P R, Ganesh C, Chacko G, Abhilash A, Satheesh S L, Aravind L, Nair SV, Sreedhar S. A comparative clinical study on the correlation of working length determined using three different electronic apex locators with radiographic working length: An in vivo study. Endodontology [serial online] 2016 [cited 2022 Dec 8];28:18-22. Available from: https://www.endodontologyonweb.org/text.asp?2016/28/1/18/184325

  Introduction Top

The apical constriction where the pulp is linked to the apical periodontal tissue referred to as the minor diameter is recommended by many as the appropriate landmark where root canal preparation and obturation should terminate. [1] The traditional method used to determine working length (WL) is based on the radiographic visualization of an instrument placed in the canal. [2] However this presents several limitations. Radiographic image being a two dimensional one, may often be overlapped with anatomic structures and thus can cause difficulty in interpretation. There can also be technical errors in projection and also the danger of radiation exposure. [3]

The development and production of electronic devices for locating the canal terminus have been a revolutionizing innovation in root canal treatment. Their advantages include comparable or better accuracy compared with the radiographic method, constant monitoring of the WL when coupled with advanced rotary systems, thus decreasing the total radiographs needed and thereby the radiation exposure too. [4],[5],[6]

The first generation of electronic apex locators (EALs) were resistance based, whereas the second generation EALs were based on impedance. [7] To overcome the inaccuracies that occur with these apex locators in the presence of irrigants and pulp tissue, third generation EALs were introduced. [8] Root ZX (J. Morita Corp, Tokyo, Japan) is a third generation EAL that uses the "ratio method" to measure the root canal length. This method measures impedance values at two frequencies (8 KHz and 0.4 KHz) simultaneously and calculates a quotient that expresses the position of the file tip in the canal. [4],[9] The Root ZX apex locator is considered as a standard to which newer EALs are compared.

The iPex (NSK Technologies, Japan), is a fourth generation apex locator that automatically selects the best possible frequency according to the canal condition by tip in the canal. [7]

Apex ID (Sybron Endo, USA) is a recently introduced apex locator that claims accuracy in almost all canal conditions. The device works by micro signals consisting of dual frequencies that are sent from the unit and which return to the unit after travelling along the electric circuit that is composed of: unit - probe cord - file holder - file - patient - lip holder - probe cord. The impedance of the electric circuit may be changed depending on the distance between the end of a file and the apex of the root canal, which results in a change in the micro signals that are input back into the unit. The microprocessor of the unit calculates the change in micro signals to convert the difference into a distance value, which will be displayed on the Apex ID liquid crystal display (LCD) display. [10] The manufacturer does not specify any other technical characteristics, and no studies are present in current literature on the ex vivo or in vivo accuracy of this EAL.

Many studies have addressed the benefits and clinical performance of the various models of EALs that have been developed in the recent years and when faced with the contrasting assertions of the manufacturers, it becomes difficult for the practitioner to choose from the various EALs available.

In spite of the high chances of image distortion, conventional bisecting angle technique of radiography is still the most often used method, and hence a comparison of EAL readings with the WL obtained using a radiograph made using short-cone technique can be extrapolated more easily to routine dental practice. [11],[12] There have not been many published reports on the correlation of WL obtained using EAL and the radiographic WL. The objective of the present study was to test in vivo a new apex locator, the Apex ID along with iPex and Root ZX as to their correlation with the radiographic WL. The study also compared the proximity of the EAL readings with the radiographic WL.

  Materials and Methods Top

This study was conducted in the Department of Conservative Dentistry and Endodontics of Sri Sankara Dental College (Varkala, Kerala) with approval from the Ethical Committee of the Institution (Ethical Clearance No: IEC No. IEC/013/2013). Informed written consent in full accordance with ethical principles was obtained from each patient before the treatment was initiated.

Nineteen maxillary central incisors with mature root apices indicated for nonsurgical root canal treatment were chosen for the study. Teeth with incomplete apical closure, calcifications, internal and external root resorption, and those which presented with uncontrollable bleeding on access opening were excluded from the study. Pregnant patients and patients with cardiac pacemakers were also excluded from the study.

A periapical radiograph was exposed for each tooth. After administering local anesthesia (2% lignocaine with 1: 200,000 adrenaline), the teeth were isolated using rubber dam and access cavity preparation was done. After canal identification, coronal flaring was done using Pro Taper SX rotary file (Dentsply Maillefer, Ballaigues, Switzerland) and the pulp extirpated using a No. 15 barbed broach. The canals were irrigated with 2 ml of 5.25% sodium hypochlorite solution. Excess fluid was removed from the pulp chamber, but the attempt was not made to dry the canal.

A single K-type file with a silicon stop was used to record WL readings in each canal using the three different EALs: Root ZX Mini (J. Morita), iPex (NSK), Apex ID (Sybron Endo, USA). The apex locator to be used first was selected in a random manner.

The EALs were used according to the manufacturer's instructions. For all the three devices, the clip was attached to the patient's lip and the electrode was connected to a No. 15 K-file. While using the Root ZX, the file was advanced within the root canal to a point just beyond the apical foramen, as indicated by the flashing APEX bar and the solid tone. The file was withdrawn until the flashing bar on the display corresponded with the 0.5 marking on the meter.

While using the iPex apex locator, the file was advanced until the "APEX" signal was seen on the LCD and then withdrawn until the display showed the 0.5 mm mark. With the Apex ID, the file was inserted slowly into the root canal until the periodontal membrane was touched as indicated by the red bar appearing at the "APEX" on the screen. The insertion of the file into the canal was continued until the display changes to −0.1 and then the file was moved back until the reading 0.0 was displayed on the screen which confirmed the location of the apex according to the manufacturer.

After recording the WL with the first EAL, the file was removed and the length was measured and recorded to the nearest 0.5 mm. This was repeated in a similar manner for the second and third apex locator.

The WL radiograph was then made and the length was determined using Ingle's radiographic method. [13] The radiographic WL and the values obtained from the three apex locators were tabulated as given in [Table 1].
Table 1: Radiographic WL and EAL values

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The data were then analyzed using the correlation coefficient and Z-test. To calculate the agreement of the readings from the EALs with that of radiographic WL, interclass correlation coefficient was calculated. The correlation coefficient (R) was obtained [Table 2]. Scatter plots were also plotted for each EAL with the readings against the radiographic WL [Figure 1],[Figure 2] and [Figure 3]. To compare the correlation with radiographic WL among the three devices, Z-test was carried out [Table 3]. Significance was set at P < 0.05.
Figure 1: Scatter plot for Apex ID values against the radiographic working length

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Figure 2: Scatter plot for iPex values against radiographic working length

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Figure 3: Scatter plot of Root ZX values against radiographic working length

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Table 2: Interclass coefficient( correlation coefficient -R)

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Table 3: Correlation of the three EAL values with radiographic working length - Z test

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  Results Top

Statistical analysis of the correlation of the reading from the three apex locators and the radiographic length were performed by calculating the correlation coefficients.

The maximum value of the correlation coefficient was shown by Root ZX (R = 0.9881), which indicated that root ZX had the most readings which had exact match with the radiographic values (11/19). This was followed by Apex ID (R = 0.9731) and iPex (R = 0.9508).

The pair-wise comparison of correlation with radiographic WL between the apex locators shows that Root ZX had a statistically significant higher correlation with radiographic WL in comparison with iPex (P < 0.05).

There was no significant difference in the correlation with radiographic WL when Apex ID was compared with Root ZX or iPex (P > 0.05).

Although the number of EAL values that matched with radiographic readings were more with using iPex (6/19) than with Apex ID (5/19), but their difference when they did not precisely match with the radiographic values were less in case of Apex ID when compared with iPex. This is clear from the scatter plots which show a higher dispersion of the values in case of iPex than Apex ID. The least dispersion among the three was shown by the scatter plot of Root ZX.

  Discussion Top

Electronic methods for WL determination have advanced considerably and have been increasingly incorporated into the current endodontic practice. The accuracy of apex locators have been investigated by several researchers by various in vitro and ex vivo studies. [6],[14],[15] Most of these studies tried to compare the values of the EAL with WL s measured till different target points such as apical foramen and apical constriction. However, these cannot be a true representative of clinical situations in which the entire treatment is done in the mouth.

This study, however, was a true reproduction of what occurs during a routine endodontic treatment. Radiographs are the universally accepted, easily available, and meaningful method of WL assessment in the clinic. In the present study, Ingle's method of radiographic measurement was taken as the control against which all the values of the EALs were compared.

In this comparative study, Root ZX was found to show the maximum correlation with the radiographic WL. Previous studies dating from mid 1990s have confirmed the accuracy of Root ZX. [3],[8],[14],[16] and have even named it the benchmark for comparison with other apex locators. [17]

Ravanshad et al. concluded in their study that the results of endodontic treatment using EAL are quite comparable to radiographic length measurement. [18] Our study also showed that Root ZX had a statistically significant higher correlation with radiographic WL when compared with iPex only. In vitro comparative evaluation of conventional radiography and Root ZX apex locator in determining WL by Javidi et al. showed an almost complete correlation between the two (correlation coefficient = 0.983). [19] In vivo radiographic evaluation by Paludo et al. showed 82% of values obtained using iPex as acceptable, [20] whereas a comparative in vivo evaluation of Root ZX and iPex have demonstrated a lower accuracy for iPex. [14]

In an in vitro comparison of the accuracy of radiographic and electronic WL determination using Root ZX compared with the actual root canal length obtained with stereoscope, Root ZX apex locator gave accurate measurements, but not superior to digital radiographic methods. [21]

In our study, Root ZX and Apex ID showed a correlation coefficient of 0.9881 and 0.9731, respectively. A literature search revealed no in vivo or ex vivo studies evaluating the accuracy of Apex ID EAL. In the present study, there was no significant difference in the correlation with radiographic WL when Apex ID was compared with Root ZX or iPex (P > 0.5). Apex ID, but when compared to iPex, showed lesser dispersion of values in those cases where there was no perfect match of the electronic values with radiographic readings. The least dispersion in values was shown by Root ZX.

But, the results do not suggest that the EAL replace radiographs. However, they are the ideal tools for complementing radiographic methods of WL determination and thus can help in reducing the number of radiographs taken in this regard.

  Conclusion Top

Under the conditions of this study, Root ZX showed the maximum correlation with radiographic WL which was followed by Apex ID and then by iPex. Moreover, Apex ID when compared to iPex showed greater proximity of readings with the radiographic WL.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Ricucci D, Langeland K. Apical limit of root canal instrumentation and obturation, part 2. A histological study. Int Endod J 1998;31:394-409.  Back to cited text no. 1
Stein TJ, Corcoran JF. Radiographic "working length" revisited. Oral Surg Oral Med Oral Pathol 1992;74:796-800.  Back to cited text no. 2
Pratten D, McDonald NJ. Comparison of radiographic working length and electronic working length. J Endod 1996;22:173-6.  Back to cited text no. 3
McDonald NJ. The electronic determination of working length. Dent Clin North Am 1992;36:293-307.  Back to cited text no. 4
Hoer D, Attin T. The accuracy of electronic working length determination. Int Endod J 2004;37:125-31.  Back to cited text no. 5
Altenburger MJ, Cenik Y, Schirrmeister JF, Wrbas KT, Hellwig E. Combination of apex locator and endodontic motor for continuous length control during root canal treatment. Int Endod J 2009;42:368-74.  Back to cited text no. 6
Gordon MP, Chandler NP. Electronic apex locators. Int Endod J 2004;37:425-37.  Back to cited text no. 7
Kobayashi C, Okiji T, Kaqwashima N, Suda H, Sinada I. A basic study on the electronic root canal length measurement: Part 3. Newly designed electronic root canal length measuring device using division method. J Conserv Dent 1991;34:1442-8.  Back to cited text no. 8
Kobayashi C, Suda H. New electronic canal measuring device based on the ratio method. J Endod 1994;20:111-4.  Back to cited text no. 9
Available from: http://www.profident.pl/media/142960/apex_id_instrukcja_01.21.13_.pdf. [Last accessed on 2014 Nov 26].  Back to cited text no. 10
Chandler NP, Koshy S. Radiographic practices of dentists undertaking endodontics in New Zealand. Dentomaxillofac Radiol 2002;31:317-21.  Back to cited text no. 11
Raoof M, Heidaripour M, Shahravan A, Haghani J, Afkham A, Razifar M, et al. General dental practitioners′ concept towards using radiography and apex-locators in endodontics. Iran Endod J 2014;9:277-82.  Back to cited text no. 12
Ingle JI. Endodontics. 1 st ed. Philadelphia, PA: Lea & Febiger; 1965.  Back to cited text no. 13
Stöber EK, Duran-Sindreu F, Mercadé M, Vera J, Bueno R, Roig M. An evaluation of root ZX and iPex apex locators: An in vivo study. J Endod 2011;37:608-10.  Back to cited text no. 14
Pascon EA, Marrelli M, Congi O, Ciancio R, Miceli F, Versiani MA. An in vivo comparison of working length determination of two frequency-based electronic apex locators. Int Endod J 2009;42:1026-31.  Back to cited text no. 15
Czerw RJ, Fulkerson MS, Donnelly JC, Walmann JO. In vitro evaluation of the accuracy of several electronic apex locators. J Endod 1995;21:572-5.  Back to cited text no. 16
Plotino G, Grande NM, Brigante L, Lesti B, Somma F. Ex vivo accuracy of three electronic apex locators: Root ZX, elements diagnostic unit and apex locator and ProPex. Int Endod J 2006;39:408-14.  Back to cited text no. 17
Ravanshad S, Adl A, Anvar J. Effect of working length measurement by electronic apex locator or radiography on the adequacy of final working length: A randomized clinical trial. J Endod 2010;36:1753-6.  Back to cited text no. 18
Javidi M, Moradi S, Rashed R, Raziee L. In vitro comparative study of conventional radiography and root ZX apex locator in determining root canal working length. N Y State Dent J 2009;75:48-51.  Back to cited text no. 19
Paludo L, Souza SL, Só MV, Rosa RA, Vier-Pelisser FV, Duarte MA. An in vivo radiographic evaluation of the accuracy of apex and iPex electronic apex locators. Braz Dent J 2012;23:54-8.  Back to cited text no. 20
Kqiku L, Städtler P. Radiographic versus electronic root canal working length determination. Indian J Dent Res 2011;22:777-80.  Back to cited text no. 21
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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3]

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