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Year : 2014  |  Volume : 17  |  Issue : 6  |  Page : 583-586
Influence of root canal curvature on the accuracy of an electronic apex locator: An in vitro study

Department of Conservative Dentistry and Endodontics, The Oxford Dental College, Bommanahalli, Bangalore, Karnataka, India

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Date of Submission24-Jun-2014
Date of Decision01-Sep-2014
Date of Acceptance21-Sep-2014
Date of Web Publication13-Nov-2014


Objective: This study investigated whether the canal curvature has an influence on the accuracy of Electronic Apex Locator.
Materials and Methods: Sixty mandibular posterior teeth were decoronated. A number (No.) 10 file was inserted into the mesiobuccal canal and radiographs were taken to determine the degree of curvature by Schneider's method. Samples were divided into three groups of mild (<20 o ), moderate (20-36°) and severe curvature (>36 o ). After enlarging the orifice, the actual canal length was determined by introducing a file until the tip emerged through the major foramen when observed under 20X magnification. The teeth were embedded in an alginate model and the Root ZX was used to determine the electronic length. The data was analyzed by Kruskal-Wallis test followed by Mann-Whitney test.
Results: The difference in measurement of Actual and Electronic working length was statistically significant between group 1 and 2 (P < 0.05) as well as between group 1 and group 3 (P < 0.05) with group 1 showing the lowest difference.
Conclusion: Considering ± 0.5 mm as tolerance limit for accuracy, the device was 95% accurate for the mild curvature group and 80% accurate for moderate and severe groups.

Keywords: Curvature; digora optime; root ZX; working length

How to cite this article:
Santhosh L, Raiththa P, Aswathanarayana S, Panchajanya S, Reddy JT, Susheela SR. Influence of root canal curvature on the accuracy of an electronic apex locator: An in vitro study . J Conserv Dent 2014;17:583-6

How to cite this URL:
Santhosh L, Raiththa P, Aswathanarayana S, Panchajanya S, Reddy JT, Susheela SR. Influence of root canal curvature on the accuracy of an electronic apex locator: An in vitro study . J Conserv Dent [serial online] 2014 [cited 2023 Sep 22];17:583-6. Available from:

   Introduction Top

The term "Working Length" (WL) is defined in the Glossary of Endodontic Terms as "the distance from a coronal reference point to the point at which canal preparation and obturation should terminate." [1]

Failure to accurately determine and maintain WL may result in length being too long leading to apical perforation, overfilling or overextension and increased post-operative pain with prolonged healing period and a lower success rate. [2] A WL too short of the apical constriction can lead to incomplete cleaning and under filling causing persistent discomfort, and continued periradicular infection.

The most widely used method for WL determination is the radiographic method. This method often leads to inaccuracies, because radiographs only provide a two-dimensional (2D) representation of the three-dimensional (3D) object and can also be interpreted differently between clinicians. [3]

The increasing concern about the radiation exposure led to the development of the electronic apex locator (EAL). A third generation EAL, Root ZX simultaneously uses two waveforms, a high (8 kHz) and low (400 Hz) frequency waveform. The accuracy of the Root ZX has been reported to range from 64-100%. If 1.0 mm difference is deemed acceptable, the accuracy is reported 100%. [4]

The accuracy of apex locators has been known to be influenced by various parameters like preflaring, [5] the stage of instrumentation (based on conductivity of canals), [6] apical constriction diameter, [7] and the type of irrigants used. [8]

Curvature of the root canals is commonly encountered in clinical situations which could be another morphological influencing factor related to working length determination. A scanning electron microscope (SEM) study evaluating Root ZX EAL for its accuracy found that the error in locating the apex was significantly smaller in cases with a normal apical foramen than in cases with a lateral foramen [4] where in a sharp curvature of canal exists at the apical third.

One study compared Raypex 5 apex locator and conventional radiography for determining WL of straight and curved canals. [9] Result of this study showed that the percentage of electronic measurements within ± 0.05 of AWL was 70% for straight canals and 35% for curved root canals.

These findings might be leading towards the assumption that curvature may be a significant factor contributing to the inaccuracy of EAL. No studies till date have been published assessing whether root canal curvature has any effect on the precision of Root ZX apex locators.

The purpose of this study was to evaluate whether the canal curvature had any effect on the accuracy of EALs. The hypothesis of this study was that the curvature of root canals has a role to play in determining the accuracy of electronic apex locators.

   Materials and methods Top

Criteria for selection of teeth

Sixty human extracted mandibular molars with various degree of root curvature were collected. Teeth were stored in a thymol solution until use. Gross debris was removed from the root surfaces with a 10 minute soak in 6% sodium hypochlorite (NaOCl). The root surface and apical portion of each tooth were examined for the absence of fractures and resorption and the presence of a mature apex under a dental operating microscope (Pico, Carl Zeiss, Jena, Germany) at 20X magnification.

Method of collection of data

The crown of each tooth was sectioned at the cemento-enamel junction with a diamond disk to gain unrestricted access to the canal system and to obtain a constant reference point for all measurements. A number (No.) 8 or No.10 K-file was inserted into the root canals until the tip of the instrument was just visible at the apical foramen to verify patency of the canal space and the apical foramen.

A No.8 or No.10 K file was inserted into the mesio-buccal canal of each tooth and the digital images were obtained in a bucco-lingual direction using the DigoraOptime® System (Soredex Orion Corporation, Helsinki, Finland) and a high-frequency Kodak 70 kV and 10 mA X-ray machine (300 kHz) (CSN IndustrieSrl, Italy). The exposure time was 0.12 seconds. The degree of root canal curvature was determined by Schneider's method. [10]

Samples were divided into three groups:

Group 1: Mild canal curvature (< 20)

Group 2: Moderate canal curvature (20-36)

Group 3: Severe canal curvature (>36)

The coronal third was preflared using the Sx files of ProTaper rotary (Denstply Maillefer) instruments. Each canal was irrigated with 2 mL of 3% NaOCl solution. Patency was constantly checked.

The actual root canal length was determined by introducing a No. 8 or No. 10 file into the canal until the tip of the file emerged through the major apical foramen when observed under a microscope (Carl Zeiss) with 20× magnification. The stopper was adjusted to correspond to the flat reference surface. A digital caliper was used to measure the length between the stopper and the tip of the file to the nearest of 0.01 mm. This was taken as the Actual Working Length (AWL).

A perforated plastic cylinder was filled with freshly mixed alginate for embedding the roots in it. Cold cure acrylic resin was used to firmly hold the root in place. The cylinder was placed in a plastic box filled with saline soaked sponge. The canals were irrigated and excess fluid was removed. The lip clip was firmly secured to the plastic box, with part of it dipped in saline. The file clip was attached to the file and the file inserted until the "Apex" reading was reached in Root ZX (J Morita Corp, Tokyo, Japan). This was taken as the Electronic Working Length (EWL).

Differences between EWL and AWL were calculated. Positive values indicated measurements that were long of the apical foramen, negative values indicated measurements that were short of the apical foramen and 0.0 values were considered coinciding measurements. The collected data was analyzed by Kruskal-Wallis test followed by Mann-Whitney test.

   Results Top

[Table 1] shows the number of canals in various groups for varying differences between actual working length and electronic working length.
Table 1: Number of canals showing difference between AWL and EWL

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Statistical analysis

The difference in mean values of AWL and EWL was not statistically significant in any of the groups (P > 0.05) using t-test.

The difference between AWL and EWL (absolute difference) was found to be slightly higher in Group 3 followed by Group 2 & Group 1 respectively [Table 2]. The difference between the groups with respect to mean value were found to be statistically significant (P < 0.05). Further, it was observed that the difference was statistically significant between Group 1 and Group 3 (P < 0.05) as well as between Group 1 and Group 2 (P < 0.05). No significant difference was observed between Group 2 and Group 3 (P > 0.05).
Table 2: Comparison of the difference (absolute difference) between AWL and EWL among the three groups: (Kruskal-Wallis test followed by Mann-Whitney test)

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   Discussion Top

Radiographs have been useful for determining the working length for many years but the studies on the apical root morphology show that radiographic interpretation alone cannot be relied upon to establish the working length accurately. [11],[12],[13]

The development of EAL has helped in making the assessment of working length more accurate and predictable. [14] The electronic root canal length measurement devices work on the basis of impedance and capacitance of the root canal system. Root ZX calculates the ratio of impedance values at 2 frequencies (8 kHz and 0.04 kHz). [15] It has a built in processor that relates the value of the ratio with the position of the file.

Root ZX was used in this study because it has become the benchmark to which other apex locators are compared. [16] It has been tested for accuracy in many clinical situations with many studies reporting an accuracy of 100%. [4],[17] Root ZX mini and Dentaport ZX, which works on the same principle as Root ZX have also demonstrated adequate precision in determining root canal length. [18],[19]

In the current study only one calibrated operator carried out the electronic readings, to obtain precise and consistent results.

The extent to which the in vitro studies depict the clinical accuracy of EALs is not known. [7] However, they are able to reproduce the clinical condition of EAL use and allow the objective assessment of several variables which is not feasible in in vivo studies. [7],[20] Hence this in vitro study was done, with some known influencing factors like irrigants, and coronal preflaring of canals, kept constant.

Only the mesiobuccal canals of mandibular molars were included in the study to eliminate the wide variation in the apical terminus sizes possible with different canals used, since electronic working length determination is influenced by the size of the canal at the apical terminus. [21]

Digora imaging software was used to calculate the angulation of the teeth in mesiodistal and bucco-lingual direction. Any specimens with marked curvature in the mesio-distal direction were eliminated as it may influence the study outcome. [10] A study done by Pangica AM et al., [22] on methods for evaluation of root canal curvatures suggested that Schneider's method is reliable to determine the degree of root canal curvature.

Huang et al., [23] suggested that EALs operate on the principle of electricity rather than the biological properties of the tissues involved. The materials most often used for immersion of extracted teeth are alginate, [16],[24] agar, [7],[20] saline solution [25] and gelatin. [8] The alginate model, is sufficiently strong to hold the roots, and allows the roots to be hidden, making it possible for measurements to be made objectively with minimum bias. Also, it is easy to prepare and is inexpensive.

Difference between the EWL and AWL was calculated. The decision to analyze these data using the absolute value of the difference in canal length determination, was to eliminate any bias since both under and over estimates of AWL would contribute to the overall error rather than cancel each other out, which would lead to larger deviation from AWL.

In the present study, the difference (absolute difference) between EWL and AWL was found to be slightly lower in Group 1 followed by Group 2 and Group 3, with statistically significant difference between Group 1 and 2 (P < 0.05) and between Group 1 and Group 3 (P < 0.05).

Thus, the hypothesis of the study was accepted when the tolerance was taken as ± 0.5 mm. Considering ± 0.5 mm as tolerance limit for accuracy, the device was 95% accurate for the mild curvature group and 80% accurate for moderate and severe groups.

Also, 95% samples showed a negative value indicating EWL being short of the apical foramen in moderate and severe curvature group whereas 65% samples in the mild curvature group showed a negative value. The frictional resistance on the file in the more curved canals, the less taper and smaller size of the canals could have contributed to such differences. The device gave 100% accuracy in detecting the apical foramen for a tolerance limit of ± 1.0 mm for all groups.

Only one study till date took curvature into consideration as an influencing factor and found that there was a significant difference between electronic and actual canal lengths for curved canals which was in accordance with the present study. [9] The greater inaccuracy of EAL in the study could be due to the use of Raypex 5 apex locator which is considered as the fourth generation EAL and Root ZX has been proven to be more accurate than Raypex 5. [26]

Thus, EALs are accurate devices (tolerance limit ± 0.5) for determining working length in curved canals, and can be used as useful adjuncts to radiographs. The radiographs still would remain as the primary method for length detection because of their added advantage in determining the anatomy of the root canal system, the number and curvature of roots, the presence or absence of disease, and to act as an initial guide for working length.

   Conclusion Top

  • Curvature of the canal has a small but significant contribution on the accuracy of the EAL tested.
  • Considering ± 0.5 mm as tolerance limit for accuracy, the EAL was 95% accurate for the mild curvature of canal and 80% accurate for moderate and severe canal curvatures.
  • The EAL gave 100% accuracy in detecting the apical foramen for a tolerance limit of ± 1.0 mm for all range of curvatures. Thus, within the limitations of the present study, Root ZX can be called as a reliable adjunct to radiography for determining working length of root canals.

   References Top

American Association of Endodontists Glossary of Endodontic Terms. 7 th ed. Chicago: AAE; 2003.  Back to cited text no. 1
Seltzer S, Soltanoff W, Smith J. Biologic aspects of endodontics. Part V. Peripical tissue reactions to root canal instrumentation beyond the apex and root canal fillings short of and beyond the apex. Oral Surg 1973;36:725.  Back to cited text no. 2
Cox VS, Brown CE Jr, Bricker SL, Newton CW. Radiographic interpretation of endodontic file length. Oral Surg Oral Med Oral Pathol 1991;72:340-4.  Back to cited text no. 3
Pagavino G, Pace R, Bacetti T. A SEM study of in vivo accuracy of the Root ZX electronic apex locator. J Endod 1998;24:438-41.  Back to cited text no. 4
Ibarrola JL, Chapman BL, Howard JH, Knowles KI, Ludlow MO. Effect of preflaring on Root ZX apex locators. J Endod 1999;25:625-6.  Back to cited text no. 5
Venturi M, Breschi L. A comparison between two electronic apex locators: An in vivo investigation. Int Endod J 2005;38:36-45.  Back to cited text no. 6
Ebrahim AK, Wadachi R, Suda H. Ex vivo evaluation of the ability of four different electronic apex locators to determine the working length in teeth with various foramen diameters. Aust Dent J 2006;51:258-62.  Back to cited text no. 7
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Sadeghi S, Abolghasemi M. A comparison between the Raypex5 apex locator and conventional radiography for determining working length of straight and curved canals. Iran Endod J 2007;2:101-4.  Back to cited text no. 9
Schneider SW. A comparison of canal preparations in straight and curved root canals. Oral Surg Oral Med Oral Pathol 1971;32:271-5.  Back to cited text no. 10
Kuttler Y. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50:544-52.  Back to cited text no. 11
Dummer PM, McGinn JH, Ree DG. The position and topography of the apical constriction and apical foramen. Int Endod J 1984;17:192-8.  Back to cited text no. 12
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Fouad AF, Reid LC. Effect of using electronic apex locator on selected endodontic treatment parameters. J Endod 2000;26:364-7.  Back to cited text no. 14
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Correspondence Address:
Lekha Santhosh
Department of Conservative Dentistry and Endodontics, The Oxford Dental College, Bommanahalli, Bangalore - 560 068, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.144610

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