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 Table of Contents  
Year : 2016  |  Volume : 4  |  Issue : 2  |  Page : 39-43

Comparison of working length determination using apex locator and manual method - ex vivo study

1 Department of Endodontics, Superior School of Health Sciences, State University of Amazonas, Manaus, AM, Brazil
2 Department of Endodontics, Federal University of Amazonas, Manaus, AM, Brazil
3 Department of Physiology and Pathology, Araraquara School of Dentistry, Univ Estadual Paulista, Araraquara, SP, Brazil

Date of Web Publication27-Jun-2016

Correspondence Address:
Lucas da Fonseca Roberti Garcia
Rua Siro Kaku, n 72, Apto. 73, Bairro Jardim Botanico, CEP: 14021-614, Ribeirao Preto, Sao Paulo
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2348-1471.184730

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Background: Electronic apex locators can be a useful adjunct with a high level of accuracy for determining the real root canal length in clinical practice. Aim: The objective of this ex vivo study was to evaluate the accuracy of electronic apex locator for real working length determination in comparison with a manual method. Materials and Methods: Forty single-rooted teeth were used in this study. After coronal access, manual measurement of the real working length of each root canal was performed by placing a size 10 K-file, using as reference the exceeding of the file in the apical foramen. The file was retracted by 1 mm, and its extension was measured to determine the real working length. The electronic measurement of the working length was performed in the same teeth using the Joypex 5 electronic apex locator. Results: Data were submitted to statistical analysis (Wilcoxon-Mann-Whitney test, P > 0.05) and no significant difference was found between the electronic and manual methods (P > 0.05). Conclusions: It may be concluded that the electronic apex locator is a reliable and accurate method for determining the working length of root canals, optimizing the odontometric procedure in clinical practice.

Keywords: Electronic apex locator, endodontics, working length

How to cite this article:
Carneiro JA, de Carvalho FM, Marques AA, Junior EC, Garcia Ld, Goncalves LC. Comparison of working length determination using apex locator and manual method - ex vivo study. Dent Med Res 2016;4:39-43

How to cite this URL:
Carneiro JA, de Carvalho FM, Marques AA, Junior EC, Garcia Ld, Goncalves LC. Comparison of working length determination using apex locator and manual method - ex vivo study. Dent Med Res [serial online] 2016 [cited 2023 Mar 31];4:39-43. Available from: https://www.dmrjournal.org/text.asp?2016/4/2/39/184730

  Introduction Top

Endodontic therapy involves several steps. [1],[2] One of the most important is odontometry, which seeks to measure the real working length of the root canal, limiting the action of instruments during biomechanical preparation and filling, avoiding damage to the periapical tissues. [1],[2],[3],[4]

The working length is the distance from a coronary reference to a point where instrumentation and root canal filling should end. [5] The distance must be well established by the endodontist to prevent over-instrumentation or over-filling of the root canal, and favor the repair process of the apical and remaining tissues. [5],[6]

It is believed that the foramen is located at the limit of cementum-dentin junction, where the periodontal ligament begins, and the dental pulp ends. [6] Several studies have determined that the limit is 0.5 mm or 1.0 mm short of the radiographic apex, but the ideal limits for instrumentation and obturation of the root canal may range from 0.0 to 2.0 mm. [7],[8],[9] However, its exact location is still a clinical challenge for the professional. [10]

Several techniques are used to determine the real working length of the root canal; however, they have limitations. [10] The main limitation of the digital sensitivity technique is the internal morphology of root canals, which prevents the detection of the apical constriction. [10] The radiographic evaluation, despite being widely used, can present distortion, overlapping, elongating, and interference of anatomical structures, making it difficult to accurately determine the working length. [9]

Thus, electronic devices that act as apex locators were developed with the purpose of minimizing the technical limitations when determining the real working length of the root canal. [11],[12] Because electronic location is based on the passage of alternating current impedance through dentin, it has been hypothesized that apex locators locate the apical foramen with more precision than other techniques. [11]

Currently, these devices have been increasingly used in endodontic therapy, becoming indispensable in clinical practice. Thus, this ex vivo study aimed to evaluate the accuracy of an electronic apex locator to determine the real working length using an extracted tooth model. The null hypothesis tested was that there would be no difference between the two methods in real working length measurement.

  Materials and methods Top

Forty single-rooted teeth from the Tooth Bank of the State University of Amazonas (UEA) were used in the study after approval from the Research Ethics Committee. The teeth were kept immersed in 2.5% sodium hypochlorite solution (Rio Química, São José do Rio Preto, SP, Brazil) for 6 h to remove remnants of periodontal ligament tissue and other debris from the external root surface. Afterward, the teeth were stored in 0.9% sterile saline solution at 9°C for 7 days [Figure 1].
Figure 1: Single-rooted teeth selected for the study

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Initially, coronal access was performed with round diamond burs No. 1011 and 1012 (KG Sorensen, São Paulo, SP, Brazil) coupled to a high-speed handpiece (Model 605, Kavo, Joinville, SC, Brazil) under abundant water cooling. Then, incisal flattening of the tooth crowns was performed to facilitate the placement of the rubber stop during the measurement of the working length, and to standardize the reference for the apex electronic locator.

Each root canal was initially explored with the aid of a size 10 K-type file (Dentsply/Maillefer, Ballaigues, Switzerland), throughout its length until beyond the apical foramen. Once the limit had been exceeded, the file was retracted by 1 mm and the stop was placed on the flat incisal surface. The file was then removed from the root canal and with the aid of a digital caliper (Digimess, Shinko Precision, Gaging, China), the extension of the file was measured from the stop to the active tip to determine the real working length [Figure 2].
Figure 2: Joypex 5 electronic apex locator (Denjoy Dental Co.) used in the study

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After determining the real working length using the manual method, electronic measurement of the working length of the root canal was performed in the same teeth using the Joypex 5 electronic apex locator (Denjoy Dental Co. Ltd, Changsha, China) [Figure 3]. The teeth were inserted on a base, consisting of a glass container with fresh alginate saturated with a 0.9% sodium chloride solution to simulate the periapical tissues (Rio Química, São José do Rio Preto, SP, Brazil), so the entire root portion remained submerged and stable. Joypex 5 lip clip was placed on the experimental base to complete its circuit. [13] To maintain the root canal moist and the pulp chamber dry before beginning the electronic measurement, the canals were irrigated with 1 ml of 2.5% sodium hypochlorite solution (Rio Química) and aspirated, following the apex locator manufacturer's recommendation. A size 10 K-type file was connected to the device and inserted into the root canal until the 0.0 mark appeared on the device display, indicating that the instrument had reached the limit of the apical foramen.
Figure 3: Root canals real length measurement by the manual method: (a) visualization of the file exceeding the apical foramen. (b) magnified visualization of the file exceeding the apex. (c) limit after withdrawal of file (1 mm) and obtaining the real length of the root canal

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The values obtained (mm) in the two measurement techniques were recorded. The normal distribution of data was measured using the Shapiro-Wilks test and the values obtained were statistically analyzed (Wilcoxon-Mann-Whitney test at a 5% significance level) using the MINITAB Release 14.1 Statistical Software (MINITAB Software Inc., State College PA, USA).

  Results Top

The values obtained in the working length measurements, and their comparisons are shown in [Table 1].
Table 1: Values (mm) of real working length of root canals obtained by manual and electronic measurement methods (Wilcoxon-Mann-Whitney U-test, P<0.05)

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No significant difference was found between manual and electronic methods (P > 0.05). In 73% of the samples, the values for real working length measurement were similar (0.0 mm), in 23% a difference of 0.5 mm was found, and in 5% a difference of 1.0 mm was found [Figure 4].
Figure 4: Values distribution (%) according to the method used for real working length measurement

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  Discussion Top

The objective of this ex vivo study was to evaluate the accuracy of an electronic apex locator in comparison with a manual method. Based on the results obtained, it can be stated that the null hypothesis tested was accepted, since the two methods for working length measurement had no significant difference. The aim of endodontic treatment is to remove all the pulp tissue, necrotic material, and microorganisms from the root canal by cleaning and shaping it with specific instruments. [1],[2],[3] Only through odontometry is it possible to obtain the real working length of the root canal and thus, create conditions for it to be prepared within its apical limit and filled accordingly. [4],[5]

Over-filling of the root canal is usually preceded by over-instrumentation, which is responsible for microorganisms and necrotic material transport beyond the apical foramen, making the postoperative period painful due to infection and inflammation of the periapical tissues. [14] The inflammatory reaction impairs the process of tissue repair in the periapical region, leading to treatment failure. [14]

On the other hand, under-filling must also be avoided, since hermetic sealing failure in the apical region may allow survival and multiplication of residual bacteria and microorganisms, which may cause leakage of tissue fluids into the root canal, leading to the appearance of periapical lesions. [10],[14]

Despite the results obtained in ex vivo studies should not be directly extrapolated to clinical conditions, they still provide important information to professionals. In this study, to bring the test closer to the clinical reality, the periapical conditions were simulated using fresh alginate, and the root canals were maintained moist with 2.5% sodium hypochlorite solution, following the recommendations of the apex locator manufacturer. [9],[14],[15],[16]

The results obtained in this study do not corroborate several previous studies, which presented precision rates of 90% for apex locators. [9],[15],[16] In this study, only 73% of the samples presented values equal to the manual method. Several authors consider this margin of precision (90%) too excessive, over-estimating the capacity of apex locators. [14],[17],[18] Furthermore, a manual method for real working length measurement was used in this study to certify the values obtained in the electronic method, ensuring more reliable results.

Previous studies adopted radiographic methods to compare the findings of electronic apex locators. [16],[17],[18] It is known that radiographic examination is still the most commonly used method for determining the working length. However, the obtainment of radiographs without any distortion or overlapping of anatomical structures in the root apices is challenging. [14],[15],[16] Furthermore, radiographic visualization of the apical constriction or even the foramen is difficult because these do not always coincide with the radiographic apex. [14]

The limitations of radiographic examination led to the development of methods that seek greater precision during odontometry. [10] Electronic methods allow the location of the apical constriction with a substantial rate of success, [15],[16] as could be seen in this study. The speed and practicality of the method associated with the ease of establishing the working length at any operative step are significant advantages over the radiographic method. [14]

However, it is worth emphasizing that the use of electronic apex locators does not eliminate the need for radiographic evaluations, which are essential both for the diagnosis and quality evaluation of the root canal filling, as well, postoperative control. [17],[18] Moreover, only using apex locators is not recommended in clinical practice due to the morphological changes in the root canal system and because they do not provide any legal documentation, requiring an initial, and final radiography of the endodontic treatment. [19]

Despite its relative importance and widespread use, Elayouti et al.[20] demonstrated that in 51% of cases in which the working length was determined radiographically, there was perforation of the root apex during instrumentation. However, the root apex was also perforated in 21% of the canals where the working length was determined with electronic apex locator, showing the inaccuracy of the technique and the need for both methods. The combination of both techniques is the best alternative to prevent placing instruments and filling material beyond the apical foramen. [20]

Third generation electronic apex locators, as that one used in this study, work on the principle that there is an impedance mismatch between two electrodes, where one of the values is calculated from a frequency of 1 kHz and the other from the frequency of 5 kHz. [21] The impedance reaches its highest value in the position of greater constriction of the canal, which often coincides with the limit of the cementum-dentin junction. [21]

Only with the advent of the third generation of electronic apex locators was it possible to measure the length of the root canal in the presence of irrigating solutions, secretions, saliva, and blood. [17] These locators have a cable connected to the device that divides into two, one being placed in contact with the oral mucosa of the patient, and the other connected to the endodontic file. [17]

Meares and Steiman [22] evaluated the influence of sodium hypochlorite solution at different concentrations on the accuracy of a third generation electronic apex locator and reported that regardless of the irrigating solution and its concentration, the determination of the real working length was accurate, results which are similar to those found in the present study.

Despite the limitations of this ex vivo study, the electronic device for measuring the root canal length presented acceptable readings for root canal length determination in single-rooted teeth. However, it should not be conclude that the electronic apex locator can replace radiographic evaluation.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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Aggarwal V, Singla M, Kabi D. An in vitro evaluation of performance of two electronic root canal length measurement devices during retreatment of different obturating materials. J Endod 2010;36:1526-30.  Back to cited text no. 16
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]

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