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Year : 2020  |  Volume : 32  |  Issue : 4  |  Page : 187-192

Comparison of Five different methods of Working length determination: An ex vivo study

1 Private Practitioner, Madurai, Tamil Nadu, India
2 Professor, HOD-Department of Conservative Dentistry and Endodontics, Best Dental College, Madurai, Tamil Nadu, India
3 Private Practitioner, Chennai, Tamil Nadu, India

Date of Submission16-Mar-2020
Date of Decision20-Jul-2020
Date of Acceptance03-Nov-2020
Date of Web Publication18-Jan-2021

Correspondence Address:
Dr. Palani Selvi Kamaraj
907, Neo Pryme Apartments, Surveyor Colony, K. Pudhur, Madurai - 625 007, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/endo.endo_30_20

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Aim: The aim of the study was to determine the accuracy and reliability of working length determination using tactile sensation method, digital radiographic method, and electronic apex locator (EAL) in lower premolars in vivo and to compare the lengths so measured to the working length measured with cone-beam computed tomography (CBCT) and the actual working length (AWL) with magnifying loupe, ex vivo.
Materials and Methods: Thirty mandibular premolars scheduled for orthodontic extraction were selected. Under local anesthesia, access cavities were prepared and the working lengths were determined by two operators after blinding, using the tactile sensation method, digital radiographic method (radiovisiography [RVG]), and EAL, and tabulated. The teeth were then extracted and subjected to CBCT to determine the working length (CBCTWL). The AWL of the teeth was measured with a K-file that was inserted into the root canal until the file tip is visible at the apical foramen which was confirmed using a magnifying loupe (×8). The values were then statistically analyzed.
Statistical Analysis: The SPSS version 20 software (IBM Corp., Armonk, NY, USA) was used to perform statistical analyses, and the confidence interval was determined at P < 0.05. Kappa test was used for the determination of the intra-observer agreement for each method. The comparison of the means of the groups was assessed using repeated measures ANOVA with Greenhouse–Geisser correction and post hoc Bonferroni test.
Results: There is a significant difference between the methods in determining the working length. Based on the correlation values on reliability, CBCT method has a more positive correlation with AWL measured using magnifying loupe, followed by EAL, RVG, and tactile sensation.
Conclusion: Hence, we conclude that the use of EAL technique is clinically effective for measuring the working length which correlates more positively with the CBCTWL and AWL. Diagnostic CBCT scan can be used as a reliable method for determining the working length.

Keywords: Cementodentinal junction, cone-beam computed tomography, histologic working length, radiographic working length, tactile sensation method

How to cite this article:
Kamaraj PS, Parandhaman H, Raguganesh V. Comparison of Five different methods of Working length determination: An ex vivo study. Endodontology 2020;32:187-92

How to cite this URL:
Kamaraj PS, Parandhaman H, Raguganesh V. Comparison of Five different methods of Working length determination: An ex vivo study. Endodontology [serial online] 2020 [cited 2021 Mar 2];32:187-92. Available from: https://www.endodontologyonweb.org/text.asp?2020/32/4/187/307311

  Introduction Top

Determination of working length is one of the most critical steps of endodontic therapy, and a clear understanding of the morphology of the root canal system, including the apex, is imperative.[1] The apical constriction has been recommended as an ideal apical termination for root canal preparation.[2] It is the part of the canal with the smallest diameter, and any violation of this area is not recommended for long-term, successful outcomes.[2] The requirements of an ideal method for determining working length include rapid location of the apical constriction in all pulpal conditions and all canal contents; easy measurement, even when the relationship between the apical constriction and the radiographic apex is unusual; rapid periodic monitoring and confirmation; patient and clinician comfort; minimal radiation to the patient; ease of use in special patients; and cost-effectiveness.[3] To achieve the highest degree of accuracy in working length determination, a combination of several methods should be used. The tactile perception technique is simple and virtually effective and considered as supplementary to high-quality, carefully aligned, parallel, working length radiographs and/or an apex locator.[4] The digital radiography produces the images using digital sensors in place of the conventional film. This method is more advantageous to the conventional method in using a much lower dose of radiation to acquire a faster image that can be manipulated and edited to give a better image clarity.[5] Apex locators have been used to locate the apical constriction without patient exposure to irradiation to get the working length,[6],[7] and various generations of electronic apex locators (EALs) are introduced with multifrequency-based systems which measure the energy of the signal with multiple signal frequencies. However, they are still used adjunctively to the radiographic methods. Cone-beam computed tomography (CBCT) imaging gives volumetric data that provide more diagnostic information and define the location of the major foramen, which is not identifiable with precision in radiographs. Their high reproducibility also aids in multiplanar reconstructions of the root canal morphology to be viewed on a computer display.[8] The actual working length (AWL) measurement after extraction should be done by taking histologic sections for locating the minor diameter. However, the reliable and feasible method is by inserting a file into the canal until the tip can be seen through the major foramen and adjusted for its position at the level of the coronal-most boundary of the major foramen. The visual evaluation could be done using magnifying glass, stereomicroscope, surgical operating microscope, or using magnifying loupes.[9]

The aim of this study was to determine the accuracy in measuring the working length of root canal using tactile method, digital radiographic method, and EAL, in mandibular premolars in vivo, comparing the lengths so measured to the working length measured after extraction using CBCT and magnifying loupe.

  Materials and Methods Top

30 mandibular premolars with mature apices, scheduled for orthodontic extraction were selected for the study and informed written consent was obtained from each patient. A preoperative radiograph was taken employing the extension cone paralleling technique and the reference point was marked at the buccal cusp tip, and the tooth length was measured using a metal ruler from the reference point to the radiographic apex. Under local anesthesia with rubber dam isolation, access cavity was prepared using Endo access bur EX41 (Mani burs, Tochigi, Japan), followed by extirpation of pulp. The canal was irrigated using 2.5% sodium hypochlorite solution (Pyrax Polymars, Roorkee, Uttarakhand) and finally flushed copiously with distilled water.

Working length determination by tactile method tactile working length

The root canal orifices were widened and coronal preflaring was done with Gates-Glidden drills of sizes No. 2 and No. 3 (Dentsply Maillefer, Ballaigues, Switzerland). A 20 K-file (Mani K-files, Mani, Tochigi, Japan) was introduced into the canal until an increase in tactile resistance was detected. Rubber stopper was adjusted on the file in such a way that it touched the reference point. The 20 K-file was carefully withdrawn and the distance from the tip of the file to the rubber stop was measured using an Endo gauge (Dentsply Maillefer, Ballaigues, Switzerland), and the values are noted down and registered as TWL.

Working length determination by radiovisiography real working length

For radiographic working length determination, a #20 K-file with a silicon stop was inserted into the root canal, digital radiograph (Sopix imaging RVG system, Satelec Pvt. Ltd., India) was taken, and the radiographic working length was measured and then 1 mm was subtracted from the measurement and registered as the radiograph tooth length (RWL).

Working length determination by electronic working length

The canal was irrigated using 2.5% sodium hypochlorite solution and flushed copiously with distilled water. Then, the canal was thoroughly dried with paper points. The lip contact of the instrument was attached to the patient's lower lip. No. 20 K-file was taken and the unit's cable was clipped to its metal shank. The Propex-II digital apex locator (Dentsply Maillefer, Ballaigues, Switzerland) was turned on and the file was inserted into the root canal. As the file moved apically inside the canal, the apex locator gave values in the digital display, which indicated the distance from the tip of the file to the apical constriction in tenths of a millimeter. When the instrument reached the apical constriction, the apex locator gave out signals in the following three ways:

  1. A digital display reading –“0”
  2. A pulsing audition
  3. A flashing light.

If the instrument penetrated the constriction, a caution light, a continuous alarm, as well as a flashing“E” signal on the digital readout provided the warning. When the Propex-II apex locator signaled the apical constriction, the rubber stop was adjusted on the file shaft in such a way that it touches the reference point. The instrument was carefully withdrawn and the distance from the tip of the instrument to the rubber stop was measured using a metal ruler; the value was noted down and registered as electronic working length (EWL).

Cone-beam computed tomography analysis of working length ex vivo

Using modeling wax, 30 extracted lower premolars were integrated and 2 dental mandibular models were fabricated. Using CBCT (NewTom DVT 9000, Italy), the length of the canal space with a field of view of 100 mm × H 80 mm was measured. The area of interest was then reconstructed with an isometric voxel size of 0.260 mm. The tube voltage was kept at 90 kVp and 8 mA, and the exposure time was 9.4 s. The teeth were inspected in the transversal, sagittal, and coronal aspect. Using the examination tool, the tooth being measured can be depicted independently and suitable plane for measurement was selected where the reference point and the foramen are simultaneously visible. A straight line from the cusp tip to the foramen will be drawn, and the distance will be recorded as CBCT WL.

All measurements were performed by two observers by blinding the values. For each assessment, the observers evaluated the images separately and the values were recorded as TWL1, RWL1, and EAL1 for observer 1. For observer 2, the values are measured as TWL2, RWL2, and EAL2 and tabulated. After determining the working length by the above three methods, the teeth were extracted and stored in 1% thymol.

Actual working length determination after extraction

A 20K-file was inserted into the root canal until the tip of the file was visible at the apical foramen. The visibility of the file tip at the apical foramen was confirmed using a magnifying loupe (Carl Zeiss Meditec AG SN-6905702071, Germany). The stopper was adjusted to the reference point and the distance was determined with a digital Vernier caliper (Thermo Industrial Corporation, India) and detected as the AWL.

  Results Top

The SPSS version 20 software (IBM Corp., Armonk, NY, USA) was used to perform statistical analyses, and the confidence interval was determined at P < 0.05.

Inter-observer variability measurement

Kappa values [Table 1] showed that both the observers agree with each other to a very low extent for the working length values measured using tactile method and RVG. Apex locator working length values showed a kappa value of 1.000 with 100% coincidence interval between observers 1 and 2 and no significant disagreement. Hence, it is concluded that in this study, there is no inter-operator variability with apex locator method of working length determination.
Table 1: Inter-observer variability using kappa test

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Intergroup comparison

The multiple intergroup comparison of the mean values was assessed using repeated measures ANOVA with Green–Geisser correction, followed by post hoc Bonferroni test [Table 2]. It is evident that there is a significant difference between the three in vivo methods while comparing the mean values. The working length values measured by CBCT (21.057 mm) and EAL (21.000 mm) show no significant difference when compared to actual length by loupe method.
Table 2: Repeated measures ANOVA with post hoc Bonferroni test

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Paired sample correlations

The correlation percentage of each method – Tactile1, RVG1, EAL1, and CBCT – was assessed in comparison with the loupe method [Graph 1]. The correlation percentage showed that CBCT and EAL methods have the almost same level of correlation (no statistically significant difference) with the AWL measured by loupe method. This was followed by RVG and tactile methods, respectively.

Pearson's coefficient correlations

The correlation between the actual root canal length measurement using magnifying loupe and the Tactile1, RVG1, EAL1, and CBCT measurements was evaluated using the Pearson correlation coefficient. The confidence interval was determined at P < 0.05. There was a strong positive relationship between the working length values measured by CBCT (0.938) and loupe (1.000), followed by EAL1 (0.926). Correlations were significant at the 0.01 level. Whereas, RVG1 (0.893) and Tactile1 (0.840) methods show the least correlation with the AWL measured with loupe method. However, the results were not statistically significant.

  Discussion Top

An accurate working length is one of the most important criteria for achieving successful endodontic results and minimizing postoperative discomfort.[2] Kuttler investigated the root apices of teeth and noted that the distance from the apical constriction to the vertex of the root increased with age and was recorded as between 0.5 and 0.6 mm. The distance between the apical constriction and the apical foramen ranged between 0.4 and 1.2 mm, while its reported location in relation to the root apex ranged between 0.5 and 1.01 mm.[10] Evaluation of the apical and periradicular tissues after root canal procedures by many investigators concluded that the most favorable prognosis was obtained when the procedures were terminated at the apical constriction.[11] Since the pulp canal does not always exist at the anatomic apex, a greater consideration should be given in obtaining a sound knowledge of different techniques of working length determination. Even the commonly used methods of length determination showed inter-operator variability to a greater extent.[12] Henceforth, this ex vivo study was conducted with two operators after blinding to check for the reliability of the methods. The anatomic variables are also considered for accurate length determination. The highest percentage (51%) of working length overestimation was reported in premolars when compared to molars (22%). This can be better explained by the mesiodistal and buccolingual radiographic investigation which showed the lateral location of the apical constriction in premolars in 78%–93% of cases.[13] Hence, this ex vivo study was conducted in single-rooted mandibular premolars which showed the highest incidence of apical ramifications. In this ex vivo study, working length values by tactile sensation method showed greater disagreement between the two observers and also least correlation with the AWL values measured using magnifying loupe when compared with other methods in this study. Seidberg et al. in 1975 reported an accuracy of just 64% using tactile sense.[14] The accuracy is only 25% by tactile sense method in comparison with the actual length. Hence, the success of this technique depends on the diligence, sensuality, and experience of the operator.[15] There are several problems, like the loss of apical constriction due to apical resorption, the ability to gauge the apical constriction which relies mainly on the presence of a natural canal taper, tactile sensation of the operator to gauge the constriction with file, and prudent selection of initial apical file. A study by Yaghooti Khorasani and Ebrahimnejad in 2017 showed that 66.4% of the teeth observed had apical foramina which did not open at the anatomic apex[16] which is in accordance with our study where only 89% of the RVG values correlate with the AWL measured with loupe method. As the apical foramen is located laterally in 78%–93% of posterior teeth,[17] the mean RVG working length value (20.950 mm) in this study showed a significant difference when compared to the AWL value (21.087 mm) measured using loupe. However, it is not statistically significant when compared with CBCT (21.057 mm) and EAL (21.000 mm). The inter-operator reliability and sensitivity are more with RVG with the kappa value of 0.141. Hence, it is concluded that the radiographic working length determination should be combined with electronic working length determination to avoid potential drawbacks of digital imaging.[16] Apex locators have become a valuable clinical tool for assessing root canal length, and several previous studies showed that EALs were accurate for canal length measurement, within a clinically acceptable range of ±0.5.[18] Propex II EAL used in this study operates by capturing the signals of two alternating currents (0.5 and 8.0 kHz), and for this calculation, the mean square root of impedances at these two frequencies is measured separately.[19] Our study clearly showed that there is a strong correlation between the EAL1 (0.926) and CBCT (0.938) root canal length measurements. Hence, when compared to the tactile and RVG methods where the measurements are two dimensional, EAL provides a three-dimensional assessment of the canal morphology and aids in locating the accurate apical termination. Our study also showed a 96% correlation of the EALWL with the actual length measured using magnifying loupes, thereby reducing the possibilities of overestimation.[20] Connert et al. described the CBCT measurements made by marking up a single line between foramen and cusp tip which was followed in this study too.[21] A study by Yildirim et al. showed that CBCT has a strong positive correlation with the gold standard actual length measured after extraction.[22] This study showed that the CBCT to determine the working length determination was 98% accurate[23] with a mean difference of 0.20 mm when compared to the AWL when compared with the RVG and EAL, of 89% and 96%, respectively. Since distances <0.5 mm are negligible in clinical conditions, our study shows that CBCT can be used to determine WL confidently. An ideal CBCT system exclusively for dentistry with lower radiation doses and more compact scanners will be a desirable addition to the endodontist's armamentarium in the near future.[24] Histologic sections of the tooth samples are the standard method to evaluate the exact location of the apical terminus. In accordance with the studies by Mandlik et al., the AWL measured as the gold standard in our study had a strong positive correlation with CBCT >EAL >RVG >Tactile methods.[25]

  Conclusion Top

Several studies have concluded that the use of a combination of methods to determine an appropriate working length may be more successful than relying on just one method. In the clinical scenario, EAL when used in combination with radiographs will give much greater accuracy of working length and can reduce the number of radiographs required and CBCT showing similar correlation with EAL and actual length can be a reliable alternative of working length determination in the near future.


This study was submitted as the THESIS- PG DISSERTATION to the Tamil Nadu Dr. MGR Medical University, Chennai, Tamil Nadu (2016-2019).

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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Dohaithem AJ, Bakarman EO, Veitz-Keenan A. Tactile working length determination for root canal therapy in underserved settings. Evid Based Dent 2014;15:56-7.  Back to cited text no. 4
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Mosleh H, Khazaei S, Razavian H, Vali A, Ziaei F. Electronic apex locator: A comprehensive literature review-Part I: Different generations, comparison with other techniques and different usages. Dent Hypotheses 2014;5:84-97.  Back to cited text no. 6
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[PUBMED]  [Full text]  
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Tampelini FG, Coelho MS, Rios MA, Fontana CE, Rocha DG, Pinheiro SL, et al. In vivo assessment of accuracy of Propex II, Root ZX II, and radiographic measurements for location of the major foramen. Restor Dent Endod 2017;42:200-5.  Back to cited text no. 19
Chand A, Kumar P, Taneja S. Influence of working length determined by three different apex locators on the apical extrusion of debris following the instrumentation with rotary Ni–Ti instrumentation system. Endodontology 2020;32:81-5.  Back to cited text no. 20
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[PUBMED]  [Full text]  
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  [Table 1], [Table 2]


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