Journal of Conservative Dentistry

: 2023  |  Volume : 26  |  Issue : 3  |  Page : 311--315

Accuracy of the electronic apex locator, tactile, and radiographic methods in working length determination

Frank Osei-Bonsu1, Patrick Caldicock Ampofo2, Ebenezer Anno Nyako2, Sandra Ama Hewlett2, Victoria Afi Buckman2, Akua Boakyewa Konadu2, Paa-Kwesi Blankson3, Tom Ndanu4,  
1 Dental Department, Greater Accra Regional Hospital; Department of Restorative Dentistry, University of Ghana Dental School, Accra, Ghana
2 Department of Restorative Dentistry, University of Ghana Dental School, Accra, Ghana
3 Department of Oral and Maxillofacial Radiology, University of Ghana Dental School, Accra, Ghana
4 Department of Community and Preventive Dentistry, University of Ghana Dental School, Accra, Ghana

Correspondence Address:
Dr. Frank Osei-Bonsu
P. O. Box KB-313, Korle-Bu, Accra


Background: Determination of working length (WL) is necessary for the successful outcome of root canal treatment (RCT). Common methods in WL determination include tactile, radiographic, and electronic apex locators (EAL). Aim: The aim of this study was to compare three methods of WL determination to the actual visualization of the apical constriction (AC). Materials and Methods: Consecutive patients with indications for extraction of single-rooted single canal teeth at the University of Ghana Dental School clinic were randomly assigned to three groups. In-vivo root canal WL was determined by tactile sensation, digital radiography, and a 5th generation EAL (Sendoline S5). Files were cemented in the canals after the in-vivo measurements. The apical 4–5 mm of the roots was trimmed to expose the inserted files and the AC. Actual WL, as determined by visualization of the AC, was done using a digital microscope. Different WLs were then compared for the various groups, and the mean actual canal lengths were reported. Results: EAL accurately predicted the AC in 31 (96.9%) teeth, while the digital radiographic and tactile sensation methods accurately predicted the constriction in 19 (59.4%) and 8 (25%) teeth, respectively, in the study population. The mean working canal lengths for single-rooted teeth showed no observable difference among sexes, age categories, and side of the jaw. Conclusion: The EAL provided more reliable and accurate WL measurements for single-rooted teeth among Ghanaians, compared to digital radiography and tactile methods.

How to cite this article:
Osei-Bonsu F, Ampofo PC, Nyako EA, Hewlett SA, Buckman VA, Konadu AB, Blankson PK, Ndanu T. Accuracy of the electronic apex locator, tactile, and radiographic methods in working length determination.J Conserv Dent 2023;26:311-315

How to cite this URL:
Osei-Bonsu F, Ampofo PC, Nyako EA, Hewlett SA, Buckman VA, Konadu AB, Blankson PK, Ndanu T. Accuracy of the electronic apex locator, tactile, and radiographic methods in working length determination. J Conserv Dent [serial online] 2023 [cited 2023 Dec 2 ];26:311-315
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Full Text


The principal objective of root canal therapy (RCT) is to eliminate pain and clear the pulpal space of infection while ultimately ensuring apical healing, especially in cases where apical pathology exists before treatment.[1] Determination of root canal length (working length [WL]) is crucial in RCT, serving as a reference point for working instruments and dictating the end point of the endodontic preparation and obturation.[2] The use of inaccurate WL during RCT may, therefore, negatively affect the aforementioned objectives.

Precise working length determination continues to challenge many dentists relying solely on tactile and radiographic methods. Many radiographic images in endodontics are taken in two-dimensional planes, thereby having inherent distortion created by the relative positions of the object (tooth), the X-ray film, and the tube head. Distortions in the image shape may be due to improper placement of the X-ray tube, the object, as well as the film.[3] Different techniques have been described under the radiographic method. These include Kuttler's, Grossman's, Ingle's, and Bramante's methods.[4]

Over the years, electronic apex locators (EAL) have been developed to aid in WL determination. The recent generations of EAL use multiple frequencies to measure impedance in the canal as the file advances toward the apical constriction (AC) of the root canal.[5] Although the EAL has a considerable advantage, the radiograph remains a popular method in WL determination.[6]

Several studies have compared the precisions of different methods in WL determination with varying results.[7],[8],[9],[10] This study, however, describes the comparison of standard clinical methods with a model in-vitro WL determination using the anatomic AC. This study also compares the WL of a unique African population with others from comparative methods.

 Materials and Methods

This was a comparative study of WL determination by three in-vivo methods: tactile sensation, digital radiography, and EAL. The tactile, radiographic, and EAL methods of WL determination were compared to an in-vitro method.

The study was conducted among consenting adult patients attending the University of Ghana Dental School clinic, Accra, from February 2020 to January 2021. Participants were patients who had a single-rooted tooth indicated for extraction. Indicated teeth should have had clinically intact crowns and completely formed root apices from radiographic evaluation. Patients who were allergic to any of the materials used were excluded. Other exclusion criteria were teeth with hypercementosis or bulbous root apices, fractured teeth, evidence of attrition, and the presence of pulp stones.

With a calculated sample size of 32 per arm, patients were randomly sampled into three groups by balloting. A ballot container with 96 pieces of labeled papers consisting of 32 for each group, A (tactile), B (digital radiographic), and C (EAL), was used. Participants were consecutively picked from the container and randomly placed into a selected arm of the study.

For all participants, a preoperative periapical radiograph (CS 2100, Carestream, USA) was taken using the extended cone technique (parallel method). Local anesthesia was administered, and the tooth isolated with a rubber dam. A conventional endodontic access cavity for the particular tooth was created with a long-shank diamond round bur in a high-speed handpiece. Routine extirpation of the canal was done.

For Group A (tactile), a K-file was inserted slowly into the canal until a resistance was felt. The rubber stopper on the file was positioned on the highest stable reference point on the clinical crown of the tooth, and this point was noted. The file was then removed, and the length to the stopper was measured using a Miltex endodontics ruler. The file was reintroduced into the canal to the same reference point on the crown. The access cavity was then sealed with Fuji I glass ionomer cement (GC, Japan) with the file in-situ. The rubber dam apparatus was removed, and tooth extraction was carefully done [Figure 1].{Figure 1}

The determination of WL for Group B (digital radiographic) was based on the Ingle's method. The root canal length was measured on the radiograph's digital interface to the apex, and 1 mm was subtracted from the obtained figure. A K-file was then inserted into the canal at the calculated length. This was confirmed with a second radiograph, and the file was reintroduced into the canal to the same dimension. Similarly, the access cavity was then sealed with glass ionomer cement with the file in-situ, rubber dam apparatus was removed, and tooth extraction was done.

For Group C (EAL), S5-Sendoline apex locator was used to determine the root canal length. A K-file was carefully introduced into the canal, and an EAL lip clip was attached. The EAL probe was connected to the file, close to the rubber handle. The file was advanced gradually until the device indicated a stable 0.5 mm to the apex on the EAL display. The rubber stopper was then adjusted to a coronal reference point. The file was removed from the canal, and the length was recorded using a Miltex endometer. After the length had been recorded, the file was reintroduced into the canal to the same dimension, confirmed, and access cavity sealed with glass ionomer cement with the file in-situ.

The extracted teeth for all participants were cleared of all soft tissues, kept in a solution of 0.5% sodium hypochlorite, and transferred into a solution of normal saline. These teeth were stored individually in well-labeled laboratory sample containers until the laboratory (in-vitro) session of actual WL determination was done. For the in-vitro determination, the buccal aspect of the roots of all teeth was trimmed at a level, 4–5 mm to the apex, using a fine size 3 diamond wheel bur to expose the inserted files [Figure 2]a. Trimming of the apical area was carefully done to preserve the apical anatomy without encroachment of the AC. A Miltex endodontics ruler was then attached to the sectioned portion of the root using an epoxy resin and a hardener (Loctite Ultra Gel, China). The AC was identified and examined under illumination using a digital microscope (Magnus High-Speed 24-bit DSP, HD-CMOS, Korea) at ×15 magnification. The middle portion of the AC was used as the reference point for all the measurements [Figure 2]b. The distance between the file tip and the mid-AC (MAC) was recorded and categorized as “favorable” when the difference between the file tip and the reference point, MAC was within ± 0.5 mm. “Unfavorable” measurements, on the other hand, referred to those with differences that were more than 0.5 mm from the reference point. The measured distance from the file tip to MAC was also used to correct the obtained WL to obtain an actual (in-vitro) WL. All measurements were taken by a single investigator, who is a consultant in restorative dentistry.{Figure 2}

The background characteristics for the study included study arm, age, sex, tooth type, arch, and the side of the jaw. The outcome variable was the proximity of clinical WLs to the in-vitro AC categorized as “favorable” and “unfavorable.” All variables were entered into Stata (16.1, StataCorp LLC, College Station, TX), and analyzed with the same. The various background characteristics were cross-tabulated against the WL approximation with application of the Chi-squared test. A binary logistic regression was also done using WL approximation as an outcome measure, with consequent test of association. Differences were considered significant when P < 0.05.

Ethical standards of the study were ensured, and the approval was obtained from the Ethical and Protocol Review Board of the University of Ghana College of Health Sciences (CHS-Et/M3 5.6/2019-2020).


There were 96 single-root, single-canal teeth from 96 different individuals included in the study. The ages of the participants ranged from 18 to 69 years. The mean and median ages were 52.3 ± 12.7 years and 55 (47.5, 61.5) years, respectively. The teeth used in the study consisted of 63 (66%) maxillary and 33 (34%) mandibular teeth. Reasons for extractions were periodontitis (80%), caries (16%), and orthodontic reasons (4%). The mean working canal lengths by direct observation are shown in [Table 1]. For all categories of teeth used in this study, there was no difference in WL among sexes, age categories, and side of the jaw.{Table 1}

There was a higher proportion of favorably approximating WLs among measurements taken with the EAL (96.9%). The radiographic method had 59.4% being favorable, while the tactile method yielded the least accurate WL measurements [Table 2]. The difference in these observations was statistically significant (P < 0.001). The odds of the EAL giving a favorable apical approximation were 9.3 times that of tactile sensation, while the odds of radiographic determination were approximately 4.4 times that of tactile sensation. Both associations were statistically significant (P = 0.000 and P = 0.007), respectively.{Table 2}

Favorable approximation of WL measurements did not vary significantly among males and females (P = 0.143). The maxillary or mandibular position (upper or lower jaw) did not also confer any statistical difference in their proximity to the AC. Furthermore, the distribution of apical approximation among the teeth type was also observed to be unremarkable [Table 2].

Concerning the errors by the individual methods of WL determination, many measurements (62.5%) of the tactile sensation method were short of the MAC, while all the remaining 37.5% were beyond. Many more (71.9%) WLs were beyond the reference point when using radiographic determination. Although the EAL had the highest favorable WL measurements, 13 (40.6%) occurred precisely at the MAC, with 18 being beyond the MAC [Table 3].{Table 3}


The current study evaluated three methods of determining WL of teeth and compared them to a gold standard WL, being the actual visualization and measurement to the MAC. The EAL was found to be the most accurate method of WL determination with 97% of the WL being within ± 0.5 mm of the MAC.

This study provides the objective mean WLs of different categories of single-rooted teeth of a Ghanaian population, which to the best of our knowledge, is the first for this population. The determined lengths showed no observable difference among sexes, age categories, and side of the jaw. Compared to a study in another West African population, Sede et al.[11] reported the average WL of the permanent maxillary central incisor of Nigerians to be 25.0 ± 1.7 mm, with the values in males and females being 25.4 ± 1.2 mm and 24.4 ± 2.2 mm, respectively (P < 0.05). The differences observed in the two studies could be due to the different methodologies employed in the two studies. The canal length for the maxillary central incisor was also found to be 24.7 mm and 25.7 mm in two Malaysian subraces,[12] and 23.5 mm in Caucasians.[13] Our finding for the WL of the maxillary lateral incisor of 21.8 mm was also comparable to Fibryanto et al.'s[12] and Clegorn's[13] findings of 22.6 mm and 22.0 mm, respectively. Furthermore, the present study recorded the average WL of the mandibular incisors to be 20.2 ± 1.3 mm. This figure compares favorably with the average length of the lower central incisors reported by Kulkarni et al.[14] and Choi et al.[15] The results of this study complement existing figures in the literature and provide suitable WL references for similar populations.

With the method used, radiographs were found to have an accuracy of 59%. A study by Vieyra and Acosta[16] found the percentage accuracy of the radiographic method of WL determination to be 34.7%. The difference compared to the current study could be because the former report used conventional radiography, which might be more amenable to operator errors.

Our results also indicate that 72% of recorded radiographic lengths were beyond the reference point (MAC), consistent with Williams et al.,[9] who observed that acceptable clinical radiographic WL was most of the time beyond the AC and apical foramen (AF). The high percentage (72%) of WL going beyond the reference point demonstrated that most of the canals did not exit at the radiographic apex, but rather laterally, which agrees with several other studies in the literature where a high percentage of AF do not open directly at the radiographic apex.[17],[18] Again, the result from the current study correlates with Stein and Corcoran,[19] who observed in their radiographic study of WL determination that most of the files were beyond the AC and AF. They, therefore, recommended a distance of 1.5–2.0 mm from the radiographic apex to the AC (instead of 0.5–1.0 mm suggested by Kuttler) to avoid overinstrumentation during root canal treatment.

Our finding of 97% accuracy for the EAL seems to agree with several models,[20],[21] but not consistent with earlier reports by Welk et al.[22] and Fouad et al.[23] These differences in accuracies could be from the sensitivity of the inbuilt processor mechanisms of the various apex locators.

One limitation of this study could be the inclusion of only one type, one generation of EAL, which may not be representative of many EALs. This study, however, describes a robust method employed in its comparisons, thereby providing reliable data of clinical relevance.


The EAL provided, by far, superior, and more reliable accurate WL measurements for single-rooted teeth among Ghanaians, was compared to digital radiography and tactile sensation methods. The mean working canal lengths for single-rooted teeth showed no observable difference among sexes, age categories, and side of the jaw.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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