Journal of Indian Society of Pedodontics and Preventive Dentistry
Journal of Indian Society of Pedodontics and Preventive Dentistry
                                                   Official journal of the Indian Society of Pedodontics and Preventive Dentistry                           
Year : 2019  |  Volume : 37  |  Issue : 2  |  Page : 157--161

Comparing the accuracy of cone-beam computed tomography and electronic apex locator for root canal length determination in primary teeth

Kiran Dattatray Ghule, Shilpa Naik 
 Department of Pedodontics and Preventive Dentistry, D Y Patil Deemed to be University School of Dentistry, Navi Mumbai, Maharashtra, India

Correspondence Address:
Dr. Kiran Dattatray Ghule
B-1/435, Kasturi Plaza, Manpada Road, Dombivli East, Thane, Maharashtra


Aims: The aims of this study were to assess the accuracy of electronic apex locator (CanalPro™) and cone-beam computed tomography (CBCT) in determination of working length in primary teeth compared to direct visual length. Subjects and Methods: Ninety-nine primary teeth (207 root canals) were subjected to CBCT scan for assessment of working length. All root canals were then measured using CanalPro™ Apex Locator. Actual length of root canal was measured using direct visual method which was kept as control. Statistical Analysis Used: One-way ANOVA and Tukey's honestly significant difference tests were performed using the Statistical Packages for the Social Sciences (SPSS) version 16. Results: Overall estimated mean values obtained using three methods show that CBCT method was more accurate than the apex locator in determining the working length in primary teeth. However, these values were statistically insignificant. Conclusions: CanalPro™ Apex Locator can be used in primary teeth to accurately determine the working length. Nevertheless, a preexisting CBCT can always be used for determination of the working length in the primary teeth.

How to cite this article:
Ghule KD, Naik S. Comparing the accuracy of cone-beam computed tomography and electronic apex locator for root canal length determination in primary teeth.J Indian Soc Pedod Prev Dent 2019;37:157-161

How to cite this URL:
Ghule KD, Naik S. Comparing the accuracy of cone-beam computed tomography and electronic apex locator for root canal length determination in primary teeth. J Indian Soc Pedod Prev Dent [serial online] 2019 [cited 2019 Oct 14 ];37:157-161
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Full Text


Pulpectomy is a technique-sensitive procedure, as instrumentation of morphologically complicated canals of primary molars encased in curved roots programmed for physiological resorption is quite challenging.

Prior to canal preparation, working length determination is a necessary step to achieve a clinical and radiographic success in pulpectomized teeth. The root canal anatomy of primary molars is difficult to predict because of the rate of resorption and hard tissue deposition. Physiologic resorption starts soon after the complete formation of the root, even while hard tissue deposition continues to modify the root canal system. Hence, the shape, dimension, and position of the root apex is continuously altered. Thus, posing a challenge to determine the exact working length in the primary teeth. Common methods to determine the working length are by digital tactile sense technique or by conventional radiography. Both of these present certain difficulties. Moreover, since the image obtained from the radiograph is bidimensional and the tooth is a three dimensional (3D), errors related to the measurement of working length are bound to occur.[1] Other techniques, such as electronic devices (apex locators) have been proposed to determine root canal working lengths. There are some published reports related to the accuracy of determination of the working length with an apex locators in primary teeth.[2] A better understanding of the three dimensions of dental roots could also help to increase the accuracy of endodontic working length measurements. Thus, the performance of root canal measurements on preexisting cone-beam computed tomography (CBCT) scans is a potential new method for determining root canal length before initiating endodontic treatment.

Thus, the presentin vitro study aims to assess the accuracy of working length determination using electronic apex locator (EAL, CanalPro™) and CBCT scan in primary teeth.

 Subjects and Methods

The presentin vitro study was conducted on the approval from the Institutional Review Board of the institution.

Teeth selection and storage

Primary teeth extracted for therapeutic reasons were collected.

Inclusion criteria

The inclusion criteria of this study were as follows:

Teeth with more than two-third of root lengthNo signs of internal and external resorptionAbsence of perforation in the internal or external furcation areaWithout any previous treatment done on them.

Exclusion criteria

The exclusion criteria of this study were as follows:

Teeth with pathologic resorption and perforation in the furcation areaTeeth with less than two-third of actual root lengthGrossly carious or destructed primary tooth and tooth with anomaly.

The selected specimens were washed under running water and stored in 3% sodium hypochlorite for 7 days for disinfection and then stored in distilled water till their use. Two hundred and seven root canals from 99 primary teeth (36 – anterior teeth, 42 – mandibular molars, and 21 – maxillary molars) were selected.


For each tooth, standard coronal access was achieved with diamond fissure bur, EX-20/BR-31, BR-41 (MANI Inc., Japan) fitted in an air-rotor handpiece (NSK, Japan). After irrigation of the root canal with normal saline, canal patency was checked using a size #8 or #10 stainless steel K-file (Dentsply Maillefer, Ballaigues, Switzerland) without attempting to instrument beyond the apex. The primary teeth were then mounted in modeling wax. The mounted teeth were subjected for a 3D analysis by CBCT (Kodak Carestream 9000 3D System) using standard template (0.2 mm voxel).

Direct determination of root canal length

A reference point was first marked on the most coronal portion of the tooth crown with a marker. A K-file with silicon stopper was passively introduced into the root canal until its tip was visible at the apical foramen. The file was flushed with the apical foramen which was confirmed with a magnifying glass. The silicon stopper was then adjusted to the reference point level and removed from the canal. Measurement of the length was done with endodontic measuring gauge.

Electronic determination of root canal length

The electronic determination of working length was undertaken using CanalPro™ Apex Locator (Coltene, Switzerland). The tooth was placed in a sponge soaked with saline, and the canals were also filled with saline. Cotton pellets were used to soak the excess saline from the pulp chamber. A #10 K file was introduced passively into the canal. The lip clip was attached to the sponge, and the working length was determined as per the manufacturer's instructions. The measurements were recorded.

Determination of root canal length using cone-beam computed tomography

The CBCT scans were saved as DICOM file and then analyzed using CS 3D Imaging Software (Carestream Dental LLC, Atlanta, GA). The coronal, sagittal, and axial planes were adjusted to intersect in the pulp chamber of the tooth. The reading was obtained in the coronal plane. The most coronal portion of the tooth crown was considered the reference point. Using the measuring scale of CS 3D Imaging software, each tooth was measured from the reference point to the apical foramen.


All the data were recorded in an excel sheet and subjected to statistical analysis (one-way ANOVA and Tukey's honestly significant difference tests) using the SPSS (Statistical Packages for the Social Sciences) for Windows Version 16.0. (SPSS Inc., Chicago).

The mean root canal length measured using direct visual method, apex locator, and CBCT of primary anterior teeth and maxillary and mandibular molars are tabulated in [Table 1], [Table 2], [Table 3], respectively.{Table 1}{Table 2}{Table 3}

On comparison of direct visual method with apex locator and CBCT, no statistical difference in working length was obtained [Table 4].{Table 4}


For a successful pulpectomy in primary teeth, establishment of working length is an important step, as this ensures a near complete chemomechanical disinfection of the root canal system without harming the periapical tissues and underlying permanent tooth germs. Tactile method and radiography have been the most common methods of choice for determination of working length. However, radiographic determination of root length may give misleading results, particularly in cases where resorption is present, error due to image magnification, distortions or the superpositioning of anatomic structures, radiation exposure, sensor size, reduced mouth opening of children, and patient cooperation.[3],[4],[5] Whereas the errors induced by tactile method may result in an increased risk of over instrumentation and/or overfilling, which can damage the permanent tooth germ.[6],[7] Therefore, one of the main concerns in root canal treatment is to determine how far instruments should be advanced within the root canal and at what point the preparation and filling should terminate. All these factors have stimulated the evolution of electronic root canal measuring devices known as EAL.[8]

Various generations of EAL have been tested in the primary teeth, out of which Root ZX and Root ZX II (J. Morita, Tokyo, Japan) have given more reliable results compared with others.[9] The fourth-generation Root ZX II apex locator though found to be most accurate EAL has a drawback that it is low in detecting the apical constriction or the apical foramen. Recently, a newer generation EAL, CanalPro™ Apex Locator (Coltene, Switzerland), has overcome this major drawback.

CanalPro™ is a newer generation apex locator which according to manufacturer has a colored 3D panel and is accurate in measuring root canal length. Its virtual apex function enables to mark a predetermined position at the required distance from the apex. It uses two alternating frequencies to accurately determine the apex location. Its function is also most efficient in wet as well as dry conditions. However, there is no literature to assess the accuracy of CanalPro™ to date. Thus, this newer generation apex locator was chosen to assess its accuracy.

The determination of working length with the help of EAL needs no debate, but in our study, the accuracy of the root canal measurements made from the CBCT images with respect to the actual length of the canals were also compared. CBCT has been used with success in the permanent teeth to evaluate the canal morphology and the working length.[5],[10],[11] In our study, working length was measured using CBCT as it produces undistorted images with a significantly lower effective radiation dose than conventional computed tomography (CT). This added advantage of improved visualization of root canal morphology, which could possibly increase the accuracy of working length measurement.[12]

With all the said advantages, CBCT (68.7–134.8 μSv) has some limitation for its use with regard to patient radiation exposure.[13] Some authors estimated the effective dose of dental CBCT to be 5–300 μSv. Although it is very low compared to CT (1320–1400 μSv) and equivalent to a conventional full-mouth intraoral series of radiographs (35 μSv), the dose is high when compared to a single intraoral radiograph (5 μSv).[14]

Connert et al.[11] in 2014 stated that, using a simplified method, CBCT images of 0.2 mm voxel size can be used to accurately determine endodontic working length. Thus, in our study, CBCT readings were obtained at 0.2 mm voxel size as it gives a higher resolution of the image.

In the present study, on comparing the mean value of working length, obtained in primary teeth using CBCT was more accurate than CanalPro™ Apex Locator. But, these results were not statistically significant.

On the other hand, when CBCT compared with Apex locator, factors which limit its use are increased cost, radiation exposure in children, and difficult to access. This means that the three basic principles of protection from radiation, i.e., “justification principle,” “limitation principle,” and “optimization principle” should be followed.[15]


CanalPro™, the latest generation apex locator, which was used in our study showed positive results though no statistical difference when compared with CBCT. Hence, further researches and morein vivo studies would substantiate our results further. Based on our results and statistics obtained, CBCT is highly accurate in determining the working length though a few contradictions such as radiation exposure and cost factor cannot be ignored. Some developments are being made to reduce the radiation dose; nevertheless, a preexisting CBCT can always be used for determination of the working length in the primary roots.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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