|Year : 2017 | Volume
| Issue : 1 | Page : 12-16
In-vitro comparison of four different working length determination techniques
Mohamed I Elshinawy
Department of Endodontics, Faculty of Dentistry, Tanta University, Tanta, Egypt; Department of Restorative Dental Sciences, College of Dentistry, King Khalid University, Abha, Saudi Arabia
|Date of Web Publication||14-Mar-2017|
Mohamed I Elshinawy
Department of Restorative Dental Sciences, College of Dentistry, King Khalid University, PO Box 3263, Abha 61471
Source of Support: None, Conflict of Interest: None
Aim: The aim of this study was to compare four different working length determination techniques.
Materials and methods: Fifty extracted single-canaled anterior teeth were decoronated. The root canals' working lengths were repetitively determined in five groups (n = 50 each) using regular radiographic film (group 1), digital radiographic image (group 2), cone-beam computed tomographic image (group 3), electronic apex locator (group 4) and direct measurement (group 5, control) by subtracting 0.5 mm from the length of # 15 k-file visible at the apical foramen. The collected data was statistically analyzed using both analysis of variance and least significant difference (LSD) comparisons at P value less than or equal to 0.05.
Results: The one-way analysis of variance indicated a difference between the data of study groups (P = 0.011). The LSD comparisons revealed a longer working length (LSD, P ≤ 0.05) in groups 1 and 2 than groups 3 and 5 (control). On the other hand, No difference (LSD, P > 0.05) was detected between the working length in groups 3 and 4 in comparison with group 5 (control).
Conclusion: The electronic apex locator and the cone-beam computed tomography are more accurate techniques to determine root canal's working length than the normal and the 2D digital radiographs.
Keywords: apex locator, cone-beam computed tomography, digital radiography, working length
|How to cite this article:|
Elshinawy MI. In-vitro comparison of four different working length determination techniques. Tanta Dent J 2017;14:12-6
| Introduction|| |
Precise working length determination is a determinant factor for successful endodontic treatment . The most commonly used methods for working length determination are radiography and electronic apex locators (EALs). However, conventional radiographic method has the disadvantages of anatomical structures overlapping, incoincidence of apical foramen with the radiographic apex in most of the cases and the long time taken for film processing ,. On the other hand, 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 ,. Nevertheless, no conclusive results about the better efficiency of digital radiographic method over the conventional method for working length determination has been encountered in the literature .
EALs have been used to locate the apical constriction without patient exposure to irradiation to get the working length, however they are still used adjunctively to the radiographic methods ,,. Attempts to validate EAL working length measurements, showed unreliable and widely variable results ,. Most recently, cone-beam computed tomography (CBCT) imaging showed the ability to locate the apical foramen and give a 3D view of root canal anatomy. Whenever CBCT scans are prescribed for diagnosis and treatment planning, it is more advantageous to use all the available information that can be given by the image manipulation and editing program ,.
Therefore, the purpose of this in-vitro study was to compare four different working length determination techniques. The null hypothesis was that, all the tested techniques 'regular radiograph, digital radiograph, CBCT and the apex locator' are of comparable accuracy in root canal working length determination.
| Materials and Methods|| |
Fifty extracted single-canaled anterior teeth were collected from patients with periodontal problems upon their written agreement and following the ethical approval of the scientific and research committee, College of Dentistry, King Khalid University. The collected teeth were mechanically cleaned up to remove both hard and soft deposits and stored in physiologic saline solution before decoronation to a flat cut surface to standardize the reference point for all test specimens.
The working lengths of the same roots were repetitively determined in five groups (n = 50 each) according to the used technique. In group 1, the working length was measured from a preoperative normal radiograph obtained on E speed X-ray film (Kodak, Rochester, New York, USA) using Sirona dental X-ray unit (Sirona Dental Systems GmbH, Bensheim, Germany) operating at 70 kVp and 0.8 mA according to manufacturer protocols. All films were processed using XR-24 NDT automatic X-ray film processor for 6 min in Kodak Dental Readymatic processing solutions (Kodak). The working length of each root canal was then calculated by subtracting 0.5 mm out of the length measured starting from the reference point to the radiographic apex. In group 2, direct 2D digital images were obtained using the previously used X-ray unit together with digital sensor (Carestream Health Inc., Rochester, New York, USA). The captured image was digitally enhanced for better visualization and the working length was measured using the ruler tool of the proprietary software. The paralleling technique was used for radiography acquisition in groups 1 and 2 with the help of the extension cone paralleling Rinn XCP instruments (Dentsply International, York, Pennsylvania, USA) in an action to standardize the position of either X-ray film or digital sensor ([Figure 1]). The verification of the correct file tip position in relation to the radiographic apex was the done for each specimen ([Figure 2]).
|Figure 1: Rinn XCP instruments used for both normal (left) and 2-D digital (right) radiographs' standardization.|
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|Figure 2: (a) Normal periapical W. L. radiographs: (b) 2-D direct digital W. L. radiographs.|
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In group 3, CBCT images of the specimens were captured with Cranex 3D imaging system (SOREDEX, Tuusula, Finland) operating at 90 KVp, 10 mA using 60 × 78 mm field of view and an exposure time of 17.6 s. The CBCT images were manipulated using the system's proprietary software and displayed in a modified sagittal view . The modification was obtained by adjusting the axis of the sagittal view image to allow vision of the entire root canal anatomy starting from its coronal orifice to apical foramen. Using the ruler tool, the working length was then measured from the reference point to 0.5 mm from the root apex ([Figure 3]). The working lengths of root canals were determined in group 4 using the EAL (Tri-Auto Zx; J. Morita, Irvine, California, USA). All specimens were remounted in a specially designed in-vitro models ([Figure 4]). Each model was designed to accommodate 10 roots in a freshly prepared alginate impression in which the lip-hook electrode of the apex locator was inserted. The other electrode was attached to the file that introduced into the root canals till the light signal indicated that the file tip was 0.5 mm from the apex. The rubber stopper was then adjusted to rest on the reference point of each specimen before taking the file out and measuring the working length to the nearest 0.5 mm using an endo ruler (FileMate Measuring Block; Dentsply Maillefer, Ballaigues, Switzerland). In group 5 (control) the working lengths of the same 50 specimens were established by introducing # 15 k-file (Dentsply International) into root canals until it became visible at the apical foramen. The rubber stoppers were then adjusted to the reference point. The file was then withdrawn and the length from its tip to the stopper was measured using the endo ruler (FileMate Measuring Block; Dentsply Maillefer). The exact working lengths were determined by subtracting 0.5 mm from the obtained measurements.
The collected data was subjected to a statistical analysis on IBM SPSS statistics for Windows, version 21.0 (IBM Corp., Armonk, New York, USA). Both one-way analysis of variance and the least significant difference (LSD) comparisons at P value less than or equal to 0.5 were used to state the significance of any differences detected between study groups.
| Results|| |
The mean and SDs of root canals' working lengths in all groups were listed in [Table 1]. The one-way analysis of variance indicated a difference among the tested groups (P = 0.011). On the other hand, further LSD comparisons ([Table 2]) indicated no differences (P > 0.05) between the measurements of groups 3 and 4 in comparison with those of group 5 (control), while the measurements of groups 1 and 2 were longer (P ≤ 0.05) than those of both the control (group 5) and CBCT (group 3) groups. In addition, the measurements obtained by the apex locator (group 4) were not different from any of the other tested groups (LSD, P > 0.05).
|Table 2: Least significant difference comparisons between different groups|
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| Discussion|| |
The success of endodontic treatment depends mainly on thorough and efficient chemomechanical debridement of the root canal system. Precise working length determination is an essential part of this procedure as it determines the most apical extension to which canal debridement and obturation should end ,. Usually, damaging the apical constriction leads to periapical tissue breakdown and subsequently overextended obturation, while ending of the root canal instrumentation 0.5–1 mm short of the anatomical apex promotes apical healing ,.
Because none of the known methods for working length determination was proved to be perfect, this study was conducted to compare the accuracy of some of the available working length determination techniques aiming to discover the most reliable one. Although, the conventional radiographic method has the major disadvantages of superimposition of anatomical structures and the difficulty observing buccolingual root curvature ,, it was utilized in this study for its popularity. On the other hand, the digital radiographic methods offer speedy capture and image editing possibility with less radiation dose ,. Recently, the electronic working length determination method became popular ,and the Tri-Auto ZX EAL was included in this in-vitro study due its known high precision and reliability in root canal's working length measurements ,. Among the various media used for in-vitro working length determination using EALs, the alginate model was selected because of its firm consistency, good electroconductivity, and ease of preparation . This in-vitro model gave the chance for fixing and testing large number of teeth in a convenient time, however it does not fully simulate the real in-vivo environment . The currently available, CBCT imaging shows the potential of apical foramen location and 3D root canal anatomy display ,.
The results of this study showed no significant difference between the measurements done using CBCT (group 3), apex locator (group 4) and the control (group 5). At the same time, CBCT group showed more accurate results than the normal and 2D digital radiograph groups. One study  indicated that the lateral location of the apical foramen in up to 93% of cases might contribute to the overestimated working length measurements encountered with both normal and 2D digital radiographic methods. Because of the 2D nature of both techniques, this lateral location might be short of the radiographic apex in a position not identifiable in either of them. In addition, radiographic magnification might also be a reason for the overestimated measurements determined by both techniques. This magnification also increases with the increase of the distance between the tooth and the film or digital sensor . This point of view was supported by Burger et al. , who reported overestimated root canals' lengths measured in vitro using 2D digital radiographic methods in comparison with the actual ones. The accurate measurements of the modified sagittal view of the CBCT technique evaluated in this study seem promising because some of the teeth scheduled for endodontic treatment might appear in that field of view of CBCT taken for diagnostic purposes. In such situations, these images can be efficiently enough to measure the working length of all teeth present in that field of view with no need for further radiographic exposure. This finding was supported by a previous one  that indicated the possibility of using the 3D CBCT, if available, for more accurate measurements of root canal lengths of curved roots than 2D measurements.
The results of this study came also in agreement with the findings of previous studies that demonstrated accurate working length determination to within 0.5 mm of the apical foramen with the use of EALs ,,,,,,. In addition, El-Ayouti et al.  reported that the conventional radiographic method showed overestimated working length measurements in 56% of the examined teeth, while this ratio was found to be only 21% when apex locator was used. Moreover, Fouad and Lester  and Orosco et al. , stated that the quality of final obturation length was improved with electronic estimation of working length in comparison with that estimated through radiographic images.
In response to the findings of this in-vitro study, further clinical evaluation of the CBCT technique is recommended to stand on its reliability in working length determination during endodontic procedures.
| Conclusion|| |
Under the circumstances of the current study it can be concluded that, the EAL and the CBCT are more accurate techniques to determine root canal's working length than the normal and the 2D digital radiographs.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]