Comparison of Accuracy and Reliability of Working Length Determination Using Cone Beam Computed Tomography and Electronic Apex Locator: A Systematic Review

INTRODUCTION

Clinicians generally agree that the successful endodontic treatment is dependent on the complete removal of diseased pulpal tissues and the total sealing of the root canal system^1,2 and reliable determination of the root canal working length (WL).^2,3 Accuracy is the degree to which a measurement conforms to the correct value, and reliability is the ability to repeatedly obtain precise measurements. Until the introduction of contemporary methods such as the electronic apex locators (EALs) and cone beam computed tomography (CBCT), WL determination was traditionally achieved through conventional radiography.³

According to Pratten and McDonald, the ideal end point of instrumentation is the cementodentinal junction, which is defined as the beginning of the periodontal ligament and the end of the pulpal tissue.^4,5 Its location varies between 0.50 and 0.75 millimeters (mm) coronal from the true anatomical foramen of the root canal. In accordance with these average measurements and higher rates of clinical success, clinicians have attempted to terminate their instrumentation 1–2 mm coronal to the radiographic apex.^2,4–6

Conventional radiographic determination in conjunction with tactile sensation can be limited by anatomic variation and errors in projection; CBCT may overcome some of these problems.^2,4 Cone beam computed tomography produces three-dimensional images using divergent X-rays that form a cone and allow for increased image quality with decreased distortion, magnification, and superimposition of the targeted structures.⁷ As a result, CBCT is being considered for several novel applications in endodontics including WL determination.⁸ The Joint American Association of Endodontists/American Academy of Oral and Maxillofacial Radiology (AAE/AAOMR) recommend the of use the smallest possible voxel size and field of view (FOV) in their position statement on CBCT.⁹ Aktan et al. determined that voxel size between 0.5 and 1 mm allowed reliable endodontic length measurement.¹⁰ The higher radiation dosage of CBCT compared to conventional radiography limits its routine use. In particular, the as low as reasonably practicable (ALARP) principle often precludes the use of CBCT except in situations where it is of exceptional diagnostic value.¹¹

Electronic apex locators determine the location of the major foramen by measuring resistance to electric current and are useful in determining the WL in more than 90% of cases.⁵ However, factors such as intact vital tissue, inflammatory exudate, canal patency, metallic restorations, size of apical constriction, and cardiac pacemakers may affect the electrical current of the EAL and consequently the accuracy and reliability of the readings.⁵

The purpose of this systematic review was to screen and analyze the literature comparing CBCT with EAL in order to establish which is more accurate and reliable in determining the WL of permanent teeth of adults. This review question was developed according to the population, intervention, comparison, outcome, and study design (PICOS) format. To the best of the authors’ knowledge, no previous attempts have been made to review the available literature for this purpose.

REVIEW PROPER

This review was registered in PROSPERO under number 2017:CRD42017056345. The review protocol was published as part of the proposal and in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. This review was designed to answer the following research question: Which is more accurate and reliable in determining WL, CBCT or EAL?

REVIEW RESULTS

The initial search from the databases produced 4,361 articles, with an additional 55 articles sourced from gray literature. After duplicates were removed, 1,358 articles remained. Of these studies, all but 129 were excluded based on titles. Six articles met the inclusion criteria upon abstract screening. On full-text assessment, one study was excluded as it did not include CBCT as a method of measurement and thus failed to meet the inclusion criteria.¹⁶ Reference lists from the eligible articles were manually searched with no additional relevant studies found. A total of five studies were selected (Flowchart 1).

DISCUSSION

Accurate WL determination is required to achieve total removal of the pulpal tissue and complete sealing of the canals, ensuring successful endodontic outcomes for the patient.^1,2 Currently, EAL with adjunctive IOPA radiography is the preferred method of WL determination.⁴ This systematic review was conducted to assess whether CBCT is able to determine WL more accurately and reliably than EAL based on the current literature. Overall, there was a lack of evidence and a lack of high-quality evidence. As such, it was not possible to conclude which measurement technique was more accurate or reliable.

All included studies demonstrated that measurements based on CBCT were not significantly different to those taken with EAL.^{13,14,17–19} As electronic measurements are currently considered a clinically acceptable means of determining WL,⁵ these findings suggested that CBCT is at least as accurate as EAL. The clinical accuracy of either method cannot be established.

In most cases, the WL will have been already determined prior to the prescription of CBCT. However, the authors of four studies suggested that CBCT may be used for WL determination when there is a preexisting CBCT scan available.^14,17–19 Acquiring a new CBCT specifically for endodontic treatment is not advised due to costs and the high level of radiation exposure to the patient.^13,14 Ustun et al. suggested that prior to using a preexisting CBCT, clinicians should ensure that there have been no pathological changes. For example, external root resorption may result in a change to the reference point, root or root canal length.¹⁸

The eligible studies elicited less evidence for reliability when compared to accuracy. Studies by Jeger et al., Janner et al., and Ustun et al. suggested that CBCT was reliable but did not consider EAL reliability.^17–19 Existing literature and the widespread clinical application of EAL suggests that it is reliable; however, this cannot be confirmed within the boundaries of this review.²⁰ No definitive conclusion can be drawn with respect to which method is more reliable.

LIMITATIONS

All studies included in this review had various flaws affecting their validity and reliability. Being in vivo in design, the included studies could not elicit the superiority of one measurement technique, despite their greater clinical relevance. All studies were likely underpowered due to small sample sizes and thus susceptible to type II error.²¹ Therefore, the failure of all eligible studies to detect a significant difference between measurement methods should be interpreted with caution.^{13,14,17–19}

All studies were assessed to be either well-conducted or moderately well-conducted with some flaws. As seen in Table 2, all studies had major inadequacies in their statistical analysis. All studies used the correlation coefficient to compare CBCT and EAL. However, differences between clinical measurement methods are more appropriately evaluated using a Bland–Altman plot.²² Sample selection was generally well-described; however, two studies were assigned at least one major or minor flaw for sample selection.^13,17 Three of the study protocols failed to randomize the order of measurement methods.^14,18,19 The effect of this is unknown but may have increased bias. Jeger et al. was the only study to comprehensively describe CBCT, EAL, and repeat measurement techniques.¹⁷ Three studies described repeated measurements, enhancing data reliability.^17–19

The primary limitation of this review was its comparison of studies with variable sample sizes, equipment brands, inclusion criteria, and outcome measurement methods. Furthermore, various CBCT slices were used to obtain WL, reducing the inter-study comparability. Additionally, three studies failed to specify voxel size, potentially resulting in different spatial resolutions across studies. This review was restricted to comparing the accuracy and reliability of CBCT and EAL. As such, other, potentially more accurate methods of WL determination such as conventional radiography were not considered.

The accuracy and reliability of CBCT WL determination demands further enquiry. It is recommended that prospective researchers complete a power analysis to acquire an adequate sample size. Further research is required to evaluate the clinical utility of CBCT in WL determination. Future studies would also benefit from investigation into voxel size, jaw type, tooth type, canal number, and morphology and their effects on WL measurement.

It may also be beneficial to compare the outcomes of RCT based on the method of WL determination used. Teeth that have undergone occlusal shortening after the CBCT scan also require investigation, as this may alter the reference point and in turn affect WL.¹⁷ It is also recommended that teeth with metallic restorations are studied in detail to determine the most effective method of establishing their WL. Metallic restorations can reduce the accuracy of CBCT through scatter and EAL through electrical short-circuiting.^13,18

Finally, a combined in vivo and ex vivo study on patients with preexisting CBCTs would be beneficial. This could involve measuring WL in vivo using CBCT and EAL, extracting the hopeless tooth and establishing actual WL ex vivo. While such a study would require ethical consideration, it would allow actual WL to be measured as the control for accuracy and reliability comparisons.

CONCLUSION

Due to significant heterogeneity between the included studies, the accuracy of CBCT compared to EAL in WL determination could not be determined. However, based on the limited evidence available, CBCT appeared to be at least as accurate as EAL in determining WL. Consequently, WL determination using a preexisting CBCT scan may be a clinically appropriate method.^14,17–19 Despite this, there was inadequate evidence to justify acquisition of a new CBCT specifically for endodontic treatment due to cost and radiation exposure.¹⁶ While preexisting scans are beneficial for WL determination, the ALARP principle should guide referral for new CBCT acquisition. There was a lack of high-level evidence comparing the reliability of CBCT with EAL. However, the eligible studies generally suggested that CBCT was reliable. These results should be interpreted judiciously. Further research is required to conclusively evaluate the accuracy and reliability of CBCT compared with EAL.

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