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 Table of Contents  
SYSTEMATIC REVIEW
Year : 2014  |  Volume : 5  |  Issue : 3  |  Page : 84-97

Electronic apex locator: A comprehensive literature review - Part I: Different generations, comparison with other techniques and different usages


1 Dental Students' Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran
2 Department of Research, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran
3 Department of Endodontics, Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran

Date of Web Publication15-Jul-2014

Correspondence Address:
Hamid Razavian
Department of Endodontics, School of Dentistry, Isfahan University of Medical Sciences, Hezar Jerib St, Isfahan-81746-73461
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2155-8213.136744

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  Abstract 

Introduction: To compare electronic apex locators (EAL) with others root canal determination techniques and evaluate other usage of this devices. Materials and Methods: "Tooth apex," "Dental instrument," "Odontometry," "Electronic medical," and "Electronic apex locator" were searched as primary identifiers via Medline/PubMed, Cochrane library, and Scopus data base up to 30 July 2013. Original articles that fulfilled the inclusion criteria were selected and reviewed. Results: Out of 402 relevant studies, 183 were selected based on the inclusion criteria. In this part, 108 studies are presented. Under the same conditions, no significant differences could be seen between different EALs of one generation. The application of EALs can result in lower patient radiation exposure, exact diagnosing of fractures, less perforation, and better retreatment. Conclusions: EALs were more accurate than other techniques in root canal length determination.

Keywords: Dental instrument, electronic apex locator, electronic medical, odontometry, tooth apex


How to cite this article:
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

How to cite this URL:
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 [serial online] 2014 [cited 2017 Mar 25];5:84-97. Available from: http://www.dentalhypotheses.com/text.asp?2014/5/3/84/136744


  Introduction Top


Ideal pulp treatment is defined as the removal of infected pulp and cleaning, shaping, and disinfecting the root canal system. [1] Subsequently, a three-dimensional filling can be provided. To achieve this goal, an essential stage is the assessment of the correct length of the root canals. [1],[2]

Working length is defined as the distance between the coronal/incisal reference point and the area that has been prepared and at which the filled canal should end. [1] Commonly, the minor apical foramen or apical isthmus is considered the end of the area for canal preparation and filling. The minor apical foramen is the border line between the dental pulp and periodontal area, which is approximately 0.5-1 mm from the anatomic apex. [1],[3] Failure to determine the root canal length can result in both over- and underestimation of the root canal length. Overestimated working length can result in preparation beyond the apical isthmus, which can damage the peri-apical region. [4] Underestimated working length and inadequate debridement can cause unsuccessful treatment and dissatisfaction of both the patient and dentist. [5] Due to the pivotal role of working length determinations in root canal therapy, several methods have been introduced as follows.

A: Tactile sensation and using the mean canal length and the application of paper cones are examples of experimental methods that are used by some clinicians due to their simplicity and relative efficiency. [6] These techniques can be inaccurate in some patients, however, due to open apex teeth and apical curvature. [6]

B: Radiography is a common method for determining the apical isthmus, which is 0.5-1 mm shorter than radiographic apex. [2] The radiographic method has its advantages, such as direct observation of the root canal system and the canal curvature and of the existence of peri-apical lesions, [2] but radiography cannot determine the apical isthmus, because it provides a two-dimensional picture of a three-dimensional object. [2],[7] In addition, a disadvantage of radiation is that it can be dangerous to both patients and dental staff.

C: Owing to the advantages of electronic apex locators (EAL), such as the elimination of radiographic obstacles and EAL's accuracy and convenience, the application of EAL has developed. [3],[8] The principal design and development of the early apex locators dates back to Suzuki (1942) [9] whom investigated on dogs and found out that the electrical resistance between the periodontal membrane and the oral mucosa was a constant value. This point was introduced into clinical practice by Sunada [10] (1962) which almost measured the electrical resistance between oral mucosa and periodontal ligament.

Over the last decade, different versions of EAL have been released. [Table 1] shows and compares the different versions of these devices, based on the functions of each generation. The aim of the present study was to investigate and compare the accuracy of EALs in determining the working length through root canal therapy.
Table 1: Different generations of electrical apex locator devices and their operation base[86]

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  Materials and Methods Top


Search strategy

Electronic searches were performed using "tooth apex," "dental instrument," "odontometry," "electronic medical," and "electronic apex locator" as keywords. Moreover, cross-references were screened to identify further study that probably missed through the search strategy.

Electronic databases

Electronic searches were performed in Medline/PubMed, Cochrane library, and Scopus data base up to 30 July 2013. Four hundred and two articles were found.

Inclusion criteria

The inclusion criteria were articles, clinical trials in humans and cohort and case-control studies in the English language only. Systematic reviews, case reports, letter to editors, editorials, and congress abstracts were excluded. The title and abstract of each article were reviewed by three of the authors (HM, AV, and FZ), and articles that fulfilled the inclusion criteria were selected.

Data extraction

Extraction of data from studies and assessment of validity was independently performed by two authors (HM and AV) and checked by a third author (FZ). In the case of disagreement between evaluators, it reassessed by discussion between two reviewers and a final consensus was agreed on (HR and SKh). [Figure 1] provides information on the number of papers identified through the search strategy. Information of the authors, their institutions, and result of primary studies were removed before assessment of the validity. Information on the first author, year of publication, study design, study population and sample size, and the outcome measurements (main results) were extracted.
Figure 1: Flow chart of selected articles

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  Results Top


Out of 402 articles, 183 studies were reviewed and 108 studies were selected for this part. The studies were categorized as follows.

Comparison of different EALs

In this part of the present study, 38 articles, consisting of 14 in vitro, [11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24] 9 ex vivo,[25],[26],[27],[28],[29],[30],[31],[32],[33] and 15 in vivo studies [34],[35],[36],[37],[38],[39],[40],[41],[42],[43],[44],[45],[46],[47],[48] were reviewed. Of the in vitro studies, four articles did not report significant differences between various devices [12],[13],[16],[19] [Table 2]. All of the ex vivo studies showed significant differences between different devices, except for the study by Comin Chiaramonti et al. [31] and Baginska et al.[32] [Table 2]. Among the in vivo studies, Welk et al.[34] and Arora et al.[47] found a significant difference between EALs [Table 2].
Table 2: Comparison of different electronic apex locators (EALs) in working length determination

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Comparison of EALs with different working length determination methods

Thirty-one studies evaluated different methods of working length determination. Among these studies, eleven compared different EALs and conventional and digital radiography as three different methods of working length determination. [7],[35],[36],[37],[38],[39],[40],[41],[42],[43],[44],[45],[46],[49],[50],[51],[52],[53],[54],[55],[56],[57],[58],[59] Among the studies that compared EALs to radiographic method, six studies did not report any significant differences, [7],[35],[36],[43],[53],[54] three studies concluded that radiography method was more accurate, [49],[55],[59] and the remainder reported greater accuracy with the EAL [Table 3]. Three studies that compared digital radiography to EAL showed that EAL was more accurate [37],[54],[60] [Table 3]. Shanmugaraj et al.[6] compared three methods of measuring root canal length (apex locator, radiography, tactile sense) and reported that EAL was the most reliable method, but Ounsi et al. [61] showed that EAL and radiography method have same accuracy and significantly were more accurate than tactile method. In the study by Subramaniam et al.[62] , there were no significant differences among conventional radiography, digital radiography, and tactile sense in primary teeth. Janner et al. [63] compared cone beam computed tomography to EAL in root canal length determination and concluded that both two methods were comparable [Table 3].
Table 3: Comparison of electronic apex locators (EALs) and different other techniques in working length
determination


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Use of EAL in root perforations, fractures, and apical foramen widening

Ten studies reported other uses of EALs, such as identification of root perforation sites and the location of horizontal and vertical fractures. EALs were only accurate in horizontal fracture diagnosis [64],[65] although Topez et al. [66] reported that EALs were accurate in both vertical and horizontal root fractures. Furthermore, Goldberg et al. [67] studied the consistency of EALs in teeth with simulated horizontal root fractures, and they showed that EALs were accurate and consistent. Several studies showed that EALs were able to detect perforation sites [Table 4]. [68],[69],[70],[71] There were five studies that evaluated EALs' ability to control apical foramen widening with rotary files, and they both concluded that use of EALs in root canals that were prepared with rotary instruments was not sufficiently accurate to control apical extensions. [72],[73],[74],[75] Hoer et al. [76] evaluated the ability of the Justy II and Endy 5000 devices in determining the canal length of 79 teeth (93 canals). They showed that these devices can specify the sites of the minor and major apical foramen, but they cannot determine apical constriction with sufficient accuracy. Also, Oishi et al.[77] investigated the accuracy of EALs in determining apical constriction, and they were accurate [Table 4].
Table 4: Other usage of electronic apex locators (EALs)

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Use of EAL in root canal retreatment

Six articles were published on this topic. [78],[79],[80],[81] Two of them evaluated the accuracy of EALs before and after canal filling and showed that, in most cases, EALs were accurate in root canal retreatment. [78],[80] In the study by Aggarwal et al. [80] , the accuracy of Root ZX and Protaper devices was evaluated in the retreatment of filled canals with: 1) gutta-percha+ zinc oxide ogenol sealer; 2) gutta-percha+ AH plus sealer; and 3) Resilon+ Epiphany sealer. Both devices showed high accuracy in the first and second treatments, and no significant differences were reported in the presence of different filling materials. Uzun et al.[79] studied the precision of two apex locators (tri auto ZX TCM, locating handpieces endo apex) in root canal retreatment with root-end-cured teeth evaluated. They demonstrated that both devices could be used for determining apical area, but for root canal retreatment, accuracy of 0.0 mm is required, which these devices could not accomplish [Table 4].

Use of EAL in patients with pacemakers

Wilson et al.[82] investigated the operation of the Endo Analyzer Model 8005 in patients with pacemakers and cardioverter/defibrillator devices. They demonstrated that there was no interference between the apex locator and pacemaker function.


  Discussion Top


Different generations of EALs, with improved functions and greater clinical applications, have entered the market over these past few decades. Our results indicate that there are no significant differences between different EALs of the same generation. The first generation apex locator was supplied by single frequency of direct current in order to measurement of electrical resistance. Pain and discomfort were often felt with using this type of apex locator. [83] The second generation apex locator known as impedance apex locators was measured opposition to the flow of alternating current or impedance. [84] The disadvantage of this generation is that electro-conductive materials in canal affect on its accuracy. [83] The third generation apex locator (frequency dependent apex locators) was supplied by two frequencies to measure the impedance in the canal. The disadvantage of this generation sensitivity to canal fluid and the machine needs a fully charged battery. [85] The fourth generation apex locator measures the impedance characteristics using more than two frequencies. [3] The disadvantage includes needing to perform in relatively dry or in partially dried canals. [84] The fifth generation apex locator was developed in 2003 which measure the capacitance and resistance of the circuit separately. [86]

Many studies compared the ability of various generations of EALs in determining root canal length. Most of these studies showed that EALs were accurate for canal length measurement, within a clinically acceptable range of ± 0.5. Some studies indicated that the most recent generation of these devices had enhanced accuracy, better patient acceptance and greater ease of use for dentists. [31],[87],[88] but other studies mentioned that some EALs of the third generation were more accurate than those of the fourth generation. [20],[27],[28]

Although most of the previous studies reported that EALs were more accurate, compared to radiography, some of the studies noted no significant differences between the two methods due to small sample sizes. However, a recent randomized, controlled clinical trial study showed no significant differences between these two methods. [2] To consider the advantages of conventional radiography, such as the ability to observe the root canal system and the canal curvature directly and to determine the existence of peri-apical lesions, the decision of which method to use should be different in each case. It should be noted that EALs could decrease the patient's radiation exposure. [42],[51]

There is controversy in the diagnosis of the horizontal and vertical root fractures by EALs. Some studies have reported that EALs have the capacity to diagnose horizontal and lateral root fractures, [66],[67] and others studies have indicated that horizontal fractures and perforation sites can be better diagnosed by EALs than vertical fractures. [64],[65] Few studies have investigated the ability of apex locators to detect root fractures and perforations. Due to limited information on this subject, a general conclusion could not be achieved. More studies are required on this subject.

The present review has some limitations. First, only relevant articles were searched in Medline/PubMed, Cochrane library, and Scopus, which might have restricted the results. Second, our keywords were limited to "Tooth apex," "Dental instrument," "Odontometry," "Electronic medical," and "Electronic apex locator" to focus on EALs. More prospective, randomized clinical trials are needed to determine various conditions that affect EALs' accuracy.


  Conclusion Top


The results of the present study showed that EAL is an appropriate technique for root canal length measurements. [118]

 
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