A comparative evaluation of accuracy of three electronic apex locators using histological section as gold standard: An ex vivo study.

INTRODUCTION: The aim of the present study was to comparatively evaluate the accuracy of iRoot, iPex II, and Propex pixi apex locator using histological sections as the gold standard.
MATERIALS AND METHODS: Thirty patients indicated for extraction of single-rooted permanent teeth with single canal system were selected. Working lengths (WLs) of teeth were determined using iRoot, iPex II, and Propex pixi. Teeth were then extracted, and the files were reintroduced to the anatomic apex to measure anatomic canal length (ACL) and fixed at the ACL using flowable composite. The apical 4 mm of the roots were longitudinally shaved away to visualize the canal under a stereomicroscope at ×24 magnification. Digital photographs were evaluated to measure the distance between the major diameter and minor diameter. Thus, the WL, that is, the minor diameter length (MDL) was ascertained.
RESULTS: Measurements of mean WLs within ±0.5 mm of minor diameter were 90% acceptable for iRoot, 86.66% for iPex II, and 80% for Propex pixi when compared with mean MDL as obtained from the histological sections.
CONCLUSIONS: All apex locators have been shown to produce acceptable level of accuracy which clearly indicates their reliability in determining the WL.

INTRODUCTION

The goal of root canal treatment is to control infection through thorough debridement, disinfection, and obturation of the root canal system.[1] It may be emphasized that these treatment procedures should be limited to within the confines of the root canal.[2] A working length (WL) that extends beyond the minor diameter may cause periapical inflammation, postoperative pain, and delayed healing. On the other hand, a WL that is too short may result in inadequate debridement, and the retained infected tissue may lead to postoperative pain and may, in turn, compromise the healing process.[3]

Minor diameter which is the narrowest diameter with least blood supply and innervation is considered to be the appropriate apical limit of endodontic treatment. Terminating endodontic procedure at this point causes a negligible wound and minimal contact of the obturating material with the periradicular tissue ensuring an excellent healing potential.[4]

Clinically, WL can be established by tactile sensation, radiography, or more recently, through the use of electronic apex locator (EAL) devices.

Anatomical variations in the size and location of the apical constriction may result in the tactile sensation being largely unreliable in assessing WL.

Radiographs have traditionally been routinely used method for determining WL; however, the reliability of radiographs may be compromised because they are technique sensitive, are subject to observer interpretation[5] and provide a two-dimensional image of the three-dimensional object. The results obtained may also be affected by the overlapping of various anatomic structures.[6] Owing to these shortcomings, electronic methods for root length determination have been developed to serve as an effective alternative as well as an adjunctive diagnostic tool.

According to manufactures, the modern electronic devices are able to precisely locate the point of maximum root canal narrowing. In this context, a number of studies have been conducted in recent years[7-9] to determine the accuracy of these devices. The purpose of the present study was to evaluate the accuracy of three EALs, that is, IRoot (E-Magic Finder) (S-Denti Seoul, South Korea), iPex II (NSK, Tokyo, Japan), and Propex pixi (Dentsply Maillefer, Ballaigues, Switzerland) in determining the location of the minor diameter.

MATERIALS AND METHODS

Thirty adult patients visiting the department of oral and maxillofacial surgery for extraction of periodontally involved single-rooted permanent teeth with completely formed apices and single canals were selected on the basis of the diagnostic radiograph. Teeth with internal and external resorption, canal obliteration, root perforation, pregnant women, and patients with pacemakers were excluded from this study. This research protocol was approved by the institutional Ethical Board. The detailed procedure was explained to each patient, and an informed written consent was obtained from each patient before the study.

Local anesthesia was administered (2% Lignocaine with 1:1,00,000 epinephrine) (Lignospan® standard, Septodont inc, USA) and the teeth involved were isolated using rubber dam. The standardized access cavity preparation was done followed by coronal flaring using Gates Glidden drills sequentially from size 4 to size 2 (Dentsply Maillefer, Ballaigues, Switzerland) in a step-down fashion. The canals were irrigated with 5 ml of 2.5% sodium hypochlorite, the pulpal remnants/debris was removed from the canals; and the canal patency was evaluated using size 10/15 K-flexofile (Dentsply Maillefer, Ballaigues, Switzerland).

WL of each tooth was measured using all the three apex locators, that is, iRoot, iPex II, and Propex pixi in random order. Each apex locator was used according to manufacturer's instructions for detecting the minor diameter. The “0.5” mark on the LCD indicated minor diameter for all the three apex locators. The endodontic file was advanced up to the “apex” mark followed by retraction till “0.5” mark was visible on the display screen. The stopper of the file was adjusted at this length. The file was then withdrawn, and the length was measured using digital caliper (Mitutoyo, Kawasaki, Kanakawa, Japan). The readings were designated as the EAL reading EALIR (iRoot), EALIP (iPex II), and EALPP (Propex pixi).

The teeth were then extracted, and the files were reintroduced up to the anatomic apex as observed under dental operating microscope at a magnification of 10X (Apex microscopes, Chippenham, UK), and this canal length was measured and designated as the anatomic canal length (ACL). The files were now fixed at ACL using flowable composite (Prime-Dent Light Cure Flowable Composite, Chicago, IL, USA), and the apical 4 mm of the roots were longitudinally shaved away using a fine diamond disc (Dentsply Raintree Essix manufactures, Sarasota, Florida) until the outline of the canal was visible under a stereomicroscope (Carl Zeiss, Jena, Germany) at ×24 magnification. A digital photograph was taken for each tooth. On each digital photograph, the location of the minor diameter and major diameter was determined by two observers simultaneously [Figure 1]. Distance from major diameter to minor diameter was calculated in millimeter on each digital image using Axiovision AC software (Carl Zeiss, Jena, Germany). Thus, the WL, that is, the minor diameter length (MDL) was measured by the formula given below.

Figure 1

Stereomicroscopic view of apical 4 mm of root apex showing (a) minor diameter, (b) cementodentinal junction, and (c) major diameter

MDL = ACL– distance from major diameter to minor diameter.

Statistical analysis

Data obtained were statistically analyzed using SPSS version 21 (SPSS Inc, Chicago, IL). Means and standard deviation were calculated for measurements. Mean values of WLs obtained from the three apex locators (iRoot, iPex II and Propex pixi), and MDL were compared using paired t-test. The P ≤ 0.05 was accepted as statistically significant.

RESULTS

Following results [Tables 1 and 2] were obtained:

Table 1

Mean working lengths measured (mm)

Table 2

Comparison of mean working length with mean minor diameter length, accuracy of individual device within±0.5 mm range, accuracy with 0.5 mm short of minor diameter, number of times working length coinciding minor diameter length, accuracy with 0.5 mm beyond the minor diameter

The mean distance of the minor diameter to the major foramen was found to be 0.51 ± 0.09 mm

iRoot showed the highest correlation with MDL followed by iPexII and Propex pixi. However, the difference in the mean values of MDL, iRoot, iPex II, and Propex pixi was found to be statistically significant (P < 0.05)

No significant difference was found between the mean values obtained from the three apex locators (P > 0.05).

DISCUSSION

The establishment and maintenance of the apical limit of instrumentation is undoubtedly an important determinant of successful cleaning and shaping procedure of root canal system. An accurate WL contributes to a safe and effective instrumentation ensuring long-term success of root canal treatment. There is vast literature supporting the minor diameter to be the ideal location for the apical limit of instrumentation.[1011] The present study determined the mean distance between major and minor diameter in the range of 0.51 ± 0.09 mm which is in accordance with the study by Kuttler et al.[12] and Tselnik et al.[13] who stated that the minor diameter lies 0.5–1 mm short of the major foramen.

Various studies conducted to evaluate the accuracy of EALs differ in determining the apical termination position. Some researchers prefer to measure the WLs up to the minor diameter,[1415] whereas others measure it up to the major foramen.[1617] The aim of this study was to determine the location of the minor diameter considering it to be the most suitable point for apical termination of root canal preparation.[4] Of the devices used in this study, iRoot showed highest correlation with MDL followed by iPexII and Propex pixi.

The results of the present study are in accordance with various previously conducted studies.[391318] Cimilli et al. conducted an ex vivo study to assess the accuracy of Root ZX II, ATR EndoPlus, Raypex 5, and Propex EALs for determining the location of the minor diameter.[18] The percentage of measurements within ±0.5 mm of the reference canal length was 82.5% for the Root ZX II and the ATR EndoPlus, and 85% for Raypex 5 and Propex. In the present study, the accuracy of determination of the MDL was 90% within ±0.5 mm of the minor diameter in contrast to iPexII and Propex pixi which reached 86.66% and 80% level of accuracy, respectively. It has been observed from previously conducted studies that measurements within the ±0.5 mm limit are acceptable in clinical practice.[14]

Single-rooted teeth with straight and wide canals were used in this study to minimize problems presented by a more complicated canal anatomy. The presence of electrolytes, differences in canal diameter, technical differences between microscopes, and variation among EALs are important factors which may influence the results of the study.[8171920] Herrera et al.[21] found that the EAL measurements were more accurate when the foramen diameter was 0.25 mm than when it was between 0.45 and 0.70 mm. Keeping this in consideration, the teeth with a small diameter in which 10/15 files could pass through the foramen were selected for standardization. Irrigation was performed using a 2.5% sodium hypochlorite solution, which is in agreement to literature stating that irrigating solutions have little influence on the accuracy of modern EALs.[82022]

The histological section of each canal is considered to be the gold standard for such studies. Sectioning of tooth provides an unobstructed view of the file tip in relation to the minor diameter and allows direct exact measurement of the distance between major and minor diameter with aided magnification. In the present study, the exact distance between the minor diameter and the major foramen has been determined using histological sections which were viewed under a stereomicroscope at 24X magnification to obtain better viewing clarity and details. The electronic AxioVision AC software was used for measurement to minimize human errors.

CONCLUSIONS

Within the limitations of the present study, all the three EALs (iRoot, iPex II, and Propex pixi) were able to determine the minor diameter within ±0.5 mm with iRoot apex locator presenting most accurate results (90%) followed by iPex II (86.66%) and Propex pixi (80%). This clearly revealed the reliability of these apex locators in determining the WL accurately in clinical situation. Further studies, however, need to be conducted to corroborate the findings of the present study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.