Accuracy evaluation of three electronic apex locators in teeth with immature apices

Bruno Martini Guimarães ^I; Marcelo de Morais Vitoriano ^I; Claudio Maniglia-Ferreira ^II; Fabio de Almeida-Gomes ^II; Marina Angélica Marciano ^I; Clovis Monteiro Bramante ^I; Marco Antonio Hungaro Duarte ^I

^I Department of Endodontics, School of Dentistry of Bauru, University of São Paulo – Bauru – SP – Brazil
^II School of Dentistry, University of Fortaleza – Fortaleza – CE – Brazil

Correspondence

Introduction and Objective: The aim of this randomized controlled study was to evaluate the accuracy of Root ZX, iPex and YS-RZ-A apex locators in tooth with incomplete apices. Material and methods: Thirty human mandibular pre-molars without dental caries, fracture and with 1-3mm apical diameter and ¾ of root development stage were used. After coronal access, tooth length was determined with the visualization of a K-file, compatible with the root canal diameter, at the apex. To determine the root canal length using electronic methods, the teeth were included in alginate. The 30 teeth were measured with the three apex locators until achieving the apex foramen. During the measurement, the canals were inundated with 1% sodium hypochlorite. Statistical analysis was performed using Qui-square test (p < 0.05). Results: The Root ZX apex locator showed the higher accuracy (53.3%), with statistical difference in relation to iPex apex locator (33.3%) and YS-RZ-A apex locator (26.7%) (p < 0.05). Regarding the security limit of ±1 mm, the Root ZX apex locator did not show statistical difference in comparison with iPex apex locator (p > 0.05), but both were statistically different in relation to YS-RZ-A apex locator (p < 0.05). Conclusion: The results showed that all the studied apex locators were efficient in determining the root canal length in tooth with incomplete apex, considering the tolerance of ±1 mm. The Root ZX apex locator showed the highest accuracy with 100% of agreement.

Keywords: odontometry; Endodontics; tooth apex.

Introduction

One of the first phases of endodontic treatment is to determine the working length (WL) which delimitates the instrumentation during chemicalmechanical preparation. By accurately determining this measurement, unpleasant consequences are avoided, among them: formation of steps on root canal walls, improper instrumentation and obturation, root perforation, and symptomatic post-operative period ⁸.

Studies similar to that of Kuttler ¹⁹ indicated the junction of dentin and cementum canal as landmark to limit endodontic treatment, an area so-called dentincementum canal (DCC). Notwithstanding, DCC limit does not precisely locate the apical foramen ⁷.

Many methods have been proposed to determine the working length of root canal from the patient's response to the pain provoked by surpassing the instrument through the apex foramen to the use of either conventional or digital radiographs ²¹.

The radiographic method is the technique most employed in working length determination, and some factors such as angulations, technical variables, interference of anatomic structures, and professional's interpretation may lead to errors ¹². Aiming to help the dentists in determining the apical limits, some devices have been developed to establish the canal length ³.

With the appearance of electronic apex locators (EAL), an auxiliary tool was available in the endodontic armamentarium aiming at the correct odontometry ¹². The search for the reliability of these devices was determinant to develop the third-generation locators ³.

The main advantage of third-generation apical locators is that they detect the apical constriction, which is not possible through radiographs. Moreover, by using the electronic method in WL determination, the patient's exposure to radiation can be reduced because of the smaller number of radiographic shots. Other advantage is the shorter and lower-cost endodontic treatment by optimizing the working time of the dentist ¹⁸.

In teeth with incomplete apices the exact WL determination is indispensable for endodontic treatment success, either apexification or revascularization ²³. Notwithstanding, WL establishment in teeth with incomplete apices is still challenging for endodontic treatment because of the anatomic features of this area ^17,26. Many authors have suggested that when root resorption is present, the use of apical locators is reliable when certain degree of apical tapering exists ^1,11,25.

In light of this, this study aimed to evaluate the in vitro accuracy of three apical locators – Root ZX (J. Morita Corp., Kyoto, Japan), iPex (NSK, Tokyo, Japan), and YS-RZ-A (Baistra, Henan, China) – in teeth with immature apices.

Material and methods

Thirty human single-rooted mandibular premolars, without caries, fracture and with 1-3 mm apical diameter, and at ¾ of root development with incomplete apices were used. All teeth had their extractions correctly indicated due to orthodontic reasons. All patients read and signed a Tooth Donation and Clarified Consent Forms. This study was submitted and approved by the Ethical Committee in Research of the University of Fortaleza (protocol no. #139/2009).

Crown accesses were performed with the aid of round diamond bur (KG Sorensen, Petrópolis, RJ, Brazil) at high speed and Endo Z drill (Dentsply Maillefer, Ballaigues, Switzerland). Irrigation was obtained through 1% sodium hypochlorite, and then, the canal was negotiated with the aid of size #15 K files. The teeth were numbered from 1 to 30 to allow the record of the WL obtained with each electrical apical locator.

Direct tooth measurement was carried out by placing a K file compatible with the root canal diameter, until the file was seen in the apex with the aid of an operating microscope at x40 magnification (DF Vasconcelos M9000, SP, Brazil) (figure 1).

Next, the teeth were placed into glass flasks filled with alginate (Jeltrate-Dentsplay, Petrópolis, RJ, Brazil), so that the crown was visible thus avoiding that the alginate penetrated inside the canal. The labial clamp of EAL was inserted into the alginate. The electronic odontometry was obtained in each canal based on the methodology proposed by et al. ¹⁵. All measurements were executed by a single operator, previously calibrated, to avoid discrepancies. The following apex locators were tested: Root ZX (J. Morita, Kyoto, Japan), iPex (NSK, Tokyo, Japan), and YS-RZ-A (Baistra, Henan, China). The reading of the apical foramen position was performed by introducing the file coupled to EAL inside root canal. The file was slowly moved towards apical direction until each device showed the correspondent sign of apical location (figure 2). Once the zero position was reached by the device, the file was disconnected and measured with the aid of a millimetric endodontic ruler. All canals were filled with 1% sodium hypochlorite during the measurements.

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The data obtained from the three apex locators were classified in scores (accurate or inaccurate), paired in two-column tables, and analyzed by Chi-square test to compare the electronic with the direct measurements (p < 0.05).

Results

The electronic measurements of the 30 teeth are expressed in table 1. A greater coincidence between the direct and electronic measurement was seen with Root ZX locator (53.3%), followed by iPex locator (33.3%), and YS-RZ-A locator, the less accurate (26.7%).

The analysis of the results obtained by the electronic measurements coinciding to the real measurements through Chi-square test showed that Root ZX locator had statistically higher results than did iPex and YS-RZ-A locators; iPex locator results were statistically higher than YR-RZ-A locator results.

Taking into consideration the tolerance limit of ±1 mm, Root ZX locator results were statistically similar to iPex locator result; but these results were statistically significant different from those of YS-RZ-A locator.

Discussion

Concerning to iPex locator, the results pointed out an accuracy of 83.3% inside the tolerance limit of ±1.0 mm. These results corroborate those found by Heidemann et al. ¹³, who reported an accuracy of 90%; and those found by Dandempally et al. ⁵, who reported an accuracy of 90.32%. It is noteworthy to mention that these authors analyzed teeth with complete apices.

As far as we are concerned, no studies on YS-RZ-A apex locator accuracy were found in the literature. In this present study, this apex locator showed an accuracy of 73.3% within the tolerance limit of ± 1.0 mm.

Root Zx and iPex locators did not exhibit statistically significant differences in the study conducted by Heidemann et al. ¹³, proving that iPex locators is as reliable as Root ZX locator, and corroborating the results of this present study.

Moore et al. ²⁴ and Fouad et al. ⁹ affirmed that marked apical foramen openings may result in inaccurate measurements when EAL are used, highlighting the cases of incomplete rhizogenesis or pulp necrosis with periapical lesions involving bone and root resorptions. Frank and Torabinejad ¹⁰ verified that EAL ineffectiveness in determine WL in teeth with immature apices and that the file taper did not interfere in the readings of the devices. Likely, Herrera et al. ¹⁴ affirmed that the accuracy of Root ZX locator varied in function of the diameter of apical constriction. In these cases, the association of the radiograph and EAL is indicated to determine WL and provide a more accurate result ¹⁷.

Spironelli Ramos and Bramante ²⁶ emphasized the difficulty in performing the electronic odontometry in teeth with immature apices by the lack of apical constriction. The use of alginate for the teeth insertion followed the suggestions of the studies of Czerw et al. ⁴, Baldi et al. ², and Lipski et al. ²⁰, which highlighted the advantage of this medium in in vitro studies on apical locators.

It is noteworthy to mention the importance that one single operator handled the EALs to obtained the results because according to Kielbassa et al. ¹⁶, two or more operators resulted in a significant difference in the WL measurements that disguised the real study result.

The results of this present study demonstrated the reliability of EALs in determining the working length in teeth with incomplete rhizogenesis. Although the results proved this effectiveness, most of the authors agree that EALs do not eliminate the need of taking a radiograph to determine the working length and root canal anatomy and morphology. Accordingly, the association of the radiograph and apical locator is the ideal method.

Conclusion

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Corresponding author:
Bruno Martini Guimarães
Al. Octavio Pinheiro Brisola, 9-75 – Vila Universitária
CEP 17012-901 – Bauru – SP – Brasil
E-mail: brunomgui@usp.br

Received for publication: March 31, 2014
Accepted for publication: September 1, 2014