The accuracy of two electronic apex locators on effect of preflaring and file size: An in vitro study.

AIM: This study was conducted to evaluate the effect of preflaring and file size on the accuracy of the Root ZX and E-PEX Pro electronic apex locators (EALs).
MATERIALS AND METHODS: The actual working length was set 1 mm short of the apical foramen in the forty extracted mandibular premolars. The teeth were embedded in an alginate mold, and two examiners performed the electronic measurements using #10, #15, and #20 K-files. The files were inserted into the root canals until the "0.0" or "APEX" signals were observed on the light-emitting diode or display screens for the E-PEX Pro and Root ZX, respectively, retracting to the 1.0 mark. The measurements were repeated after the preflaring using the S1 and SX Pro-Taper instruments. The mean differences between the actual length and electronic length values were analyzed by the Wilcoxon signed-ranked test with a significance level of P < 0.05. The factors evaluated were "Accuracy of EALs," "size of file," and "presence of preflaring.
RESULTS: No significant differences were observed in the accuracy of both EALs when compared with the actual lengths. On the size of the file, significant difference noticed with #20 K-file. The preflaring procedure significantly (P < 0.05) increased the accuracy of the measurements for the Root ZX and Epex Pro.
CONCLUSIONS: The tested EALs showed acceptable accuracy, whereas the preflaring procedure revealed a more significant effect than the used file size. Copyright:

INTRODUCTION

The establishment and maintenance of working length (WL) are a critical step during endodontic therapy.[1] An appropriate microbial disinfection, correct cleaning and shaping, and hermetic sealing of the root canal depend on the correct determination of WL. The apical constriction is also referred to as the minor constriction diameter and marks the transition between the pulpal and periodontal tissue.[2] This anatomic landmark might be located at 0.5–1 mm from the major foramen,[23] and it has been stated that it is an ideal point to end the instrumentation and obturation of the root canal system.[3]

Methods of WL establishment include tactile sense, radiographs, and electronic apex locators (EALs). Radiography has conventionally been used to establish the apical limit; unfortunately, however, the apical constriction varies considerably in shape and is not detectable by radiography. In 1962, Sunada[4] reported a new method for measuring the length of the root canal, giving rise to the development and marketing of the first EALs, based on the electrical resistance theories of Suzuki.[5] However, although the use of EALs is well established, predictable and reproducible electronic readings were only possible with the development of last-generation devices.[1]

Root ZX (J. Morita CO., Tokyo, Japan) and Epex Pro (Eighteeth Medical Technology Co., Ltd., Changzhou, China) are commercially available modern EALs that measure the impedance between the file tip and the root canal at different frequencies.[1] and provides precise measurements even in the presence of blood, pus, or pulp tissue.

According to ElAyouti et al.,[6] several factors can influence the electronic measurements, such as apical constriction diameter, instrument size, preflaring, and the irrigating solution used during the procedure.

Files inserted in preflared canals can easily reach the apical constriction, presenting a lower incidence of overextension than those placed in unflared canals.[7] Moreover, some studies,[89] found that the preflaring procedure increased the accuracy of some EALs, although other authors[10] reported divergent results.

Small-diameter hand files are systematically used to determine the initial WL and to establish patency of the root canal. In wide canals, EAL accuracy might be influenced by file size, because a slim file is likely to leave space within the canal, whereas a larger-diameter file will yield a tighter fit.

The purpose of this ex vivo study was to evaluate the effect of preflaring and the size of the measuring file on the accuracy of the Root ZX and Epex Pro in the extracted mandibular premolars.

MATERIALS AND METHODS

Sample selection and preparation

Twenty extracted mandibular first premolars were selected after a radiographic examination. The following criteria were used for the tooth selection: Well-preserved coronal and radicular structures, fully formed apices, and similar root lengths.

Exclusion criteria were the presence of metallic restorations and a root presenting resorption or fractures. Coronal access to the teeth was initially performed with a #1557 tapered carbide bur (S. S. White Dental products) at high speed and refined with an Endo-Z bur (Dentsply-Maillefer). The occlusal surfaces of the premolars were sectioned using a diamond disc (Isomet, Buehler) to expose a flat dentin surface. This procedure was performed to provide a stable and reproducible reference point for root canal measurements. The root apex was fixed in contact with a rigid plate to determine the actual work length. A #10 K-file with a rubber stop was inserted in the canal and advanced until the file tip met the rigid plate. Thus, the file tip was flush with the apical foramen. At this moment, the rubber stop was adjusted to the chosen reference point, the file was removed, and a millimeter ruler (Dentsply-Maillefer) was used to measure the verified length. From this measurement, 1 mm was subtracted to achieve the actual work length.

Electronic working length determination

The electronic WL was obtained using Root ZX or E-PEX PRO EALs and #10, #15, or #20 K-files (Dentsply-Malleifer). Thus, six experimental conditions were determined. An ex vivo experimental model based on a previous study was used. The teeth were immersed in a plastic box containing fresh alginate (Jeltrate II; Dentsply). Two orifices were performed, one localized in the center of the box to permit the placement of the teeth and the other laterally to insert the lip electrode of the EALs. Before determining the electronic length, the root canals were irrigated with 1% sodium hypochlorite (NaOCl) solution. Excess from the pulp chamber was removed with cotton pellets. The lip electrode was inserted in the respective orifice in contact with the alginate and the experimental condition file under evaluation was connected to the other electrode for the electronic measurements. For each EAL used, the file was inserted into the root canal until the “0.0” or “APEX” signals were observed on the light-emitting diode (LED) or display screens for the E-PEX PRO and Root ZX, respectively. The file was retracted until the LED or display showed the 1-mm mark. A rubber stop was then adjusted to the reference level, and the distance between the rubber stop and the file was measured with an endodontic ruler (Dentsply-Maillefer). Another factor evaluated was the effect of the preflaring procedure in the electronic measurements. Preflaring was performed by root canal enlargement from the cervical up to the middle third. An engine-driven instrument (X-Smart; Dentsply-Maillefer) with the S1 and SX ProTaper instruments (Dentsply-Maillefer) was used for this purpose. The S1 instrument was introduced into the canal until 3 mm from the previously determined WL. Afterward, the SX instrument was used with a brushing motion up to the middle third. Irrigation with 2 mL 1% NaOCl was performed after the use of each rotary instrument. Two measurements at 3-week intervals were performed for each experimental condition, before and after the preflaring procedures by two examiners (specialists in endodontics). Electronic measurements restricted to 1 mm short of the apical foramen or presenting ± 0.5 mm of error variation were classified as precise and acceptable, respectively. Mistaken measurements were higher or lower than the acceptable values 5.

Statistical analysis

The mean of the measurements of each EAL was used for the statistical analysis. The accuracy was calculated only on the stable measurements. The mean of the measurements of each EAL was used for the statistical analysis. The mean differences between the actual length and electronic length values were analyzed by the Wilcoxon signed-ranked test with a significance level of P < 0.05. The factors evaluated were “Accuracy of EALs,” “size of file” and “presence of preflaring.

RESULTS

No significant differences were observed in the accuracy of both EALs when compared with the actual lengths. The preflaring procedure significantly (P < 0.05) increased the accuracy of the measurements for the Root ZX and Epex Pro [Figure 1]. On the size of the file significant difference noticed with #20 K-file.

Figure 1

Composite images of relative frequency of precise, acceptable and mistaken measurements for Root ZX and EPEX apex locater in unflared and preflared canals and Comparison of mean differences in the accuracy of apex location by 2 electronic apex locators with different file sizes in unflared and preflared root canals

DISCUSSION

EALs have gained huge popularity in recent years as they are commonly used for WL determination and several EALs, differing in their electrical basis of function, are available in the market. The Root ZX function is based on detecting the changes in electrical capacitance in the vicinity of the AF. It works by calculating the impedance ratio of two simultaneously produced frequencies (0.4 and 8 kHz). The ratio represents a definite value that reflects the file position inside the canal.[11] While Epex Pro apex locater work based on advanced multi-frequency network impedance measurement technology and it has high precision in wet and dry canals.

Ex vivo experimental methods for studying the accuracy of EALs often use electroconductive materials such as alginate, gelatine, agar, or saline media.[81213] These embedding media may reproduce the impedance values of human tissues, thus simulating the clinical situation. However, some substances can leak through the apical foramen and cause premature readings.[12] Thus, protocols involving the use of alginate are reportedly more reliable and reproducible.[1214] The relative stiffness, good electroconductive property, and gel consistency, which allow ions to circulate, are favorable characteristics of alginate that simulate the periodontal ligament.[1214] For these reasons, the teeth were embedded in an alginate mold for electronic measurements in the present study. This model was constantly moistening and refrigeration when not in use.

Diverse studies have considered different precision ranges to evaluate the EAL within ± 0.5 mm,[1516] whereas others use ± 1 mm.[1718] The tolerance chosen in this study is considered clinically acceptable and highly accurate.[1419] This is important because those specific ranges of ± 0.5 mm or ± 1 mm might lead to an accuracy variation. Thus, the precision of some EALs can be overestimated.

The Root ZX was able to measure the WL (±0.5 mm) in >97% of the cases by taking the apical foramen as a landmark for the actual length.[814] In another similar study, accurate measurements (±0.5 mm) were found in 89.7% of the cases using the Root ZX.[20] Accuracy ranges from 89.7% to 97% (±0.5). In this study considering an error range of 1 mm, the root canal length obtained using the Root ZX was accurate in 100% of the samples using 10# and 15# file and 95% using 20# file. In the case of Epex Pro, 95% accuracy obtained using 10# file and 100% accuracy obtained using 15# and 20# k file. The high accuracy rates verified in the present study for both EALs, regardless of the tested experimental condition, support the results of the cited investigations. In addition, no cases of overextension were observed, which is consistent with another ex vivo study,[20] although other authors[21] have reported overestimated measurements in 7.6% of the cases for the Root ZX.

The coronal preflaring procedure during endodontic treatment is important to remove cervical dentin interferences. It allows easier insertion of manual or rotary instruments into the apical portion of the root canals and avoids changes in the WL during the root canal preparation.[7] Moreover, previous studies[8922] stated that this procedure increases the accuracy of some EALs, such as the Root ZX, which was also verify in the present study.

Nickel-titanium instruments such as the ProTaper have been recommended for coronal preflaring, presenting a greater dentin cutting ability and safety during the preparation procedures.[23] In the present study, the use of the S1 and SX ProTaper instruments ensured a suitable enlargement of the cervical and middle thirds of the root canals, as previously verified.[8] The number of precise readings was superior in the preflared canals for both Root ZX and Epex-Pro apex locaters, increasing for acceptable readings by using a ± 0.5 mm tolerance range Preflaring increased the efficiency of the Root ZX in the mandibular molars,[9] palatal canals of maxillary molars[22] and incisor[8] canals, corroborating with the present data obtained in the mandibular premolars.

Instrument sizes 10 and 15 are commonly used to verify the root canal patency and to make the first electronic WL determination. In this study, we used #10, #15 and #20 K files for measuring WL. Equivalent performances of the Root ZX and Epex Pro apex locator was found using a #10, #15 and #20 K-file in both unflared and preflared canals in the present study. Some studies showed that higher accuracy tendency was not observed with any of the EALs as the instrument size increased.[1320] Other studies[2024] also verified that the size of the endodontic file does not need to be proportional to the size of the canal for predictability of the electronic measurements.

CONCLUSIONS

Within the limitations of this ex vivo study, it may be concluded that the Root ZX and Epex Pro EALs showed an acceptable accuracy in the mandibular premolars. The cervical preflaring presented significantly increased accuracy in the electronic measurements that the file size used.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.