Accuracy and consistency of four electronic apex locators in the presence of different irrigants

Abstract

Methods

The working length (WL) was determined electronically of 390 teeth (248 maxillary and 142 mandibular teeth), which had a total of 1,095 root canals and completely formed apices, with a #15 K-file as the measuring file. Measurements were taken in sequence once the canals had been irrigated with 5 ml of 2.5% NaOCl, 2% CHX, and 17% EDTA, respectively, with an endodontic syringe and a 30-gauge needle. The data was analysed using Student’s t-test, and significance was set at p < 0.05.

Results

The statistical analysis revealed no significant differences in the accuracy of the four EALs in determining the WL when 2.5% NaOCl, 2% CHX, and 17% EDTA were used as irrigants (p = 0.05). For anterior teeth and premolars, the Root ZX, Elements, PAL and Ray-pex 5 EALs located the apical constriction 95.29% of the time in CHX, 95.29% in NaOCl, 95.88% in CHX, and 94.11% in CHX, respectively. For molars, Root ZX, Elements, PAL and Ray-pex 5 located the apical constriction 95.34%, 95.34%, 92.38% and 98.63% of the time in EDTA, respectively.

Conclusion

The results showed that no statistically significant differences in accuracy and consistency were found between the four EALs.

Correct determination of WL is a key factor that can influence the outcome of root-canal treatment.[1] Failure to determine the correct WL might result in overfilling or underfilling, and has the potential to increase the failure probability of root-canal treatment within a ten-year observation period from around 10% to around 50% as shown in a retrospective clinical study.[2]

Anatomically, the apical constriction (AC)[3] is a logical location for WL because it often coincides with the narrowest diameter of the root canal.[4] However, locating the AC clinically is problematic. Dummer et al.[5] concluded that it is impossible to locate the AC clinically with certainty because of its position and topography.

The cemento-dentinal junction (CDJ) is thought of as the ideal limit for endodontic instrumentation because of the small diameter of the root canal at that point. Moreover, it has been established that endodontic procedures must take place inside the root canal and should not affect the cementum, thereby preserving the remaining apical periodontal tissue.[6–9]

The CDJ has also been suggested as the ideal place for WL determination because it represents the transition between pulpal and periodontal tissue.[10] The location of the CDJ is widely accepted as being 0.5–0.75 mm coronal to the apical foramen[11] but, as with the AC, the exact location of the CDJ is impossible to identify clinically. In general, the CDJ is considered to be co-located with the minor foramen;[12] however, this is not always the case.[5]

 

The consistency of a device describes the regularity of its function. A measuring device that is able to give a reading each time used is considered to function consistently, regardless of the quality of the performance. The dysfunction (inconsistency) may be recognised when the scale bars on the display of EALs are either unstable (jump from one point to the other) or do not appear at all.

The quality of the performance or measurements can be described in terms of reliability, which is the probability that a device will perform a required function (e.g. high accuracy, repeatability, and reproducibility)[13] under stated conditions (e.g. on patients) for a stated period of time. The reliability of apex locators in terms of accuracy and repeatability is well studied,[14–18] but there is little data on the consistency or regularity of the function of EALs.

As far as we know, the clinical consistency of the function of EALs has not been studied. A limited number of ex vivo studies have described the inconsistent function of EALs as a secondary finding.[8,19] Furthermore, the clinical factors influencing the function of EALs need to be studied.

To date, no study has been published on the effects of irrigants on the accuracy and consistency of EALs. The purpose of this study was to examine the accuracy and consistency of four EALs in the presence of various intra-canal irrigants used in non-surgical endodontic therapy in an in vivo model.

Materials and methods

This study took place at the faculty of dentistry of the Autonomous University of Baja California in Tijuana, Mexico. The subjects review committee approved the study and all the participants were treated in accordance with the Declaration of Helsinki.

Calculation of sample size by setting the power of the study to 90%, standard deviation of the outcome to 1 mm based on earlier studies,[20] and the minimum detectable difference to 0.5 mm yielded a minimum number of 1,095 root canals for this study. Consequently, 390 teeth (248 maxillary and 142 mandibular teeth), which had a total of 1,095 root canals and completely formed apices, were selected (Table 1). All selected teeth had mature apices with no radiographic signs of root resorption. Exclusion criteria were previous endodontic treatment, non-restorable teeth, internal or external root resorption, intra-canal calcification, active systemic disease, and physical or mental disability. The selected teeth had been scheduled for extraction due to periodontal disease or for orthodontic reasons from adult patients (between 21 and 65 years old).

All teeth responded positively to hot and cold sensitivity tests, and clinically all pulps were confirmed to be vital on entry into the pulp chamber. Informed consent was obtained in writing from each patient in accordance with the approval of the study by the ethics board of the faculty of dentistry of the Autonomous University of Baja California. All clinical procedures and measurements were performed by the author.

A standardised periapical radiograph was taken for each tooth in buccolingual projection to allow proper selection. After local anaesthetic had been administered using 2% lidocaine with 1:100,000 epinephrine (Septodont) and rubber dam isolation, the tooth was disinfected with 5.25% NaOCl (Ultra bleach).

The cusps or the incisal edges of the teeth were flattened with a diamond bur (DENTSPLY Maillefer) to obtain a stable reference point for all measurements. All caries and existing metal restorations were removed, and endodontic access cavities made with sterile high-speed #331 carbide (SS White) and Zekrya Endo burs (DENTSPLY Maillefer). After identification of the root canals, the cervical third of each canal was flared with an SX file and S1 ProTaper file (DENTSPLY Maillefer).

Measurements were taken in sequence after the canals had been irrigated with 5 ml of 2.5% NaOCl, 2% CHX (Vista Dental), and 17% EDTA (Vista Dental), respectively, with an endodontic syringe and a 30-gauge needle. Excess fluid was removed, but no attempt was made to dry the canal. Between measurements, the canals were irrigated with 10 ml of distilled water and dried with paper points before application of the next irrigant. A computerised method of randomisation selected the order in which the irrigants and the EALs were used.

Each EAL was used in accordance with the manufacturer’s instructions. The AC of each tooth was located with four EALs and double stoppers were used to reduce the possibility of stopper movement during measurements. Measurements were considered to be valid if the reading remained stable for at least 5–10 seconds.

For Root ZX (Morita),[21] the buccal clip was attached to the patient’s lip, and the probe was connected to a #15 stainless-steel K-file. The file was advanced within the root canal to a point just beyond the major foramen, as indicated by the flashing APEX bar on the liquid crystal display of the EAL. When the file was in position, the LCD display showed a flashing bar between APEX and 1.

The AC was located with Elements (SybronEndo) by advancing the same size K-file in the canal until the locator indicated that the AC had been reached.[22] The two silicone stoppers on the file were positioned at the reference point and the insertion length measured. The sequence of testing alternated between the two locators.

For PAL (NSK),[23] the AC was located at the 0.0 mark, at which point the EAL produced a constant audible tone.

For Ray-pex 5 (DENTSPLY), the reading was recorded when all three green bars lit up. The file was advanced within the root canal to the major foramen (red light) and retracted until the flashing green bars appeared.

For determining consistency, an EAL was considered inconsistent if the WL determination in one or more of the root canals was inconsistent. The EAL was considered consistent when all root-canal measurements within a tooth were consistent. The consistency of the EALs was determined by calculating the number of consistent measurements and the 99% confidence interval. The significance of these results[13, 14, 18] regarding the consistency of the EALs was calculated by performing a regression analysis. The unit of further analysis was the root canal and not the tooth. The percentage of acceptable long and short measurements and the corresponding 99% confidence interval were calculated. The function of the EAL was recorded as consistent when the scale bars of the EAL were stable and their movement corresponded with the movement of the measuring file in the root canal.

The AC was located radiographically by advancing the #15 K file until its tip was 1 mm from the radiographic apex (determined from a pretreatment parallel technique radiograph). A radiograph was exposed, and if the file tip was seen not to be 1 mm from the radiographic apex the file was repositioned and another radiograph taken to ensure that it was. The distance from the stop to the tip was the insertion length. The file was then reinserted to the insertion length (1 mm from the radiographic apex) and cemented in place with GC Fuji II LC dual-cure glass ionomer cement (GC Corporation). The file handle was sectioned with a high-speed bur, and the tooth was extracted without disturbing the file by an experienced oral surgeon, immersed in 2.5% NaOCl for 30 minutes to remove any residual organic tissue from the root, and then kept in a 1% thymol solution in a numbered specimen cup.

The apical 5 mm of the root was clipped in a longitudinal direction using a fine, flat cylinder diamond bur (Brasseler) under a stereomicroscope (Zeiss Stemi 2000-C, Carl Zeiss) at 16x magnification to expose the file tip.

The remaining tooth structure was removed carefully until the file tip and the root canal were both visible. A digital photograph was taken and stored in Adobe Photoshop 5.5 (Adobe Systems), and the distance from the file tip to the minor foramen was measured using Image Tool 3.1 software (University of Tennessee Health Science Center).

The distance from the file tip to the AC was measured. This distance was recorded as being (a) -1 mm from the AC; (b) -0.5 mm from the AC; (c) at the AC; (d) +0.5 mm from the AC; and (e) +1 mm from the AC. A minus symbol (-) indicated a file short of the AC, and a plus symbol (+) indicated that it was beyond the AC.

The position of the file tip in each root canal was evaluated by two examiners. If the two examiners disagreed, a third previously calibrated researcher was asked to make the final decision. The final WL was established to be 0.5 mm coronal to the major foramen.24 Once the actual length to the AC had been measured visually, the distance from the AC determined by the four EALs was also calculated (-1 mm from the AC, -0.5 mm from the AC, etc.), by comparing their insertion lengths to the actual length (i.e. distance to the AC; Tables 2 & 3).

The measurements obtained (accuracy and consistency) by the four EALs and radiographs relative to the actual location of the AC with three different irrigants were compared using a paired samples t-test, chi-squared test and repeated measures ANOVA conducted at the 0.05 level of significance.

Results

The statistical analysis revealed no significant differences in the accuracy of the four EALs in determining the WL when 2.5% NaOCl, 2% CHX, and 17% EDTA were used as irrigants (p = 0.05).

For anterior teeth and premolars, Root ZX, Elements, PAL and Ray-pex 5 located the AC 95.29% of the time in CHX, 95.29% in NaOCl, 95.88% in CHX, and 94.11% in CHX, respectively. For molars, Root ZX, Elements, PAL and Ray-pex 5 located the AC 95.34%, 95.34%, 92.38% and 98.63% of the time in EDTA, respectively. There were no statistically significant differences between the four EALs, but there was a difference between the EALs and radiographs (Tables 2 & 3).

For anterior teeth and premolars, two of the measurements were 1 mm short of the AC. For anterior teeth and premolars, 18 of the measurements were 0.5 mm beyond the AC. For molars, 1.47%, 2.5%, 2.3% and 2.3% of the measurements using Root ZX, Elements, PAL and Ray-pex 5, respectively, were 0.5 mm beyond the AC (Tables 2 & 3).

No EAL measurements were 1 mm beyond the AC for anterior teeth, premolars or molars. There were no statistically significant differences between the four EALs.

The statistical analysis revealed no significant differences in the consistency of the four EALs in determining the WL when 2.5% NaOCl, 2% CHX, and 17% EDTA were used as irrigants (Table 3).

Discussion

The present study was performed to examine the accuracy and consistency of four EALs in the presence of various intra-canal irrigants used in non-surgical endodontic therapy in an in vivo model. Earlier studies have demonstrated that EALs often yield inaccurate readings in the presence of fluids.[25, 26] However, the use of irrigants and their benefits in endodontics have been demonstrated, and most clinicians use the irrigants that were used in this study for their antimicrobial and tissue-dissolving abilities. Our results showed that the irrigants evaluated largely did not have an effect on the accuracy of the EALs.

The use of electronic devices to determine WL has gained popularity. When using them, an important consideration is being aware of the possible sources of error, such as metallic restorations, salivary contamination, dehydration, etc. However, as shown in this and other studies, the accuracy of EALs is superior to radiographs.[19, 27, 28]

One of the reasons that a radiographically determined WL lacks accuracy is that it is based on the radiographic apex rather than the apical foramen (the end of the canal). WL is obtained with a radiograph by positioning the tip of a file a certain distance (usually 1 mm) from the radiographic apex. However, WL should be based on the location of the AC rather than that of the radiographic apex because the apical foramen frequently is not at the radiographic apex.[29] The measurements of the present study were attained in a target interval of ± 0.5 mm to the minor diameter of the AC, using Image Tool 3.1. This clinical tolerance of ± 0.5 mm is considered to be the strictest tolerance. Measurements within this minimal tolerance are very accurate.[30]

In this study, Root ZX and Elements correctly located the AC in anterior teeth and premolars 95.29% and 95.29% of the time, respectively, whereas the PAL and Ray-pex 5 achieved this 95.88% and 94.11% of the time, respectively. An in vivo study by Shabahang[26] reported that Root ZX was within 0.5 mm of the AC 96% of the time, a value similar to the present findings. In general, this study also corroborates the findings of other studies[31] that EALs are more accurate than radiographs are and greatly reduce the risk of instrumenting and filling short of or beyond the canal terminus.

A matter of debate in endodontics is the apical limit of root-canal treatment and obturation. Traditionally, the apical point of termination has been 1 mm from the radiographic apex. Kuttler[3] found the average distance between the apical foramen and the AC to be 0.5–0.75 mm and that this distance increases with age because of cementum deposition.

In this study, Root ZX and Elements correctly located the AC in molars 95.34% and 95.34% of the time, respectively, whereas the PAL and Ray-pex 5 achieved this 92.38% and 98.63% of the time, respectively.

The Root ZX and Ray-pex 5 devices showed better scores in consistency in CHX and EDTA because of their superior repeatability,[14] although the consistency of Ray-pex 5 in EDTA was statistically significantly higher than that of Root ZX. Clinically, this difference is not significant (Table 3).

Chapman[31] found that the AC was located 0.5–1 mm from the apical foramen in 92% of observed teeth. Another study documented the average distance between the AC and the apical foramen to be 0.9 mm and found that 95% of the constrictions were between 0.5 and 1 mm from the apical foramen.[5] Hassanien[32] identified the AC to be at an average distance of 1.2 mm from the apical foramen. In light of these studies, it seems that there is ample reason to establish WL 1 mm short of the radiographic apex and use this reference point as a target for comparison of EALs in terms of measurement accuracy or at least near accuracy.

Our results are in relative agreement with other studies that reported the accuracy to be 73%,33 75–91.7%,34 90%,[35] and 89–100%.[36, 37] The different results obtained in previous studies could be explained partly by the nature of the teeth and irrigants used in those studies.

In the present study, significant differences were observed between the measurements obtained using the four EALs. For example, greater accuracy of Ray-pex 5 was observed in the presence of either 2% CHX or 17% EDTA, compared with the accuracy of Root ZX, Elements and PAL. However, the irrigant used did not influence the accuracy of the EAL.

Conclusion

Under clinical conditions, the EALs identified the AC with a high degree of accuracy and consistency. EALs were accurate and consistent to a high degree, with the potential to reduce the risk of instrumenting and filling beyond the apical foramen greatly.
Within the limitations of this study, the results showed that there were no statistically significant differences in accuracy and consistency between the four EALs. All tested EALs achieved an acceptable determination of the root canal WL.

Editorial note: A complete list of references is available from the publisher.

This article was published in roots international magazine of endodontology No. 2/2013.