Introduction

Electronic Apex Locators (EALs) have revolutionized endodontic practice by offering a non-invasive and highly accurate method for determining the working length (WL) of root canals. These devices operate by utilizing electronic signals and impedance measurement techniques to precisely locate the apical constriction or apex of the tooth, providing real-time feedback to the clinician during root canal treatment.¹ Unlike traditional radiographic methods, EALs offer numerous advantages, including reduced radiation exposure, enhanced accuracy, and the ability to overcome challenges posed by anatomical variations or calcified canals.¹ These advantages make EALs an indispensable tool in modern endodontics, contributing significantly to improved treatment outcomes, increased procedural efficiency, and enhanced patient comfort, thereby underscoring their pivotal role in contemporary root canal therapy.

The evolution of EAL technology has progressed through multiple generations, with each iteration offering refinements in accuracy and usability. First-generation devices utilized single-frequency impedance measurements, while subsequent generations incorporated multiple frequencies, advanced algorithms, and improved signal processing techniques to enhance precision even in the presence of intracanal fluids. Contemporary fourth-generation devices, such as the E-Connect S used in this study, feature automatic calibration, digital displays, and enhanced resistance to electromagnetic interference, making them suitable for use in various clinical scenarios.¹

The introduction of sodium hypochlorite (NaOCl) into the root canal environment is a routine practice due to its excellent antimicrobial properties and ability to dissolve organic tissue. This irrigant plays a crucial role in eliminating endodontic pathogens, including Enterococcus faecalis and other resistant microorganisms, while also facilitating the removal of pulpal tissue and smear layer.However, NaOCl can alter the physical and chemical properties of dentin, particularly its permeability and dimensional stability. ²The high surface tension and tissue-dissolving capacity of NaOCl may change the dielectric properties of dentin, potentially affecting the electrical conductivity measurements upon which EALs rely.Such alterations may lead to changes in EAL readings or the radiographic appearance of the root apex, potentially affecting the determination of the true WL. Specifically, the diffusion of NaOCl into dentinal tubules can influence the electrical conductivity of dentin, which is the fundamental principle behind the operation of electronic apex locators, potentially compromising their accuracy. ²The ionic nature of NaOCl solutions, particularly their chloride content and electrolytic properties, may create electrical shunts that interfere with the precise localization of the apical constriction, leading to either overestimation or underestimation of the working length.²

Thus, investigating the effects of NaOCl irrigant on WL measurements is essential for clinicians to make informed decisions regarding treatment protocols and ensure optimal outcomes for patients. Additionally, understanding the impact of NaOCl on WL determination is vital for minimizing procedural errors and avoiding complications during endodontic treatment. Inaccurate WL measurements can result in over-instrumentation, leading to unnecessary removal of tooth structure, postoperative pain, or periapical tissue damage. Conversely, underestimating the WL may leave residual infected tissue or debris, jeopardizing the success and longevity of the treatment.³ Therefore, elucidating the influence of NaOCl irrigant on WL measurements contributes to refining clinical protocols, enhancing the efficacy and predictability of endodontic procedures, and ultimately improving patient care.

Hence, the aim of this study was to evaluate the influence of sodium hypochlorite irrigation on WL measurements using EALs at different stages of root canal treatment, with emphasis on tooth type differences.The null hypothesis was that NaOCl irrigation would not significantly affect EAL-based WL measurements in any tooth type.

Materials and Methods

Study design and sample

This prospective comparative clinical study was conducted in two primary care dental clinics in Bahrain. Adult participants attending the dental clinics with any chief complaint requiring endodontic intervention of anterior or posterior teeth were recruited using a simple random sampling technique. Random numbers for patient selection were generated using a computer-generated random number table to ensure unbiased sampling. All root canals in the included teeth were considered for the study. A sample size of 35 patients was calculated based on preliminary power analysis to detect a significant difference in working length measurements with 80% power and 5% significance level. All root canals treated in these 35 patients were included in the analysis. The study was conducted in accordance with the Declaration of Helsinki. The study protocol was reviewed and approved by the Primary Care Ethics Committee, Ministry of Health, Bahrain. Informed consent was obtained from all participants prior to enrollment.

Inclusion and exclusion criteria

Patients aged 18 years and above requiring primary root canal treatment on permanent teeth with fully formed apices were included. Teeth with vital or necrotic pulps, without radiographic evidence of significant root resorption or perforation, were considered eligible for inclusion. Patients who did not provide written informed consent and those with contraindications for the use of an apex locator were excluded. Root canals presenting anatomical challenges such as calcified canals, C-shaped canals, or open apices were excluded due to referral to specialized care. Additionally, root canal treatment on third molar teeth was excluded due to their complex anatomy and limited accessibility.Teeth with previous root canal treatment, extensive coronal destruction precluding rubber dam isolation, or radiographic evidence of vertical root fracture were also excluded from the study.

Data collection

Pre-operative working length (WL) was measured on pre-operative digital radiographs using the digital ruler tool embedded within the imaging software. After rubber dam isolation and access cavity preparation, WL was determined using the digital radiographic method with a size 8 or 10 K-file inserted into the canal. The file was inserted until it was just visible at the radiographic apex, and the distance from the coronal reference point to the file tip was measured.Subsequently, irrigation of the canals was performed using 2.5% sodium hypochlorite (NaOCl). WL measurements were then recorded using an electronic apex locator (E Connect S, Eighteeth, China, 4th generation) before and after drying the canals with sterile paper points. A final WL measurement was taken after biomechanical preparation of the root canal using the same apex locator. The apex locator was operated strictly according to the manufacturer’s instructions. The coronal reference point for WL measurements was consistently maintained throughout the procedure to ensure reproducibility. WL was defined as the distance from the coronal reference point to the point where canal preparation and obturation should terminate. Data collection was performed by two calibrated investigators who were trained by a subject matter expert on a pilot group of 10 patients to ensure inter-examiner reliability. All WL readings were documented on a standardized data collection form.The investigators performing the measurements were blinded to the previous readings to minimize recall bias. Intra-examiner reliability was assessed using intraclass correlation coefficients, with values exceeding 0.90 considered acceptable.

Statistical analysis

Descriptive statistics were used to summarize demographic data and WL measurements. The Kolmogorov-Smirnov test was employed to assess the normality of data distribution. Comparisons between two groups were performed using the independent t-test, while one-way ANOVA was applied to compare WL measurements across multiple groups. A significance level of P ? 0.05 was set for all statistical tests. All analyses were conducted using GraphPadInStat software (GraphPad Software, Inc., USA). Confidentiality of participant data was strictly maintained, with access limited to the principal investigator.

Results

Demographic data of study participants

Thirty-five participants that required endodontic treatment of either anterior or posterior teeth were included based on the inclusion criteria. The mean (SD) age of included study participants was 38.7 (4.23). 18 participants were males, and the rest were females.  5 central incisors, 3 lateral incisors, 8 canines, 10 premolars and 8 molars were the teeth included. A total of 44 root canals were included for analysis, of which 16 belonged to anterior teeth and 28 to posterior teeth.

WL measurements

Pre-operative versus after access opening

The mean pre-operative WL for anterior teeth was 21.5 (3.92), and for posterior teeth was 19.2 (2.57).  There was no significant difference between the WL measured pre-operatively using digital radiograph and after access opening using apex locator, in the anterior and posterior teeth. However, the estimates show that there was significant difference between the pre-operative WL, and WL measured after access opening specifically in molar teeth (p=0.025). (Table 1).

Effect of NaOCl on WL measurements

The WL was measured before and after using 2.5% NaOCl irrigant. There was significant difference in WL measurements of molars with and without the use of irrigant (P=0.006). The use of irrigant did not influence the WL measurements for other anterior and posterior teeth. (Table 3).

WL measurements at various stages of root canal preparation:

The WL measured pre-operatively, after access, before irrigant, after irrigant, and after biomechanical preparation of the canal was compared. There were significant differences in the WL measurements for molar teeth only. (Table 2,4,5) The WL measurements were not significantly different for other teeth.

Discussion

The present study was aimed to understand the influence of NaOCl irrigant on WL measurements made using EAL in both anterior and posterior teeth. Results from the present study indicate that there is significant difference in WL measurements of molar teeth made at different stages of root canal access. The findings of this study provide valuable insights into the clinical factors that can affect EAL accuracy and support the recommendation for thorough canal drying before WL determination, particularly in multi-rooted teeth.

An idealized description of the main apical opening of the root canal, known as the apical foramen (AF), suggests a gradual tapering from the apical constriction (AC) to a wider major apical diameter. ⁴ However, AF anatomy often deviates from this idealized form due to factors such as tooth type, age, functional adaptation, and pathological changes. The number of foramina and their distances from the root apex vary widely, making it challenging to clinically identify the WL. ^3,4 Furthermore, there is debate regarding the optimal termination point of root canal preparation. Some authors advocate for the cementodentin junction (CDJ) as ideal, but its histologic nature makes it detectable only post-extraction. ⁴ Moreover, the irregularity of the CDJ and the variability of cementum extension into the canal complicate its use as a reference point. The AC has been proposed as an optimal WL due to presumed optimal healing and minimal periapical tissue damage. However, AC topography and morphology vary, and fewer than half of teeth exhibit a single, traditional AC. EALs provide a method for determining WL during root canal procedures. Double-frequency EALs are particularly reliable in identifying AC compared to traditional radiographic methods. ²The variability in AC location and morphology underscores the importance of using multiple methods, including EALs, tactile sensation, and radiographs, to confirm WL, especially in teeth with complex anatomy.

EALs have undergone several generations of development, each offering advancements in accuracy, usability, and features. Introduced in the late 20th century, first-generation EALs were the pioneering devices for electronic apex localization. They typically utilized impedance-based measurement techniques, where the device measured the electrical impedance between the file tip and the surrounding tissues to determine the position of the apex. These early models, while revolutionary, often lacked the precision and reliability of later generations.⁵ Second-generation EALs emerged with improvements in accuracy and functionality. They incorporated multiple frequency measurements to enhance precision, along with features like automatic calibration and digital displays for easier readings. These devices gained wider acceptance in the dental community due to their enhanced performance and reliability compared to their predecessors.⁵ Third generation EALs represented a significant leap forward in technology and accuracy. They employed advanced algorithms and signal processing techniques to provide more precise apex localization, even in challenging clinical conditions. These devices often featured enhanced displays, customizable settings, and ergonomic designs for improved usability. Subsequent generations of EALs continued to refine accuracy, reliability, and user-friendliness. Fourth-generation models might integrate additional features such as apex locator-assisted root canal navigation, real-time imaging, or connectivity with other dental equipment for comprehensive treatment planning. Manufacturers continually innovate to meet the evolving needs of dental practitioners and improve patient outcomes.^5,6 A recent meta-analysis by Nasiri et al findings indicate that all four generations of apex locators examined demonstrated accuracy in measuring WL. Consequently, the specific generation of an apex locator appears to have little bearing on the device's ability to determine WL accurately. ⁶

The rise in the use of cardiovascular implantable electronic devices has sparked apprehensions regarding the suitability of employing EALs in patients possessing such implants. The concern primarily revolves around potential electromagnetic interference (EMI) between the EAL and the cardiovascular devices, which could lead to inaccurate readings or device malfunction. Consequently, careful consideration and risk assessment are essential when using EAL in patients with cardiovascular implantable electronic devices, necessitating close collaboration between dental and medical professionals to ensure patient safety and accurate treatment outcomes. ⁷

NaOCl is commonly used in endodontic irrigation at various concentrations, typically ranging from 0.5% to 6%. ⁸ The choice of concentration depends on several factors, including the specific clinical situation, the level of antimicrobial efficacy required, and the potential for adverse effects. Lower concentrations, such as 0.5% to 2.5%, are often used for routine irrigation to aid in the dissolution of organic debris and disinfection of the root canal system without causing significant tissue irritation. Higher concentrations, such as 5% to 6%, may be employed in cases where there is a greater need for antimicrobial activity, such as in the presence of severe infection or microbial biofilms. However, higher concentrations pose an increased risk of tissue irritation and other adverse reactions, necessitating careful application and monitoring during use. Ultimately, the selection of the appropriate concentration of NaOCl should be based on a thorough assessment of the clinical situation and consideration of the balance between antimicrobial efficacy and safety. ⁸

Conflicting evidence exists regarding the accuracy of WL measurements made using apex locators in the presence of irrigants such as NaOCl during endodontic procedures. Some studies suggest that the presence of irrigants can influence apex locator readings, leading to inaccuracies in determining the WL. ^2,10 Factors such as the electrical conductivity of irrigants, variations in their composition and concentration, and interactions with the root canal environment may contribute to discrepancies in measurements. ⁸ On the other hand, other research indicates that modern apex locators are designed to compensate for the presence of irrigants and can provide accurate measurements even in their presence. These studies highlight advancements in apex locator technology, including improved algorithms and signal processing capabilities, which enhance their reliability in challenging clinical conditions. ^11,12 The conflicting evidence underscores the complexity of assessing apex locator accuracy in the presence of irrigants and the need for further research to elucidate the factors influencing measurement outcomes. Additionally, clinical judgment and consideration of multiple diagnostic methods, including radiographs and tactile sensation, may be necessary to ensure precise determination of the WL in endodontic procedures conducted with irrigants. In our current study, we observed that WL measurements on molars were impacted by the presence of irrigant.

Endodontic treatment of multi-rooted teeth poses numerous challenges due to their complex anatomy and varied canal structures. Thorough cleaning, disinfection, and obturation are crucial for success. Negotiating intricate canal systems requires advanced skills and specialized tools. ¹³ The presence of curved and narrow canals increases difficulty, emphasizing the importance of proper instrumentation and irrigation. Variations in canal morphology further complicate treatment, necessitating thorough preoperative assessment. Success depends on meticulous clinical expertise, comprehensive understanding of root canal anatomy, and advanced techniques to achieve optimal outcomes. ¹³

Based on the findings of our current study, we recommend ensuring complete drying of the root canals in multi-rooted teeth before utilizing apex locators for WL determination. This suggestion aims to minimize the potential influence of residual irrigants, such as sodium hypochlorite, on apex locator readings, which our study indicates can affect measurement accuracy. By thoroughly drying the canals, clinicians can enhance the reliability of apex locator measurements, particularly in cases of complex root canal anatomy, such as multi-rooted teeth, thereby improving the precision of endodontic treatment outcomes.

Table 1: Working length measurements: Pre-operative radiographic WL versus WL after access opening using file

Table 2: Working length measurements after access opening.

Table 3: Working length measurements with and without irrigant

Table 4: Working length measurements for molar teeth

Table 5: Pre-operative versus post-operative WL for molars

Conclusion