Successful treatment of root canal perforations and prognoses for affected teeth depend on the location and size of the perforation area, the time between the onset of perforation and treatment, determination of the exact location of the perforation and the ability to seal the perforation area with endodontic treatment . Diagnosis of perforations that occur on lingual or buccal root surfaces can be quite difficult, even for experienced endodontists, due to reasons such as superposition of anatomical structures with 2D conventional radiographic methods .
Recently, clinicians have suggested that cone-beam computed tomography (CBCT) images already taken for other procedures can be used in determining the working length during root canal treatment. However, the deficiencies of CBCT images in teeth with endodontic treatment and the detection of root fractures constitute the limitations of CBCT. Given that these limitations have some unwanted effects on the prognosis of the tooth and bone tissue, immediate detection of root perforations is of utmost importance .
It has been previously suggested that the location of major and minor apical foramen, apical root resorption and horizontal root fractures can be determined with EAL [4, 15–17]. In addition, the accuracy of EALs in locating root canal perforations has been tested under in vitro conditions, and the results have shown that EALs are a clinically acceptable method to detect root canal perforations [14, 18, 19]. In our study, one hundred extracted lower premolar teeth were artificially perforated on the lateral root surfaces with different perforation diameters (1.25, 1.00, 0.75, 0.50 and 0.25 mm). All teeth were then embedded in the alginate model to evaluate the accuracy of EALs in determination of minimum root perforation diameter.
In previous studies, various electro-conductive materials such as alginate, agar-agar, saline solution, and gelatin were used for in vitro evaluation of EALs [14, 19–21]. In this study, alginate was used as an embedding mold because of its easy manipulation, proper electroconductivity, high elasticity and viscosity. It can wrap and adapt to the root surface tightly for simulating the periodontal tissue quite well .
Manufacturers recommend using the largest file that can reach apical constriction to measure working length. Herrera et al. stated that although small files are routinely used to determine the working length, accuracy of EALs might be influenced by file size, as slim files leave empty space within root canals, especially in wider canals. On the other hand, the effects of hand file sizes (#8, #10 and #15) on the result of electronic measurement were investigated, and it was found that the file size did not affect the accuracy of EALs [24, 25]. In addition, it has been shown the use of nickel titanium files or stainless-steel files does not affect the accuracy of EALs to determine the working length [7, 26]. In accordance with the manufacturer's instructions, a size 40 stainless steel K-file, which has the best adaptation to the root canal when the perforation area is reached, was used in electronic measurements in this study.
Numerous studies investigating the accuracy of EALs in detecting apical foramen have been reported that large apical diameters may affect the measurements of EALs [27, 28]. Venturi et al. indicated a clear relationship between apical foramen diameter and working length accuracy, showing that 11.3% of the measurements they obtained were ahead of apical foramen, and 85.3% of these results belonged to teeth with an apical foramen diameter of 0.40 and 0.60 mm. A study by Sübay et al. highlighted that as the apical foramen diameter increased, the number of results obtained from the EALs beyond the apical foramen increased. They indicated that Propex II has higher accuracy than Raypex 6 and Root ZX in diameters of 0.15 to 0.60 mm 30. In another study, it was shown that apical foramen diameter did not affect the accuracy of Root ZX II, while Propex II had more accurate results in diameters of 0.25 mm than wider foramen sizes . Although there have been many studies evaluating the effect of apical foramen diameter on the success of EALs, there was only one study evaluating the accuracy of EALs in detecting different size of root perforations .
In previous studies evaluating the detection of perforations with EALs, perforation sizes were 1, 0.60, 0.40, 0.30, and 0.27 mm. Fuss et al.  reported that the results were clinically acceptable for the Sono Explorer III and Apit (Endex) devices for a perforation diameter of 0.27 mm created by a #25 engine plugger. In another study , perforations with diameters of 0.55–0.6 mm and 0.25–0.4 mm were created with #25 and #30 spreaders, respectively. A significant difference was not indicated, but it was shown that Root ZX has a higher accuracy than Sono Explorer III ve Apit. On the contrary, EALs were not successful in determining the perforation size of 0.50 and 0.25 mm in the present study. These results, which are inconsistent with those of the present study, can be explained by the different tooth morphologies used in the experiment and by the use of transportation as the perforation technique. In our study, artificial perforations of the roots were performed in the areas marked on the external root surfaces with diamond burs perpendicularly directed to the long axis of roots to achieve an equal perforation diameter on both surfaces. In addition, we used a new bur in every 5 samples to prevent changes in diameter due to friction of burs. To avoid the differences in perforation diameter that may be caused by varying dentin thicknesses, we preferred to use the mesial or distal root surfaces instead of the buccal or lingual root surfaces to create perforation areas, as described in a previous study.
The effect of irrigation solutions on the accuracy of EALs has been evaluated in many studies, and the general belief is that root canal conditions affect accuracy of EALs [4, 21, 33]. Shin et al. investigated the effects of liquid-form and gel-form irrigants on perforation detection with Root ZX. It was shown that the device’s accuracy in locating root perforations was higher in liquid-form irrigants than in gel-form. Researchers explained this situation in the simulated perforation areas by the fact that the good flow of liquid-form irrigants better enabled them to reach the outer lateral surface of the root . Altunbaş et al. revealed that the most accurate result in determining perforation was obtained when the root canals were dry. Although the root canal perforations were detected by both devices within a clinically acceptable range in the presence of NaCl, NaOCl, and EDTA, the Dentaport ZX provided more accurate results than the Rootor . Another study by Khatri et al. indicated that Vdw gold (GmbH, Munich, Germany) presented better results than iPex in locating root perforation in dry condition. They found that in the presence of 2% CHX, EALs were able to accurately determine the perforation area, but in the presence of 3% NaOCl, both EALs showed significantly different results than the actual length determined under the stereomicroscope . Considering all these studies, we used saline solution during electronic measurements in order to ensure electro-conductivity between the alginate and the root canal.
Iatrogenic perforations often occur when preparing the post cavity or placing the post after root canal treatment. Traditional approaches on placing post restorations are centered around achieving good width and length for the post, which induces the risk of apical and strip perforation. Marroquin et al. created perforation areas located at mesiolingual canals to place metal posts, and they connected EALs to metal posts to detect root perforations. They recommended the use of an EALs to diagnose root perforations occurring during metal post placement, with high specificity and sensitivity and inter-device agreements .
In the previous studies evaluating both the determination of working length or root perforation, ± 0.5 mm tolerance was clinically accepted [4, 14, 21]. Thus, for perforation diameters less than 1 mm, it can be said that the success rate of the accuracy of EALs decreases as the perforation diameter gets narrower.
The study has some limitations that derive from its being an in vitro experiment, as the EALs were not in contact with living tissue, electro-conductive fluids such as blood and saliva were absent, and the electrical resistance of the periodontal ligament was different from that of the alginate impression material.