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Journal of Oral Science, Vol. 63, No. 2, 167-169, 2021

Original article The use of micro-computed tomography to determine the accuracy of electronic working length with two apex locators Hisashi Suguro1,2), Anna Nishihara3), Takahito Tamura4), Takeshi Nakamura4), Yurika Toyama4), and Osamu Takeichi1,2)

1) Department of , Nihon University School of Dentistry, Tokyo, Japan 2) Division of Advanced Dental Treatment, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan 3) Division of Oral Structural and Functional Biology, Nihon University Graduate School of Dentistry 4) Division of Applied Oral Sciences, Nihon University Graduate School of Dentistry, Tokyo, Japan (Received September 7, 2020; Accepted January 9, 2021)

Abstract anatomical structure is complex [5-7]. Anatomical changes in AC site, size, tooth type, and age cause WL assessments to be unreliable [5-7]. It is well Purpose: This study evaluated the precision of electronic working length known that the AF is not always at the radiographic apex of the root, which by microcomputed tomography using two electronic apex locators (EALs). is often located on the lingual/buccal or mesial/distal side [2]. At present, Methods: Twenty single-rooted permanent teeth without caries or restora- while many radiographs are taken, electronic apex locators (EALs) are also tions were selected as the subject teeth. The positions of the minor apical widely used. The development of EALs, used with appropriate radiographs constriction (AC) and major (AF) were measured by elec- [8-12], has enabled the assessment of WL to be more accurate and predict- tronic length, and microcomputed tomography was performed able, and has made EALs more accurate and reliable in determining WL with the file inserted and fixed in the root canal. All teeth were measured [8-12]. As a result, many devices have been developed as clinical aids for individually and independently by two operators. The Mann-Whitney determining apex location. Osada Electric Co., Ltd (Tokyo, Japan) and U-test was used to statistically test the AC and AF values using two EALs; other companies have developed and improved electric root canal mea- P < 0.05 was defined as statistically significant. suring devices based on basic research on root canal length [1,13-15]. In Results: This was 65.0% within 1.5 mm in the case of two EALs on AC. recent years, qualitative evaluation based on microcomputed tomography This was more than 90.0% within 1.0 mm in the case of two EALs on (CT) has attracted considerable attention in the field of histomorphologi- AF. Comparison of the differences between the respective AC and AF of cal research [16-18]. At present, microcomputed tomography (micro-CT) the measurements obtained using the two EALs revealed no significant imaging is the most accurate imaging method for assessing the internal difference. structure of the root canal system [18]. Furthermore, micro-CT images are Conclusion: The two EALs are devices that can greatly improve the accu- nondestructive research tools that can effectively identify, evaluate, and racy of WL control. measure the root canal system in 3D [19,20]. The purpose of this study was to compare the accuracy of two EALs using micro-CT imaging and Keywords; cementodentinal junction, , determine anatomical variations that may affect their accuracy. microcomputed tomography, working length Material and Methods

Introduction The EALs used in this study consisted of Apit 7 (Osada Electric Co, Ltd, Tokyo, Japan) and Apit 15 (Osada Electric Co., Ltd) (Fig.1a, b). Written Removal of all pulp tissue, necrotic matter, and microorganisms from the consent was obtained from each patient according to the stipulations of root canal is essential for successful endodontic therapy [1]. It is generally the institutional review board of Nihon University Faculty of Dentistry accepted that endodontic therapy should be limited to the root canal system (EP16D012). Twenty single-rooted permanent teeth without caries or [2]. To realize this goal, working length (WL) must not only be accurately restorations were selected as the study specimens. Roots with root resorp- detected during , but it must also be maintained. Accu- tion, tooth fracture, open apex, or root canals not radiographically visible rate WL determination is a prerequisite for successful root canal treatment, were excluded from the study. After extraction, the teeth were placed in reducing the likelihood of inadequate root canal irrigation or damage to the 5.25% sodium hypochlorite solution to remove residual tissue from the tissue surrounding the apex from excessive instrumentation. Appropriately external root surface. The cusps were flattened with a diamond burr using determining WL is one of the most important factors in the success of a high-speed handpiece. Opening of the root canal was performed using endodontic treatment. Conventional methods of establishing WL consist a Gates-Glidden drill. After locating the root canal orifice, the specimens of (a) finger sensation, (b) use of radiographic images, and (c) information were cleansed with 1% sodium hypochlorite to wash away root canal debris using anatomical mean values. While the fingers are useful in determin- and subsequently perforated with a No.15 K-file. Root canal enlargement ing WL, this method has many limitations. Radiography for measurement was not performed. An in vitro model was developed in which the teeth, of WL has been used for many years. Radiographs are an important and root canals included, were fitted in a plastic case while being immersed in integral part of endodontics, but there is a need to reduce exposure to ion- a 0.9% saline solution. The present study compared the accuracy of two izing radiation as much as possible [3,4]. The apical foramen (AF) is not EALs on the same tooth in combination with No. 20K-file. Figure 2a shows always located at the anatomical apex of the tooth [5-7]. The approach the idealized anatomy of the apex. In accordance with the manufacturer’s generally recommended has been that using the mean value obtained from instructions, the meter screen of both EALs for WL indicated minor AC, anatomical study, and based on the assumption that the cementodentinal and regarding the apex on the meter screen, the major AF was displayed. junction (CDJ) is located at the site of apical constriction (AC), the WL Herein, the K-file was inserted until the meter screen showed that it had should be 1-2 mm short of the radiographic apex [2]. However, the apical reached the AC and the AF, with the EALs used in random order. After inserting the file into the root canal and performing fixation, micro-CT Correspondence to Dr. Hisashi Suguro, Department of Endodontics, Nihon University School of imaging was performed immediately. The imaging conditions of micro-CT Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan (R_mCT; Rigaku Corp., Tokyo, Japan) were imaging magnification: 6.7× Fax: +81-3-3219-8348 E-mail: [email protected] (voxel size: 30 × 30 × 30 µm), tube voltage: 90 kV, tube current: 120 A, J-STAGE Advance Publication: March 18, 2021 and filming duration: 17 s. The imaging data were observed by i-View-R Color figures can be viewed in the online issue at J-STAGE. doi.org/10.2334/josnusd.20-0466 (Rigaku Corp., Tokyo, Japan) and qualitatively evaluated. In the evaluation DN/JST.JSTAGE/josnusd/20-0466 method, as shown in Fig. 2b, the radiographic apices were designated as 168

Fig. 3 a: micro-CT images of the buccolingual side (left) and mesiodistal side (right) of Apit 7 AC. b: micro-CT images of the buccolingual side (left) and mesiodistal side (right) of Apit 15 AC. c: micro-CT images of the buccolingual side (left) and mesiodistal side (right) of Apit 7 AF. d: micro- Fig. 1 EAL. a: Apit 7 and meter screen used in the present study. b: Apit 15 and meter screen. CT images of the buccolingual side (left) and mesiodistal side (right) of Apit 15 AF.

Fig. 2 Terminal canal morphology. a: idealized anatomy of apical constriction (AC); apical foramen (AF). b: measurement method used in this study. In the evaluation method, as shown in Fig. 2b, the radiographic apices were designated as A and B, and lines were drawn there. The center of the line drawn was C, and the distance (D) from C to the file tip measured. Fig. 4 Results of AC and AF of the two EALs (P < 0.05). The black horizontal line represents the median (50% of cases), while the lower and upper edges of the box represent the 25th and 75th percentiles, respectively.

Table 1 Number of cases and percentage of AC of the two EALs Table 2 Number of cases and percentage of AF of the two EALs

Apit 7 Apit 15 Apit 7 Apit 15 n = 20 % n = 20 % n = 20 % n = 20 % 2.0 more 2 10 2 10 2.0 more 0 0 0 0 2.0 to 1.5 5 25 5 25 2.0 to 1.5 0 0 0 0 1.5 to 1.0 4 20 9 45 1.5 to 1.0 1 5 2 10 1.0 to 0.5 9 45 3 15 1.0 to 0.5 11 55 12 60 0.5 to 0.0 0 0 1 5 0.5 to 0.0 7 35 6 20 0.0 to −0.5 0 0 0 0 0.0 to −0.5 1 5 0 0 −0.5 to −1.0 0 0 0 0 −0.5 to −1.0 0 0 0 0 −1.0 more 0 0 0 0 −1.0 more 0 0 0 0

A and B, and lines were drawn at those locations. With the center of the AC was 1.119 mm (first quartile: 0.806 mm, third quartile: 1.629 mm) drawn line set as C, this study measured the distance (D) from C to the file by Apit 7 and 1.319 mm (first quartile: 1.062 mm, third quartile: 1.541 tip. In performing the measurement, the mesiodistal and buccolingual sides mm) by Apit 15. Median AF was 0.586 mm (first quartile: 0.423 mm, third were measured three times each, and the mean value of the two was used quartile: 0.768 mm) by Apit 7 and 0.634 mm (first quartile: 0.478 mm, for the value. All teeth were measured individually and independently by third quartile: 0.7745 mm) by Apit 15. Comparison of the respective dif- two operators. ferences between AC and AF of the measurements obtained using the two EALs revealed no significant differences. Table 1 shows the number and Statistical analysis percentage of cases of AC by Apit 7 and Apit 15. This was 65.0% within The Mann-Whitney U-test (SPSS version 16.0, Chicago, IL, USA) was 1.5 mm in the case of Apit 7 and 65.0% within 1.5 mm in the case of Apit used to statistically test the AC and AF values using two EALs; P < 0.05 15. Table 2 shows the number and percentage of cases of AF by Apit 7 and was defined as statistically significant. Apit 15. This was 95.0% within 1.0 mm in the case of Apit 7 and 90.0% within 1.0 mm in the case of Apit 15. In all studies, there were no data Results concerning protrusion from the apex.

Accuracy was calculated only with stable measurements. Discussion Figure 3 shows the micro-CT images of AC and AF of Apit 7 and AC and AF of Apit 15 on the mesiodistal and buccolingual sides. Figure 4 EALs are currently considered to be accurate devices for determining WL shows the Box-plot illustrating the AC and AF of the two EALs. Median [1]. Recent studies have reported that the use of an electronic apex locator 169 generally reduces the number of radiographs that need to be taken. It has References also been demonstrated that even higher accuracy can be realized by using 1. Gordon MPJ, Chandler NP (2004) Electronic apex locators. IntEndod J 37, 425-437. a combination of both these techniques [1]. An important consideration in 2. Nekoofar MH, Ghandi MM, Hayes SJ, Dummer PM (2006) The fundamental operating root canal treatment is apex anatomy [5-7]. In terms of conventional thera- principles of electronic root canal length measurement devices. Int Endod J 39, 595-609. pies, it has been established that root canal treatment and subsequent root 3. Brunton P, Abdeen D, MacFarlane T (2002) The effect of an apex locator on exposure to radiation during endodontic therapy. J Endod 28, 524-526. canal filling should end at the site of AC, the narrowest diameter of the root 4. Vertucci F (2005) Root canal morphology and its relationship to endodontic procedures. canal [21,22]. This point appears to be consistent with the CDJ and is based Endodontic Topics 10, 3-29. on data from histological sections and specimens [22]. However, the loca- 5. Kuttler Y (1955) Microscopic investigation of root apexes. J Am Dent Assoc 50, 544-552. tion and anatomy of the CDJ differs considerably for each tooth, root, and 6. Green D (1960) A stereomicroscopic study of 700 root apices of maxillary and mandibular posterior teeth. Oral Surg Oral Med Oral Pathol 13, 728-733. root canal wall [22]. Furthermore, the CDJ cannot be accurately placed on 7. 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Fouad AF, Reid LC (2000) Effect of using electronic apex locators on selected endodontic root canal. It is also most often used by clinicians as the apical terminus treatment parameters. J Endod 26, 364-367. and the reference point for expansion, shaping, cleaning, disinfection, and 12. ElAyouti A, Weiger R, Lost C (2001) Frequency of overinstrumentation with an acceptable radiographic working length. J Endod 27, 49-52. filling [5]. To improve the likelihood of long-term success, injuries in this 13. Fouad AF, Rivera EM, Krell KV (1993) Accuracy of the Endex with variations in canal area due to devices or filling material should be avoided. Microcomputed irrigants and foramen size. J Endod 19, 63-67. tomography was used in this study. Previous studies have utilized visual 14. Ounsi HF, Haddad G (1998) In vitro evaluation of the reliability of the Endex electronic apex locator. J Endod 24, 120-121. inspection, scanning electron microscopy, or root sectioning to determine 15. Hoer D, Attin T (2004) The accuracy of electronic working length determination. Int Endod EAL accuracy [25-27]. When using these methods, the apex is partially J 37, 125-131. destroyed during examination, making it highly likely that an error will 16. Ejima K, Omasa S, Motoyoshi M, Arai Y, Kai Y, Amemiya T et al. (2012) Influence of occur during measurement [25-27]. However, microcomputed tomog- metal artifacts on in vivo micro-CT for orthodontic mini-implants. J Oral Sci 54, 55-59. 17. Udagawa A, Sato S, Hasuike A, Kishida M, Arai Y, Ito K (2013) Micro-CT observation of raphy (micro-CT) imaging is a nondestructive research tool that enables angiogenesis in bone regeneration. Clin Oral Implan Res 24, 787-792. 3D identification, evaluation, and measurement of the root canal system 18. Suguro H, Takeichi O, Hayashi M, Okamura T, Hira A, Hirano Y et al. (2018) Microcom- [19,20]. The 3D reconstruction of scanned teeth was extremely useful for puted tomographic evaluation of techniques for warm gutta-percha obturation. J Oral Sci 60, 165-169. measuring AC and AF. In addition, it allowed visualization and accurate 19. Meder-Cowherd L, Williamson AE, Johnson WT, Vasilescu D, Walton R, Qian F (2011) measurement of anatomical details of the apical one-third [19,20]. To date, Apical morphology of the palatal roots of maxillary molars by using micro-computed no studies have used micro-CT imaging to study the EAL. The results of tomography. J Endod 37, 1162-1165. 20. ElAyouti A, Hülber-J M, Judenhofer MS, Connert T, Mannheim JG, Löst C et al. (2014) this study confirmed that the two EALs could accurately determine the Apical constriction: location and dimensions in molars-a micro-computed tomography root canal length within 1.5 mm from the site of AC in the case of AC and study. 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Chugal NM, Clive JM, Spångberg LS (2003) Endodontic infection: some biologic and reduces the risk of instruments’ crossing the AF. Therefore, the EAL is treatment factors associated with outcome. Oral Surg Oral Med Oral Pathol Oral Radiol an instrument that uses appropriate radiographs and is a device that can Endod 96, 81-90. 25. Pagavino G, Pace R, Baccetti T (1998) A SEM study of in vivo accuracy of the Root ZX greatly improve the accuracy of WL control. electronic apex locator. J Endod 24, 438-441. 26. Tselnik M, Baumgartner JC, Marshall JG (2005) An evaluation of root ZX and elements Conflict of interest diagnostic apex locators. J Endod 31, 507-509. 27. Guise GM, Goodell GG, Imamura GM (2011) In vitro comparison of three electronic apex None. locators. J Endod 36, 279-281.