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The Use of Micro-Computed Tomography to Determine The 167 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 Endodontics, 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 apical foramen (AF) were measured by elec- [8-12], has enabled the assessment of WL to be more accurate and predict- tronic root canal 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, electronic apex locator, 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 root canal treatment, 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.
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