Basic Research—Technology
Accuracy of Cone-beam Computed Tomography in the Detection of a Second Mesiobuccal Root Canal in Endodontically Treated Teeth: An Ex Vivo Study Hesam Mirmohammadi, DDS, MSc, PhD,*† Lamees Mahdi, MSc,‡ Poerya Partovi, Drs,§ Abbasali Khademi, DDS, MSc,k Hagay Shemesh, DDS, PhD,† and Bassam Hassan, BDS, MSc, PhD¶ Abstract Introduction: There is a high incidence of a second mesiobuccal root canal (MB2) in maxillary molars. The study aim is to assess the accuracy of cone-beam computed tomographic (CBCT) imaging in detecting a second mesiobuccal root canal in endodontically treated maxillary molars. Methods: The study sample consisted of 60 extracted maxillary molars, which were endodontically opened and examined under a dental operating microscope for the presence of an MB2. The teeth were then further examined using micro–computed tomographic imaging as the gold standard. Root canals were filled (except the MB2) and were then subdivided into an experimental and a control group. After fixing the teeth in a dry human skull, they were scanned using CBCT imaging (AccuiTomo 170; Morita Inc, Tarumi-cho Suita City, Osaka, Japan). The observers for this study were 2 experienced radiologists blinded to the group allocation of controls and experiments; they evaluated the images twice independently. Sensitivity, specificity, and accuracy were calculated as well as the kappa values for both interand intraobserver agreement. Results: From 30 teeth, which were diagnosed without an MB2 under examination with a dental operating microscope, 6 teeth proved to have an MB2 using mCT (20%). Intraobserver reliability was high for both observers 1 (R = 0.85) and 2 (R = 0.96). Interobserver reliability as assessed by the Cohen kappa was excellent (R = 0.89). CBCT sensitivity for detecting an MB2 was 96%, specificity was 100%, and total accuracy was 98%. Conclusions: CBCT imaging is a suitable diagnostic technique for detecting a missed MB2 in endodontically treated teeth. (J Endod 2015;-:1–4)
Key Words Cone-beam computed tomography, endodontics, maxillary molars, microscope, second mesiobuccal
A
ccurate assessment of the internal anatomy of the maxillary molars remains challenging. In the past decade, cone-beam computed tomographic (CBCT) imaging has been introduced in clinical dentistry as a diagnostic imaging method and has been widely applied in several dental fields. The applications of CBCT imaging in endodontics have been previously reported in the literature (1). These include detection and follow-up of periapical lesions, diagnosis of vertical root fractures, assessment of the proximity of the root canal to adjacent anatomic structures including the maxillary sinus and the inferior dental canal (2, 3), detection of traumatic injuries, and presurgical assessments. Moreover, the added advantage of the third dimension in assessing the complex anatomy of the root canal has been emphasized (4, 5). CBCT imaging has also been used for the detection of a second mesiobuccal (MB2) root canal in maxillary molars (6, 7). However, recent literature showed that the visibility of anatomic structures including the root canal space is dependent on the CBCT machine type and scan settings such as field of view (FOV), number of projections, and resolution (8). In addition, the root filling materials (eg, Gutta-percha and sealer) have been reported to compromise the quality of the images (6, 9). In 1995, it was shown that micro–computed tomographic (mCT) scanning could image the internal and external tooth morphologies nondestructively (10). mCT imaging can be considered the reference (gold) standard for laboratory studies of canal anatomy (11). The aim of this study was to assess the accuracy of CBCT imaging in detecting an MB2 canal in endodontically treated maxillary molars using mCT measurements as the reference gold standard.
Materials and Methods Sample Preparation Sixty extracted maxillary molars were included in this study. The inclusion criteria were complete intactness of all roots and crowns, normal root numbers (3 roots) with no severe curve, no visible signs of external root resorption, no root filling, no root caries, and/or restorations. All the teeth were embedded in putty impression material and were endodontically accessed using the standard technique. Thereafter, the teeth were examined by 2 last-year dental students under a dental operating microscope (DOM) (Kaps 1100; Kaps GmbH, Asslar/Wetzlar, Germany) to assess the existence of an MB2 canal. Two groups were formed: experimental (with MB2 canal, n = 30) and control (without MB2 canal, n = 30). All teeth were scanned with mCT scanning, which acted as the gold stan-
From the *Dental Materials Research Center, Department of Restorative Dentistry, School of Dentistry, University of Medical Sciences, Isfahan, Iran; †Departments of Cariology Endodontology Pedodontology and ¶Oral Implants and Prosthetic Dentistry, Academic Centre for Dentistry Amsterdam, Universiteit van Amsterdam and Vrije Universiteit, the Netherlands; ‡Private Practice, Rotterdam, The Netherlands; §Private Practice, Niuew-Vennep, The Netherlands; and kDepartment of Endodontics, Torabinejad Dental Research Center, School of Dentistry, University of Medical Sciences, Isfahan, Iran. Address requests for reprints to Dr Hesam Mirmohammadi, ACTA, Department of Cariology Endodontology Pedodontology, Gustav Mahlerlaan 3004, 1081 LA Amsterdam, The Netherlands. E-mail address:
[email protected] 0099-2399/$ - see front matter Copyright ª 2015 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2015.06.011
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CBCT Imaging and Detection of MB2
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Basic Research—Technology dard for this study. For each tooth, the DICOM mCT data sets were exported and viewed in image analysis software (Amira 4.2; Visage Imaging, San Diego, CA). The reconstructed mCT 3-dimensional models of the root canal systems and 2-dimensional slices were viewed by 2 radiologists who, by consensus, determined canal numbers. Analyzing data collected by mCT scans proved that 6 teeth in the control group had MB2 canals, which were excluded from the rest of the study.
Endodontic Treatment and Radiographic Scans The teeth were endodontically treated using the Mtwo rotary system (VDW Silver; VDW GmbH, Munich, Germany) until file 40/ .06 and filled with gutta-percha (Maxima; Henry Schein, Melville, NY) and AH 26 cement (Dentsply DeTrey, Konstanz, Germany) using the lateral compaction technique. In teeth with a confirmed MB2 (according to the mCT results), all roots were filled except the MB2 canal (n = 30). In the control group, all roots were filled (n = 24). Subsequently, 1 maxilla not identified by age, sex, or ethnic group was obtained from the department of functional anatomy. The maxilla was a dried skull sample. The jaw bone was immersed in water for 24 hours to soften the sockets, and the maxillary molars were bilaterally extracted. Subsequent to extraction, the sockets were examined to assess their integrity, and the damaged labial alveolar plates were built up (mended) with wax where necessary. The teeth were labeled and placed in the sockets of the dry skull at a predefined order, which remained unknown to the observers. The teeth were fixated using putty impression material to their respective sockets. Three layers of dental wax were used to cover the alveolar bone and the maxillary sinus bilaterally to simulate soft tissue. The maxillary jaw and the teeth were then scanned by CBCT imaging (AccuiTomo 170) using a 6 6 cm FOV, 90 kVp and 5 mA, 360 arm rotation, a voxel size of 0.125 mm, and the high resolution scan setting. The positioning of the maxilla followed the manufacturer’s recommended protocol with the occlusal plane parallel to the floor (Fig. 1).
Figure 1. Example of a CBCT scan of molars (A) with and (B) without MB2.
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Observations Two observers (maxillofacial radiologists) with more than 5 years of experience in interpreting CBCT data sets assessed the visibility of the MB2 canal independently. The observers were blind to the teeth order and the number of root canals in each tooth. They were asked to assess the visibility of the MB2 canal on a dichotomous scale (MB2 canal present/absent). All measurements were entered into an Excel (Microsoft, Redmond, WA) spreadsheet. To assess intraobserver reliability, the radiographic observations were repeated by each observer individually after a 2-week interval.
Statistical Analysis Statistical analysis was performed using SPSS software (v20.0; IBM Corp, Armonk, NY). A 2-sided chi-square test was used to measure the sensitivity and specificity of CBCT imaging for the detection of an MB2 canal using mCT as the gold standard. A univariate analysis of variance was used to assess the influence of Gutta-percha filling material (filled or nonfilled) on the overall accuracy in detecting an MB2 canal. The overall agreement among the observers was measured using the Cohen kappa. The alpha value was set to 0.05.
Results The visibility of an MB2 on the mCT data served as the gold standard (Fig. 2) against which DOM and the CBCT measurements were compared. Twenty percent of MB2 canals were missed under DOM evaluation (6/30 teeth). Intraobserver reliability was high for both observers 1 (R = 0.85) and 2 (R = 0.96). Interobserver reliability as assessed by the Cohen kappa was excellent (R = 0.89). CBCT sensitivity for detecting an MB2 canal in root-filled teeth was 96%, specificity was 100%, and total accuracy was 98% (Table 1), whereas for DOM, it was 83.33%, 100%, and 90%, respectively, for detecting an MB2 canal in nonfilled teeth (Table 2).
Figure 2. Example of a mCT scan of a first upper molar with MB2. JOE — Volume -, Number -, - 2015
Basic Research—Technology TABLE 1. Accuracy of CBCT for Detecting Missed Second Mesiobuccal Canals Consensus observation for CBCT Present Absent
Gold standard Present
Absent
Accuracy percentages
26 0
1 27
96 100
Discussion Endodontic treatment of maxillary molars remains challenging because of complex root canal anatomy, which requires an integrated and holistic diagnostic approach to achieve correct and adequate treatment. In addition to direct clinical inspection of the tooth, several diagnostic modalities including DOM, dental loupes, and conventional radiographs are routinely applied in the clinic to assess the presence of an MB2 canal (12–14). Root canals have complex 3-dimensional anatomy, and representations of this anatomy provided by 2dimensional intraoral radiographs contain little information on the buccolingual dimension. Canals that are aligned in a buccolingual plane cannot be easily differentiated from each other. CBCT imaging has the unique ability to provide high-resolution images in multiple planes of space while eliminating superimposition of surrounding structures (15). However, the presence of root canal filling materials and metallic posts has been suggested as a limiting factor for CBCT image quality, resulting in several streak and beam hardening artifacts, which could negatively influence the detectability of an MB2 canal (16). The results of this study showed excellent accuracy of CBCT imaging for detecting an MB2 canal, and the presence of a root canal filling material (gutta-percha and AH 26 sealer) does not seem to influence detection accuracy. The intra- and interobserver reliability were both very good, indicating high fidelity for CBCT measurement. In this study, the teeth in the control group did not have an MB2 canal because obturated MB2 canals could make it easier for observers to differentiate the teeth in the control group from the experimental group. Six samples, in which MB2 canals could not be detected with DOM, revealed an MB2 canal using mCT imaging and were excluded from the rest of the study. The failure to see 20% of MB2 canals with DOM is in agreement with some previous studies (17, 18) and could be of clinical importance. This study did not aim to compare CBCT imaging with DOM because the microscope was used by unexperienced operators and before endodontic treatment, whereas CBCT imaging was evaluated by experienced radiologists and after obturation. In a previous study regarding the efficacy of CBCT imaging in detecting an MB2 canal in extracted first molars, it was positively identified in 68.4% on clinical sectioning, whereas i-CAT CBCT imaging (i-CAT; Imaging Sciences International, Hatfield, PA) only correctly identified MB2 canals in 57.9% of the non–root-filled samples (15). The higher accuracy of CBCT imaging reported in our study in endodontically treated teeth could be because of the different CBCT system used, FOV, and scan setting selections. In this study, a small FOV of 6 6 cm coupled with 360 arm rotation were used to improve image quality because it has been previously proven that these scan settings improve the visibility of the root canal space (8). It has been previously reported that CBCT voxel size selection could play an important role in detecting a missed MB2 canal (6). In that study regarding the accuracy of CBCT imaging in detecting MB2 canals in root-filled teeth, 89 extracted human maxillary molars were scanned using the i-CAT CBCT system; their results showed that the influence of root canal filling on detection accuracy is dependent on voxel size selection. Smaller voxels of 0.2 mm resulted in greater accuracy compared with 0.3-mm voxels. In the JOE — Volume -, Number -, - 2015
TABLE 2. Accuracy of DOM for Detecting Second Mesiobuccal Canals Consensus observation for DOM Present Absent
Gold standard Present
Absent
Accuracy percentages
30 6
0 24
100 80
current study, a voxel size of 0.125 mm was used, resulting in improved detection accuracy. However, the voxel size in the present study remained constant to reduce the number of variables. It is noteworthy to mention that the results of a recent systematic review regarding the influence of voxel size on diagnostic outcomes with CBCT imaging showed that there is no evidence to support the use of a specific voxel size for any endodontic application (19). However, it has been previously noted that voxel size is not the sole determinant for image quality in CBCT imaging. Rather, a variety of factors including contrast-to-noise ratio, detector specification, FOV, and scan setting selections and image artifacts play an equally important role in determining the visibility and contrast appearance of small anatomic structures such as the pulp chamber and root canal. These findings show the need to develop standardized scanning and image reconstruction protocols for endodontic applications. In conclusion, CBCT imaging (0.125 voxel size, small FOV) was found to be accurate in detecting an MB2 canal in endodontically treated maxillary molars. More research is needed to assess whether the obtained results are applicable to other CBCT systems and scan settings. Additionally, in vivo research is required to validate these ex vivo results.
Acknowledgments The authors deny any conflicts of interest related to this study.
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