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Analysis of the Width of Vertical Root Fracture in Endodontically Treated Teeth by 2 Micro–Computed Tomography Systems Chih-Chia Huang, DDS, MS,* Ya-Chi Chang, DDS,* Meng-Che Chuang, DDS,* Hsueh-Jen Lin, DDS, MS,‡ Yi-Ling Tsai, DDS, MS,† Shu-Hui Chang, PhD,† Jyh-Cheng Chen, PhD,§ and Jiiang-Huei Jeng, DDS, Specialist, PhD† Abstract Introduction: Early detection of vertical root fracture (VRF) is important for clinical endodontic practice. The purpose of this study was to measure the fracture width (distance between 2 sides of the fracture) of VRF teeth in vitro by using 2 micro–computed tomography (m-CT) systems with different spatial resolution and voxel size. Methods: Thirty-seven endodontically treated teeth with VRF were scanned by 80-mm pixel size m-CT. Fifteen teeth with no obvious fracture line, blurred image, or fracture space less than 100 mm were scanned by 9-mm pixel size m-CT. Results: Presence of 2 VRF lines was more common in premolars (82%) than in molars (53%). In 7 premolars (32%) and 9 molars (60%), the VRF lines extended to within the apical 3 mm of the root. All fracture lines were detected by 9-mm pixel size m-CT, but only 22 of 37 VRF teeth had vertical fracture identified by 80-mm m-CT. From m-CT examination, none of the fracture lines showed consistent and uniform fracture space. If 2 fracture lines were present, they were typically in opposite (not linear) directions. There was a significant correlation between 2 fracture lines or fracture lines extending within the 3 mm of the apex and fracture width greater than 100 mm. Conclusions: Application of 9-mm m-CT can be accurately used for early detection of VRF. Fracture characteristics (eg, number of fracture lines, extension of fracture line) may affect the fracture width. Appropriate use of m-CT technology can be helpful for early diagnosis of VRF. (J Endod 2014;40:698–702)
Key Words Cone-beam computed tomography (CBCT), endodontically treated teeth, micro-computed tomography (m-CT), vertical root fracture (VRF)
D
efinitive diagnosis of vertical root fracture (VRF) in clinical dental practice is important to avoid unnecessary endodontic retreatment or periapical surgery. In addition, prolonged infection, inflammation, and swelling caused by VRF compromise adjacent alveolar bone used in implant placement and prosthetic reconstruction. However, definitive diagnosis of VRF in endodontically treated teeth by using periapical radiographs is problematic (1–4). Recent research has focused on the development of appropriate non-radiographic methods to detect VRF; however, current techniques are inadequate (5–7). Although 2-dimensional radiography with image processing by fractal dimension method can be helpful in evaluating the outcome of endodontic treatment (8), 3-dimensional imaging with computed tomography (CT) allows for earlier evaluation of apical healing (9). Since the introduction of cone-beam CT (CBCT) in dental treatment, endodontists have used CBCT in the evaluation of root canal distribution, detection of apical lesions, verification of horizontal and vertical root fracture, and the diagnosis of odontogenic infection (10–14). Studies evaluating CBCT in VRF have shown higher sensitivity and specificity than periapical radiographs in detecting artificial fracture lines in teeth (15–22). The spatial resolution of CBCT images depends on the voxel size of the detector, focal spot, kV, and different CBCT settings (23). The smaller voxel size translates into higher resolution of CBCT. Prior studies used CBCT to detect artificially created VRF and evaluated different CBCT parameters (18). One case report described 140-mm spatial resolution of flat panel volume detector computer tomograph system in 5 VRF teeth (24). However, longitudinal root fracture may require higher resolution for detection. Knowing the possible width of fracture in VRF teeth helps to delineate CBCT with adequate voxel size and spatial resolution to detect the presence of longitudinal root fracture. VRF may show 1 or 2 fracture lines in roots (25). The possible correlation between the number of fracture lines and width of the fracture is an interesting issue awaiting investigation. Micro-CT (m-CT) with higher spatial resolution and very small voxel size could be a tool to analyze tooth structure without distortion (26, 27). Because different m-CTs have differential spatial resolution, voxels, and computer memory, this study used an endodontic microscope and 2 m-CT systems with different voxel size and spatial resolution to measure the vertical fracture width in endodontically treated teeth.
From the *Department of Dentistry, Cardinal Tien Hospital, New Taipei City; †Graduate Institute of Clinical Dentistry and Department of Dentistry, National Taiwan University Hospital and National Taiwan University Medical College, Taipei; ‡Department of Dentistry, Show Chwan Memorial Hospital, Changhua; and §Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan. Jyh-Cheng Chen and Jiiang-Huei Jeng contributed equally to this work. Address requests for reprints to Dr Jiiang-Huei Jeng, Department of Dentistry and School of Dentistry, National Taiwan University Hospital and National Taiwan University Medical College, No. 1, Chang-Te Street, Taipei, Taiwan; or Prof Jyh-Cheng Chen, Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, No 155, Li-Nong Road, Taipei, Taiwan; E-mail addresses: [email protected] or [email protected] 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.12.015
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Basic Research—Technology Materials and Methods Sample Collection and Preparation Thirty-seven VRF teeth (15 molars and 22 premolars) were collected by 8 endodontists during the previous 5 years (2007– 2011). These study teeth were extracted after clinical diagnosis of VRF, which was confirmed microscopically after surgical exposure of the root surfaces. After removal of the granulation tissue on the root surface, the teeth were placed in formalin and stored at 4 C. Two teeth (1 molar and 1 premolar) without crown/root fracture were extracted and preserved in dry conditions for 3 years to serve as control. Only teeth extracted without evident root surface damage were included in this study. Microscope Examination All study teeth were soaked in 5% b-iodine solution for 5 minutes. The number of VRF lines on the root surfaces was observed under microscope (Moller-Wedel Denta 300, Wedel, Germany) with 4 and 8 magnifications. For inclusion in the study, all study teeth must have had at least 1 VRF line on the root surface confirmed by 2 endodontists. The number of fracture lines and any fracture lines extending to within the apical 3 mm of the root apex were recorded. Micro-CT Image (Image Voxel Size: 80 mm Mode) Acquisition All study teeth were scanned by m-CT (Triumph X-O CT System; Gamma Medica Ideas, Northridge, California) with the following parameters: 80 kV, 90 mA, field of view 29.59 mm, acquisition time 5 minutes, and 512 slices. The images were imported into DICOM file format and visualized and analyzed with Mimics software (Mimics Innovation Suite, Leuven, Belgium). After m-CT scanning, the 37 study teeth were divided into 4 groups on the basis of the width of the fracture: group A (fracture line detected by 9-mm m-CT, but not in 80-mm mode m-CT), group B (fracture width < 100 mm), group C (fracture width between 100 and 200 mm), and group D (fracture width > 200 mm) (Table 1). Micro-CT Image (Image Voxel Size: 9 mm) Acquisition The 2 control teeth and 15 study teeth (7 molars and 8 premolars) with fracture < 100 mm (not detected or obscured by the 80-mm mode CT acquisition) were scanned again by m-CT (Skyscan 1076; BRUKER MICROCT, Kontich, Belgium) with higher resolution (9-mm mode). The scanned parameters were 49 kV, 139 mA, field of view 25 mm, acquisition time 21 minutes, and 2000 slices. The images were imported into DICOM file image and visualized by the Mimics software. Measurement of Maximal Fracture Space by m-CT Image Analysis Sequential slices of m-CT images were taken, and VRF appearance and disappearance were recorded (Fig. 1A). One transverse section in the middle of the VRF line was used to measure the maximum VRF space. The width of the fracture was measured at 3 points (S1, S2, and S3) (Fig. 1B). The widest distance at S1, S2, and S3 was regarded as the maximum width of the fracture. If 2 fracture lines were present, the larger fracture line was recorded. Statistical Analysis The Fisher exact test was used to evaluate whether fracture width > 100 mm and # 100 mm and extension of the fracture line to within the apical 3 mm of the root apex were associated with the number of fracture lines. JOE — Volume 40, Number 5, May 2014
TABLE 1. Number (percentage) of Teeth (n = 37, 15 molars, 22 premolars) with Different VRF Spaces as Detected by 2 Modes of m-CT Group A Group B Group C Group D
Total
Molar
Premolar
2 (13) 5 (33) 5 (33) 3 (20)
3 (14) 5 (23) 12 (55) 2 (9)
5 (11) 10 (27) 17 (46) 5 (14)
Group A, fracture line detected by 9-mm m-CT, but not in 80-mm mode m-CT; group B, detected fracture space < 100 mm; group C, width of the fracture between 100 and 200 mm; group D, width of the fracture > 200 mm.
Results Microscope View All study teeth (15 molars, 22 premolars) showed 1 or 2 fracture lines on the root surface as observed under a microscope (Fig. 1C). The presence of 2 fracture lines was more common in premolars (18 of 22, 82%) than in molars (8 of 15, 53%) (Table 2). In 7 premolars (7 of 22, 32%) and 9 molars (9 of 15, 60%), the VRF extended to within 3 mm of the root apex (Fig. 1D). Micro-CT Image (Image Voxel 80 mm) Acquisition and Fracture Space Analysis In group A (5 teeth), no fracture line was detected in the 80-mm mode m-CT. In group B (10 teeth), the fracture line was obscure in the 80-mm m-CT (Fig. 1E). Fracture lines were clearly visualized in group C (17 teeth) and group D (5 teeth) by using 80-mm m-CT (Fig. 1F). Micro-CT Image (Image Voxel 9 mm) Acquisition in the Control Teeth The control molar showed no marked fracture line by using 9-mm m-CT. Three fracture lines extending from cementum into root dentin from different directions were detected in the control premolar. The 3 fracture lines disappeared near the root canal wall and did not merge. Micro-CT Image (Image Voxel 9 mm) Acquisition and Fracture Space Analysis Fracture lines were not consistent and regular in the root dentin. None of the teeth had uniform width fractures as observed under m-CT. If 2 fracture lines were present, they were often in opposite (non-linear) directions. The mean widths of the fractures measured at S1, S2, and S3 were 133 28.4, 131 27.0, and 128 26.9 mm, respectively (P > .05) (Table 2). Although fracture lines in groups A and B could not be clearly identified by the 80-mm m-CT, fracture lines were detected by 9-mm m-CT. As shown in Figure 1G, no marked fractures were seen on images from the 80-mm m-CT, whereas fracture lines were detected in sequential 9-mm m-CT images. Sequential transverse sections of 9-mm m-CT images from root apex to cementoenamel junction (Fig. 1H–L) showed that the first fracture line started from outer cementum surface near the apex; the fracture did not originate from the inner root canal (Fig. 1H). The fracture line subsequently extended through dentin into the root canal wall (Fig. 1I). As the VRF extended coronally, the width of the fracture enlarged. In all cases, the maximal fracture space was present in the mid-root section. As the size of the first fracture decreased, a second fracture line was detected in the contralateral side of the middle root (Fig. 1J). The second fracture line extended through the dentin into cementum of the outer root surface (Fig. 1K). Moving coronally, the 2 fracture lines merged in the root canal, and the size of the first fracture line decreased (Fig. 1L). Characterization of Vertical Root Fracture Space
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Figure 1. (A) Transverse slices were selected from root tip to cementoenamel junction (CEJ) (arrows). The median of slice was selected for measurement (arrowhead). (B) The selected slice of the width of the fracture was measured at 3 points (S1, S2, and S3) (arrows). (C) Observation of the tooth and root surface by microscope. One or 2 fracture lines on the root surface were noted under 8 magnification (arrows). (D) Example of VRF extending to apical 3 mm of the root (arrow). (E) A blurred image was observed when the VRF line (arrow) in the group B teeth was analyzed by 80-mm m-CT. (F) A clear VRF line was observed on axial section of affected tooth in group C (arrow) when analyzed by 80-mm mode m-CT. Image of a representative tooth is shown. (G) No VRF line was detected by the 80-mm mode m-CT in teeth in group A. Image of a representative tooth is shown. (H) Sequential 9-mm mode m-CT images of the same tooth. Fracture line was first identified on the outer root surface (arrow) in the apical region. (I) Fracture line subsequently extended through the root dentin (arrow) into the root canal. (J) The 9-mm mode m-CT detected the first VRF line (arrows) in the middle third of the root. A second fracture line was noted on the contralateral side (arrowhead). (K) While the first fracture line is still visible (arrows), the second fracture line extended through the dentin into cementum of the outer root surface (arrowhead). (L) The 2 fracture lines (arrows) merged in the root canal, and the first fracture line decreased in size in the 9-mm mode m-CT image.
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Basic Research—Technology TABLE 2. Width of the Fracture (S1, S2, and S3) and Fracture Lines (1 or 2) on the Root Surface of VRF teeth (n = 37, 22 premolars, 15 molars) Sample no.
S1 (mm)
S2 (mm)
S3 (mm)
1 (M) 10 10 20 2 (M) 29 19 14 3 (Pm) 13.5 33.3 18.5 4 (Pm) 15 16 36 5 (Pm) 16 18 14 6 (M) 60 70 60 7 (M) 90 60 60 8 (M) 60 60 80 9 (M) 24.3 48.6 13.5 10 (M) 20.1 32 25.2 11 (Pm) 45 76 68 12 (Pm) 64 72 36 13 (Pm) 54 63 36 14 (Pm) 60 90 70 15 (Pm) 60 70 80 16 (M) 160 170 140 17 (M) 140 90 120 18 (M) 170 170 140 19 (M) 190 140 140 20 (M) 130 140 160 21 (Pm) 110 100 100 22 (Pm) 150 80 60 23 (Pm) 150 190 170 24 (Pm) 130 130 150 25 (Pm) 110 70 80 26 (Pm) 130 150 180 27 (Pm) 70 100 70 28 (Pm) 110 110 70 29 (Pm) 180 150 110 30 (Pm) 170 140 130 31 (Pm) 100 140 180 32 (Pm) 100 150 100 33 (M) 240 220 190 34 (M) 180 200 380 35 (M) 1070 1030 980 36 (Pm) 280 200 290 37 (Pm) 230 250 160 Total (mean 133 28.4 131 27.0 128 26.9 standard error)
Fracture line 1 1 1 2 2 2 2 1 1 1 2 1 2 2 1 1 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 —
M, molar; Pm, premolar.
Statistical Analysis between the Microscope and Width of the Fracture Space Of the 37 study teeth, 22 had fracture widths > 100 mm, and 15 did not. Among those with fracture widths > 100 mm, 20 showed 2 fracture lines, and 2 did not. Among study teeth with fracture width < 100 mm, 7 had 2 fracture lines, and 8 did not. Fracture width > 100 mm was significantly associated with the presence of 2 fracture lines on the root (P = .006). There was 82% or 90% power of detecting significant association for the 2-sided test conducted at 0.05 or 0.1 level of significance. Among 22 study teeth with fracture widths > 100 mm, 15 showed fracture lines extending to within 3 mm of the apex. Among 15 study teeth with fracture widths < 100 mm, 4 had fracture lines extending to the apical 3 mm. Fracture width > 100 mm was significantly related to VRF extending to the apical 3 mm (P = .02). The power of this 2-sided test was about 70% or 80% at 0.05 or 0.1 level of significance.
Discussion To achieve early and correct diagnosis of VRF in endodontically treated teeth, proper voxel size of CBCT is required. However, little clinical information is available regarding the fracture width in VRF teeth to JOE — Volume 40, Number 5, May 2014
guide selection of proper voxel size of CBCT. In this study, only 5 teeth showed fracture widths larger than 200 mm (Table 1). Thus, CBCT with voxel size greater than 200 mm may not be suitable for clinical identification of most VRFs. In groups C and D, only 56% of teeth had fracture widths greater than 100 mm (Tables 1 and 2) that can be potentially detected by 80-mm voxel size CBCT. Of note, the properties of maxillary and mandibular bone, root canal filling materials, and metal posts can create image artifacts in horizontal or vertical root fractures (28, 29) and can potentially affect the accuracy of VRF identification. Micro-CT in 80-mm pixel size mode showed blurry images of VRF teeth with fracture widths of approximately 100 mm in group B (Fig. 1C). Although CBCT with voxel size of 80 mm could detect VRF in vivo, metal artifacts or image blurring may complicate diagnosis even by using a small field of view (9, 13, 29, 30). Further development of CBCT with very small voxel size and improved image processing programs (that mitigate image artifacts) may be helpful in achieving accurate and early diagnosis of VRF. Although we found that 9-mm m-CT could detect fracture lines in all groups, reduction in cost of equipment and decreased radiation dose are necessary for widespread clinical application. We found that 2 fracture lines were more common in premolars (18 of 22, 82%) than in molars (8 of 15, 53%). In 7 premolars (7 of 22, 32%) and 9 molars (9 of 15, 60%), VRF extended to within 3 mm of the root apex. The etiology for differences in the distribution and extension of VRF in premolars and molars is not fully clear. However, statistical analysis showed that large fracture width significantly correlated with the presence of 2 fracture lines or the fracture extending to the apical 3 mm of the root. Statistical analyses showed no difference in the mean width of the fracture at the 3 measurement points (S1, S2, and S3) in the 37 study teeth (Table 1). However, images showed that VRFs were not homogeneous and uniform (Fig. 1H–L). Unlike our study, prior investigations that used dental CT images to analyze the characteristics of artificially created VRF teeth showed that VRF lines are regular and large, with 2 fractures contacting the canal and fracture lines in the root furcation (21). It is possible that artificially created VRF teeth may show some differences relative to natural teeth by m-CT examination. Intriguingly, we found a common fracture pattern as observed by 9-mm mode m-CT. When 2 fracture lines were present, they were in different vertical planes, but they merged together and finally disappeared in different directions. Whether this fracture pattern is limited to endodontically treated teeth awaits further clarification. Collection and analysis of more VRF teeth will be helpful to answer this question. Our study also found that vertical fracture lines were usually irregular, and fracture spaces were not uniform. Data from further in vitro and in vivo studies may be useful to evaluate the correlation between the fracture width and morphology (eg, fracture line, ratio of fracture line, and root length). As suggested by the European Academy of Dental and Maxillofacial Radiology, CBCT examinations should not be conducted unless a history and clinical examination have been performed (31). On the basis of our findings, we suggest CBCT examination with spatial resolution of 100 mm in patients with VRFs consisting of 2 fracture lines and fractures extending to the apical 3 mm of the root because teeth with these characteristics typically have fracture widths greater than 100 mm. Other investigators have suggested using CBCT imaging in patients with suspected horizontal middle root fracture to examine the fracture line extending to the buccal or palatal surface (12). Only 4 CBCT studies have detected VRF in vivo with the same CBCT, and their sample sizes were 42, 29, 14, and 10 patients (9, 13, 32, 33). Thus, our study, which collected 37 extracted teeth from 37 patients, was comparable to previous studies in sample size.
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Basic Research—Technology Furthermore, our sample size was sufficient to achieve at least 70% power of detecting statistical significance for 2-sided Fisher exact test conducted at the 5% significance level. Because all VRF teeth showed the same number of fracture lines as observed by both endodontic microscopic and m-CT examination, the former could be a reliable method for identification of VRF directly during periapical surgery. The use of DIAGNOdent (KaVo Dental, Charlotte, NC) with methylene blue solution or optical coherence tomography during surgery may help to detect VRF on the root surface quickly (5, 34). In conclusion, most VRF teeth in this study had fracture widths smaller than 200 mm, although the width of the fracture and morphology are different for each tooth. The number of fracture lines and fracture lines extending to the apical 3 mm are correlated with width of the fracture greater than 100 mm. The development and application of the 9-mm mode m-CT can be successfully and accurately used for early detection of VRF. This technology is potentially helpful for clinical diagnosis and treatment of VRF.
Acknowledgments The authors acknowledge the financial support from the Cardinal Tien Hospital (CTH-101-1-2A07). They also thank the Taiwan Mouse Clinic, which is funded by the National Research Program for Biopharmaceuticals (NRPB) at the National Science Council (NSC) of Taiwan, for technical support in teeth scanning by Sky scan micro-CT and Triumph X-O CT experiments. They thank engineer Mr Jack in Digital-can Company for Mimics software help. The authors deny any conflicts of interest related to this study.
References 1. Walton EMRRE. Longitudinal tooth fractures: findings that contribute to complex endodontic diagnoses. Endod Topics 2009;16:82–111. 2. Cohen S, Berman LH, Blanco L, et al. A demographic analysis of vertical root fractures. J Endod 2006;32:1160–3. 3. Tsesis I, Rosen E, Tamse A, et al. Diagnosis of vertical root fractures in endodontically treated teeth based on clinical and radiographic indices: a systematic review. J Endod 2010;36:1455–8. 4. Tamse A, Kaffe I, Lustig J, et al. Radiographic features of vertically fractured endodontically treated mesial roots of mandibular molars. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:797–802. 5. Kimura Y, Tanabe M, Amano Y, et al. Basic study of the use of laser on detection of vertical root fracture. J Dent 2009;37:909–12. 6. Shemesh H, van Soest G, Wu MK, et al. Diagnosis of vertical root fractures with optical coherence tomography. J Endod 2008;34:739–42. 7. Topuz O, Uzun O, Tinaz AC, et al. Accuracy of two apex-locating handpieces in detecting simulated vertical and horizontal root fractures. J Endod 2008;34:310–3. 8. Huang CC, Chen JC, Chang YC, et al. A fractal dimensional approach to successful evaluation of apical healing. Int Endod J 2013;46:523–9. 9. Youssefzadeh S, Gahleitner A, Dorffner R, et al. Dental vertical root fractures: value of CT in detection. Radiology 1999;210:545–9. 10. Huang CC, Chang YC, Chuang MC, et al. Evaluation of root and canal systems of mandibular first molars in Taiwanese individuals using cone-beam computed tomography. J Formos Med Assoc 2010;109:303–8.
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11. Mozzo P, Procacci C, Tacconi A, et al. A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results. Eur Radiol 1998;8: 1558–64. 12. May JJ, Cohenca N, Peters OA. Contemporary management of horizontal root fractures to the permanent dentition: diagnosis—radiologic assessment to include cone-beam computed tomography. J Endod 2013;39:S20–5. 13. Metska ME, Aartman IH, Wesselink PR, et al. Detection of vertical root fractures in vivo in endodontically treated teeth by cone-beam computed tomography scans. J Endod 2012;38:1344–7. 14. Ball RL, Barbizam JV, Cohenca N. Intraoperative endodontic applications of conebeam computed tomography. J Endod 2013;39:548–57. 15. Monaghan P, Bajalcaliev JG, Kaminski EJ, et al. A method for producing experimental simple vertical root fractures in dog teeth. J Endod 1993;19:512–5. 16. Nair MK, Grondahl HG, Webber RL, et al. Effect of iterative restoration on the detection of artificially induced vertical radicular fractures by tuned aperture computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;96:118–25. 17. Nair MK, Nair UDP, Grondahl HG, et al. Detection of artificially induced vertical radicular fractures using tuned aperture computed tomography. Eur J Oral Sci 2001;109:375–9. 18. Ozer SY. Detection of vertical root fractures by using cone beam computed tomography with variable voxel sizes in an in vitro model. J Endod 2011;37:75–9. 19. Nair MK, Nair UP. Digital and advanced imaging in endodontics: a review. J Endod 2007;33:1–6. 20. Bernardes RA, de Moraes IG, Hungaro Duarte MA, et al. Use of cone-beam volumetric tomography in the diagnosis of root fractures. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:270–7. 21. Hassan B, Metska ME, Ozok AR, et al. Comparison of five cone beam computed tomography systems for the detection of vertical root fractures. J Endod 2010;36: 126–9. 22. Hassan B, Metska ME, Ozok AR, et al. Detection of vertical root fractures in endodontically treated teeth by a cone beam computed tomography scan. J Endod 2009;35:719–22. 23. Scarfe WC, Farman AG. What is cone-beam CT and how does it work? Dent Clin North Am 2008;52:707–30. v. 24. Hannig C, Dullin C, Hulsmann M, et al. Three-dimensional, non-destructive visualization of vertical root fractures using flat panel volume detector computer tomography: an ex vivo in vitro case report. Int Endod J 2005;38:904–13. 25. Walton RE, Michelich RJ, Smith GN. The histopathogenesis of vertical root fractures. J Endod 1984;10:48–56. 26. Rhodes JS, Ford TR, Lynch JA, et al. Micro-computed tomography: a new tool for experimental endodontology. Int Endod J 1999;32:165–70. 27. Nielsen RB, Alyassin AM, Peters DD, et al. Microcomputed tomography: an advanced system for detailed endodontic research. J Endod 1995;21:561–8. 28. Mora MA, Mol A, Tyndall DA, et al. In vitro assessment of local computed tomography for the detection of longitudinal tooth fractures. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;103:825–9. 29. Costa FF, Gaia BF, Umetsubo OS, et al. Detection of horizontal root fracture with small-volume cone-beam computed tomography in the presence and absence of intracanal metallic post. J Endod 2011;37:1456–9. 30. Costa FF, Gaia BF, Umetsubo OS, et al. Use of large-volume cone-beam computed tomography in identification and localization of horizontal root fracture in the presence and absence of intracanal metallic post. J Endod 2012;38:856–9. 31. Horner K, Islam M, Flygare L, et al. Basic principles for use of dental cone beam computed tomography: consensus guidelines of the European Academy of Dental and Maxillofacial Radiology. Dentomaxillofac Radiol 2009;38:187–95. 32. Kajan ZD, Taromsari M. Value of cone beam CT in detection of dental root fractures. Dentomaxillofac Radiol 2012;41:3–10. 33. Edlund M, Nair MK, Nair UP. Detection of vertical root fractures by using cone-beam computed tomography: a clinical study. J Endod 2011;37:768–72. 34. Imai K, Shimada Y, Sadr A, et al. Noninvasive cross-sectional visualization of enamel cracks by optical coherence tomography in vitro. J Endod 2012;38:1269–74.
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Analysis of the Width of Vertical Root Fracture in Endodontically Treated Teeth by 2 Micro–Computed Tomography Systems Chih-Chia Huang, DDS, MS,* Ya-Chi Chang, DDS,* Meng-Che Chuang, DDS,* Hsueh-Jen Lin, DDS, MS,‡ Yi-Ling Tsai, DDS, MS,† Shu-Hui Chang, PhD,† Jyh-Cheng Chen, PhD,§ and Jiiang-Huei Jeng, DDS, Specialist, PhD† Abstract Introduction: Early detection of vertical root fracture (VRF) is important for clinical endodontic practice. The purpose of this study was to measure the fracture width (distance between 2 sides of the fracture) of VRF teeth in vitro by using 2 micro–computed tomography (m-CT) systems with different spatial resolution and voxel size. Methods: Thirty-seven endodontically treated teeth with VRF were scanned by 80-mm pixel size m-CT. Fifteen teeth with no obvious fracture line, blurred image, or fracture space less than 100 mm were scanned by 9-mm pixel size m-CT. Results: Presence of 2 VRF lines was more common in premolars (82%) than in molars (53%). In 7 premolars (32%) and 9 molars (60%), the VRF lines extended to within the apical 3 mm of the root. All fracture lines were detected by 9-mm pixel size m-CT, but only 22 of 37 VRF teeth had vertical fracture identified by 80-mm m-CT. From m-CT examination, none of the fracture lines showed consistent and uniform fracture space. If 2 fracture lines were present, they were typically in opposite (not linear) directions. There was a significant correlation between 2 fracture lines or fracture lines extending within the 3 mm of the apex and fracture width greater than 100 mm. Conclusions: Application of 9-mm m-CT can be accurately used for early detection of VRF. Fracture characteristics (eg, number of fracture lines, extension of fracture line) may affect the fracture width. Appropriate use of m-CT technology can be helpful for early diagnosis of VRF. (J Endod 2014;40:698–702)
Key Words Cone-beam computed tomography (CBCT), endodontically treated teeth, micro-computed tomography (m-CT), vertical root fracture (VRF)
D
efinitive diagnosis of vertical root fracture (VRF) in clinical dental practice is important to avoid unnecessary endodontic retreatment or periapical surgery. In addition, prolonged infection, inflammation, and swelling caused by VRF compromise adjacent alveolar bone used in implant placement and prosthetic reconstruction. However, definitive diagnosis of VRF in endodontically treated teeth by using periapical radiographs is problematic (1–4). Recent research has focused on the development of appropriate non-radiographic methods to detect VRF; however, current techniques are inadequate (5–7). Although 2-dimensional radiography with image processing by fractal dimension method can be helpful in evaluating the outcome of endodontic treatment (8), 3-dimensional imaging with computed tomography (CT) allows for earlier evaluation of apical healing (9). Since the introduction of cone-beam CT (CBCT) in dental treatment, endodontists have used CBCT in the evaluation of root canal distribution, detection of apical lesions, verification of horizontal and vertical root fracture, and the diagnosis of odontogenic infection (10–14). Studies evaluating CBCT in VRF have shown higher sensitivity and specificity than periapical radiographs in detecting artificial fracture lines in teeth (15–22). The spatial resolution of CBCT images depends on the voxel size of the detector, focal spot, kV, and different CBCT settings (23). The smaller voxel size translates into higher resolution of CBCT. Prior studies used CBCT to detect artificially created VRF and evaluated different CBCT parameters (18). One case report described 140-mm spatial resolution of flat panel volume detector computer tomograph system in 5 VRF teeth (24). However, longitudinal root fracture may require higher resolution for detection. Knowing the possible width of fracture in VRF teeth helps to delineate CBCT with adequate voxel size and spatial resolution to detect the presence of longitudinal root fracture. VRF may show 1 or 2 fracture lines in roots (25). The possible correlation between the number of fracture lines and width of the fracture is an interesting issue awaiting investigation. Micro-CT (m-CT) with higher spatial resolution and very small voxel size could be a tool to analyze tooth structure without distortion (26, 27). Because different m-CTs have differential spatial resolution, voxels, and computer memory, this study used an endodontic microscope and 2 m-CT systems with different voxel size and spatial resolution to measure the vertical fracture width in endodontically treated teeth.
From the *Department of Dentistry, Cardinal Tien Hospital, New Taipei City; †Graduate Institute of Clinical Dentistry and Department of Dentistry, National Taiwan University Hospital and National Taiwan University Medical College, Taipei; ‡Department of Dentistry, Show Chwan Memorial Hospital, Changhua; and §Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan. Jyh-Cheng Chen and Jiiang-Huei Jeng contributed equally to this work. Address requests for reprints to Dr Jiiang-Huei Jeng, Department of Dentistry and School of Dentistry, National Taiwan University Hospital and National Taiwan University Medical College, No. 1, Chang-Te Street, Taipei, Taiwan; or Prof Jyh-Cheng Chen, Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, No 155, Li-Nong Road, Taipei, Taiwan; E-mail addresses: [email protected] or [email protected] 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.12.015
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Basic Research—Technology Materials and Methods Sample Collection and Preparation Thirty-seven VRF teeth (15 molars and 22 premolars) were collected by 8 endodontists during the previous 5 years (2007– 2011). These study teeth were extracted after clinical diagnosis of VRF, which was confirmed microscopically after surgical exposure of the root surfaces. After removal of the granulation tissue on the root surface, the teeth were placed in formalin and stored at 4 C. Two teeth (1 molar and 1 premolar) without crown/root fracture were extracted and preserved in dry conditions for 3 years to serve as control. Only teeth extracted without evident root surface damage were included in this study. Microscope Examination All study teeth were soaked in 5% b-iodine solution for 5 minutes. The number of VRF lines on the root surfaces was observed under microscope (Moller-Wedel Denta 300, Wedel, Germany) with 4 and 8 magnifications. For inclusion in the study, all study teeth must have had at least 1 VRF line on the root surface confirmed by 2 endodontists. The number of fracture lines and any fracture lines extending to within the apical 3 mm of the root apex were recorded. Micro-CT Image (Image Voxel Size: 80 mm Mode) Acquisition All study teeth were scanned by m-CT (Triumph X-O CT System; Gamma Medica Ideas, Northridge, California) with the following parameters: 80 kV, 90 mA, field of view 29.59 mm, acquisition time 5 minutes, and 512 slices. The images were imported into DICOM file format and visualized and analyzed with Mimics software (Mimics Innovation Suite, Leuven, Belgium). After m-CT scanning, the 37 study teeth were divided into 4 groups on the basis of the width of the fracture: group A (fracture line detected by 9-mm m-CT, but not in 80-mm mode m-CT), group B (fracture width < 100 mm), group C (fracture width between 100 and 200 mm), and group D (fracture width > 200 mm) (Table 1). Micro-CT Image (Image Voxel Size: 9 mm) Acquisition The 2 control teeth and 15 study teeth (7 molars and 8 premolars) with fracture < 100 mm (not detected or obscured by the 80-mm mode CT acquisition) were scanned again by m-CT (Skyscan 1076; BRUKER MICROCT, Kontich, Belgium) with higher resolution (9-mm mode). The scanned parameters were 49 kV, 139 mA, field of view 25 mm, acquisition time 21 minutes, and 2000 slices. The images were imported into DICOM file image and visualized by the Mimics software. Measurement of Maximal Fracture Space by m-CT Image Analysis Sequential slices of m-CT images were taken, and VRF appearance and disappearance were recorded (Fig. 1A). One transverse section in the middle of the VRF line was used to measure the maximum VRF space. The width of the fracture was measured at 3 points (S1, S2, and S3) (Fig. 1B). The widest distance at S1, S2, and S3 was regarded as the maximum width of the fracture. If 2 fracture lines were present, the larger fracture line was recorded. Statistical Analysis The Fisher exact test was used to evaluate whether fracture width > 100 mm and # 100 mm and extension of the fracture line to within the apical 3 mm of the root apex were associated with the number of fracture lines. JOE — Volume 40, Number 5, May 2014
TABLE 1. Number (percentage) of Teeth (n = 37, 15 molars, 22 premolars) with Different VRF Spaces as Detected by 2 Modes of m-CT Group A Group B Group C Group D
Total
Molar
Premolar
2 (13) 5 (33) 5 (33) 3 (20)
3 (14) 5 (23) 12 (55) 2 (9)
5 (11) 10 (27) 17 (46) 5 (14)
Group A, fracture line detected by 9-mm m-CT, but not in 80-mm mode m-CT; group B, detected fracture space < 100 mm; group C, width of the fracture between 100 and 200 mm; group D, width of the fracture > 200 mm.
Results Microscope View All study teeth (15 molars, 22 premolars) showed 1 or 2 fracture lines on the root surface as observed under a microscope (Fig. 1C). The presence of 2 fracture lines was more common in premolars (18 of 22, 82%) than in molars (8 of 15, 53%) (Table 2). In 7 premolars (7 of 22, 32%) and 9 molars (9 of 15, 60%), the VRF extended to within 3 mm of the root apex (Fig. 1D). Micro-CT Image (Image Voxel 80 mm) Acquisition and Fracture Space Analysis In group A (5 teeth), no fracture line was detected in the 80-mm mode m-CT. In group B (10 teeth), the fracture line was obscure in the 80-mm m-CT (Fig. 1E). Fracture lines were clearly visualized in group C (17 teeth) and group D (5 teeth) by using 80-mm m-CT (Fig. 1F). Micro-CT Image (Image Voxel 9 mm) Acquisition in the Control Teeth The control molar showed no marked fracture line by using 9-mm m-CT. Three fracture lines extending from cementum into root dentin from different directions were detected in the control premolar. The 3 fracture lines disappeared near the root canal wall and did not merge. Micro-CT Image (Image Voxel 9 mm) Acquisition and Fracture Space Analysis Fracture lines were not consistent and regular in the root dentin. None of the teeth had uniform width fractures as observed under m-CT. If 2 fracture lines were present, they were often in opposite (non-linear) directions. The mean widths of the fractures measured at S1, S2, and S3 were 133 28.4, 131 27.0, and 128 26.9 mm, respectively (P > .05) (Table 2). Although fracture lines in groups A and B could not be clearly identified by the 80-mm m-CT, fracture lines were detected by 9-mm m-CT. As shown in Figure 1G, no marked fractures were seen on images from the 80-mm m-CT, whereas fracture lines were detected in sequential 9-mm m-CT images. Sequential transverse sections of 9-mm m-CT images from root apex to cementoenamel junction (Fig. 1H–L) showed that the first fracture line started from outer cementum surface near the apex; the fracture did not originate from the inner root canal (Fig. 1H). The fracture line subsequently extended through dentin into the root canal wall (Fig. 1I). As the VRF extended coronally, the width of the fracture enlarged. In all cases, the maximal fracture space was present in the mid-root section. As the size of the first fracture decreased, a second fracture line was detected in the contralateral side of the middle root (Fig. 1J). The second fracture line extended through the dentin into cementum of the outer root surface (Fig. 1K). Moving coronally, the 2 fracture lines merged in the root canal, and the size of the first fracture line decreased (Fig. 1L). Characterization of Vertical Root Fracture Space
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Figure 1. (A) Transverse slices were selected from root tip to cementoenamel junction (CEJ) (arrows). The median of slice was selected for measurement (arrowhead). (B) The selected slice of the width of the fracture was measured at 3 points (S1, S2, and S3) (arrows). (C) Observation of the tooth and root surface by microscope. One or 2 fracture lines on the root surface were noted under 8 magnification (arrows). (D) Example of VRF extending to apical 3 mm of the root (arrow). (E) A blurred image was observed when the VRF line (arrow) in the group B teeth was analyzed by 80-mm m-CT. (F) A clear VRF line was observed on axial section of affected tooth in group C (arrow) when analyzed by 80-mm mode m-CT. Image of a representative tooth is shown. (G) No VRF line was detected by the 80-mm mode m-CT in teeth in group A. Image of a representative tooth is shown. (H) Sequential 9-mm mode m-CT images of the same tooth. Fracture line was first identified on the outer root surface (arrow) in the apical region. (I) Fracture line subsequently extended through the root dentin (arrow) into the root canal. (J) The 9-mm mode m-CT detected the first VRF line (arrows) in the middle third of the root. A second fracture line was noted on the contralateral side (arrowhead). (K) While the first fracture line is still visible (arrows), the second fracture line extended through the dentin into cementum of the outer root surface (arrowhead). (L) The 2 fracture lines (arrows) merged in the root canal, and the first fracture line decreased in size in the 9-mm mode m-CT image.
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Basic Research—Technology TABLE 2. Width of the Fracture (S1, S2, and S3) and Fracture Lines (1 or 2) on the Root Surface of VRF teeth (n = 37, 22 premolars, 15 molars) Sample no.
S1 (mm)
S2 (mm)
S3 (mm)
1 (M) 10 10 20 2 (M) 29 19 14 3 (Pm) 13.5 33.3 18.5 4 (Pm) 15 16 36 5 (Pm) 16 18 14 6 (M) 60 70 60 7 (M) 90 60 60 8 (M) 60 60 80 9 (M) 24.3 48.6 13.5 10 (M) 20.1 32 25.2 11 (Pm) 45 76 68 12 (Pm) 64 72 36 13 (Pm) 54 63 36 14 (Pm) 60 90 70 15 (Pm) 60 70 80 16 (M) 160 170 140 17 (M) 140 90 120 18 (M) 170 170 140 19 (M) 190 140 140 20 (M) 130 140 160 21 (Pm) 110 100 100 22 (Pm) 150 80 60 23 (Pm) 150 190 170 24 (Pm) 130 130 150 25 (Pm) 110 70 80 26 (Pm) 130 150 180 27 (Pm) 70 100 70 28 (Pm) 110 110 70 29 (Pm) 180 150 110 30 (Pm) 170 140 130 31 (Pm) 100 140 180 32 (Pm) 100 150 100 33 (M) 240 220 190 34 (M) 180 200 380 35 (M) 1070 1030 980 36 (Pm) 280 200 290 37 (Pm) 230 250 160 Total (mean 133 28.4 131 27.0 128 26.9 standard error)
Fracture line 1 1 1 2 2 2 2 1 1 1 2 1 2 2 1 1 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 —
M, molar; Pm, premolar.
Statistical Analysis between the Microscope and Width of the Fracture Space Of the 37 study teeth, 22 had fracture widths > 100 mm, and 15 did not. Among those with fracture widths > 100 mm, 20 showed 2 fracture lines, and 2 did not. Among study teeth with fracture width < 100 mm, 7 had 2 fracture lines, and 8 did not. Fracture width > 100 mm was significantly associated with the presence of 2 fracture lines on the root (P = .006). There was 82% or 90% power of detecting significant association for the 2-sided test conducted at 0.05 or 0.1 level of significance. Among 22 study teeth with fracture widths > 100 mm, 15 showed fracture lines extending to within 3 mm of the apex. Among 15 study teeth with fracture widths < 100 mm, 4 had fracture lines extending to the apical 3 mm. Fracture width > 100 mm was significantly related to VRF extending to the apical 3 mm (P = .02). The power of this 2-sided test was about 70% or 80% at 0.05 or 0.1 level of significance.
Discussion To achieve early and correct diagnosis of VRF in endodontically treated teeth, proper voxel size of CBCT is required. However, little clinical information is available regarding the fracture width in VRF teeth to JOE — Volume 40, Number 5, May 2014
guide selection of proper voxel size of CBCT. In this study, only 5 teeth showed fracture widths larger than 200 mm (Table 1). Thus, CBCT with voxel size greater than 200 mm may not be suitable for clinical identification of most VRFs. In groups C and D, only 56% of teeth had fracture widths greater than 100 mm (Tables 1 and 2) that can be potentially detected by 80-mm voxel size CBCT. Of note, the properties of maxillary and mandibular bone, root canal filling materials, and metal posts can create image artifacts in horizontal or vertical root fractures (28, 29) and can potentially affect the accuracy of VRF identification. Micro-CT in 80-mm pixel size mode showed blurry images of VRF teeth with fracture widths of approximately 100 mm in group B (Fig. 1C). Although CBCT with voxel size of 80 mm could detect VRF in vivo, metal artifacts or image blurring may complicate diagnosis even by using a small field of view (9, 13, 29, 30). Further development of CBCT with very small voxel size and improved image processing programs (that mitigate image artifacts) may be helpful in achieving accurate and early diagnosis of VRF. Although we found that 9-mm m-CT could detect fracture lines in all groups, reduction in cost of equipment and decreased radiation dose are necessary for widespread clinical application. We found that 2 fracture lines were more common in premolars (18 of 22, 82%) than in molars (8 of 15, 53%). In 7 premolars (7 of 22, 32%) and 9 molars (9 of 15, 60%), VRF extended to within 3 mm of the root apex. The etiology for differences in the distribution and extension of VRF in premolars and molars is not fully clear. However, statistical analysis showed that large fracture width significantly correlated with the presence of 2 fracture lines or the fracture extending to the apical 3 mm of the root. Statistical analyses showed no difference in the mean width of the fracture at the 3 measurement points (S1, S2, and S3) in the 37 study teeth (Table 1). However, images showed that VRFs were not homogeneous and uniform (Fig. 1H–L). Unlike our study, prior investigations that used dental CT images to analyze the characteristics of artificially created VRF teeth showed that VRF lines are regular and large, with 2 fractures contacting the canal and fracture lines in the root furcation (21). It is possible that artificially created VRF teeth may show some differences relative to natural teeth by m-CT examination. Intriguingly, we found a common fracture pattern as observed by 9-mm mode m-CT. When 2 fracture lines were present, they were in different vertical planes, but they merged together and finally disappeared in different directions. Whether this fracture pattern is limited to endodontically treated teeth awaits further clarification. Collection and analysis of more VRF teeth will be helpful to answer this question. Our study also found that vertical fracture lines were usually irregular, and fracture spaces were not uniform. Data from further in vitro and in vivo studies may be useful to evaluate the correlation between the fracture width and morphology (eg, fracture line, ratio of fracture line, and root length). As suggested by the European Academy of Dental and Maxillofacial Radiology, CBCT examinations should not be conducted unless a history and clinical examination have been performed (31). On the basis of our findings, we suggest CBCT examination with spatial resolution of 100 mm in patients with VRFs consisting of 2 fracture lines and fractures extending to the apical 3 mm of the root because teeth with these characteristics typically have fracture widths greater than 100 mm. Other investigators have suggested using CBCT imaging in patients with suspected horizontal middle root fracture to examine the fracture line extending to the buccal or palatal surface (12). Only 4 CBCT studies have detected VRF in vivo with the same CBCT, and their sample sizes were 42, 29, 14, and 10 patients (9, 13, 32, 33). Thus, our study, which collected 37 extracted teeth from 37 patients, was comparable to previous studies in sample size.
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Basic Research—Technology Furthermore, our sample size was sufficient to achieve at least 70% power of detecting statistical significance for 2-sided Fisher exact test conducted at the 5% significance level. Because all VRF teeth showed the same number of fracture lines as observed by both endodontic microscopic and m-CT examination, the former could be a reliable method for identification of VRF directly during periapical surgery. The use of DIAGNOdent (KaVo Dental, Charlotte, NC) with methylene blue solution or optical coherence tomography during surgery may help to detect VRF on the root surface quickly (5, 34). In conclusion, most VRF teeth in this study had fracture widths smaller than 200 mm, although the width of the fracture and morphology are different for each tooth. The number of fracture lines and fracture lines extending to the apical 3 mm are correlated with width of the fracture greater than 100 mm. The development and application of the 9-mm mode m-CT can be successfully and accurately used for early detection of VRF. This technology is potentially helpful for clinical diagnosis and treatment of VRF.
Acknowledgments The authors acknowledge the financial support from the Cardinal Tien Hospital (CTH-101-1-2A07). They also thank the Taiwan Mouse Clinic, which is funded by the National Research Program for Biopharmaceuticals (NRPB) at the National Science Council (NSC) of Taiwan, for technical support in teeth scanning by Sky scan micro-CT and Triumph X-O CT experiments. They thank engineer Mr Jack in Digital-can Company for Mimics software help. The authors deny any conflicts of interest related to this study.
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