|Year : 2019 | Volume
| Issue : 4 | Page : 346-352
Cone beam computed tomography – the importance of z-axis
Anusuya G Savalagi, Roshan A Chandwani, Sagar A Khairnar
Department of Oral Medicine and Radiology, YCMM and RDF's Dental College, Vadgaon Gupta, Ahmednagar, Maharashtra, India
|Date of Submission||26-Aug-2019|
|Date of Acceptance||16-Jan-2020|
|Date of Web Publication||03-Mar-2020|
Dr. Anusuya G Savalagi
YCMM and RDF's Dental College, Vadgaon Gupta, Ahmednagar, Maharashtra
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Conventional imaging is the backbone of dentistry. Intraoral and extraoral radiographs are commonly used for diagnosis and clinical management for multiple maxillofacial pathologies. However, they are of a two-dimensional nature and have numerous limitations and disadvantages. Cone beam computed tomography (CBCT) adds a third dimension to the two-dimensional image. The multiple pathological conditions that remain undetected in two-dimensional imaging can be easily diagnosed with CBCT and, to a large extent, help with treatment planning and prognosis. Aim: To compare intraoral and extraoral two-dimensional imaging to CBCT to prove the importance of CBCT in diagnosis and treatment planning. Setting and Design: Different cases in which patients underwent two-dimensional intraoral / extraoral imaging and CBCT were reported and variations in radiographic diagnosis were compared.
Conclusion: CBCT is a boon to dentistry. The third dimension adds invaluable information that modifies the diagnosis and treatment plan and hence helps improve the prognosis.
Keywords: Cone beam computed tomography, conventional imaging, third dimension, z-axis
|How to cite this article:|
Savalagi AG, Chandwani RA, Khairnar SA. Cone beam computed tomography – the importance of z-axis. J Indian Acad Oral Med Radiol 2019;31:346-52
|How to cite this URL:|
Savalagi AG, Chandwani RA, Khairnar SA. Cone beam computed tomography – the importance of z-axis. J Indian Acad Oral Med Radiol [serial online] 2019 [cited 2020 Jul 2];31:346-52. Available from: http://www.jiaomr.in/text.asp?2019/31/4/346/279853
| Introduction|| |
Following the discovery of x-rays by Sir Wilhelm Roentgen, dental surgeons around the world began working on imaging techniques for teeth and surrounding structures. Over time, various intraoral and extraoral radiographic techniques have been identified of which intraoral periapical radiographs (IOPARs) and orthopantomographs (OPGs) have been and are still widely preferred and practiced around the world.
It is, however, an unhidden fact that these widely used imaging systems are essentially two-dimensional (2D). In addition to their various disadvantages, such as superimposition, magnification and distortion, they have limited information on pathological conditions.
On a two-dimensional grid, the smallest single component of an image is a pixel. A volume pixel is called a voxel. While the 2D image only provides information on width (x-axis) and height (y-axis), the voxel incorporates the third dimension of the z-axis (depth) which renders the three-dimensional (3D) digital image [Figure 1].
The drawbacks of 2D imaging limit their contribution in diagnosing several occult pathologies. The third axis modifies the diagnosis and, therefore, the treatment plan.
Cone beam computed tomography (CBCT) for the oral and maxillofacial region was introduced by Arai et al. and Mozzo et al. In a single rotation, the cone-shaped X-ray beam and reciprocating x-ray sensor rotates around the patient's head and captures a series of lateral cephalogram-like images in the region of interest. The raw data obtained undergo primary reconstruction and the patient's anatomy is replicated into 3D volume (containing voxels). The size of each voxel is 0.1–0.4 mm and, hence, CBCT provides images of submillimeter resolution (2 line pairs/mm).
CBCT is a multiplanar reformatting (MPR) imaging system. It enables the diagnostician to recreate images in axial, sagittal, and coronal planes thus increasing the diagnosing efficacy in an unparalleled way.
Intraoral and extraoral radiographs often fail to provide the required data and present a diagnostic challenge to dental surgeons. The third axis was found to be potentially an advantage when the same patients were exposed to CBCT as the final diagnosis was different from what 2D imaging presented.
The study was conducted in Yashwantrao Chavan Dental College, Ahmednagar Maharashtra. Ethical committee approval was taken from the institute (YCDC/854/2019-20).
The study focuses on the variations between conventional and CBCT images. It sheds light on how CBCT imaging is an incomparable screening approach when grappling with some undiagnosed clinical conditions. The article presents a number of examples that clearly show the advantage of 3D imaging over 2D imaging.
Diagnosis and management of endodontic cases are commonly done using periapical radiographs. Superimposition of various structures such as maxillary sinus, the zygomatic process of maxilla limits the diagnostic ability forcing the dentist to take multiple radiographs in different angulations to determine the exact anatomy of the tooth. In the case of periapical pathology in the mandible, it is not possible to appreciate lesions when covered by thick cortical plates. In [Figure 2]a, a periapical radiograph of 27 displays three roots, however, the axial section [Figure 2]b shows the tooth having four separate roots with four root canals. [Figure 2]c and [Figure 2]d display reconstructed 3D view. Every tooth has different anatomy and different canal configuration. An experienced clinician working with a microscope may identify the number of canals, however, when root configurations are different or when the anatomy of the tooth is unusual, CBCT is an imaging modality of choice.
|Figure 2:(a) An intraoral periapical radiograph (IOPAR) showing only three roots (red arrows) with tooth 27. (b) However, cone beam computed tomography (CBCT) of the axial section shows that the same tooth has four roots (yellow arrows): two buccal and two palatal with four root canals. (c and d) reconstructed 3D view|
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Diagnosis of coronal fractures
The IOPAR reveals blurred maxillary sinus in [Figure 3]a. However, none of the teeth reveal any pathology. In the same area, this patient complained of intense pain. History of pain exacerbating on biting was positive. The coronal section on CBCT [Figure 3]b revealed a vertical fracture line running from the occlusal surface to the furcation region. [Figure 3]c and [Figure 3]d display axial and 3D views, respectively. CBCT is a safe screening tool to diagnose fractures (in teeth without restorations). Tooth fractures can be clinically diagnosed when the fracture lines are large and can be seen on intraoral radiographs as well. But if the crack line is short or narrow, then 3D imaging is required to detect its presence. Nevertheless, it becomes difficult to diagnose fractures by CBCT in teeth with restorative materials because metallic fillings in the oral cavity lead to streak or ring-like artifacts due to extreme beam hardening. The operator should be aware that the image quality adjacent to the teeth having metallic restorations and other dense material is compromised and can lead to misdiagnosis.
|Figure 3: (a) IOPAR 25,26,27 region showing opaque maxillary sinus. None of the teeth shows pathologic findings. (b) However, a coronal section with 27 shows fracture line (red line) running from occlusal surface to furcation region explaining the cause of opaque sinus. (c) Axial view showing fracture line. (d) reconstructed 3D view|
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Diagnosis of root fractures
Several times conventional imaging confuses a clinician or does not show the real anatomy. [Figure 4]a displays the IOPAR of tooth 17. It was tender on percussion and the patient was complaining of discomfort. It was diagnosed by the dental surgeon as an external root resorption. Nonetheless, it was proposed that the etiology of resorption be determined. The sagittal segment of the CBCT [Figure 4]b revealed a root fracture at the apical third of the distobuccal root believed to be related to the eruption of 18. [Figure 4]c and [Figure 4]d display coronal and axial sections. [Figure 4]e represents reconstructed 3D view. It is, therefore, not possible to rely entirely on conventional imaging for diagnosis. The final explanation by CBCT results in a more effective treatment strategy which leads to a good prognosis.
|Figure 4:(a) IOPA radiograph 15,16,17,18 region showing erupting 18 hitting distal root of 17. External root resorption in distal root suspected (red arrow). (b) However sagittal section in 17 shows distal root fracture at apical third (yellow arrow). Note opaque maxillary sinus. (c) Coronal view of the same. (d) Axial view showing fractured distobuccal root fragments. (e) reconstructed 3D view|
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Diagnosis of unusual anatomy of the tooth
Unusual anatomies of the teeth pose a major problem in the endodontic cases. The anatomy of the root canal remains unclear and the surgeon is puzzled about the number and position of the canals. Tooth 17 [Figure 5]a appears to be larger in size on IOPAR. [Figure 5]b is a sagittal section showing mesial root curved which appears straight on IOPAR. The axial section on CBCT [Figure 5]c reveals a fusion of tooth 17 with the supernumerary tooth. [Figure 5]d and [Figure 5]f display sagittal and axial sections, respectively and [Figure 5]g and h are reconstructed 3D images. The division of root canals in supernumerary teeth is also a surprising finding [Figure 5]d The tooth has a total of five canals. Coronal section [Figure 5]e displays abscess and polyp in the maxillary sinus. These anatomically complicated teeth provide the oral health professional a diagnostic challenge if only 2D scanning is pursued. CBCT offers a thorough understanding and a crystal-clear view of the intricate anatomy of the tooth and simplifies the treatment plan.
|Figure 5: (a) Tooth 17 appearing like a macrodont in IOPAR. (b) IOPAR shows straight mesial root, but CBCT sagittal section showing the same root curved. (c) Axial view showing fused supernumerary tooth (palatal) to tooth 17. (d) The sagittal section showing a supernumerary tooth has two canals. (e) Coronal section showing fused 17 and supernumerary. (f) Axial section showing fused 17 and supernumerary having 5 canals in total. (g and h) Reconstructed 3D|
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Missed canals and periapical lesions
IOPAR with 17 [Figure 6]a indicates successful endodontic treatment. But the cause of opacity in maxillary sinus remains unexplained. Surprisingly, CBCT indicates an unfilled palatal canal. [Figure 6]b shows an axial perspective in which MB1, MB2 and DB canals are obturated and the palatal canal is not. [Figure 6]c shows filled MB1 and MB2 and [Figure 6]d displays filled DB canal. Furthermore, [Figure 6]e (axial section) indicates that the palatal root is fractured indicating the origin of the blurred sinus. [Figure 6]f is reconstructed 3D view. CBCT makes it extremely easier to detect tooth fractures, particularly when using a smaller field of vision.
|Figure 6:(a) IOPAR tooth 17 showing satisfactory endodontic treatment, but maxillary sinus appears opaque (red arrow). (b) Axial section CBCT shows filled MB1, MB2, and DB canals (red arrows) but unfilled palatal canal (yellow arrow). (c) MB1 and MB2 (coronal section). (d) DB canal- (yellow) and fractured palatal root (coronal section). (e) Axial section showing # palatal root and discontinuous palatal wall. (f) Reconstructed 3D view|
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The consequences of unfilled canals are also shown in another case [Figure 7]. [Figure 7]a demonstrates an IOPAR showing satisfactory endodontic treatment with tooth 26. However, a well-defined periapical lesion is noted. An axial section indicates the missing canal (MB2) of the mesiobuccal root [Figure 7]b. [Figure 7]c demonstrates a coronal section showing an unfilled MB2 canal. The inter radicular radiolucency (thick yellow arrow); a well-defined periapical radiolucency with palatal root [Figure 7]d and opaque maxillary sinus can be observed as well. CBCT is superior to 2D imaging in detecting periapical pathologies. A clear and thorough understanding of the size of the lesion, borders, extensions, and effect on surrounding structures can be obtained. Additionally, in complicated endodontic cases, CBCT can be used to determine the number of roots, the morphology of root canals, angulations/curvatures of roots, and assessment of obturations.
|Figure 7: (a) IOPAR 26 shows endodontic treatment done with all canals filled adequately. But still, the periapical lesion is seen. (b) Axial view of the same showing missed (unfilled) MB2 canal (yellow). Note the periapical radiolucency around the palatal root. (c) Coronal section with 26 showing unfilled MB2 canal (orange arrow). Note well-defined periapical radiolucency in MB root. (d) Sagittal section showing slightly overextended endo filling material in the palatal root. Note the large periapical radiolucency and opacity in the sinus|
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Assessment of nerve relation with impacted teeth
One of the major limitations of 2D scanning is that the true relationship between the teeth and the surrounding vital structures can not be shown. In [Figure 8]a (IOPAR), it appears that impacted 38 is in contact with the Inferior alveolar nerve (IAN). Crosssections in CBCT [Figure 8]b, however, suggest that the mesial root is about 3 mm above the IAN and 2 mm above the distal root. [Figure 8]c is 3D view.
|Figure 8:(a) IOPAR 38 region showing root apices of 38 closely contacting inferior alveolar nerve (IAN). (b) CBCT cross-sections in 38 showing both the roots not contacting the nerve. (c) Reconstructed 3D view|
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[Figure 9] shows another case of IAN's relationship with the impacted supernumerary tooth 35. In [Figure 9]a (IOPAR), it looks as if the root apex of the affected supernumerary tooth lies over the mental foramen. IOPAR provides no clue whether the impacted tooth is located on the buccal surface or on the lingual. CBCT cross-sections reveal a lingual positioning of the affected supernumerary tooth and its close proximity to the IAN. [Figure 9]b shows crosssections of impacted tooth. The tooth is located lingually and in close proximity to mental foramen and IAN. [Figure 9]c and [Figure 9]d are reconstructed 3D views. In order to avoid complications, it is necessary to thoroughly evaluate the relationship of the affected teeth with vital structures. This can be easily understood by way of CBCT and treatments can be planned accordingly.
|Figure 9: (a) IOPAR 35 region showing impacted supernumerary between premolars. The apex of the impacted tooth appearing to lie over mental foramen. (b) CBCT cross-sections in impacted tooth. The tooth is located lingually and in close proximity to mental foramen and IAN. (c and d) Reconstructed 3D view|
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Detailed evaluation of odontogenic cysts and tumors
A panoramic radiograph is the most common imaging method for odontogenic cysts and tumors' evaluation and surgical planning. However, the limited information available from these imaging techniques makes it difficult to diagnose and treat. As shown in [Figure 10]a (OPG), the ramus of the mandible on the left side shows a well-defined corticated radiolucency. The lesion's epicenter cannot, however, be clearly demarcated. [Figure 10]b is a sagittal section that shows the lesion epicenter as lower left second molar. 2D imaging may give some indication of the anteroposterior expansion of the lesion, but information on buccolingual expansion cannot be obtained. CBCT provides detailed information on anteroposterior extension and buccolingual expansion of the lesion together with the relationship between the lesion and the surrounding vital structures. In [Figure 10]b, a hypodense area extending from the coronal surface of the lower second molar to the posterior border of the ramus of the mandible can be seen. [Figure 10]c is an axial section displaying posterior extent of the lesion. Also, note the discontinuity in the buccal and lingual plates [Figure 10]d and the involvement of IAN in the lesion [Figure 10]b. [Figure 10]e is the 3D view.
|Figure 10:(a) Orthopantomograph (OPG) showing well-defined radiolucency seen in left ramus (red) suggesting cystic lesion, but the epicenter of the lesion cannot be traced. (b) Sagittal section of the CBCT temporomandibular joint of the same patient showing the lesion originating from the lower second molar (yellow). Note the involvement of IAN in the lesion. (c and d) axial views showing the posterior extension of the lesion into the ramus. e. Reconstructed 3D view|
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In another case, in [Figure 11]a, OPG shows no pathologic findings. [Figure 11]d displays 3D view. Axial and coronal sections [Figure 11]b and [Figure 11]c show labial wall expansion in 23, 24, 25 region. Note the erosion of the anterior wall of the left maxillary sinus that is not visible in OPG. This patient had swelling of soft tissue in a region of 22, 23, 24. OPG has shown no sinus involvement. However, CBCT was advised to check the involvement of the maxillary sinus and changes were found in the anterior wall of the sinus. This explains the true significance of CBCT.
|Figure 11: (a) Normal OPG seen with no pathologic findings. (b) Axial section of maxillary arch showing a well-defined lesion in 23,24,25 region with thinning and expansion of buccal plate and erosion of the anterior wall of the left maxillary sinus (yellow circle). However, the walls of the maxillary sinus in OPG appears normal. (c) Sagittal sections showing a well-defined lesion in the same region. Note the discontinuity in the anterior wall of the maxillary sinus (red circle).(d) Reconstructed 3D view|
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Importance of third dimension in maxillofacial trauma
Maxillofacial fractures are not visible in OPG due to the superimposition of different anatomical structures and especially overlapping contacts in canine-premolar fracture lines. [Figure 12]a displays fracture (#) of the right maxillary sinus wall (green), but the left maxillary region appears normal. Axial sections [Figure 12]b shows a dentoalveolar fracture in the left anterior maxilla. [Figure 12]h shows the posterior extension of fracture over the hard palate. [Figure 12]c, [Figure 12]d, [Figure 12]e show fracture in walls of left maxillary sinus as well as soft tissue opacity. [Figure 12]f, [Figure 12]g, [Figure 12]h are 3D views). CBCT's benefits over conventional imaging have helped researchers choose the imaging system for studying and treating dentoalveolar, midfacial, and orbital fractures.
|Figure 12:(a) OPG shows # medial, lateral wall of the right maxillary sinus (green). However, no abnormality is seen in the left anterior region (dotted circle). (b) Axial section of maxillary arch showing fracture line running from the left anterior region toward hard palate (yellow). (c-e) showing coronal and axial sections. Note # lateral wall of the nose and medial and lateral walls of the right maxillary sinus. Also, note soft tissue opacity in Figures d and e (red). (f and g) and h showing reconstructed 3D views. Note # in the anterior maxilla in Figure g (blue circle)|
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Evaluation of periodontal status
The diagnosis of periodontal pathologies is mainly based on 2D imaging. Nevertheless, the drawbacks of 2D imaging in periodontal cases contribute to over/under measurement of bone loss. As shown in [Figure 13]a, in 22, 23, 24, IOPAR indicates moderate to severe bone loss. But sagittal sections show periodontal abscess in 22 [Figure 13]b, complete loss of labial wall and periapical radiolucency in 23 [Figure 13]d and maxillary sinus opacity [Figure 13]c. The 3D view [Figure 13]e, [Figure 13]f, [Figure 13]g demonstrates the patient's actual periodontal condition. Due to the absence of superimposition from surrounding structures, CBCT is much more effective than 2D radiographs in the identification of buccal/lingual defects.
|Figure 13: (a) IOPAR 22,23,24 region showing moderate to severe bone loss. (b) CBCT cross-section showing periodontal abscess in 22, not seen in IOPAR. (c) Note opaque maxillary sinus in 24. (d) The cross-section in 23 showing complete loss of labial wall and periapical radiolucency. (e and f) and g showing the generalized periodontal status of the patient|
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| Discussion|| |
For dentistry, 3D scanning is of utmost importance. Although standard intraoral x-rays are available at ease, they are cost-effective and provide excellent resolution, certain situations require descriptions of the spatial relationship generated by CBCT. The 3D information facilitates the diagnosis and influences the treatment plan.
It is a well-known fact that CBCT extends to all dentistry branches, including forensics. The ability of 3D imaging to display anatomical structures in three orthogonal planes (axial, sagittal, and coronal) makes it an imaging technique of choice for some circumstances where 2D scanning cannot help. The reconstructed 3D view can also be obtained. The isotropic voxels generated by CBCT (CT scan creates anisotropic voxels) give in any plane a geometrically accurate image and are also free from distortion.
As shown in the above cases, CBCT's higher detection rates are significant in patients with unusual symptoms in which conventional radiography seems normal and CBCT is an eye-opener.
Root canal treatment's success depends on root canal exploration. It is necessary to access, clean, and obturate all the channels. It is also mandatory to postoperatively monitor periapical lesions. The detection of coronal fractures, root fractures, root resorption requires the third axis. CBCT has a particular application in the diagnosis of root fractures. In a study by Hassan et al., it was found that the overall accuracy of detecting vertical root fractures using CBCT was 0.86 compared to periapical radiographs which were 0.66.
In an interesting case reported by Maini et al., OPG revealed impacted maxillary canine and widened tooth pulp chamber of 21. Close examination of both the occlusal and panoramic radiographs indicated no abnormality in the outline of the incisor roots or the lamina dura on the mesial, distal, or apical aspects of 21. CBCT reported not only the degree of internal root resorption but also perforation on the distal surface of 21 which could not be detected on the OPG. Various authors have studied the effectiveness of CBCT in predicting the resorption of roots and in assessing treatment and prognosis.,,
In periodontal diagnosis, Misch et al.'s study found that CBCT can find all periodontal defects, while intraoral radiographs can diagnose only 67%. CBCT detected buccal and lingual cortical defects that could not be diagnosed with conventional X-rays. Vadenberghe has measured periodontal bone abnormalities by a charge-coupled device (CCD) and CBCT on two adult skulls. The detection of crater and furcation involvements failed in 29% and 44% for the CCD, respectively, in contrast to 100% detectability for both defects with CBCT. If orthodontic applications are to be discussed, other uses of CBCT that are beneficial over 2D imaging apart from the location of impacted canines, include assessment of palatal bone thickness, dental age estimation, skeletal growth pattern assessment, evaluation of upper airways, and planning orthognathic surgery., In their analysis, Georgescu et al. reported that CBCT indicated an incisive canal presence of 87.76% in mandibular central incisors, 74% in lateral incisors, and 16.67% in canines. On OPGs, this visibility was lower; central incisors 28.57%; lateral 24%; and canines 1.04%. CBCT provides a pictorial guide for mini-implant placement, thus, avoiding accidental and irreparable injury to vital structures. These advantages cannot be provided through 2D imaging. The advantage of the CBCT temporomandibular joint is that it is possible to examine the joint space and study the true position of the condylar head in the glenoid fossa. The benefit of CBCT paranasal sinus over OPG or water's view is that all the sinuses can be clearly seen. Nasal septum deviation may be studied [Figure 14].
|Figure 14:(a) Coronal section-paranasal sinus note right and left maxillary sinuses, infraorbital foramen, nasal septum. (b) Axial view showing ethmoidal air sinuses and sphenoid sinuses. (c) Sagittal section—note frontal sinus. Also, note impacted supernumerary in an inverted position. (d) Sphenoid sinuses. (e) Reconstructed 3D view|
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| Conclusion|| |
This paper highlighted the advantages of CBCT for oral and maxillofacial pathologies over 2D imaging. 2D scanning is definitely the cornerstone of dentistry, and it is the first choice of imaging modality. But 2D scanning limitations act as an obstacle in the diagnostic path. CBCT incorporates the third dimension, the Z-axis, which offers images with a submillimeter resolution in all planes with a fast scanning period and a diminished and pulsed radiation dosage. The treatment plans based on assumptions may be replaced with CBCT. Both the dentist and the patients benefit from this. It is possible to expect a better prognosis. Further examples demonstrating the variations between 2D and 3D scanning should be applied to the literature in order to raise awareness of the importance of the third dimension or the Z-axis—a blessing to dentistry.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14]