CBCT – An Advanced Diagnostic Tool for Orthodontics and Other Specialties in Dentistry – A Systematic Review
Dr. Vishwanath A E-
Reader, Department of Orthodontics,
Vydehi Institute of Dental Sciences & Research Centre
Dr. Sandesh S pai
Prof & HOD
Department of Orthodontics,
Vydehi Institute of Dental Sciences & Research Centre
Dr. Nandini S. Nelivegi
Department of Orthodontics,
Vydehi Institute of Dental Sciences & Research Centre
Dr. Neelima Anand
Department of Orthodontics,
Vydehi Institute of Dental Sciences & Research Centre
Accurate diagnostic imaging is an essential requirement for the optimal diagnosis and treatment planning of orthodontic patients. In addition, it is a critical tool that allows the clinician to monitor and document the treatment progress and outcome.1 The cone-beam computed tomography (CBCT) scanners were introduced in the late 1990’s as an evolutionary process resulting from the demand for three-dimensional (3D) information obtained by conventional computerized tomography (CT) scans2. A CBCT scanner was built for angiography at the Mayo Clinic in 1982.Shortly after, the US Food and Drug Administration (FDA) approved the first CBCT unit in 2001. Since then, there has been an enormous interest in this new technology for its clinical and research applications. The CBCT is an imaging acquisition technique that utilizes a volumetric scanning machine. This technology is based on a cone-shaped X-ray beam directed at a flat two-dimensional (2D) detector. As both rotate around the patient’s head, a series of 2D images are generated. The software then reconstructs the images into three dimensional. With the rapid 180° or most frequently 360° of an x-ray tube and digital detector, CBCT provides essentially immediate and accurate two dimensional (2D) and three-dimensional (3D) radiographic images of an anatomical structure, limited only by the system’s innate or selected field of view.3-4
Conventional computerized tomography (CT):
Computerized tomography was developed by Sir Godfrey Hounsfield in 1967 and since the first prototype, there has been a gradual evolution to five generations of such systems. The method of classification for each system is based on the organization of the individual parts of the device and the physical motion of the beam in capturing the data.
1. First generation scanners consisted of a single radiation source and a single detector. The information was obtained slice by slice.
2. Second generation was introduced as an improvement and multiple detectors were incorporated within the plane of the scan. However, these detectors were not necessarily continuous nor did they span the diameter of the object.
3. Third generation was made possible by the advancement in detector and data acquisition technology. These large detectors reduced the need for the beam to translate around the object to be measured and were often known as the ‘fan-beam’
4. Fourth generation was developed to counter this problem. A moving radiation source and a fixed detector ring were introduced. This meant that modifications to the angle of the radiation source had to be taken into account and more scattered radiation was seen.
5. Fifth and Sixth generation scanners were introduced to reduce ‘motion’ or ‘scatter’ artefacts. As with the previous two generations, the detector is stationary and the electron beam is electronically swept along a semi-circular tungsten strip anode. The radiation is produced at the point where the electron beam hits the anode and results in a source of X-rays that rotates about the patient with no translation components or moving parts. Projections of the X-rays are so rapid that even the heart beats of a person may be captured. This has led some clinicians to hail it as a 4D motion capture device.
There are several limitations with these systems.
- They require a considerable physical space and more expensive than conventional radiographic machines.
- The images captured on the detector screens are made up of multiple slices, which are ‘stacked’ to obtain a final complete image making it time consuming and less cost efficient.
- The radiation exposure to the patient was partially responsible in limiting the CT usage to complex craniofacial problems and specialized diagnostic information.5
Craniofacial CBCT’s were designed to counter some of the limitations of the conventional CT scanning devices.6 The object to be evaluated is captured as the radiation source falls onto a two-dimensional detector. This simple difference allows a single rotation of the radiation source to capture an entire region of interest, as compared to conventional CT devices where multiple slices are stacked to obtain a complete image. 7 The cone beam also produces a more focused beam and considerably less scatter radiation compared to the conventional fan-shaped CT devices (Fig 1).8 This significantly increases the X-ray utilization and reduces the X-ray tube capacity required for volumetric scanning.9 It has been reported that the total radiation is approximately 20% of conventional CTs and equivalent to a full mouth peri-apical radiographic exposure.10
Advantages of CBCT over Conventional CT
- The CBCT to be less expensive and smaller.
- The exposure chamber (i.e. head), is custom built and reduces the amount of radiation
CBCT in Oral and Maxillofacial Imaging
The first commercial CBCT system for oral andmaxillofacial imaging was the NewTom (Quantitative Radiology, Verona, Italy), which was first approved by the Food and Drug Administration (FDA) in April 2001, and is currently in its fourth generation as the NewTom VG. Since that time numerous additional systems have been approved or are in development. These can be divided roughly into three groups: (1) CBCT systems capable of imaging a large portion of the maxillofacial and cranial complex with one exposure (large FOV); (2) dedicated CBCT systems with smaller FOV; and (3) hybrid digital panoramic/CBCT systems including separate for the two functions. Some of the latter systems also provide a 2D digital cephalogram option.3
CBCT acquisition systems :
There are currently four main system providers in the world market:
- NewTom 3G (Quantitative Radiology, Verona, Italy),
- i-CAT (Imaging Sciences International, Hatfield, USA),
- CB MercuRay (Hitachi Medical Corporation, Tokyo, Japan),
- 3D Accuitomo (J Morita Mfg Corp, Kyoto, Japan).
The available CBCT machines differ in size, possible settings, area of image capture (field of view), and clinical usage .
Radiation exposure of CBCT
Even though the cone beam technology is able to provide three-dimensional volumetric images with up to four times less radiation than a conventional CT,11 the resulting effective radiation is dependent on the settings used (kVp and mA). The use of lower mAs and/or collimation are some of the ways to reduce the amount of radiation the patient receives, but at the same time can produce a lower image quality than by using higher settings.
Patient effective exposure dose from a CBCT machine has been reported to be as low as 45 μSv to as high as 650 μSv. As a reference, published exposure for an analogue full mouth series has been reported as 150 μSv;12 for an analogue panoramic radiograph as 54 μSv.13
APPLICATION OF CBCT IN ORTHODONTICS
Orthodontics has traditionally relied on 2-dimensional x-rays in evaluating 3-dimensional structures. With Cone Beam CT imaging, a more comprehensive orthodontic diagnosis and more accurate treatment planning is possible. CBCT allows the 3D visualization of the craniofacial skeleton.14-16
- Cleft palate assessment
- Planning for placement of dental implants for orthodontic anchorage and for placement of temporary anchorage devices (TADs)
- 3D evaluation of impacted tooth position and anatomy
- Resorption related to impacted teeth
- TMJ assessments of condylar anatomy in three dimensions
- Assessment of rapid maxillary assessment
- 3 dimentional cephalometric assessment
- Airway assessments
- Assessment of age
- Investigation of orthodontic-associated paraesthesia
- Orthognathic surgery treatment planning and growth assessments in true 1:1 imaging
- 3D views of vital structures
- Assessment skeletal symmetry or asymmetry
Cleft palate assessment
CBCT in patients with cleft lip and palate is useful for preoperative evaluation of the borders of the cleft, for assessment of palatal bone thickness, as well as, for the clinical assessment of bone graft quality following alveolar surgery. 15, 16
Measuring bone dimensions for mini-implant placement
The mini-implants have been widely used in orthodontic practice as temporary anchorage devices. Their diameter is ≈ 1.8 mm. They can be either immediate or delayed loading. They can be positioned in many areas of the alveolar bone. It is crucial to identify the ideal site for insertion of the mini-implants. Particularly, to insure that the placement of mini-implants will be safe and won’t cause damage to anatomical structures or teeth. Consequently, the cortical bone thickness and bone pattern are important criteria in mini-implant selection and factors that affect their stability.
CBCT scanners can provide information needed to locate the ideal site for insertion of the mini-implants like, the thickness of cortical bone, the location of the maxillary sinus or inferior alveolar canal, the exact locations of the roots the inter-root distance. 17, 18-22
A frequent application of CBCT is for assessment of the position of an unerupted tooth, particularly where the tooth is impacted 23, 24.
Cone Beam CT scans can provide a more accurate and 3-dimensional assessment to provide more predictable treatment results while reducing the risks associated with any impacted tooth.
- Visualize an impacted tooth’s position in relation to surrounding vital structures and nearby teeth and their roots
- Better assess the risk of treatment or non-treatment based on more accurate 3-dimensional analysis
The most frequently impacted teeth (after third molars) are the permanent maxillary canines. In particular, it is important to know the exact position and orientation of the impacted canine, as well as its relation with other anatomical structures. Also the CBCT allows for a more precise analysis of the extent of the pathology related to the impacted tooth. Consequently it is possible to design treatment strategies that would result in less invasive surgical intervention. 23, 24-26
External resorption in relation to unererupted teeth
In cases of impacted teeth, an integral aspect of the assessment is often the accurate identification of any resorption of adjacent teeth.
Such a situation is most often seen where maxillary canines are ectopic and incisor roots are suspected of having undergone resorption23,24.
For the localized assessment of an impacted tooth (including consideration of resorption of an adjacent tooth) where the current imaging method of choice is conventional dental radiography, CBCT may be used when the information cannot be obtained adequately by lower dose conventional (traditional) radiography 23.
Clinical reports using 3-dimensional imaging have shown that the incidence of root resorption of teeth adjacent to impacted teeth is greater than previously thought 14,27.
TMJ assessments of condylar anatomy in three dimensions
CBCT volume allows for better visualization and provides more details about the morphology and position of the TMJ and the condyles from different views. In addition, the TMJ cross-section view permits complete and thorough examination of the joint through a group of cross section slices.
Accurate evaluation of the temporomandibular joint (TMJ) has been difficult due to the superimposition of other structures in conventional radiographs. With Cone Beam CT imaging, it is now possible to:
- Assess the condylar anatomy of the TMJ without superimposition and distortion of the image
- Obtain a true 1:1 imaging of the condylar structures for more accurate assessments
CBCT images allow to view the temporomandibular joint complex without interference from surrounding dense temporal tissues (13). Majority of patients with symptoms and signs related to the temporomandibular joint (TMJ) are suffering from myofascial pain/dysfunction or internal disc derangements. Bony abnormality is not seen in the former and only occasionally in the latter. In such cases, radiographs do not add information of relevance to management. Where imaging of the TMJ disc is needed, Magnetic Resonance Imaging is the method of choice (2).
Other pathoses encountered in the TMJ include osteoarthrosis and rheumatoid arthritis. In both these conditions, there are often bony changes that may be detectable on conventional radiographs and CBCT. When considering the justification for CBCT, however, the clinician should consider whether the information obtained will alter the management of the patient. The identification of bony erosions, remodelling or deformity may be purely documentary and have no impact on treatment strategy (2,14).
Internal disc derangement (IDD) is common, and may be seen in asymptomatic temporomandibular joints. Longstanding IDD and the associated arthropathy may progress to osteoarthritis (OA), which is usually apparent on panoramic tomography and MRI, but is optimally visualised with CBCT. Fibrous and bony ankylosis, tumours and tumour-like conditions in the region of the TMJ include osteochondromas and synovial chondromatosis are also well seen with CBCT. 14,21,24
Assessment Rapid maxillary expansion
Rapid maxillary expansion treatments have been used widely to correct maxillary transverse deficiency problems in adolescents. Limitations of the two-dimensional (2D) cephalometric radiographs such as overlapping of structures leading to landmark identification errors and measurement errors obstruct the assessment of the skeletal and dental changes that occurs after the rapid maxillary expansion. The CBCT scanning technology overcomes these obstacles and provides superior reliability and greater accuracy in the evaluation of bone changes. 28,29
Lateral and frontal cephalometric radiographs are a valuable tool for pre-treatment patient evaluation, monitoring treatment response, as well as for treatment outcome assessment Moreover, by identifying specific landmarks and calculating angular and linear dimensions in cephalometric radiographs is possible to predict the growth of the craniomaxillofacial complex.14-16,18,30 With the conventional cephalometric techniques, complex 3D structures are projected onto a 2D plane. Consequently there are restrictions including superimposition of anatomical structures which obstacles the landmark identification, magnification and distortion. Also with conventional cephalometric techniques are not provided information concerning anatomical relationships in the coronal plane.
CBCT allows the 3D visualization of the craniofacial skeleton, so accurate evaluation of the anatomic structures it’s achievable. Cross-sectional slices in all 3 views of space take full advantage of the 3D CBCT information. Moreover, from the evaluation of landmarks, lines, distances and angles CBCT allows the assessment of surfaces, areas and volume. In general, CBCT is very useful for selected orthodontic and surgical patients. 14, 16,30
Sinus And Airway Airway assessment
The normal airway has been described as oval shaped with a larger lateral distance compared with the anterior posterior distance.31
CBCT technology provides a major improvement for evaluation of the airway, allowing for 3-dimensional and volumetric analysis. Airway analysis conventionally has been carried out by using lateral cephalograms.
Three-dimensional airway analysis will be useful for the understanding of more complex conditions such as obstructive sleep apnea (OSA) and enlarged adenoids. 14,15,27
Volumetric data obtained from a CBCT survey can be used to visualize the sinuses and the entire airway path from the nasal and oral entrances to the laryngeal spaces for:
- Identification of anatomical borders
- Determination of degree of infection and presence of polyps
- Assistance in airway studies for diagnosis and treatment of obstructive sleep apnea
- Calculation of actual volume of airway space
- Determination of the point of airway constriction
CBCT imaging has recently been explored for orthodontic applications, including dental age estimation.15 In particular, age estimation is important in forensic cases, since criminals usually pretend to be subadults, in order to benefit from the law. Moreover, dental age estimation is crucial for cases of unaccompanied asylum seekers with no official identification documents. Yang et al (2006) have create a software to calculate the pulp/tooth volume ratio based on the cone-beam CT tooth images. This was the first study concerning dental age estimation based on CBCT images. The results of the present study were promising although the research should be continued.32
Investigation of orthodontic-associated paraesthesia
Although paraesthesia of the lower lip, may occur after orthognathic surgery to the lower jaw, removal of mandibular third molar, dento-alveolar surgery and following endodontic treatment, it is an uncommon complication during conventional orthodontic treatment. 33-37 The iatrogenic lower lip paraesthesia related with orthodontic treatment usually is temporary. In such cases the tooth apices and nerves are related. The relationship of bone, root apex and neurovascular canal can be evaluated only in CBCT images and not in 2D x-rays. The mental nerve paresthesia related to orthodontic treatment is rare since usually the distal root of 2nd lower molar and the neurovascular canal are not related.33-35
surgical treatment planning and growth assessments in true 1:1 imaging
Large volume CBCT should not be used routinely for orthodontic diagnosis. For complex cases of skeletal abnormality, particularly those requiring combined orthodontic/surgical management, large volume CBCT may be justified, particularly where MSCT is the current imaging method of choice.27
CBCT images provide valuable information in cases of orthognathic surgery especially concerning patients with congenital deformities in the oral and maxillofacial region or malocclusions. Using CBCT images and DICOM (Digital Imaging and Communications in Medicine) compliant software, three-dimensional objects can be prepared by using preset intensity levels of soft and hard tissue. Once this is accomplished, the clinician can view the object’s skeletal or soft-tissue surfaces by themselves or together. CBCT images grate a potential to link equal pre-treatment expectations with post-treatment results.21
CBCT has become widely available and acceptable by the orthodontic community especially
as the radiation exposure and cost decreases. The continuous advancements in the imaging machines, techniques, and software have added valuable improvement in its diagnostic capabilities. In addition, the ease of image manipulation and its relevancy to the clinical setting offers orthodontists and clinicians the chance for improved diagnosis. The orthodontic community needs to increase their knowledge, and evaluate its clinical relevancy and reliability, as well as consider its other applications.
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