|Year : 2015 | Volume
| Issue : 2 | Page : 89-94
Cone-beam computed tomography: A miracle for orthodontics!
Jeevan M Khatri, Gaurav Tated
Department of Orthodontics and Dentofacial Orthopaedics, C.S.M.S.S. Dental College and Hospital, Aurangabad, Maharashtra, India
|Date of Web Publication||11-Dec-2015|
Department of Orthodontics and Dentofacial Orthopaedics, C.S.M.S.S. Dental College and Hospital, Kanchanwadi, Paithan Road, Aurangabad - 431 005, Maharashtra
Source of Support: None, Conflict of Interest: None
The branch of oral medicine and radiology has always played a role of back stage worker for the branch of orthodontics and dentofacial orthopaedics. It would have been difficult for an orthodontist to gift the bright smiles to his/her patients without the 2D and 3D black and white pictures provided by the oral radiologist. Moreover, the series of advances in the various imaging modalities are playing the role of a magician for the branch of orthodontia. The present article provides valuable information about one such miracle for the field of orthodontics-cone beam computed tomography (CBCT).
Keywords: Cone-beam, imaging, orthodontia, radiograph, tomography
|How to cite this article:|
Khatri JM, Tated G. Cone-beam computed tomography: A miracle for orthodontics!. J Dent Allied Sci 2015;4:89-94
| Introduction|| |
Computed tomography (CT) has been used successfully to represent the true three-dimensional (3D) morphology of the skeletal structures of the cranium. Way back in 1971, CT scan started helping the medical practitioners.  Emergence of this new radiographic imaging modality was considered a revolution, but was costly and had high levels of radiations and so its use in the dental faculty was restricted. To overcome this limitation of the CT, cone-beam CT (CBCT) was developed in 1998 specifically for imaging the structures related to dentistry.  The cost-benefits of CBCT scanning are superior to the combination of several two-dimensional (2D) radiographic images with respect to the valuable information, and to CT with respect to radiation dose and cost. There are many evidences which proved that 2D radiography is incapable of leading to the perfect diagnosis and so is the advent of 3D radiography. 
| Need for Cone-beam Computed Tomography|| |
Every new invention has to prove its vitality and CBCT was no exception to it.
Clinicians in the field of orthodontia primarily use it for:
- Accurate identification of anatomical landmarks.
- Measurement of angular and linear parameters between the landmarks.
There are studies in literature which have compared the diagnostic and treatment outcome measurements taken from CBCT images against measurements taken from conventional 2D radiographs. The detailed analysis of the studies showed that CBCT images are better than conventional 2D lateral cephalograms, ,,, posterior-anterior cephalograms,  and panoramic radiographs  for both landmark identification and measurement accuracy.
Hence, CBCT is an important radiographic imaging modality in use today for the accurate measurements, which help the clinician in diagnosis and treatment planning.
| Applications in Orthodontics|| |
For more than half a century, orthodontics was based on the 2D images provided by the radiologist. With the advent of CBCT such as 3D imaging techniques, the following help is provided to the orthodontist.
Evaluation of dental and skeletal structures (cephalometrics)
Gribel et al. stated that conventional cephalometric radiography gives the 2D image of the 3D structure. As a result, the superimposition of anatomical structures interferes with landmark identification and can lead to magnification and distortion of the image obtained. On the contrary, CBCT imaging with the help of newly developed software helps to represent anatomical structures in all three planes - sagittal, coronal, and transverse. The adjustments in magnification, sharpness, and contrast have made the identification of anatomical structures much easier.  Van Vlijmen et al. when compared the cephalometric radiographs of CBCT and conventional radiographs concluded that CBCT scans gave more accurate measurements. 
Neiva et al. did the evaluation of cephalometric landmark identification on CBCT multiplanar and 3D reconstructions and concluded that the frequency of highly reliable values was greater for multiplanar than 3D reconstructions. They also found that lower reliability was found for points on the condyle and higher reliability for those on the midsagittal plane. The area of interest of the observer thus decides the most reliable type of image visualization. 
Location and condition of impacted teeth
CBCT is a vital tool to locate the exact position and the condition of impacted tooth [Figure 1].
Haney et al. has shown that enhanced precision in the localization of canine teeth and improved estimations of the space conditions in the arch can be obtained with CBCT, and this can greatly affect diagnosis and treatment planning to facilitate a more clinically-orientated approach. 
Wriedt et al. stated that CBCT should be used as an adjuvant for routine panoramic radiographs in the following cases:
- Canine inclination in the panoramic X-ray exceeds 30°,
- Root resorption of adjacent teeth is suspected, and/or
- Canine apex is not clearly discernible in the panoramic X-ray, implying dilacerations of the canine root. 
Growth evaluation using cervical vertebra
Joshi et al. stated that CBCT scans can be used to reliably assess cervical vertebrae maturity, which provides for a consistent evaluation of skeletal maturity. 
Temporomandibular joint evaluation
The comparison of the CBCT imaging with complex panoramic radiography and linear tomographic views was made by Honey et al. where he presented the accuracy and superior reliability of the CBCT images for the diagnosis of condylar morphology and erosion.
Advantages of CBCT for a complete bilateral temporomandibular joint (TMJ) examination are:
- Less time,
- Inclusive of image data for both right and left joint in a single 360° rotation scan, and
- Simplifies patient positioning. 
Hintze et al. said that the CBCT delivers potentially low radiation dose and also allows for multiplanar views with image manipulation in the form of rotated views thus offering an additional advantage to the conventional imaging modalities. 
An average of four tomographic cuts in both lateral and frontal planes are needed for each joint, in addition to the scout images preceding the actual tomographic evaluation.
Evaluation of airways
Lateral cephalograms have been routinely used to assess the airway using techniques involving both hard tissue and soft tissue points [Figure 2].
Vizzotto et al., stated that conventional radiography and reconstructed 2D CBCT images provide similar assessments of the airway. Axial cuts of 3D CBCT scans provide soft tissue points that are derived from the projection of shaded areas, which are more clearly visible in axial CBCT cuts when compared with conventional radiographs, thereby enhancing airway assessment. 
Ogawa et al. investigated airway morphology in obstructive sleep apnea affected patients. The apnea-affected subjects showed a significant decrease in airway volume, area, and distance, thereby highlighting the importance of CBCT in the diagnosis of this condition. 
Cleft lip and cleft palate patients
Cleft lip/palate (CL/P) is the most common craniofacial anomaly.  Schneiderman et al., presented a study where he used 18 cephalometric measurements specifically for CBCT images of CL and P patients. 3D reconstructions of images in association with 3D navigation systems allowed preoperative evaluations of the cleft palate, the volume and location of the bone defect, presence of supernumerary teeth, and an appraisal of permanent teeth and alveolar bone morphology. 
In a study by Albuquerque et al., CBCT was found to be equivalent to multi-slice CT in both the volumetric assessment of bone defects in alveolar and palatal regions and in establishing donor area and the volume of the bone graft to be used in the rehabilitation of cleft patients. 
Orthodontic treatment planning
Placement of temporary anchorage devices (miniscrew implants)
Bone-borne point of force application through temporary anchorage devices (TADs) or miniscrews has revolutionized how orthodontists move teeth. TADs avoid unwanted tooth movement and give orthodontists much greater control over the movement of single teeth or groups of teeth than previously possible. 
Quality of cortical bone is a significant factor in the success of miniscrew implants. Min et al. evaluated the factors (root proximity and cortical bone thickness) affecting the success rate of orthodontic micro-implants using CBCT images. Though both the factors played a role in the success of the miniscrew implant, the proximity of root surface to miniscrew implants was more statistically significant.  Thus, CBCT images help to place the miniscrew implants in the safe zones.
Rapid maxillary expansion
CBCT images provide an invaluable resource for assessing the effect of rapid maxillary expansion (RME).  While all studies on rapid palatal expansion treatment demonstrated both dental and alveolar tipping, none found detrimental effects (such as dehiscence's or fenestrations) to the alveolar bone supporting the posterior teeth. 
Kanomia et al. studied the CBCT of skeletal changes following RME to increase arch-length with a development-dependent bonded or banded appliance and concluded that RME is an effective treatment option for all growing patients, but expansion efficiency (skeletal effect) is inversely related to age. CBCT is an important 3D diagnostic tool for managing crowding due to maxillary deficiencies. 
External apical root resorption
Failure to direct impacted canine eruption forces properly can result in external apical root resorption (EARR) of the adjacent teeth [Figure 3]. Moreover, routine orthodontic tooth movement causes irreversible EARR. Precisely quantifying EARR could not be done prior to CBCT imaging because of distortion and magnification on 2D radiographs. 
|Figure 3: Cone-beam computed tomography image depicting apical root resorption|
Click here to view
Planning of orthognathic surgery
For the examination of the craniofacial skeleton, the various imaging modalities are used in combination with recently developed software. The virtual anatomical models (patent-specific) customized by the CT volumes are configured with the available 3D image data present. The generated models are then used for various treatment considerations, for example: Use for fabrication of anatomical substituted grafts or an aid during a surgical procedure.
The acquired databases can be interlinked with the subsequent anatomical models to create a virtual image of the tissues and their response to development, treatment, and function [Figure 4].
|Figure 4: Cone-beam computed tomography image of orthognathic surgery in orthodontia|
Click here to view
The distinctive and anticipated changes subsequent to a surgery are depicted very easily through a CBCT than in comparison to the cumbersome computer modeling. 
For example: Maxillofacial soft tissues can be ascribed with viscoelastic properties and can be associated with related hard tissues so that replicated manipulation of the hard tissues (e.g., teeth and skeleton) produces a correct deformation reaction in the attached soft tissues.
Root angulations in posttreatment orthodontics
Bouwens et al. compared mesiodistal root angulation with posttreatment panoramic radiographs and CBCT and concluded that panoramic radiograph are less reliable than CBCT regarding the idea of mesiodistal tooth angulations and might exhibit deviations in both mesial and distal directions for all teeth. CBCT allows clinicians to obtain 3D images of the craniofacial complex with similar absorbed doses as dental radiographs, and the 3D volume renderings provide a powerful tool for the visualization of root angulation. 
| Cone-beam Computed Tomography Machines|| |
Examples of commonly used CBCT machines are enlisted as follows:
- 3D Accuitomo.
- 3D Accuitomo FPD 170.
- 3D Accuitomo FPD 60.
- 3D Accuitomo FPD 80.
- Art 3 D.
- CB Mercuray.
- CB Throne.
| Discussion|| |
To observe the application of innovative technologies in orthodontics has been very interesting. The development of CBCT as a preferred imaging procedure for comprehensive orthodontic treatment is of particular interest. The information obtained from CBCT imaging provides several substantial advantages.
Newaz et al. presented with the cases of skull base abnormalities diagnosed accidently in the CBCT scans. The orthodontic patient was tentatively diagnosed with a notochord remnant in the clivus and the another implant patient exhibited an empty sella turcica. 
Mostafa et al. presented few more cases which are incidental findings on CBCT imaging. The conventional panoramic radiograph showed no apparent abnormality. A CBCT scan as part of our routine orthodontic records was done. The MPR tool was used to generate a panoramic view from the CBCT, and it showed a radiopaque structure in the nasal region. Initially, it was suspected as an artifact, but it was also visible on the 3D volume rendering. After adjusting the threshold and subtracting the surrounding bone on the 3D surface rendering, the structure maintained its radiopacity and resembled an ectopic tooth crown-like structure. The ear, nose, and throat specialist's differential diagnosis was a tooth crown, a rhinolith, or a foreign body. To surprise of all, on aspiration, it was found to be a pencil eraser. 
Another incidental finding was in a patient who came with the TMJ disorder to the dentist and reported unhealed fracture in the symphyseal region extending from the inferior border of the mandible and approaching the alveolar margin in the 3D view. This finding was not visible on the panoramic view. 
The contributions of CBCT to the field of dentistry have been demonstrated in several studies of technology appraisal, in craniofacial morphology as it relates to health and disease, and in the usefulness of CBCT images for diagnosis, treatment planning, and treatment outcome.
| Limitations of Cone-beam Computed Tomography|| |
Below are the disadvantages of CBCT as listed as follows: 
- It is definitely more expensive than classic 2D radiologic investigations.
- The dose of ionizing radiation generated is greater than in a pantomography investigation.
- As a new technology, it requires new competences from the clinician and the value of information obtained is interpretation-sensitive.
- Any movement artifacts affect the whole data set and the whole image rather than just one part.
- It provides limited resolution of deeper (inner) soft tissues, and magnetic resonance imaging and classic CT are better for soft tissue imaging.
- It has low contrast range (dependent on the type of X-ray detector).
- It has increased noise from scattered radiation and concomitant loss of contrast resolution.
| Summary - Future of Cone-beam Computed Tomography in Orthodontics|| |
Alginate impressions will soon become history with the advent of CBCT. The virtual models fabricated with the help of CBCT imaging helps to reduce the patient discomfort and save the chair side time. Moreover, in comparison to other digital imaging modalities, it also gives an idea about root anatomies, impactions, and the alveolar bone condition.  In the coming years, CBCT shall also offer several advantages in the fabrication of custom-made brackets and wires. The day is not far when CBCT digital data will be used to fabricate the sets of envisaging aligners, and same will be the case with the fabrication of retainers. 
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]