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J Am Dent Assoc, Vol 139, No suppl_3, 20S-24S.
© 2008 American Dental Association |
ARTICLES |
What Is New and on the Horizon?
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ABSTRACT |
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 TOP ABSTRACT CONE BEAM COMPUTED TOMOGRAPHYTHE FUTURE OF DIAGNOSTIC...CONCLUSIONReferences |
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Conclusions and Clinical Implications. The information gained from using CBCT requires careful interpretation to achieve optimum results for the patient and provider.
Key Words: Computed tomography; oral and maxillofacial radiography; digital radiography; dental radiography
Abbreviations: CBCT: Cone beam computed tomography • CT: Computed tomography • DICOM: Digital Imaging and Communications in Medicine • TACT: Tuned-aperture computed tomography • 3-D: Three-dimensional • 2-D: Two-dimensional
Within the last 20 years, diagnostic digital imaging modalities in dentistry, including periapical, bitewing, panoramic and cephalometric imaging, have been replacing conventional (film-based) radiography. Drawbacks of two-dimensional (2-D) imaging include inherent magnification, distortion and overlap of anatomy.1
As early as the 1920s, manufacturers attempted to overcome the inherent problems of 2-D imaging by devising movement of the receptor and source in opposite directions to produce tomographic "slices" of oral and maxillofacial anatomy; this process is termed "linear" or "multidirectional tomography." In the 1990s, researchers used software to reconstruct 2-D images of an object from random angles and distances into a three-dimensional (3-D) image in a process termed "tuned-aperture computed tomography" (TACT) (Wake Forest University, Winston-Salem, N.C.).1 Abreu and colleagues2 found that the diagnostic performance of TACT imaging was comparable with that of bitewing images with regard to detecting proximal caries in vitro.
Within the past decade, technology termed "cone beam computed tomography" (CBCT) has evolved that allows 3-D visualization of the oral and maxillofacial complex from any plane. This imaging modality eliminates the shortcomings of 2-D imaging, produces a smaller radiation dose than that produced by medical CT and enables clinicians to make more accurate treatment planning decisions, which can lead to more successful surgical procedures.3,4 In this article, we describe how CBCT works, describe its use in dentistry today and envision how it will be used in the future.
Although all CBCT units provide 3-D information, each manufacturer uses slightly different scanning parameters and viewing software. For example, patients may sit, stand or be supine, depending on the CBCT unit. The radiation beam is 3-D in shape and similar in photon energy to that used in conventional and digital radiography. The receptor captures 2-D images and is solid-state (digital) or an image intensifier. Solid-state receptors absorb photons that are converted to an electric charge, which is measured by the computer. One advantage of solid-state receptors is improved photon utilization; one disadvantage is the high cost of production. Image intensifiers capture photons and convert them to electrons that contact a fluorescent screen that emits light captured by a charge-coupled device camera.
As the source and receptor rotate once around the patient, many exposures are made, ranging in duration between 8.9 and 40 seconds. The software "reconstructs" the sum of the exposures via algorithms specified by the manufacturer into as many as 512 axial slice images. These images are in the Digital Imaging and Communications in Medicine (DICOM) (National Electrical Manufacturers Association, Rosslyn, Va.) data format.5 DICOM is a standard for handling, storing, printing and transmitting information in medical imaging. During a single rotation of the source and receptor, the receptor captures the entire volume of anatomy within the field of view.
Medical CT differs in that it uses a fan-shaped beam and captures portions or slices of anatomy as the source and receptor move along the long axis of the section of anatomy being examined. The clinician imports the DICOM data into viewing software, enabling him or her to see axial, coronal and sagittal multiplanar reconstructed images of the volume, as well as 3-D volume renderings. One advantage of using a DICOM data format is that the dentist can make precise measurements in any plane within the viewing software. DICOM viewers are available readily and can be downloaded from the Internet free of charge or purchased from third-party retailers. Figure 1
CONE BEAM COMPUTED TOMOGRAPHY
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ABSTRACT
CONE BEAM COMPUTED TOMOGRAPHY
THE FUTURE OF DIAGNOSTIC...
CONCLUSION
References
How CBCT works.
Currently available CBCT units include the following: 3D Accuitomo FPD XYZ Slice View Tomograph (J. Morita USA, Irvine, Calif.), 3D X-ray CT Scanner Alphard Series (Asahi, Kyoto, Japan), Quolis Alphard Alphard-3030-Cone-Beam (Belmont Equipment, Somerset, N.J.), CB MercuRay (Hitachi Medical Systems America, Twinsburg, Ohio), Galileos 3D (Sirona Dental Systems, Charlotte, N.C.), i-CAT (Imaging Sciences International, Hatfield, Pa.), Iluma Ultra Cone Beam CT Scanner (Care-stream, Rochester, N.Y.), NewTom 3G and VG (AFP Imaging, Elmsford, N.Y.), Picasso (E-woo Technology, Houston), PreXion 3D (TeraRecon, San Mateo, Calif.), ProMax 3D (Planmeca USA, Roselle, Ill.) and Scanora 3D (Soredex, Tuusula, Finland). In addition, some digital panoramic radiographic systems include CBCT technology. 
shows examples of images produced with a third-party DICOM viewer.
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Uses in dentistry. Dentists can use the information obtained from the data to evaluate hard tissues for possible dental implant placement and/or grafting, orthodontic treatment planning, temporomandibular joint complex evaluation, pathosis evaluation, demonstration of anatomic variations and evaluation of patients who have experienced trauma. CBCT can aid in presurgical planning for dental implant placement by localizing the anatomy to be avoided during surgery, measuring bone volume precisely and assessing the quality of hard tissue.
In orthodontics, CBCT can improve clinicians’ evaluation of impacted canines and delayed tooth eruptions in relationship to adjacent teeth. In fact, a recent study8 demonstrated that, as a result of using CBCT, clinicians altered more than one-half of treatment plans involving canine-related diagnoses. Also, dentists can view the temporomandibular joint complex without interference from surrounding dense temporal bone to demonstrate erosion, osteophytic formation of the condyle or both. In endodontics, it is difficult at times for clinicians to evaluate the extent of inferior cortical border erosion of the maxillary sinus or of associated mucosal thickening extending to the periapical region of the roots of maxillary teeth using 2-D periapical imaging owing to superimposition of structures. At spatial resolutions of 300 micrometers (0.3 millimeters) and less, images produced with CBCT show the position of the apexes of roots of maxillary teeth extending to the nasal cavity and maxillary sinus, as well as cortical border erosion of these structures resulting from apical rarefying osteitis.9
DICOM format. Clinicians also can import the DICOM data format into third-party software that serves as an adjunct in treatment planning. For example, SimPlant (Materialise Dental NV, Leuven, Belgium) dental implant computer-guided software converts DICOM data into a file that provides information for presurgical planning. The software incorporates computer-aided design/computer-aided manufacturing replicas of dental implants for the clinician to place into the region of interest. The clinician sends the file to a manufacturing facility, which creates a surgical guide through a process termed "stereolithography." The guide includes metal cylinders that direct osteotomy drills into precise locations in the maxilla and/or mandible, as planned by the software.
Another computer-guided software that uses CBCT data (Procera Software 2.0, Nobel Biocare USA, Yorba Linda, Calif.) allows the dentist to place dental implants by using a surgical guide (NobelGuide, Nobel Biocare USA) and a fixed prosthesis during a single dental visit. Other examples of third-party computer-guided DICOM-compliant software are EasyGuide (Keystone Dental, Burlington, Mass.), ImplantMaster (iDent, Ft. Lauderdale, Fla.) and VIP Virtual Implant Placement Software (Implant Logic Systems, Cedarhurst, N.Y.). Because different practitioners often are responsible for the placement and restoration of dental implants, this technology enhances communication between practitioners, as well as patients’ understanding and education. DICOM-compliant software also aids in orthognathic surgery and 3-D cephalometric analysis.
Disadvantages of CBCT. Because radiation from the source is transmitted through tissues in the body, the receptor receives nonuniform information from radiation scattered in many directions; this is termed "noise." In addition, radiation is attenuated when passing through dense objects (such as nonprecious alloys in metal restorations, crowns and titanium materials). Sometimes, radiation is attenuated completely and does not reach the receptor. When this "radiation-less" information is reconstructed, streak artifacts in images are formed that can obstruct the surrounding anatomy. Manufacturers attempt to remove noise and streak artifacts during reconstruction of the raw data by using their own specific algorithms and filters.10 Another form of image degradation is motion artifact, which occurs when a patient moves during the scanning process. Practitioners can reduce patient movement by using head-stabilizing devices and by providing oral instructions to the patient to remain still during the scanning process.
Cost. The high cost of CBCT technology prohibits its use in most dental offices. CBCT machines can range in cost from $150,000 to $300,000. Thus, purchasers of this technology typically work in a multidentist practice or an imaging center servicing a dental community.
Training. Many practitioners who incorporate this technology into their practices have not had the training required to interpret anatomy beyond the maxilla and mandible using 2-D multiplanar images reconstructed into three dimensions. They need to recognize calcifications within the cerebral hemispheres, paranasal sinuses and oropharyngeal regions, as well as soft-tissue asymmetries. Clinicians must exercise care and draw precise image layer curves, resulting in orthogonal slices that allow correct measurement of anatomical relationships. Also, time and skill are required to create 3-D volume images that confirm 2-D relationships. To ensure the correct and safe use of this technology, educational institutions are incorporating CBCT into their curricula, and continuing education courses are being offered to help dental practitioners use and interpret DICOM data.
In 1999, the American Dental Association recognized the specialty of oral and maxillofacial radiology.11 Presently, two-year certificate and three-year master’s-level graduate dental specialty programs are offered.12 Oral and maxillofacial radiologists are trained to interpret hard-tissue changes within the oral and maxillofacial complex, and they may distinguish themselves by becoming diplomates of the American Board of Oral and Maxillofacial Radiology. The American Academy of Oral and Maxillofacial Radiology has stated that CT and implant imaging should be performed only by a board-certified oral and maxillofacial radiologist or a dentist with adequate training or experience.13
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. Companies providing this technology include Anatomage (San Jose, Calif.), Dolphin Imaging & Management Solutions (Chatsworth, Calif.) and Materialise Dental NV.
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Finally, dental imaging centers staffed with board-certified oral and maxillofacial radiologists will become more commonplace, providing patient care that includes acquisition, interpretation and conversion of DICOM data. In addition, oral and maxillofacial radiologists will be charged with educating the private practice dental community about the advantages of using DICOM data for better patient care.
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CONCLUSION |
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FOOTNOTES |
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