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What is new and on the horizon? W. Bruce Howerton Jr., DDS, MS; Maria A. Mora, DDS, MS

ithin 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 twodimensional (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 threedimensional (3-D) image in a process termed “tuned-aperture

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ABSTRACT Background and Overview. Cone beam computed tomography (CBCT) is a diagnostic imaging technology that is changing the way dental practitioners view the oral and maxillofacial complex. CBCT uses radiation in a similar manner as does conventional diagnostic imaging and reformats the raw data into Digital Imaging and Communications in Medicine (DICOM) data. DICOM data are imported into viewing software that enables the manipulation of multiplanar reconstructed slices and three-dimensional volume renderings. DICOM data also may be used in third-party software to aid in dental implant placement, orthognathic surgery and orthodontic assessment. 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. JADA 2008;139(6 supplement):20S-24S.

Dr. Howerton is in private practice in oral and maxillofacial radiology, Carolina OMF Imaging, 3200 Blue Ridge Road, Suite 218, Raleigh, N.C. 27612, e-mail “[email protected]”. Address reprint requests to Dr. Howerton. Dr. Mora is in private practice in oral and maxillofacial radiology, Carolina OMF Imaging, Raleigh, N.C.

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Advancements in digital imaging

CONE BEAM COMPUTED TOMOGRAPHY

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 (Carestream, 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. 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. Solidstate 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 shows examples of images produced with a third-party DICOM viewer. Another important advantage of CBCT over medical CT is that the amount of radiation received by the patient is markedly less than the dose received with medical CT units. Ludlow and colleagues6 reported that the effective dose equivalent measured after an exposure using indirect digital panoramic imaging was 6 to 7 microSieverts. (The effective dose equivalent is the amount of radiation received after taking into account the tissue’s sensitivity to radiation.7 It is calculated by multiplying the dose received by the organs by a weighting factor that represents the organs’ sensitivity. One sums up the various doses to

ABBREVIATION KEY. 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. JADA, Vol. 139

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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.

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Figure 1. OnDemand3DApp software (CyberMed, Seoul, South Korea). A. Hard-tissue evaluation for dental implant planning. B. Threedimensional (3-D) volume rendering of the anatomy captured within the field of view. C. Sculpting of the 3-D volume rendering with softtissue overlay (in this case, the airway space).

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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 computerguided 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 DICOMcompliant 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.

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obtain the effect on the body.) The effective dose equivalent measured using CBCT is between 30 and 400 µSv,6 depending on the manufacturer and technical factors involved. This compares with an effective dose equivalent of 2,100 µSv from a conventional medical CT scan of the maxilla and mandible.6 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

Figure 2. Images created with Dolphin 3D software (Dolphin Imaging & Management Solutions, Chatsworth, Calif.). With this 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. (Reprinted with permission of Dolphin Imaging & Management Solutions, Chatsworth, Calif.).

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 hardtissue 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 THE FUTURE OF DIAGNOSTIC IMAGING

The future of diagnostic imaging using DICOM data is bright. For example, DICOM-compliant software known as “volumetric imaging software” is being used in orthodontics to merge photographic images with radiographic images so that clinicians can assess true soft- and hard-tissue relationships, as shown in Figure 2. Companies providing this technology include Anatomage (San Jose, Calif.), Dolphin Imaging & Management Solutions (Chatsworth, Calif.) and Materialise Dental NV. For example, consider a patient with a congenital deformity in the oral and maxillofacial region, malocclusion and missing teeth. Using DICOMcompliant software, the oral surgeon, orthodontist, implantologist and restorative dentist can JADA, Vol. 139

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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 headstabilizing 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

link their communication such that pretreatment expectations equal posttreatment results. 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. CONCLUSION

Disclosure. Drs. Howerton and Mora did not report any disclosures. 1. Webber RL, Horton RA, Tyndall DA, Ludlow JB. Tuned-aperture computer tomography (TACT): theory and application for three-

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Two-dimensional diagnostic imaging has served dentistry well and will continue to do so for the foreseeable future. However, the advent of CBCT allows complete visualization of the oral and maxillofacial complex. Through education regarding the correct interpretation of data and training in the scanning process, better treatment planning and surgical treatment will result. The future of this technology lies within an increased number of imaging centers staffed with oral and maxillofacial radiologists who understand the needs of dentists, as well as the benefits of using DICOMcompliant software. 

dimensional dento-alveolar imaging. Dentomaxillofac Radiol 1997;26(1):53-62. 2. Abreu M Jr, Yi-Ching L, Abreu AL. Comparative diagnostic performance of TACT slices and its multiple source images: an in vitro study. Dentomaxillofac Radiol 2004;33(2):93-97. 3. Nakajima A, Sameshima GT, Arai Y, Homme Y, Shimizu N, Dougherty H Sr. Two- and three-dimensional orthodontic Imaging using limited cone beam-computed tomography. Angle Orthod 2005;75(6):895-903. 4. Cotton T, Geisler T, Holden D, Schwartz S, Schindler W. Endodontic applications of cone-beam volumetric tomography. 2007;33(9):1121-1132. 5. Digital Imaging and Communications in Medicine. DICOM. Rosslyn, Va.: NEMA. “http://medical.nema.org/”. Accessed April 16, 2008. 6. Ludlow JB, Davies-Ludlow LE, Brooks SL, Howerton WB. Dosimetry of 3 CBCT devices for oral and maxillofacial radiology: CB Mercuray, NewTom 3G and i-CAT. Dentomaxillofac Radiol 2006;35(4):219-226. 7. International Commission on Radiological Protection (ICRP). “www.icrp.org/”. Accessed April 16, 2008. 8. Bjerklin K, Ericson S. How a computerized tomography examination changed the treatment plans of 80 children with retained and ectopically positioned maxillary canines. Angle Orthod 2006;76(1): 43-51. 9. Hauman CH, Chandler NP, Tong DC. Endodontic implications of the maxillary sinus: a review. Int Endod J 2002;35(2):127-141. 10. Tu S, Shaw C, Chen L. Simulation of cone beam computer tomography chest imaging with parallel computing: nodule detectability versus dose. Physics Medical Imaging 2005;5745:910-920. 11. American Dental Association. Dental professionals. Specialty National Organizations. “www.ada.org/prof/ed/specialties/ specorgs.asp”. Accessed April 2, 2008. 12. American Academy of Oral and Maxillofacial Radiology. Directory of advanced educational programs. “www.aaomr.org/adv_edu_prog.php”. Accessed April 2, 2008. 13. White SC, Heslop EW, Hollender LG, Mosier KM, Ruprecht A, Shrout MK; American Academy of Oral and Maxillofacial Radiology, ad hoc Committee on Parameters of Care. Parameters of radiologic care: an official report of the American Academy of Oral and Maxillofacial Radiology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91(5):498-511.