Cone Beam Computed Tomography: The New Generation of Dental CT SCAN
Cone Beam Computed Tomography (CBCT) scanners have been available for craniofacial three dimensional imaging in Europe since 1999 and introduced in the United States in 2001. The classical medical Computed Tomography, or CT scan, is well known through the characteristic tunnel-like machine. Medical CT scanners use an X-ray source that rotates around the body to make cross-sectional images. Computers stack up the resulting “slices” to create a unified, three dimensional image of a chest, heart, jaw or other body part. Medical CT scanners often produce many more times the dose of radiation to produce their images than do X-ray machines and CBCT. For instance, an abdominal or craniofacial scan can expose the site to 50 times the radiation that X-rays would. For dental applications, the medical CT scanner requires a separate scan of the mandible and of the maxilla which will result in very high levels of radiation.
A Cone beam CT scanner can scan both jaws in total scan time of approximately 8.5-18 seconds with 3.6-6 seconds of actual exposure time depending on the manufacturer. This represents less radiation than one would receive with a full series of periapical radiographs. CBCT also differs from the medical CT scanner in that it does not image “slices.” Instead its cone shaped beam scans a complete volume of the craniofacial structures at once utilizing a narrow cone beam of radiation, and provides a volume of data in its field. With the subject in a sitting position, rotating the beam around the subject’s head making an image every few degrees, and subsequent reconstruction software applied on the volumetric data, both jaws and craniofacial areas of interest are observed. This results in real time 3-D images from every angle with high resolution, exacting and optimal detail.
The compact size and low radiation dosage of the CBCT scanner, sitting position of the patient, and high level of accuracy of the 3-D images of the areas of interest, makes it ideally suited for imaging the craniofacial structures. The CBCT is reported to be accurate to approximately 0.1 mm while the medical CT scanners are accurate to approximately 0.5 mm. The CBCT is emerging as the imaging “standard of excellence” for diagnostic and treatment planning, and patient education, in all phases of dentistry.
There are a multitude of dental indications for the use of CBCT maxillofacial imaging, including evaluation of the jaws and facial bones for infection, impactions, tumors, fractures, and developmental and congenital deformities; three dimensional assessments by the restorative dentist and surgeon of the quality and quantity of alveolar bone of one or both jaws for combined treatment planning for restorative driven virtual implant placement with optimal emergence profile, and identifying critical anatomical landmarks including the inferior alveolar canal, and maxillary sinus; visualization of the temporomandibular joint and its components, and condylar changes following orthognathic surgery; stability, predictability and three dimensional assessments of mandibular changes prior to and after orthognathic surgery; orthodontic 3D cephalometrics, and study of changes over time by comparative cephalometric overlays, surgical positioning of orthodontic mini-implants with guides fabricated on models replicated with cone-beam computed tomography; and airway analysis by assessment of lateral cephalometric diagnosis of adenoid hypertrophy and posterior upper airway obstruction.
CBCT currently is also used in a number of medical applications including ENT, Computerized Tomography Angiography (CTA), and mammography. In Science Daily ( January 1, 2008 ) it has been reported that, “Cone-beam breast CT provides exceptional tissue contrast and can potentially reduce examination time with comparable radiation dose to conventional 2D mammography, according to a new study by a team of researchers from the University of Texas M. D. Anderson Cancer Center in Houston.”