Cone Beam Computed Tomography (CBCT)
The use of CBCT is valuable adjunct in assessing and diagnosing pathology in endodontics, oral pathology, anomalies of the developing dentition like impacted, ectopic, supernumerary teeth, and oral maxillofacial surgery, for example, cleft palate, dental and facial trauma, orthognathic surgery and orthodontics (Figure 5).7
A CBCT scanner uses a collimated radiation source producing a cone or pyramid shaped beam of radiation in a single, full, or partial revolution around the patient. Two dimensional images are reconstructed into three dimensional images which can be viewed in a variety of ways, including cross-sectional images and volume renderings of the oral cavity.
Although CBCT units produce higher radiation doses than from a single traditional dental radiograph, the radiation dose is delivered is typically less than that produced during a medical computed tomographic scan.
The International Commission on Radiological Protection (IRCP) has updated the methodology of determining effective dose based on the tissue weighting factors.8
|Imaging Technique||Estimated Dose
|Four posterior bitewings with phosphor plates or F speed film||5.0|
|Cephalometric radiograph lateral||5.6|
|Full mouth radiographs
|Dento-alveolar CBCT (small field of view)||103|
|Maxillo-facial CBCT (medium or large field of view)||175|
The use of CBCT should be considered when conventional radiographs are inadequate to complete diagnosis and treatment planning and potential benefits outweigh the risk of additional radiation dose. It is not to be used routinely for diagnosis or screening purposes in the absence of clinical indication. Basic guidelines for the use of CBCT include:
A written report of the imaging and full interpretation of the findings is required to be placed in the patient's chart.11