CBCT

Question 1

What’s the difference between CBCT and panoramics?

Answer 1

CBCT machines resemble panoramic units but uses a cone-shaped x-ray beam rather than a flat fan-shaped beam.

Question 2

Describe how a CBCT image is created

Answer 2

1. Data Acquisition
   The equipment rotates around the patient imaging a cylindrical or spherical volume referred to as ‘field of view’ (FOV). This FOV can vary in size enabling small, medium or large volumes of the patient to be imaged.
2. Primary reconstruction
   With the data from the one scan, the computer divides up the volume into tiny cubes or ’voxels’ of which it then calculates the X-Ray absorption. Each voxel is allocated a number, then a colour from the grey scale from black to white.
3. Secondary or multi-planar reconstruction
   After the primary reconstruction, the computer software can allow the voxels to be reconstructed into sagittal, coronal or axial images which appear simultaneously on the computer screen. The software will allow these images to be scrolled through in real time and reconstruct the information into 3-D images.

Question 3

What are the clinical indications of a CBCT?

Answer 3

• Localisation of unerupted teeth
• Localisation of an impacted tooth
• Assessment of a cleft lip and palate
• Orthodontic/Orthognathic planning
• Assessment of root canal anatomy in multi-rooted teeth
• Assessment of periodontal fraction lesions
• Dental trauma
• Implant placement
• Assessment of pathology of the jaws
• Assessment of fractures
• Assessment of TMJ

In 2011 the European wide ‘ Safety and Efficacy of a New and Emerging Dental X-Ray Modality’ SEDENTEXCT project

Question 4

What is a CBCT not indicated for?

Answer 4

• Diagnosis of dental caries
• Routine periodontal support
• Routine periapical disease
• Routine assessment of root canal anatomy

Question 5

Name some advantages of CBCTs

Answer 5

• Multi-planar reformatting and data manipulation allows images to be viewed in different planes.
• Lower dose than medical CT
• Geometrically accurate images
• Good spatial resolution
• Fast scanning time
• Compatible with implant and orthodontic planning software

Question 6

Name some disadvantages of CBCTs

Answer 6

• The patient must remain perfectly still throughout the scan
• Soft tissues are not well imaged
• Artefact caused by metal objects e.g. metal fillings cause streak artefacts
• Computer constructed panoramic images are not comparable with conventional panoramic images