Cone Beam CT

Question 1

what does CBCT stand for and what is it?

Answer 1

Cone beam computed tomography

Cross sectional imaging suitable for assessing radiodense structures

Question 2

what is patient head positioning in a CBCT?

Answer 2

Frankfort plane parallel to floor

same as an OPT machine

Question 3

what are the BENEFITS of CBCT over plain radiography?

Answer 3

No Superimposition

ability to view subject from any angle

no magnification/distortion

Allows for 3D reconstruction

Question 4

DOWNSIDES of CBCT vs Plain radiography?

Answer 4

INCREASED RADIATION DOSE TO PT

Lower resolution (image not as sharp)

More expensive

Images more complicate to interpret

Additional training needed

Question 5

CBCT vs Conventional CT

Answer 5

CBCT:
- lower dose
- potential for sharper image
- cheaper

CT:
- able to differentiate soft tissues better
- cleaner images (better signal to noise)
- large field of view

Question 6

what are the common uses of CBCT in dentistry?

Answer 6

• clarifying relationship between impacted Lower 8 to IAN canal prior to tx
• Measuring alveolar bone dimension for implant placement
• Visualising complex root canal morphology for RCT
• Investigating external root resorption next to impacted teeth (if unclear on xray)
• assessing large cystic jaw lesions & their involvement of important anatomical structures

Question 7

What are the names of these COMMON orthogonal planes?

Answer 7

Axial - from below

Sagittal - from side

Coronal - from front

Question 8

What is ALARP?

Answer 8

It is a principle used for radiographic imaging where the person in charge makes sure to control the radiation to

As Low As Reasonably Practicable (ALARP)

Question 9

what is a voxel?

Answer 9

a voxel is a 3D pixel

never as small as intraoral radiograph pixels (image not as sharp on CBCT)

Question 10

what FOV and voxel size would you need for ENDODONTIC cases if taking a CBCT?

Answer 10

• FOV as small as possible
• Smaller voxel size (for better clarity)

Question 11

What FOV & Voxel size for planning implants?

Answer 11

FOV - depends on number/position of implants

Voxel - larger since small anatomy isnt too common

Question 12

What is the order of HIGHEST TO LOWEST radiation dose for:

Intraoral
CBCT
CT
Panoramic/OPT

Answer 12

HIGHEST

CT - 400-1000μSv
CBCT - 13-82μSv
OPT - 3-24μSv
Inraoral - 4μSv

LOWEST

Question 13

what is an artefact on a radiograph and what are the 2 main types called?

Answer 13

visualised structures on scan that arent actually present on the object being investigated

• Movement artefact
• Streak artefacts

Question 14

What is a MOVEMENT artefact and the issues it can cause?

Answer 14

occurs if pt not completely still during full exposure

General blurriness

Chin rest/head strap helps prevent this

Question 15

what is a STREAK artefact and the issues it can cause?

Answer 15

Caused by High-attenuation objects (metals, amalgam etc)

Issues:
- prevents caries assessment adjacent to restorations
- difficulty assessing radiographs due to distortion

Question 16

Contraindications for CBCT?

Answer 16

• If plain radiographs sufficient
• Pathology requiring soft tissue visualisation (CBCT better for hard tissue)
• Patient factors: unable to stay still/fit in machine

Question 17

what is needed for a clinical practitioner to take CBCT?

Answer 17

Postgraduate training

Question 18

what is the justification for CBCT?

Answer 18

• Clinical exam needed BEFORE
• CBCT only considered if plain radiography unable to provide sufficient info