CBCT Reading in Ortho

Question 1

What triggers the need for a CBCT examination

Answer 1

Need to know dento-facial anatomy that is not visible from clinical examination and 2D X-ray examination in order to drive better decisions

Question 2

What are some -ves of CBCT

Answer 2

Increased radiation (Esp for kids)
Expensive

Question 3

What are the radiation dosage issues in the use of CBCT
7

Answer 3

1. Radiation damages tissues
2. X-rays are a type of EM radiation
3. Radiation is a carcinogen
4. Stochastic effects - no threshold radiation dose below which they will not occur
5. Deterministic effects - no damage until threshold radiation is reached
6. Children are more radiosensitive than adults (risk x3 for <10)
7. X-ray effects are cumulative

10x more likely to get cancer than from DPT
ALARA

Question 4

What are the different Field of Views (FOV) of CBCTs

cm is of spherical volume diameter or cylinger height

Answer 4

Large FOV (>15cm):
- TMJ, quantitative ceph and/or airway assessment
- Orthognathic jaw surgery

Medium FOV (10-15cm)
- 1-2 dental arches

Small FOV (<10cm)
- Few teeth, a quad, up to 2 dental arches

Question 5

What are the British Orthodontic Society’s and Prof Foong’sindications for CBCT

Answer 5

1. Highly selected cases where conventional radiography cannot supply satisfactory diagnostic information
2. Cleft palate case
3. Assessment of unerupted tooth position, particularly where resorption is a concern
4. Identification of root resorption caused by unerupted teeth (upper laterals)
5. Orthognathic surgery planning

Prof Foong’s:
1. Bone thickness surrounding teeth
2. Tooth impaction and possibility of root resorption and/or ankylosis