9 - Radiographic localisation

Question 1

Why is radiographic localisation necessary?

Answer 1

• determine location of structure in relation to other structures
• required when clinical exam is not sufficient

Question 2

What clinical situations is localisation commonly used?

Answer 2

• position of unerrupted teeth
• location of roots or canals
• pathological lesions
• trauma
• soft tissue swellings

Question 3

What combination of radiographs can give you views at right angles?

Answer 3

• panoramic and lower true occlusal
• paralleling periapical and lower true occlusal
• CBCT

Question 4

What is required for localising a radiograph?

Answer 4

Two radiographs at different angles, and the difference needs to be known (tube shift aids interpretation)

Question 5

Define parallax.

Answer 5

Apparent change in position of object caused by a real change in the position of the observer

Question 6

What direction does the beam pass through patients?

Answer 6

Buccal to lingual

Question 7

What mnemonic aids parallax?

Answer 7

S - same
L - lingual
O - opposite
B - buccal

If the subject moves in the same direction as you then it is lingual or palatal to the item “in front” of it

Question 8

How do you observe parallax?

Answer 8

• identify direction of tube movement
• identify what you are observing (?)
• choose a reference point
• observe movement of ?

Question 9

What pairs of radiographs can be used to observe horizontal tube shift?

Answer 9

• 2 PAs
• 2 BWs
• 2 oblique occlusals

Question 10

What pairs of radiographs can be used to observe vertical tube shift?

Answer 10

• panoramic and oblique occlusal
• panoramic and lower (bisecting angle) PA