Radiographic localisation

Question 1

Why do we need radiographic localisation?

Answer 1

• To determine location of a structure or pathological lesion in relation to other structures
• Only needed where clinical examination insufficient to provide answer

Question 2

What clinical situations do we need radiographs?

Answer 2

Position of unerupted teeth
- Normal but impacted/ectopic
- Supernumerary
- Proximity to important structures e.g. IAN

Location of roots/root canals
- Endodontics
- Surgery

Relationship of pathological lesions

Trauma
- Dental
- Bone fractures

Soft tissue swellings to find tissue or source

Question 3

What are the stages of spotting and correcting faults seen in radiographs?

Answer 3

• Perception
• Recognition
• Resolution

All requiring knowledge

Question 4

How to radiograph a Orientated transverse molar?

Answer 4

• Need to take a right angle radiograph
  Can use
• Panoramic and lower true occlusal
• Paralleling periapical and lower true occlusal
• CBCT (cone beam CT) each of the MPRs is at right angles to others

Question 5

What are the methods of radiographic localisation?

Answer 5

• Normally two views required
• Views at right angles in their protectory geometry
• Views with any different projection, provided the difference is known
• With aid of opaque objects (e.g. GP point)
• Anatomical knowledge crucial

Question 6

What is a Parallax?

Answer 6

• An apparent change in the position of an object, caused by a real change in the position of the observer

Question 7

How to set up a x-ray tube for horizontal or vertical shift?

Answer 7

• Consider position of x-ray tube when each view is taken
• Imagine looking at patient from that position
• Your viewing point is interchangeable with the X-ray tube head position

Question 8

Why are panoramic radiographs different for horizontal and vertical tube shift?

Answer 8

• In panoramic consider looking from in front of patients as if back along the x-ray beam

Question 9

When looking at a radiograph what side are we viewing?

Answer 9

• Radiographs normally viewed from buccal aspect of patient
• Beam passes from buccal to lingual
• Buccal is closest to observer
• Lingual/palatal is further from observer

Question 10

What is the Parallax mnemonic?

Answer 10

SLOB
Same Lingual Opposite Buccal
If object moves in same direction of tube then its lingual and if its opposite then its buccal

Question 11

What is the sequence of events we need to know for Parallax localisation?

Answer 11

1. Identify direction of tube movement (horizontal etc)
2. What structure do we need to know location of
3. Choose a reference point
4. Observe a movement of structure in correct direction

Question 12

In regard to Parallax localisation what views do we have that showcase Horizontal tube shift?

Answer 12

• 2 equivalent views
• 2 periapical
• 2 bitewings
• 2 oblique occlusal

Question 13

In regard to Parallax localisation what views do we have that showcase Vertical tube shift?

Answer 13

• 2 different views
• Panoramic and oblique occlusal
• Panoramic and lower (bisecting angle) periapical