Radiographic Localisation

Question 1

What is the need for radiographic localisation?

Answer 1

• to determine location of a structure or pathological lesion in relation to other structures
  
  • only needed where clinical examination insufficient

Question 2

In what clinical situations may radiographic localisation be required?

Answer 2

• position of unerupted teeth
• location of roots and root canals
• relationship of pathological lesions
• trauma
• soft tissue swellings

Question 3

What radiographs can be used for views at right angles?

Answer 3

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

Question 4

What do all methods of radiographic localisation include?

Answer 4

• normally two views required
• views ay right angles in their projection geometry
• views with any different projection, provided difference is known
• with aid of opaque objects (e.g. GP point)
• anatomical knowledge crucial

Question 5

What must be considered for views not at right angles?

Answer 5

• known projection geometry
• must both include item to be localised and stable reference point
• multiple combinations possible
• utilises horizontal or vertical tube shift to aid interpretation

Question 6

What is 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 is viewing and beam direction considered for parallax?

Answer 7

• radiographs normally viewed from the buccal aspect
  
  • beam passes from buccal to lingual
  • buccal is closest to observer
  • lingual is furthest from observer
• SLOB
  
  • lingual moves in the same direction as observer
  • buccal moves in opposite direction from observer
  • same
  • lingual
  • opposite
  • buccal
• PAL
  
  • palatal moves in the same direction

Question 8

What is the sequence of events when using parallax?

Answer 8

• identify the direction of tube movement
• what is the structure of interest
• choose a reference of point
• observe the movement of structure of movement

Question 9

What are the options for parallax localisation?

Answer 9

• horizontal tube shift
  
  • 2 periapicals
  • 2 bitewings
  • 2 oblique occlusifs
• vertical tube shift
  
  • panoramic and oblique occlusal
  • panoramic and lower periodical