RAD02 - Lecture 8 - Parallax

Question 1

Define Parallax

Answer 1

The apparent displacement of an object because of 2 different positions of the observer

Question 2

Explain the how parallax can be seen in radiographs of the same unerupted tooth

Answer 2

2 radiographs of unerupted tooth are taken

The X-ray tubehead was in 2 different positions

The resultant films with show a difference in the position of the unerupted tooth relative to the erupted tooth

Question 3

Explain how can you use parallax to determine the position of a unerupted tooth

Answer 3

If unerupted tooth moves in the same direction as x-ray tube head -> palatal/lingual

If unerupted tooth moves in the opposite direction as x-ray tubehead -> buccal

If unerupted tooth doesnt move with x-ray tube-head -> in line of the arch

(You can tell which direction the X-ray is moving by looking at the other teeth in the image)

Question 4

What is the acronym to remember parallax of teeth?

Answer 4

SLOB

Same -> lingual

Opposite -> buccal

Question 5

What are the clinical indications for using parallax? (3)

Answer 5

Assess position of unerupted maxillary canines/odontomes and supernumeraries

Question 6

What are 2 two different methods of parallax’ing unerupted maxillary canines/odontomes?

Answer 6

Parallax -> horozontal plane

2 periapicals are taken (one of upper central incisor, and other on canine)

Central inscisor -> upper standard occlusal

Canine -> PA or upper oblique occlusal

Parallax -> vertical plane

Dental panoramic radiograph + upper standard occlusal