PROJECTION GEOMETRY INTRAORAL RADIOGRAPHIC TECHNIQUE

Question 1

What are the different geometric characteristics?

Answer 1

1.Image sharpness
2.Image magnification
3.Image shape distortion

Question 2

What is unsharpness?

Answer 2

• Fuzzy, unsharp margin of radiographic image.
• Penumbra or edge gradient

Question 3

What are the 3 rules to maximize sharpness?

Answer 3

Rule #1.
- Radiation source should be as small as possible.
Rule #2.
- Source-to-object distance should be as long as possible.
Rule #3.
- Object-to-receptor distance should be as short as possible.

Question 4

To maximize sharpness the radiation source should be as ____ as possible

Answer 4

small

Question 5

What is a pneumbra?

Answer 5

edge gradient
- blurriness

Question 6

To maximize sharpness the source-to-object distance should be as _____ as possible

Answer 6

long

Question 7

To maximize sharpness the object-to-receptor distance should be as _____ as possible

Answer 7

short

Question 8

Can you adjust the size of the radiation source to adjust sharpness?

Answer 8

No, the companies/manufacturers decide this

Question 9

Why should the object-to-receptor distance be as short as possible?

Answer 9

photons will not diverge as much after they interact with the tooth before getting to the receptor

Question 10

Why should the source-to-object distance be as long as possible?

Answer 10

photons will be less divergent and more parallel before interacting with tooth

Question 11

What is magnification (equal enlargement)?

Answer 11

• Enlargement of radiographic image, compared to actual size of object.
• Image shows true shape of object

Question 12

What are the two rules to minimize magnification?

Answer 12

Rule #1.
- Source-to-object distance should be as long as possible.
Rule #2.
- Object-to-receptor distance should be as short as possible.

Question 13

To minimize magnification the source-to-object distance should be as _____ as possible

Answer 13

long

Question 14

To minimize magnification the object-to-receptor distance should be as _____ as possible

Answer 14

short

Question 15

What is distortion (unequal enlargement)?

Answer 15

• Variation from true shape of object.
• Unequal magnification of parts of object.
• Improper alignment of receptor, object, beam.

Question 16

What are the two rules to minimize shape distortion?

Answer 16

Rule #1:
- Object and receptor should be parallel.
Rule #2:
- Beam should be perpendicular to object and receptor

Question 17

To minimize shape distortion the object and receptor should be _______

Answer 17

parallel

Question 18

To minimize shape distortion the beam should be _________ to object and receptor?

Answer 18

perpendicular

Question 19

What are the two types of distortion?

Answer 19

• foreshortening
• elongation

Question 20

What is foreshortening?

Answer 20

Tooth not parallel to receptor, and beam directed perpendicular to the RECEPTOR.

Question 21

What is elongation?

Answer 21

Tooth not parallel to receptor, and beam directed perpendicular to the TOOTH

Question 22

What are the 5 rules for an accurate image formation?

Answer 22

1. Focal spot as small as possible.
2. Source-object distance as long as possible.
3. Object-receptor distance as short as possible.
4. Object parallel to receptor.
5. Beam perpendicular to object and receptor.

Question 23

What projection technique do we use at UMKC?

Answer 23

paralleling technique

Question 24

What cone can you use for the paralleling technique?

Answer 24

long cone

Question 25

What cone can you use for the bisecting angle technique?

Answer 25

long or short cone

Question 26

What are the two projection technqiues for periapical radiography?

Answer 26

• Paralleling technique
• Bisecting Angle technique

Question 27

What is the preferred method of projection technqiues for periapical radiography?

Answer 27

paralleling technique

Question 28

What is the paralleling technique?

Answer 28

1.Receptor parallel to tooth
–increased object-receptor distance
–increased source-object distance
2. Beam perpendicular to tooth/receptor.

Question 29

What are the two techniques for the paralleling technique?

Answer 29

• vertical angulation
• horizontal angulation

Question 30

What are you wanting to see on periapical radiographs?

Answer 30

• at least 2 mm of bone surrounding the roots of the teeth
• if contacts can be seen then the horizontal angulation was correct

Question 31

What is the bisecting angle technique based on?

Answer 31

Rule of isometry

Question 32

What is the rule of isometry?

Answer 32

If two triangles have two equal angles and a common side, then the two triangles are equal.

Question 33

What is the bisecting angle technique?

Answer 33

The angle formed by plane of tooth and plane of receptor is bisected, and the beam is directed perpendicular to the bisecting line.

Question 34

What are you trying to view/diagnose with a bitewing?

Answer 34

• crowns
• interproximal areas
• alveolar bone support
• caries
• periodontal condition
• calculus
• crown margins

Question 35

What would happen on a bitewing radiograph if you have an incorrect horizontal angulation?

Answer 35

overlapped contacts

Question 36

What are the two methods for radiographic localization?

Answer 36

1. Right angle method
2. Tube shift method (SLOB)/Buccal object rule

Question 37

What method of radiographic localization is shown?

Answer 37

right angle method

Question 38

What method of radiographic localization is shown?

Answer 38

tube shift method (SLOB)/buccal object rule

Question 39

Why would you need to use radiographic localization?

Answer 39

• radiographs only show something in 2 planes
• if you need to see exactly where something is located you need more “planes” to visualize it