Projection Geometry

Question 1

GEOMETRIC CHARACTERISTICS
(3)

Answer 1

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

Question 2

Unsharpness

Answer 2

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

Question 3

Rule #1.

Answer 3

Radiation source should be as small as
possible.

Question 4

Rule #2.

Answer 4

Source-to-object distance should be as
long as possible.

Question 5

Rule #3.

Answer 5

Object-to-receptor distance should be as
short as possible.

Question 6

MAGNIFICATION (Equal Enlargement)

Answer 6

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

Question 7

2 Rules to Minimize Magnification

Answer 7

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 8

DISTORTION (Unequal Enlargement)

Answer 8

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

Question 9

2 Rules to Minimize Distortion

Answer 9

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

Question 10

5 RULES FOR ACCURATE IMAGE FORMATION
(5)

Answer 10

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 11

PROJECTION TECHNIQUES FOR PERIAPICAL RADIOGRAPHY
(2)

Answer 11

1. Paralleling Technique – use long cone
2. Bisecting Angle Technique – use long or short cone

Question 12

PARALLELING TECHNIQUE
(2)

Answer 12

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

Question 13

— technique is the preferred
method.

Answer 13

Paralleling
 If the paralleling technique cannot be
used, the bisecting angle technique
may be used.

Question 14

BISECTING ANGLE TECHNIQUE
Based on Rule of Isometry:

Answer 14

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

Question 15

BISECTING ANGLE TECHNIQUE

Answer 15

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

Question 16

PROJECTION ERRORS IN PERIAPICAL RADIOGRAPHY
(3)

Answer 16

Vertical Angulation
Horizontal Angulation
Alignment of Beam and Receptor

Question 17

FORESHORTENING

Answer 17

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

Question 18

ELONGATION

Answer 18

Tooth not parallel to receptor, and beam
directed perpendicular to tooth.

Question 19

Improper horizontal
angulation results in

Answer 19

overlapping of contacts.

Question 20

Improper alignment of
beam and receptor results
in

Answer 20

cone cutting.

Question 21

BITEWING TECHNIQUE
(3)

Answer 21

Crowns, interproximal areas and alveolar bone support
Caries, periodontal condition, calculus, crown margins
Premolar and molar bitewing

Question 22

BITEWING TECHNIQUE
Incorrect horizontal angulation:

Answer 22

overlapped contacts

Question 23

FULL MOUTH SERIES:

Answer 23

periapical and bitewing radiographs showing all teeth

Question 24

RADIOGRAPHIC LOCALIZATION

Answer 24

1. Right angle method
2. Tube shift method (SLOB)
   Buccal object rule
   SLOB – same lingual, opposite buccal.