Projection Geometry Flashcards
GEOMETRIC CHARACTERISTICS
(3)
- Image sharpness
- Image magnification
- Image shape distortion
Unsharpness
Fuzzy, unsharp margin of
radiographic image.
Penumbra or edge gradient
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.
MAGNIFICATION (Equal Enlargement)
Enlargement of radiographic image, compared
to actual size of object.
Image shows true shape of object
2 Rules to Minimize Magnification
Rule #1.
Source-to-object distance should be as
long as possible.
Rule #2.
Object-to-receptor distance should be as
short as possible.
DISTORTION (Unequal Enlargement)
Variation from true shape of object.
Unequal magnification of parts of object.
Improper alignment of receptor, object, beam.
2 Rules to Minimize Distortion
Rule #1:
Object and receptor should be parallel.
Rule #2:
Beam should be perpendicular to object
and receptor.
5 RULES FOR ACCURATE IMAGE FORMATION
(5)
- Focal spot as small as possible.
- Source-object distance as long as possible.
- Object-receptor distance as short as possible.
- Object parallel to receptor.
- Beam perpendicular to object and receptor.
PROJECTION TECHNIQUES FOR PERIAPICAL RADIOGRAPHY
(2)
- Paralleling Technique – use long cone
- Bisecting Angle Technique – use long or short cone
PARALLELING TECHNIQUE
(2)
- Receptor parallel to tooth
increased object-receptor distance
increased source-receptor distance - Beam perpendicular to tooth/receptor.
— technique is the preferred
method.
Paralleling
If the paralleling technique cannot be
used, the bisecting angle technique
may be used.
BISECTING ANGLE TECHNIQUE
Based on Rule of Isometry:
If two triangles have two equal angles and a
common side, then the two triangles are equal.
BISECTING ANGLE TECHNIQUE
The angle formed by plane of tooth and plane of
receptor is bisected, and the beam is directed
perpendicular to the bisecting line.
PROJECTION ERRORS IN PERIAPICAL RADIOGRAPHY
(3)
Vertical Angulation
Horizontal Angulation
Alignment of Beam and Receptor
FORESHORTENING
Tooth not parallel to receptor, and beam
directed perpendicular to receptor.
ELONGATION
Tooth not parallel to receptor, and beam
directed perpendicular to tooth.
Improper horizontal
angulation results in
overlapping of contacts.
Improper alignment of
beam and receptor results
in
cone cutting.
BITEWING TECHNIQUE
(3)
Crowns, interproximal areas and alveolar bone support
Caries, periodontal condition, calculus, crown margins
Premolar and molar bitewing
BITEWING TECHNIQUE
Incorrect horizontal angulation:
overlapped contacts
FULL MOUTH SERIES:
periapical and bitewing radiographs showing all teeth
RADIOGRAPHIC LOCALIZATION
- Right angle method
- Tube shift method (SLOB)
Buccal object rule
SLOB – same lingual, opposite buccal.
