Projection Geometry Flashcards
What are the 3 geometric factors that affect the quality of radiograph?
Image Sharpness
Image Magnification
Image shape distortion
Fuzzy, unsharp margin of radiographic image.
Penumbra or edge gradient
Unsharpness
____ is the area around the margin of the object being radiographed; amount of unsharpness
Penumbra
Rule #1 to maximize sharpness of radiographic images:
Radiation source should be as small as possible.
Rule #2 to maximize sharpness of radiographic images:
Source-to-object distance should be as long as possible.
Rule #3 to maximize sharpness of radiographic images:
Object-to-receptor distance should be as short as possible.
How do we increase source to object distance to increase sharpness?
Increase length of collimator
Enlargement of radiographic image, compared to actual size of object.
Image shows true shape of object
MAGNIFICATION (Equal Enlargement)
Rule #1 to minimize magnification of radiographic images:
Source-to-object distance should be as long as possible.
Rule #2 to minimize magnification of radiographic images:
Object-to-receptor distance should be as short as possible.
Variation from true shape of object.
Unequal magnification of parts of object.
Improper alignment of receptor, object, beam.
DISTORTION (Unequal Enlargement)
Rule #1 to minimize distortion of radiographic images:
Object and receptor should be parallel.
Rule #2 to minimize distortion of radiographic images:
Beam should be perpendicular to object and receptor.
What are the 2 intraoral projection techniques for PA radiography?
Paralleling
Bisecting Angle
\_\_\_\_\_\_ technique 1.Receptor parallel to tooth increased object-receptor distance increased source-receptor distance 2. Beam perpendicular to tooth/receptor.
Paralleling technique
In the paralleling technique, do you want to use a long or short cone?
Long cone
Is the bisecting angle or paralleling technique the preferred method?
Paralleling
_____ technique:
Based on Rule of Isometry:
If two triangles have two equal angles and a common side, then the two triangles are equal.
The angle formed by plane of tooth and plane of receptor is bisected, and the beam is directed perpendicular to the bisecting line.
Bisecting angle technique
Tooth not parallel to receptor, and beam directed perpendicular to receptor.
FORESHORTENING
Tooth not parallel to receptor, and beam directed perpendicular to tooth.
ELONGATION
Improper _______ angulation results in overlapping of contacts.
horizontal angulation
Improper alignment of beam and receptor results in ______.
cone cutting
_______ technique:
Crowns, interproximal areas and alveolar bone support
Caries, periodontal condition, calculus, crown margins
Premolar and molar bitewing
BITEWING TECHNIQUE
: periapical and bitewing radiographs showing all teeth
FULL MOUTH SERIES
What are the 2 methods for radiographic localization?
Right angle method
Tube Shift method (SLOB)
____ method of localization:
Radiographs taken at right angles of each other provides better localization
Right angle method
According to the SLOB method, if the tubehead is moved to the mesial and the object also moves to the mesial on the radiograph, is it on the buccal or lingual?
Lingual
According to the SLOB method, if the tubehead is moved to the mesial and the object moves to the distalbon the radiograph, is it on the buccal or lingual?
Buccal
