Projection Geometry, Intraoral Radiographic Technique Flashcards
what are the geometric characteristics
-image sharpness
- image magnification
- image shape distortion
what is unsharpness
- fuzzy, unsharp margin of radiographic image
- penumbra or edge gradient
what are the 3 rules to maximize sharpness
- radiation source should be as small as possible
- source to object distance should be as long as possible
- object to receptor distance should be as short as possible
how do you ensure the radiation source is as small as possible
smaller focal spot
how do you ensure the source to receptor distance is as long as possible
use a long cone
what is magnification
enlargement of radiographic image compared to the actual size of object
- image shows true shape of object
what are the 2 rules to minimize magnification
- source to object distance should be as long as possible
- object to receptor distance should be as short as possible
what is distortion
- unequal enlargement
- variation from true shape of object
- improper alignment of receptor, object and beam
what are the 2 rules to minimize shape distortion
- object and receptor should be parallel
- beam should be perpendicular to object and receptor
what are the 2 types of distortion
-foreshortening
- elongation
what causes foreshortening
tooth not parallel to receptor and beam directed perpendiculat to receptor
what does foreshortening cause
the radiographic image is shorter than the actual object
what causes elongation
tooth not parallel to receptor and beam directed perpendicular to tooth
what happens in elongation
radiographic image is larger than the actual object
what are the 5 rules for accurate image formation
- 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
what are the projection techniques for periapical radiography and what cones do you use
- paralleling technique- use long cone
- bisecting angle technique- use long or short cone
describe the paralleling technique
-receptor parallel to tooth: increased object- receptor distance. increased source- receptor distance
- beam perpendicular to tooth/receptor
what do you want to see on a good radiograph
2-3 mm on bone around apices
- buccal and lingual cusps to be superimposed
- contacts should be open on areas of interest
what would tell you the vertical angle is correct
buccal and lingual cusp tips superimposed
what would tell you horizontal angle is correct
contacts should be open in area of interest
what is the preferred method
paralleling technique
what is the 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
- the angle formed by plane of tooth and plane of receptor is bisected and the beam is directed perpendicular to the bisecting line
what does the bitewing show you diagnostically
-crowns
- interproximal areas
- alveolar bone support
- interproximal caries
- periodontal condition
- calculus
- crown margins
- premolar and molar bitewing
why do you want to use a slightly positive vertical angulation in bitewings
because maxillary molars flare buccally
