Projection Geometry, Intraoral Radiographic Technique

Question 1

what are the geometric characteristics

Answer 1

-image sharpness
- image magnification
- 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

• 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

Question 4

how do you ensure the radiation source is as small as possible

Answer 4

smaller focal spot

Question 5

how do you ensure the source to receptor distance is as long as possible

Answer 5

use a long cone

Question 6

what is magnification

Answer 6

enlargement of radiographic image compared to the actual size of object
- image shows true shape of object

Question 7

what are the 2 rules to minimize magnification

Answer 7

• source to object distance should be as long as possible
• object to receptor distance should be as short as possible

Question 8

what is distortion

Answer 8

• unequal enlargement
• variation from true shape of object
• improper alignment of receptor, object and beam

Question 9

what are the 2 rules to minimize shape distortion

Answer 9

• object and receptor should be parallel
• beam should be perpendicular to object and receptor

Question 10

what are the 2 types of distortion

Answer 10

-foreshortening
- elongation

Question 11

what causes foreshortening

Answer 11

tooth not parallel to receptor and beam directed perpendiculat to receptor

Question 12

what does foreshortening cause

Answer 12

the radiographic image is shorter than the actual object

Question 13

what causes elongation

Answer 13

tooth not parallel to receptor and beam directed perpendicular to tooth

Question 14

what happens in elongation

Answer 14

radiographic image is larger than the actual object

Question 15

what are the 5 rules for accurate image formation

Answer 15

• 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

Question 16

what are the projection techniques for periapical radiography and what cones do you use

Answer 16

• paralleling technique- use long cone
• bisecting angle technique- use long or short cone

Question 17

describe the paralleling technique

Answer 17

-receptor parallel to tooth: increased object- receptor distance. increased source- receptor distance
- beam perpendicular to tooth/receptor

Question 18

what do you want to see on a good radiograph

Answer 18

2-3 mm on bone around apices
- buccal and lingual cusps to be superimposed
- contacts should be open on areas of interest

Question 19

what would tell you the vertical angle is correct

Answer 19

buccal and lingual cusp tips superimposed

Question 20

what would tell you horizontal angle is correct

Answer 20

contacts should be open in area of interest

Question 21

what is the preferred method

Answer 21

paralleling technique

Question 22

what is the bisecting angle technique

Answer 22

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

Question 23

what does the bitewing show you diagnostically

Answer 23

-crowns
- interproximal areas
- alveolar bone support
- interproximal caries
- periodontal condition
- calculus
- crown margins
- premolar and molar bitewing

Question 24

why do you want to use a slightly positive vertical angulation in bitewings

Answer 24

because maxillary molars flare buccally

Question 25

when is overlapping in BW acceptable

Answer 25

if the overlapping is not greater than half the thickness of the enamel

Question 26

what is radiographic localization

Answer 26

• right angle method
• tube shift method (SLOB) buccal object rule

Question 27

what does radiographic localization account for

Answer 27

lack of 3D radiographic images

Question 28

what does SLOB stand for

Answer 28

same lingual, opposite buccal

Question 29

what is the right angle method

Answer 29

if you take radiographs at right angles to each other at area of interest you can localize area of question

Question 30

what does the buccal object rule / SLOB rule say/ tube shift method

Answer 30

• take a radiograph of the premolars you notice a radiolucent lesion apical take a second radiograph of same area but change horizontal angulation

Question 31

if the object moves in the same direction as the you move the tube head what does the SLOB rule tell you

Answer 31

the object is lingual

Question 32

if the object moves in a different direction as you move the tube head what does the SLOB rule tell you

Answer 32

the object is buccal