projection geometry- intraoral radiographic technique

Question 1

geometric characterisitcs

Answer 1

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

Question 2

fuzzy, unsharp margin of radiograph image
-penumbra or edge gradient

Answer 2

unsharpness

Question 3

penumbra(shadow) or edge gradient

Answer 3

(shadow) unsharp margins

Question 4

3 rules to maximize sharpness

Answer 4

1. radiation source(focal spot) should be as small as possible
   2.source-to-object (focal spot) distance should be as long as possible
2. object-to-receptor distance should be as short as possible

Question 5

compare radiation source(focal spot) size[smaller to larger] with unsharpness

Answer 5

larger the focal spot, the more x-ray photons are produced, and the less sharp it is

the smaller the focal spot, the less x-ray photons are produced, and the sharper image it is

Question 6

explain source-to-object distance (rule 2)

Answer 6

(want as far as possible)

longer= less divergent=more parallel= sharper

shorter= more divergent=less parallel=less sharp

Question 7

explain object- to-receptor distance (rule 3)

Answer 7

want short as possible

shorter= closer/less distance= sharper
longer= further away/more distance=less sharp

Question 8

(equal enlargement)
enlargement of radiographic image, compared to actual size of object

Answer 8

magnification

Question 9

2 rules to magnification:

Answer 9

1. source(focal spot) to object distance long as possible
2. object to receptor distance short as possible

Question 10

(unequal enlargement)
-variation from true shape of object
-unequal magnification of parts of object
-improper alignment of receptor, object, beam

Answer 10

distortion

Question 11

2 rules to minimize shape distortion

Answer 11

1. object and receptor parallel
2. object/receptor perpendicular to beam

Question 12

two types of distortion:

Answer 12

1. foreshortening
2. elongation

Question 13

tooth not parallel to receptor and beam IS perpendicular to tooth/receptor

-image of tooth is shorter than actual tooth size

Answer 13

foreshortening

Question 14

tooth not parallel to receptor and beam IS perpendicular to tooth/receptor

-image of tooth is longer than actual size of tooth

Answer 14

elongation

Question 15

5 rules for accurate image formation

Answer 15

1. focal spot/source is small
2. source to object is long distance
3. object to receptor is short distance
4. tooth and receptor are parallel
5. tooth/receptor perpendicular to beam

Question 16

2 projection techniques for periapical radiography

Answer 16

1. paralleling technique
2. bisecting angle technique

Question 17

use long cone

Answer 17

paralleling technique

Question 18

use long or short cone

Answer 18

bisecting angle technique

Question 19

paralleling technique 2 ways

Answer 19

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

Question 20

use long cone to compromise by moving _______distance back

Answer 20

object to receptor distance

Question 21

make ring parallel to buccal surfaces of teeth:

Answer 21

horizontal angulation

Question 22

if alignment of beam and receptor are not right what happens

Answer 22

conecut

Question 23

how many mm do you want to see above apices with vertical angulation

Answer 23

2mm

Question 24

this tehcnique is the preferred method for periapical radiography

Answer 24

paralleling technique

Question 25

if the paralleling technique cant be used, this technique may be used

(like low palate or angulation)

Answer 25

bisecting angle technique

Question 26

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

Answer 26

bisecting angle technique (based on rule of isometry)

want beam to be perpendicular to bisecting angle

Question 27

for the bisecting angle technique, the angle formed by plane of tooth and place of receptor is bisected, and the beam is directing_______ to the bisecting line

Answer 27

perpendicular

Question 28

when do you used the bitewing technique

Answer 28

for crowns, interproximal areas, alveolar bone(bone level), caries, periodontal condition, calculus, crown margins, premolar and molar bitewing

Question 29

what do you want to see with bitewing technique

Answer 29

-contact open
-alveolar crest/bone level
-B/L cusps

Question 30

with this technique, you want slight vertical positive angulation of 10 degrees

Answer 30

bitewing technique

Question 31

if you get incorrect horizontal angulation:

Answer 31

get overlapped conacts

Question 32

radiographic localization methods:

Answer 32

1. right angle method (easier)
2. tube shift method (SLOB-> same lingual= opposite buccal)