Intra-oral techniques and Paralleling

Question 1

If the ideal projection geometry is met what will this result in

Answer 1

the image size will be identical to the object size

Question 2

What is the ideal projection geometry

Answer 2

Image receptor and object in contact and parallel

Parallel beams of X-rays coming towards the patient and the image receptor

X ray beam is perpendicular to object plane and image receptor plan

Question 3

What are problems in projection geometry

Answer 3

image receptor and object not in contact
the beams of X-rays are NOT parallel
X -ray beam central ray may nor may not be perpendicular to the object plane and image receptor
Image size is not identical to object size

Question 4

Why can the image receptor and object not fully be in contact

Answer 4

because the tooth is supported by bone so you cannot contact all of it

Question 5

Why are beams of X-rays not parallel

Answer 5

X-ray beams are divergent beams so the rays will not be parallel

Question 6

Why is the image size not identical to object size

Answer 6

due to magnification caused by the divergent beam

Question 7

What type of X-ray does not have magnification

Answer 7

cone beam ct

Question 8

What are two solutions to the problems in projection geometry

Answer 8

paralleling technique

bisecting angle technique

Question 9

What is the paralleling technique

Answer 9

the image receptor and object are parallel but they are not touching

Question 10

What is the bisecting angle technique

Answer 10

image receptor and object partially in contact but not parallel to each other

Question 11

Are all beams parallel in the paralleling technique

Answer 11

no only the central ray is perpendicular to the long axis of the tooth, the outer rays are not quite perpendicular

Question 12

Why does magnification happen

Answer 12

Due to the image receptor and the object being some distance apart, there is potential for undesirable magnification

Question 13

What is the fsd

Answer 13

distance between the focal spot of the x-ray tube (where x-rays are produced) marked with a red dot on the intra-oral x-ray head to the skin surface of the patient

Question 14

Wha can be done to reduce magnification

Answer 14

Use long X-ray focus skin distance

Question 15

What is the minimum length for X-ray focus-skin distance

Answer 15

20cm

Question 16

What does the long X-ray focus skin distance allow for

Answer 16

more parallel, non-diverging X ray beam as the outer part of the beam are not quite as divergent leading to less magnification

Question 17

Where should the beam aiming device of the film holder be placed

Answer 17

close to but not actually touching the patient

Question 18

How do you measure the fsd

Answer 18

you measure the mark on the outside of the tube head to the patient end of spacer cone

Question 19

What should rectangular collimation be combined with

Answer 19

beam-aiming devices and film holders

Question 20

What is the benefit of film holders, BAD and RC

Answer 20

Dose reduction
Improved quality
Fewer rejects

Question 21

What are the different colors of film holders

Answer 21

red blue and yellow

Question 22

What part of the film holder is color coded

Answer 22

bite block, beam aiming device and rod

Question 23

What is the blue FH

Answer 23

anterior periapicals

Question 24

What is the red FH

Answer 24

bitewings

Question 25

What is the yellow FH

Answer 25

posterior periapicals

Question 26

What is the image receptor support for

Answer 26

holding and supporting the image receptor

Question 27

What is the bite block for

Answer 27

what the patients bite on

Question 28

How are the film holders cleaned

Answer 28

autoclaved

Question 29

How can you tell if you have assembled the film holder correctly

Answer 29

○ If you look through the circle you should see the support for the image receptor right in the middle, if you don’t then something is wrong

Question 30

What does incorrect film holder assembly result in

Answer 30

coning off

Question 31

What do endodontic film holders consist of

Answer 31

``` ○ Image receptor support (receptor vertical or horizontal) ○ Bite block ○ Beam-aiming device ○ Connecting rod - no colour Autoclavable ```

Question 32

What does endodontic film holders also have

Answer 32

○ Basket to support instrument heads or gutta percha points so that the patient does not bite the tooth with the files in it, the basket ensures the teeth are kept apart and protect the heads of the instruments

Question 33

What is collimation

Answer 33

controlling the shape and size of x ray beam

Question 34

Why does the beam aiming device have rectangular marks

Answer 34

so that it can be lined up easily with the x ray device

Question 35

What machines should RC be on

Answer 35

should be provided on new equipment and retrofitted to existing equipment

Question 36

What is the collimator made of

Answer 36

lead

Question 37

What are the shapes of collimator

Answer 37

circular or rectangular

Question 38

What is the maximum diameter of a circular collimator

Answer 38

60mm

Question 39

What is the silver bit of the collimator that lets x ray out

Answer 39

aluminium

Question 40

Why does rectangular collimator emit less radiation

Answer 40

Reduction in surface area | but is more technically difficult as need to ensure everything is lined out

Question 41

What are the different sizes of image receptors for periapicals

Answer 41

Size 0 vertical anteriors image receptor (blue holder) - smallest, use that with long axis vertical for anterior teeth Size 2 horizontal posteriors image receptor (yellow holders) - bigger, use that for long axis going horizontally

Question 42

What is the procedure for a periapical

Answer 42

Select the film holder and correct image receptor Assemble correctly - be careful with sensors Position patient at right height, open wide Position against teeth of interest, parallel to line fo arch and long axis of tooth

Question 43

Where should beam aiming device be when putting film holder into mouth

Answer 43

at free end

Question 44

How do you position film holder into mouth

Answer 44

○ Bite block against the teeth ○ Cotton roll between bite block and teeth on opposite side to stabilise ○ Beam aiming device to patient (was previously on the free end); close to but not touching ○ Rectangular collimator: correct orientation to match image receptor, and spacer cone close to beam-aiming device ○ Align tube head - check from 2 directions, for a periapical check from underneath and from infront

Question 45

Summarise the paralleling technique

Answer 45

- Image receptor and object parallel but not in contact for a paralleling periapical - Image receptor and object some distance apart - potential for undesirable magnification - Use long X-ray focus-skin (fsd) distance to reduce magnification - at least 20cm - Requires use of film holders, cannot do it without them Stabilise with cotton roll between bite block and teeth in arch opposite to that being x-rayed, if you put it on the wrong side then there is risk of not getting the apex of the tooth in the image

Question 46

What is the ideal bitewing

Answer 46

- Of the side teeth (premolars and molars) - Symmetry of upper and lower teeth (film holder should guarantee this) - Minimal overlap of adjacent teeth - Want to see inter-dental bone One or two per side

Question 47

Describe procedure for taking bitewing

Answer 47

Select film holder (red holder) and image receptor (long axis horizontal for both) Assemble correctly Position against lower teeth, parallel to line of arch, tongue out the way Front edge of film packet mesial to canine/premolar contact

Question 48

What are the different sizes of image receptor

Answer 48

size 2 (adults) and size 0 (children)

Question 49

Describe how the film holder is positioned in the mouth for bitewings

Answer 49

○ Patient to bite together ○ Beam-aiming device to patient, again make sure it is close but not touching ○ Rectangular collimator orientation correct ○ Spacer cone to beam-aiming device Align tube head - check from 2 directions. In front and from below

Question 50

What are the critical points for bitewings

Answer 50

- Image receptor is parallel to the line of arch - Central ray at 90 degrees to arch Vertical angle controlled by the film angle If no film holder then vertical angle needs to be +5-10

Question 51

Why do you need to change vertical angle for bitewing if no film holder

Answer 51

takes into account curve of Monson

Question 52

What is curve of spee

Answer 52

anterior-posterior ○ Curves up posteriorly ○ Produces a happy smile ○ Useful to us when we are trying to see what way the radiograph is

Question 53

What is curve of monson

Answer 53

buccal-lingual Influences X-ray technique e.g bitewings and panoramic radiography (Panoramic vertical angle is negative to occlusal plane (-8) Curve of Monson influences the position of the film holder which determines the vertical angle

Question 54

How can you determine orientation of x-ray

Answer 54

curve of spee look at the molars, you can't see how many roots there are in the upper one, only in the lower and this is due to the mesial distal roots of the lower so this is the most reliable way of checking the orientation of the X-rays