Dental Radiography

Question 1

What is the definition of Radiography?

Answer 1

Uses x-rays to produce images.

Question 2

What is the definition of Radiology?

Answer 2

The use of images to diagnose and treat disease..

Question 3

What does EMR waves stand for?

Answer 3

Electromagnetic Radiation.

Question 4

what is the definition of EMR?

Answer 4

• Use energy and momentum
• Electric and magnetic
• Travel at 90 degrees to each other
• Wave packets (Photon/Quantum
• No mass
• Measured in electron Volts (eV)
• Can travel through a vacuum
• Vibrates transferring energy from one place to another without matter being transferred
• some waves require a medium to travel through eg sound waves

Question 5

What is a photon?

Answer 5

A wave/ energy packet and can be both wave and particle and should the frequency be doubled then the energy of the photon is doubled.

Question 6

what is frequency?

Answer 6

• number of repetitions in a given time period
• Greek symbol is Nu or V
• more repetitions the higher the frequency but a shorter wave length
• measured in hertz HZ

Question 7

The shorter a wave length…….?

Answer 7

the more dangerous they are

Question 8

Cancer can be caused by……?

Answer 8

Any waves shorter than visible light eg Gamma rays are the shortest then xrays!

Question 9

What is Ionising radiation?

Answer 9

• It carries more energy than non- ionising radiation
• can create charged ions by displacing electrons in atoms
• radiation from radioactive sources and naturally occurring radiation.

Question 10

What is Ionising radiation used for?

Answer 10

used in medicine - Diagnostically, caries in teeth

-Therapeutic, treatment in cancer

Question 11

What is Non-Ionising Radiation?

Answer 11

Changed position of atoms but does not change or alter the make up, structure or properties

Question 12

Are dental xrays safe?

Answer 12

the risk of biological damage is small but there is still a risk

Question 13

In the UK how many xrays are taken in a year?

Answer 13

approximately 20-25 million intra and extra oral a year

Question 14

In the UK how many fatalities per year?

Answer 14

Approximately 10 fatalities per year

Question 15

All exposures must be kept…..?

Answer 15

ALARP as low as reasonably practical

Question 16

Name X-ray equipment…?

Answer 16

• Tube head
• positioning arm
• control panel

Question 17

All x-ray equipment must be….?

Answer 17

• safe and robust
• accurate and simple to operate
• must produce suitable x-rays, both film and digitak
• small
• easy to position, move and store
• stable and balances when positioned
• outer casing made of lead and checked daily for damages
• x-ray tube in glass envelope which is filled with oil to remove heat
• step up transformer which increases the voltage from 240V to 60-90 kV
• step down transformer which decreases 240V to 7-10V required to heat the filament
• Spacer cone/beam indicating device
• Collimator
• Aluminium filtration removes harmful low energy x-rays (Soft xrays less than 30KeV)
• Focal spot

Question 18

What happens at the glass envelope inside the xray tube?

Answer 18

located at the back of the tube head, completed surrounded by lead which absorbs unwanted x-rays which are travelling in all directions which creates a vacuum.

Question 19

What is a cathode?

Answer 19

-made up of a tungsten filament which is centred in a focusing cup
-electrons are produced by the filament and focused onto the target on the anode
-Focussing cup has a negative charge ( same as electrons) and helps direct to target
-

Question 20

What is Thermionic Emission?

Answer 20

• when the exposure button is pressed the electricity flows from the filament in the cathode and the filament gets hot
• the hot filament then releases electrons which surround the filament
• the hotter the filament gets the greater number of electrons released

Question 21

What is the anode?

Answer 21

• comprised of a tungsten target on copper base
• when the electrons from the filament hit the target and generate the xrays, heat is produced
• the copper target helps take the heat away as it could get to hot

Question 22

What is the focussing cup?

Answer 22

Aims the stream of electrons to the focal spot on the target

Question 23

What is the focal point to skin distance?

Answer 23

• Not less than 200mm for kV under 60kV

- Not less than 100mm for kV over 60kV

Question 24

Older pointed xray machines must not be used why?

Answer 24

They produce scatter on x-rays

Question 25

Blurring of image is called...?

Answer 25

the penumbra effect

Question 26

The collimator should be....?

Answer 26

-rectangular with a maximum diameter of 40mm X 50mm, this will ensure that the maximum overlap when using an intraoral film size 2 is 2mm

Question 27

what is Filtration....?

Answer 27

-reduces skin dose -removes non diagnostic/low energy xrays/soft radiation (which is more readily absorbed by patient hence why so damaging -thickness must be 1.5mm below 70kV and 2.5mm above 70kV

Question 28

Control Panel must include....?

Answer 28

-mains on/off switch with warning light -Timer electronic impulse or clockwork Exposure time selector, numerical/ anatomical (picture of teeth) -exposure warning light with audible signal May also include - film speed selector -patient size selector -mains voltage compensator -kilovoltage selector - Miliamperage switch -exposure adjustment for digital imaging

Question 29

What is the alternating current in relation to radiography?

Answer 29

- Measured in Voltage (V) - half is negative, half is positive current - only positive is needed for production of xrays - A step up of voltage is needed to eliminate negative - equipment is working at peak output at top of cycle measured in kVpeak or kvP

Question 30

Direct Current is used by modern xray machines

Answer 30

- keeps the kV at kVpeak throughout all exposure - xray production per unit time is more efficient - more high diagnostically useful photons are produced per exposure - few lower energy photons are produced - shorter exposure time

Question 31

what factors affect the intensity of the beam?

Answer 31

- size of the tube voltage kV - size of tube current mA - distance from target d - time = length of exposure - filtration - target material - tube v waveform

Question 32

in free space xrays travel in straight lines and obey then inverse square law which means?

Answer 32

-Intensity=I/d2 which means it decreses the further away it gets from the beam

Question 33

shorter wave lengths=

Answer 33

greater energy and can therefore penetrate a greater distance

Question 34

longer wave lengths=

Answer 34

low energy and have little penetrating power. (soft energy)

Question 35

Xrays are referred to as....?

Answer 35

Ionising radiation

Question 36

xrays can affect film emulsion....?

Answer 36

to produce a visual image and can cause certain salts of flourescence

Question 37

In a year approximately how many dental xrays are taken per year?

Answer 37

20-25 million

Question 38

How many fatal malignancies a year?

Answer 38

10

Question 39

What is a step up transformer?

Answer 39

Step up transformer – increase the voltage from 240V to 60-90kv

Question 40

What is a step down transformer?

Answer 40

Step down transformer – decreases the 240v to 7-10v required

Question 41

Aluminium Filtration reduces skin dose....

Answer 41

1. 5mm below 70kV | 2. 5mm above 70 kV