Extra Oral Radiography

Question 1

what is the radiographic baseline?

Answer 1

• Radiographic baseline - line from outer canthus of eye to EAM. represents base of skull

Question 2

what is scatter radiation?

Answer 2

when xrays pass through tissues - some are scattered = compton effect
skull radiography - increase in field of beam - more scatter produced
adds to background fog
greyer film - lack of contrast

Question 3

what is an anti scatter grid?

Answer 3

stop photons scattered in patient reaching the film
avoids degrading image and reducing contrast
narrow strips of lead alterating with plastic
fixed/stationary or moving/oscillating

Question 4

what is a postero - anterior mandible used for?

Answer 4

fractures - medio lateral displacement

cusps/malignancy causing medio lateral expansion or bone destruction

Question 5

what does a PA give good visualisation of?

limited visualisation of?

Answer 5

posterior body and ramus

head/neck of condyle

Question 6

in a PA what can the spine obstruct?

Answer 6

the midline

Question 7

advantages of PA?

Answer 7

reduced magnification of facial structures

reduced dose to eyes

Question 8

positioning for a PA?

Answer 8

patient faces film - nose/forehead touching holder
radiographic baseline = horizontal
centre of beam to midline of patient at height of mid ramus

Question 9

what are reverse townes used for?

Answer 9

improve visualisation oh head/neck of condyle

trauma or pathology

Question 10

positioning for reverse townes?

Answer 10

xray beam angled 30 degrees up

centre of beam aimed to midline of pt and through condyle

Question 11

indications for taking a lateral oblique of the jaw?

Answer 11

fractures of body,ramus,condyle
pathology - cysts
assess wisdom teeth
dental assessment of special needs patients
caries in children - bitewings not tolerated

Question 12

positioning for lateral oblique jaw?

Answer 12

isocentric positioning with a skull unit
dental tube + vertical angulation
dental tube + horizontal angulation

Question 13

what is isocentric positioning?

Answer 13

patient supine - position for area to be imaged
rotate machine into horizontal plane
angle 25 degrees towards head
tilt top of pt’s head towards film

Question 14

what is vertical angulation?

Answer 14

pt holds cassette against and parallel to area under exam
tubehead positioned underneath lower body of mandible - not under exam
aim tube towards teeth under investigation
tubehead angled slightly upwards

Question 15

what does vertical angulation allow?

Answer 15

will project opposing body of mandible up and away from area of interest

Question 16

disadvantages of vertical angulation?

Answer 16

angulation can cause vertical distortion of teeth

maxillary teeth not always shown clearly

Question 17

horizontal angulation?

Answer 17

pt holds cassette against/parallel to area under exam
tubehead aimed along occlusal plane below ear towards max/mandib teeth to be examined
aims through radiographic keyhole = triangular space between back of ramus and cervical spine

Question 18

disadvantages of horizontal angulation?

Answer 18

xray beam may not pass directly between the contact points of teeth = overlapped on film

Question 19

what are ceph radiographs used for?

Answer 19

ortho assesment

pre ortho surgery

Question 20

what is used during a ceph to standardise the image and make the image reproducible?

Answer 20

patient positioned with ear rods

Question 21

what must a ceph have?

Answer 21

must have means of calculating amount of magnification
must be able to visualise hard and soft tissue
means of calculating magnification/calibrating digital image

Question 22

positioning for a lateral ceph?

Answer 22

mid saggital plane parallel to film/receptor
frankfurt plane horizontal
centre of xray beam aimed at EAM
teeth in occlusion

Question 23

how to keep maginification to a minimum?

Answer 23

long focus to patient distance

short patient to film distance

Question 24

distance from xray to patient?

Answer 24

1.5-2m distance

Question 25

what are aluminium filters used for?

Answer 25

positioned over anterior part of face
attenuate beam in anterior facial region
allows visualisation of bone and soft tissue on one film despite high exposure factors for facial bones
if digital - soft tissue made up by software

Question 26

reducing the beam size reduces what?

Answer 26

dose

Question 27

other type of ceph?

Answer 27

postero anterior ceph

Question 28

what is a lateral skull used for?

Answer 28

trauma - fractures
pathology - pagets, myeloma
used primarily to visualise vault of skull

Question 29

difference of a lateral ceph compared to lateral skull?

Answer 29

lateral ceph uses cephalostat, has an aluminium filter, large focus to patient distance, patient must be in occlusion

Question 30

what is an occipito mental used for?

Answer 30

facial bone fractures - zygoma, le fort and orbital blowout
pathology - occasionally used in sinus disease
different angulations give views of different areas

Question 31

positioning for occipito mental?

Answer 31

patient faces film holder
nose/chin touching the holder
radiographic baseline 45 degrees to film
centre of xray bea,m to midline of pt through base of nose
beam 10-30 degrees to feet

Question 32

increased angulation causes what>?

Answer 32

projects dense bones of skull base down away from facial structures = improved view of zygomatic arch = diff perspective - useful for evaluation of bony displacement

Question 33

what is the frankfurt plane?

Answer 33

Frankfurt plane - inferior orbital border IOB to upper border represents anthropological base line

Question 34

what is the maxillary occlusal plane?

Answer 34

Maxillary occlusal plane - ala of nose to tragus of ear