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Ortho > ortho radiology > Flashcards

ortho radiology Flashcards

1
Q

IRR1999

A

safety of workers and public

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2
Q

IRMER2000

A

safety of patients

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3
Q

what are X-rays?

A

beam of high energy photons

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4
Q

mutation

A

permanent alteration of a portion of a chromosome

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5
Q

what can mutations result in?

A

uncontrolled cell replication and tumour

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6
Q

deterministic effects

A

direct damage to tissues

skin erythema, ulceration, mucositis, hair loss

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7
Q

stochastic effects

A

chance/random

pt may develop cancer from any single dose

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8
Q

what pts are at greatest risk from radiation?

A

children

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9
Q

effective dose

A

different tissues have different radiosensitivity

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10
Q

dose limitation

A

ALARP

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11
Q

components of dose limitation

A

equipment
staff training
justification

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12
Q

legislation for radiation equipment

A

NRPB guidelines 2001 - dept of health

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13
Q

how can you ensure equipment contributes to dose limitation?

A

use correct settings - highest kV that still gives diagnostically acceptable contrast (for OPT 60-90kV)
traditional film - use fastest film speed and intensifying screens for EO
digital - ensure settings optimised for dose limitation as not every machine the same (ask RPA)
wherever possible collimate beam to decrease field of view - dentition only in an OPT = 50% dose reduction

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14
Q

staff training as a contribution to dose limitation

A

avoid repeat exposures
check pt identity
pt positioning
remove jewellery, glasses, ortho appliances

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15
Q

justification

A

benefit to pt from diagnostic info should outweigh detriment of exposure
most appropriate view
record in notes why required - always examine pts clinically first
radiographic report

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16
Q

Qs before requesting radiograph

A

do I need to take it? - will outcome affect pt management?
can I get info any other way e.g. palpation?
any prev radiographs available?
most appropriate view?

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17
Q

indications for OPT

A

state of development
ectopics/supernumeraries
stage of development of individual teeth
morphology of UE teeth
alv bone (PDD)
teeth - Rxs, gross caries, PA infection, other pathology
oral surgery - jaw lesions, surgery, trauma/fractures

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18
Q

faults in OPTs

A

limitations in width of focal trough - esp at front of mouth
faults in pt positioning
movement of pt during exposure

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19
Q

what direction does the X-ray source move in OPT?

A

L to R

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20
Q

what direction does the receptor move in OPT?

A

R to L

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21
Q

why is the focal plane portrayed clearly in an OPT?

A

because objects in the focal plane are projected to the same point of film whereas other objects outside the focal trough may be blurred or not visible at all

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22
Q

why are anterior teeth narrower in an OPT?

A

they are closer to the rotation centre

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23
Q

why are posterior teeth wider in an OPT?

A

they are further from the rotation centre

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24
Q

explain the relevance of focal trough to malocclusion

A

anything outwith focal trough blurred/not visible
when a malocclusion prevents pt from biting edge to edge within groove on bite block, either whole tooth/roots may end up outwith focal trough

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25
Q

what needs to be synchronised on OPT to get clear image?

A

speed of X-ray beam through teeth and speed of receptor through xray beam

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26
Q

what happens if the patient is too far forward in the OPT machine and why?

A

teeth narrower
because teeth further from centre of rotation and so xray beam passed more quickly through these teeth relative to speed of IR

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27
Q

what happens if the patient is too far back in the OPT machine and why?

A

teeth wider

because teeth closer to CofR and so xray beam passes more slowly through these teeth relative to speed of IR

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28
Q

ghost images

A

shadows created on opp side from the object which caused them
caused by tomographic movement of xray machine
always at higher level on opp side due to upward 8 degree beam angulation
metal objects, Rxs, earrings, normal anatomic features

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29
Q

uses of standard U occlusals

A

look for pathology in U anterior region of maxilla
confirm presence of UE teeth
root resorption (PA better)
aid localisation of UE teeth in combination with another view (parallax)

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30
Q

uses of PAs

A 
assess for RR
look for evidence of PA infection
assess if a tooth might be ankylosed
 - loss of PDL space
 - but 2D so could still be ankylosed
aid localisation of UE teeth in combination with another radiographic view (parallax)
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31
Q

uses of BWs

A

assess caries status
more info on tooth prognosis
alv bone levels

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32
Q

why is quality assurance and audit important?

A

ensure consistently adequate diagnostic info is obtained whilst radiation doses are ALARP

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33
Q

how is QA and audit carried out?

A

daily monitoring of correct equipment fct e.g. use step wedge as a test object (compare the image produced with a prev taken reference film)
clinical audit of film quality on visual inspection

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34
Q

why do some OPTs have a “smiley face” appearance?

A

pt positioned with Frankfort plane tipped down

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35
Q

lateral ceph

A

standardised lateral radiographs of the face and base of skull

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36
Q

why are lat cephs reproducible?

A

pt positioned in a cephalostat a set distance from the cone and the film

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37
Q

cephalometry

A

the analysis and interpretation of lat cephs

38
Q

what plane is parallel to the film in a lat ceph?

A

mid sagittal plane

39
Q

what collimation is used in a lat ceph?

A

triangular

40
Q

what techniques are used in lat ceph to ensure doses ALARP?

A 
aluminium ST filter
thyroid collar
triangular collimation
rare earth screen LANEX screen
fastest film possible (60-70kv)
41
Q

how do lat ceps allow for the magnification due to divergent xray beam?

A

ruler in front of face

42
Q

analysis methods of lat ceph

A

hand traced onto paper

digitised using computer - Eastman analysis

43
Q

what does the Eastman analysis involve?

A 
measures AP position of M+M relative to base of skull - SNA, SNB
position of mandible relative to maxilla
 - ANB (AP)
 - MMPA/FMPA (vertical)
angulation of teeth to M+M
 - UiMxP
 - LiMnP
vertical facial proportions
 - LAFH/TAFH ratio
44
Q

lat ceph - Frankfort plane

A

porion to orbitale

45
Q

lat ceph - SN line

A

sella to nasion

46
Q

lat ceph - maxillary plane

A

ANS through PNS

47
Q

lat ceph - pogonion

A

anterior point on mandibular symphysis

48
Q

lat ceph - menton

A

most inferior point on mandibular symphysis

49
Q

lat ceph - mandibular plane

A

menton to gonion

50
Q

lat ceph - gonion

A

most posterior inferior point on angle of mandible

51
Q

lat ceph - porion

A

superior of EAM

52
Q

lat ceph - what do you use to measure AP discrepancy?

A

ANB

53
Q

class 1 ANB angle (AP)

A

2-4 degrees

54
Q

mild class 2 ANB angle (AP)

A

4-6

55
Q

mod class 2 ANB angle (AP)

A

6-8

56
Q

severe class 2 ANB angle (AP)

A

> 8

57
Q

mild class 3 ANB angle (AP)

A

0-2

58
Q

mod class 3 ANB angle (AP)

A

-3-0

59
Q

severe class 3 ANB angle (AP)

A

less than -3

60
Q

what is used to measure vertical discrepancy on a lat ceph?

A

MMPA or FMPA

61
Q

average FMPA

A

27 degrees

62
Q

mildly increased FMPA

A

27-32

63
Q

mod increased FMPA

A

32-37

64
Q

severely increased FMPA

A

> 37

65
Q

mildly decreased FMPA

A

22-27

66
Q

mod decreased FMPA

A

17-22

67
Q

severely decreased FMPA

A

<17

68
Q

normal value for Ui/MxP

A

109 +/- 6

69
Q

normal value for Li/MnP

A

93 +/- 6

70
Q

normal value for Ui/Li

A

135 +/- 10

71
Q

uses of cephalograms

A 
gross inspection (anatomy/pathology)
assess dent-skeletal relationships
assess ST relationships to underlying HTs
prognosis and tx planning
monitoring facial growth
predict future growth?
assess changes due to tx and growth
72
Q

Facial plane

A

nasion to pogonion

73
Q

Ricketts E plane

A

tip of nose to tip of chin

74
Q

A

A

point of deepest concavity anteriorly on maxillary alveolus

75
Q

B

A

The point of the deepest concavity anteriorly on the mandibular symphysis

76
Q

S

A

The midpoint of the sella turcica (pituitary fossa)

77
Q

N

A

The most anterior point on the fronto-nasal suture

78
Q

Or

A

The most anterior, inferior point on the infraorbital rim

79
Q

Po

A

The upper midpoint point on the external auditory meatus

80
Q

ANS

A

The tip of the anterior nasal spine

81
Q

PNS

A

The tip of the posterior nasal spine

82
Q

normal SNA

A

81 +/- 3

83
Q

normal SNB

A

78 +/- 3

84
Q

normal ANB

A

3 +/- 2

85
Q

indications for a lat ceph

A

to aid diagnosis
tx planning
progress monitoring

86
Q

errors in lateral cephalometry

A

radiographic projection errors
errors within measuring system
errors in landmark identification

87
Q

lat ceph reference structures for superimposition

A

middle cranial fossa
anterior wall of sella
occ plane not as stable

88
Q

CBCT

A

a 3D radiograph
a scanning image produced by the machine moving around pts head and creating a cylindrical or spherical FOV
computer software produces images in axial, sagittal and coronal planes and can scroll through these images

89
Q

uses of CBCT in ortho

A

localisation of impacted teeth if we need more info on their proximity to adjacent teeth and the possibility of resorption
get a better view of structural anomalies e.g. gemination of teeth/fusion/supernumeraries
some orthognathic cases
some CP cases

90
Q

why isn’t CBCT used more often?

A

radiation dose likely considerably higher than when using plain films
pt set up time takes longer and for some machines the exposure time is longer than an OPT so pt needs to keep still for longer
reporting - need more training beyond BDS
cost

Ortho (21 decks)

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