ortho radiology Flashcards
IRR1999
safety of workers and public
IRMER2000
safety of patients
what are X-rays?
beam of high energy photons
mutation
permanent alteration of a portion of a chromosome
what can mutations result in?
uncontrolled cell replication and tumour
deterministic effects
direct damage to tissues
skin erythema, ulceration, mucositis, hair loss
stochastic effects
chance/random
pt may develop cancer from any single dose
what pts are at greatest risk from radiation?
children
effective dose
different tissues have different radiosensitivity
dose limitation
ALARP
components of dose limitation
equipment
staff training
justification
legislation for radiation equipment
NRPB guidelines 2001 - dept of health
how can you ensure equipment contributes to dose limitation?
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
staff training as a contribution to dose limitation
avoid repeat exposures
check pt identity
pt positioning
remove jewellery, glasses, ortho appliances
justification
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
Qs before requesting radiograph
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?
indications for OPT
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
faults in OPTs
limitations in width of focal trough - esp at front of mouth
faults in pt positioning
movement of pt during exposure
what direction does the X-ray source move in OPT?
L to R
what direction does the receptor move in OPT?
R to L
why is the focal plane portrayed clearly in an OPT?
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
why are anterior teeth narrower in an OPT?
they are closer to the rotation centre
why are posterior teeth wider in an OPT?
they are further from the rotation centre
explain the relevance of focal trough to malocclusion
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
what needs to be synchronised on OPT to get clear image?
speed of X-ray beam through teeth and speed of receptor through xray beam
what happens if the patient is too far forward in the OPT machine and why?
teeth narrower
because teeth further from centre of rotation and so xray beam passed more quickly through these teeth relative to speed of IR
what happens if the patient is too far back in the OPT machine and why?
teeth wider
because teeth closer to CofR and so xray beam passes more slowly through these teeth relative to speed of IR
ghost images
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
uses of standard U occlusals
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)
uses of PAs
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)
uses of BWs
assess caries status
more info on tooth prognosis
alv bone levels
why is quality assurance and audit important?
ensure consistently adequate diagnostic info is obtained whilst radiation doses are ALARP
how is QA and audit carried out?
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
why do some OPTs have a “smiley face” appearance?
pt positioned with Frankfort plane tipped down
lateral ceph
standardised lateral radiographs of the face and base of skull
why are lat cephs reproducible?
pt positioned in a cephalostat a set distance from the cone and the film
cephalometry
the analysis and interpretation of lat cephs
what plane is parallel to the film in a lat ceph?
mid sagittal plane
what collimation is used in a lat ceph?
triangular
what techniques are used in lat ceph to ensure doses ALARP?
aluminium ST filter thyroid collar triangular collimation rare earth screen LANEX screen fastest film possible (60-70kv)
how do lat ceps allow for the magnification due to divergent xray beam?
ruler in front of face
analysis methods of lat ceph
hand traced onto paper
digitised using computer - Eastman analysis
what does the Eastman analysis involve?
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
lat ceph - Frankfort plane
porion to orbitale
lat ceph - SN line
sella to nasion
lat ceph - maxillary plane
ANS through PNS
lat ceph - pogonion
anterior point on mandibular symphysis
lat ceph - menton
most inferior point on mandibular symphysis
lat ceph - mandibular plane
menton to gonion
lat ceph - gonion
most posterior inferior point on angle of mandible
lat ceph - porion
superior of EAM
lat ceph - what do you use to measure AP discrepancy?
ANB
class 1 ANB angle (AP)
2-4 degrees
mild class 2 ANB angle (AP)
4-6
mod class 2 ANB angle (AP)
6-8
severe class 2 ANB angle (AP)
> 8
mild class 3 ANB angle (AP)
0-2
mod class 3 ANB angle (AP)
-3-0
severe class 3 ANB angle (AP)
less than -3
what is used to measure vertical discrepancy on a lat ceph?
MMPA or FMPA
average FMPA
27 degrees
mildly increased FMPA
27-32
mod increased FMPA
32-37
severely increased FMPA
> 37
mildly decreased FMPA
22-27
mod decreased FMPA
17-22
severely decreased FMPA
<17
normal value for Ui/MxP
109 +/- 6
normal value for Li/MnP
93 +/- 6
normal value for Ui/Li
135 +/- 10
uses of cephalograms
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
Facial plane
nasion to pogonion
Ricketts E plane
tip of nose to tip of chin
A
point of deepest concavity anteriorly on maxillary alveolus
B
The point of the deepest concavity anteriorly on the mandibular symphysis
S
The midpoint of the sella turcica (pituitary fossa)
N
The most anterior point on the fronto-nasal suture
Or
The most anterior, inferior point on the infraorbital rim
Po
The upper midpoint point on the external auditory meatus
ANS
The tip of the anterior nasal spine
PNS
The tip of the posterior nasal spine
normal SNA
81 +/- 3
normal SNB
78 +/- 3
normal ANB
3 +/- 2
indications for a lat ceph
to aid diagnosis
tx planning
progress monitoring
errors in lateral cephalometry
radiographic projection errors
errors within measuring system
errors in landmark identification
lat ceph reference structures for superimposition
middle cranial fossa
anterior wall of sella
occ plane not as stable
CBCT
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
uses of CBCT in ortho
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
why isn’t CBCT used more often?
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
