Radiology Flashcards
oblique occlusal
similar to a large periapical
true occlusal
more of a plain view of the floor of the mouth
film packet parallel with the occlusal plane
indications for oblique occlusal radiographs (4)
- if pathology is too large to be seen on a periapical
- if there has been trauma causing fractures to the teeth or alveolus
- periapical assessment when periapicals are not possible
- localisation using parallax
head position for oblique occlusal
mandible - corner of mouth to tragus line should be horizontal & beam centring point should be through lower border of mandible
maxilla - ala-tragus line should be horizontal & beam centring point should be 1cm above ala-tragus line
indications for true occlusal (4)
- detection of submandibular duct calculi
- assessment of bucco-lingual position of unerupted teeth
- evaluation of pathological bucco-lingual expansion
- horizontal displacement of fractures
true occlusal head position
head tipped back as far as possible and x ray beam directed at 90 degree to film in the midline or point of interest
rectangular collimation
lead placed around the circular cone to produce a rectangular image to cut down radiation to make it ALARP for practitioner’s safety
paralleling technique
for periapicals & bitewings; image receptor & object are parallel but not in contact as x ray beams are never truly parallel so long spacer cone is used to reduce divergence of beam making it more parallel - at least 20cm but 30cm in GDH
size 0
used for vertical anteriors
size 2
used for horizontal posteriors
bitewing film sizes for kids and adults
adults = size 2
kids = size 0
bisecting angle technique
for occlusals; image receptor & object partially in contact but not parallel. distance from receptor & object = different at different parts of tooth so x ray beam must be at an angle between perpendicular to the tooth and perpendicular to the film packet to produce an image on the receptor of the correct size
angles used in bisecting angle technique
maxilla = molar 60, premolar 55, canine 50, anterior 45
mandible = molar premolar canine 40, anterior 35
radiopaque v radiolucent
Radiolucent – Refers to structures that are less dense and permit the x-ray beam to pass through them. Radiolucent structures appear dark or black in the radiographic image e.g. periodontal ligament
Radiopaque - Refers to structures that are dense and resist the passage of x-rays. Radiopaque structures appear light or white in a radiographic image e.g. lamina dura
cervical burnout
causes radiolucency at cervical margin mimicking caries
caused by change in volume of structure the x ray beam is going through as at cervical portion of root there is only dentine
circular lesion
expanding at same speed in all directions - includes oval shapes
unilocular lesion
just a single cavity in the bone
multilocular lesion
has a bumpy/scalloped edge - worrying as it is growing irregularly in different directions
irregular lesion
very worrying as it may be aggressive
corticated margins
thickened cortical bone surrounding the lesion (will appear as a white line) - slow growing
uncorticated margins
fast growing so no time to placed thickened layer of bone so is non corticated
when discussing lesions what do you say
site / size / shape / margins / provisional or differential diagnosis
e.g. approx 1cm, well defined cortical margins, related to apices of 25 and maybe 26, provisional diagnosis of cystic lesion or maybe remnant pathology from previous cyst
limitations of panoramic radiography (4)
- width of layers so what we are looking for may be omitted e.g. anteriors
- long exposure time ptx struggles to stay still etc
- positioning difficulties with ptx of atypical occlusions i.e. class II & III, elderly, obese
- if too close to beam the image will be magnified horizontally and further away shorted vertically
true lateral cephalogram
film and mid sagittal plane will be parallel and x ray beam will be perpendicular to both
lateral oblique
film and mid sagittal plane will not be parallel and the x ray beam is not perpendicular
what collimation is used on lateral cephalograms
triangular collimation
positioning for lateral cephalogram
ptx position with frankfurt plane horizontal then MSP should be vertical and parallel to cassette, teeth should be in centric occlusion, ear rods in external acoustic meatus and nasion support may be necessary, thyroid collar should be placed on ptx and x ray beam will travel centred through ear rods from right to left
positioning for lateral oblique
cassette held by ptx next to side of head and region of interest, head then rotated so region of interest is parallel to cassette, chin raised and tilted to cassette
for mandible beam should be placed below aiming at area of interest and to get upper and lower teeth bimolar technique should be used
bimolar technique
an oblique lateral view only with the upper and lower teeth on the same film. right & left sides may also be incorporated onto same film too using lead shielding
when bitewings not practical these are indicated
positioned same as for oblique lateral
Frankfort plane
connects inferior infraorbital rim with porion (superior external auditory meatus)
should be parallel in lateral cephs and panoramics
orbitomeatal line
links central part of the external auditory meatus with outer canthus of eye - differs from frankfort plane by 10 degrees
interpupillary line
joins the 2 pupils and when ptx is seated this should be parallel to the floor
mid sagittal plane
passes through centre of the head and face - in seated / standing position it should be parallel to the floor
PA mandible indications
posterior anterior of mandible
1. fracture of angle/posterior body/ramus - taken with OPT & used to see medial / lateral displacement
2. cysts / tumours of angle, posterior body, ramus - for medial / lateral expansion or destruction
3. facial deformity - often taken in a cephalostat
positioning of PA mandible
‘nose forehead’ position
nose & forehead often touching image receptor. orbitomeatal line will be perpendicular to image receptor, mid sagittal plane perpendicular to floor & image receptor, x ray beam perpendicular to image receptor and will be angled between angles of mandible
to view entirety of maxillary sinus
CBCT
when do you need radiographic localisation
- unerupted tooth position
- location of root canals
- relationship to pathological lesions
- trauma
- pocket depths
- soft tissue swellings
localisation at right angles
take 2 views at right angles to work out position e.g.
- periapical & mandibular true occlusal
- panoramic & lower true occlusal
- paralleling periapical & lower true occlusal
- lateral / PA cephs & CBCT
localisation not at right angles
when there is a stable reference point but horizontal / vertical tube shift will move rest of image e.g. parallax
parallax
apparent change in position of object caused by a real change in position of observer
the further back the object the more it will move with the observer
my PAL goes with me i.e. if palatal it moves with & buccal it moves away
indications for CBCT
impact planning, impacted teeth, pathology, orthognathic surgery, hypodontia, cleft palate & bone defects, dental abnormalities, endo problems & autotransplantation
guidelines on CBCT
SEDENTEXCT
EADMFR - use only when question cannot be answered with lower dose method, use smallest volume compatible with clinical situation & choose resolution compatible
quality of radiograph
- excellent - no errors in ptx prep, exposure positioning or film handling
- diagnostically acceptable - some of the above errors do not distract from diagnostic utility
- unacceptable - errors make film diagnostically unacceptable so needs to be retaken
4 official legal personnel names in radiography
employer
referrer
practitioner
operator
in practice dentist may be all of these
employer
may be the hospital board / principal GDP - responsibilities include setting up standard operating and quality assurance procedures
referrer
individual requesting the radiograph & required to give following info to practitioner:
- info to enable IRMER practitioner to justify examination
- unique ID of ptx
- clinical info to justify exposure
- info on pregnancy
- unique identifying signature
practitioner
IRMER practitioner so qualified & follow these standards, responsible for confirming justification & authorising & ensure dose is ALARP
operator
entitled to carry out practical aspects of radiographic exposure
can take radiograph once practitioner has justified exposure & will evaluate images
clinical evaluation report
must be undertaken as a legal requirement after each radiograph taken by dentist
3 characteristics of a ghost image
- Always on opposite side of radiograph
- Always magnified
- Always higher to compensate for curve of Monson
to reduce scatter of x rays
- increasing focal to skin distance
- collimation which lowers area irradiated
- lead foil included within film packet to prevent back scatter of photons
optimisation to reduce dose of radiograph
- use e speed film or faster where possible
- use kV rang of 60-70kV
- focus to skin distance of 200mm or greater
- rectangular collimation should be adopted for bitewing and PA radiographs
- use film holders for bitewings & PA
