Imaging techniques Flashcards
how many meters should the controlled area be?
1.5-2m
what is the controlled area?
the required distance between the operator and the X-ray beam
Why do periapical radiographs?
- assess periodontal problems
- endodontics
- trauma/fractures
- tooth morphology (pre-extraction)
- evaluation of implants
- detect apical inflammation/infection (incl cysts)
- presence/position of un-erupted teeth
what two techniques can you use for a periapical radiograph?
- paralleling technique
2. bisected angle technique
what is the paralleling technique?
the tooth is parallel to the film and the X-ray beam at right angles to the film/tooth using a holder.
what are the 3 benefits of the paralleling technique ?
- reproducible image given
- accurate geometry
- minimises magnification
the negative point of using the paralleling technique is..
the holder may not be tolerated by the patient as relatively bulky.
when would you carry out the bisected angle technique?
if your patient isn’t co-operating and you want to reduce the number of repeat images = reducing the exposure.
benefit of the bisected angle technique?
more comfortable for the patient
3 disadvantages of bisected angle technique?
- operator dependant
- not reproducible
- easily distorted (foreshortening and elongating)
what are the 3 components of the holder?
- bite block
- indicator arm/rod
- aiming ring
for paralleling technique, the horizontal positioning is..
horizontal plane of the film must be parallel to the occulsal plane of the teeth being examined.
for paralleling technique, the vertical positioning is..
the vertical plane of the film must be parallel to the long axis of the tooth
if the horizontal plane is incorrect then..
crossover
if the vertical plane is incorrect then..
elongation or foreshortening of the teeth
if the X-ray beam is not at right angles to the teeth/film then you will get…
elongation or foreshortening or crossover of the teeth
name the two things affecting image size.
- the X-ray source (focal spot) to film distance
2. the tooth to film distance
if the tooth to film distance increases then…
the magnification will increase.
if the X-ray source (focal spot) to film distance increases then…
the magnification will decrease
the 2 things you need to reduce magnification are…
- a long X-ray source (focal spot) to film distance
2. a short tooth to film distance
Why would you use a bitewing radiograph? 4 points
- detect caries
- monitor caries progression
- assess periodontal status
- asses existing restorations
give 4 points about vertical bitewings
- long axis of the tooth and film vertical to one another
- pre-molars and molars
- usually need two on each side
- will show more of the roots (incl bone levels)
give 4 points about horizontal bitewings
- long axis of the film and tooth horizontal
- shows distal of the 4 to medial of the 8
- usually only need 1 each side
- will demonstrate crowns and 1/3 of root
which technique do you need for bitewings?
the paralleling technique (must always se a holder)
give the two types of holder you can use for bitewings.
- rigid plastic holder
2. paper tab
when is it difficult to avoid horizontal overlap?
- crowding
2. tilting
a bitewing must show … & … for it to be diagnostically acceptable
- the ADJ
2. at least half of enamel
if the vertical plane in a bitewing is wrong then..
- separation of cusps (they should be almost fully superimposed upon each other)
by what % does a rectangular collimator reduce the dose?
50%
for adults which size of psp do you use for bitewings?
size 2
for children over 10 which psp size for bitewings?
size 2
for children under 10 which size of psp used for bitewing?
size 1 or 0
what is the size of an occulsal film?
5.7 - 7.6cm
why would you take an occlusal radiograph? 5 things
- unerupted teeth (bucco-palatal position of 3’s for ortho)
- supernumerancy teeth
- cysts and tumour
- assessment of canine fractures and surrounds alv bone
- periodical assessment of upper anteriors
what technique is used for an occlusal radiograph?
modified bisected angle technique
the process of taking an occlusal radiograph, 4 points
- film placed in mouth
- head positioned horizontal to occlusal plane
- film inserted as far back as patient can tolerate
- X-ray beam angled (dependant upon area)
name the two types of maxillary occlusal projections.
- anterior (standard) oblique occlusal
2. lateral oblique occlusal
what angulation is use for an anterior oblique occlusal maxilla?
65 degrees to occlusal plane (tube at nose)
what angulation is used for a literal oblique occlusal maxilla?
60-70 degrees to the occlusal plane (tube at cheek)
name the 3 types of mandibular occlusal projections
- true occlusal mandible
- anterior (standard) oblique occlusal
- lateral oblique occlusal
the angulation for a true mandible is?
90 degrees to the occlusal plane (pt head tilted back)
the angulation for an anterior oblique occlusal mandible is?
45 degrees to the occlusal plane (pt sitting straight)
the angulation for a lateral oblique occlusal mandible is?
45 degrees to the occlusal plane
