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BDS3 - radiology > occlusal radiography > Flashcards

occlusal radiography Flashcards

1
Q

how are occlusal radiographs taken

A
  • image receptor in occlusal plane
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2
Q

what size is image receptor

A
  • 7x5cm

- can get smaller for smaller mouths and children

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3
Q

what is a oblique radiograph like

A
  • similar to a large periapical but more teeth
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4
Q

when are oblique occlusal taken

A
  • can’t open mouth
  • when periapicals are not possible
  • pathology too large to be seen on periapical = but nowadays would just use CBCT
  • less painful for those with trauma
  • localisation using parallax (along with panoramic, other occlusal, or periapical)
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5
Q

what do circular radiolucencies often have

A
  • often contain cysts
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6
Q

what is the ideal projection geometry

A
  • image receptor and object in contact and parallel
  • parallel beam of x-rays
  • x-ray beam perpendicular to object plane and image receptors
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7
Q

why do you never get the image size the same as the objext

A
  • due to divergent beam
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8
Q

what are problems with projection geometry

A
  • image receptor and object no in contact
  • beam of x-rays not parallel
  • x-ray beam central ray may or may not be perpendicular to object plane and image receptor
  • image size not identical to object size due to magnification = divergent beam
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9
Q

what are the solutions to projection geometry problems

A
  • bisecting angle technique
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10
Q

what is the bisecting angle technique

A
  • image receptor and object partly in contact but not parallel
  • image receptor and object close together at crowns, but apart at apices
  • still use long FSD for machines working at 60kV and over
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11
Q

how does the angle affect the image in bisecting angle technique

A
  • if x-ray beam at 90 degrees to long axis of tooth = elongated image
  • if x-ray beam at 90 degrees to plane of image receptor = short image (foreshortened)
  • neither of these are ideal
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12
Q

what is the correct vertical angle

A
  • x-ray beam at 90 degrees to line bisecting angle formed by long axis of tooth and plane of image receptor
  • image receptor positioned with 2-3mm beyond tooth edge
  • vertical angle judged by eye
  • adjust angle to adapt to incisor angulation = proclined then increase, retroclined then decrease
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13
Q

how does oblique occlusal require head position to be

A
  • need occlusal plane (of the jaw being examined) to be horizontal
  • want head in a standardised position = different for upper and lower
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14
Q

how is the head placed in correct position for oblique occlusal

A
  • use soft tissue points
  • maxilla
    = ala-tragus line horizontal (fleshy bit of side of nose, to the ear, lateral border of nose opening to auditory meatus)
  • mandible
    = corner of mouth-tragus line
    = slightly tip head back
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15
Q

what are storage phosphor plates

A
  • multi use sensors
  • protected by plastic cover
  • protected from tooth marks by cardboard or plastic
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16
Q

how are storage phosphor pates used

A
  • insert into plastic so writing can be seen through clear side =seal
  • black side of cover must face x-ray source
  • go between upper and lower and held in place by patient biting
  • slide in so dot goes in first
  • active surface is pale blue
  • open end is outside patients mouth
  • hold it against the teeth you are x-raying
17
Q

how do you ensure the sensor is kept in the correct position

A
  • patient to bite gently to hold protected sensor still
  • watch them to ensure no chewing action
  • plastic protectors can be used as an alternative to card
  • check tube head from 2 angles
18
Q

what are the centring points for periapical

A
  • maxilla = on ala-tragus line

- mandible = 1cm above lower border of mandible

19
Q

what the centring points for oblique occlusals

A
  • maxilla = 1cm above ala-tragus line

- mandible = through lower border of mandible

20
Q

what should the horizontal angle always be

A
  • 90 degrees to the teeth being examined
21
Q

what are guideline vertical angles for oblique occlusals

A
  • Upper anterior (standard) - 60º
  • Upper occlusal centred on canine - 55º
  • Upper occlusal centred on premolar - 50º
  • Upper occlusal centred on molar - 45º
  • Lower anterior occlusal - 40º to occlusal plane
  • Lower occlusal centred laterally - 35º to occlusal plane
  • drops by 5 as move back in arch, larger angle makes teeth shorter
22
Q

summary of oblique occlusal

A
  • bisecting angle technique used
  • standardised head position
  • mid-sagittal plane perpendicular to floor
  • occlusal plane correct for arch
  • image receptor in occlusal plane, active surface towards teeth
  • orientation of image receptors dependent on size of mouth and patient tolerance - long axis front to back probably most comfortable
23
Q

what is true/cross-sectional occlusal radiography

A
  • occlusal size image receptor of periapical size
  • plan view when beam is through long axis of a tooth
  • only do in lower
24
Q

what are the indications to do a mandibular true occlusal

A
  • detection of submandibular duct calculi
  • assessment of buck-lingual position of unerupted teeth
  • evaluation of pathological bucco-lingual expansion
  • horizontal displacement of fractures
  • CBCT may be used nowadays if available
25
Q

why do we not use mandibular true occlusal often

A
  • mainly just use CBCT
26
Q

how can submandibular duct calculi grow

A
  • concentric growth

- conforms to duct

27
Q

what are ‘kissing teeth’

A
  • teeth which are close together and need to be treated together
  • facing each other in radiograph
28
Q

how is mandibular true occlusal done

A
  • image receptor transverse in occlusal plane OR lengthwise over region of interst
  • head tipped as far back as comfortable
  • x-ray beam directed at 90 degrees to image receptor in midline OR through region of interest
  • only thing we can move is patient’s head
  • image receptor at different angles depending on the angle, and X-ray tube is then placed on chest facing upwards

BDS3 - radiology (19 decks)

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