ch 22 radiography exam III

  1. what cannot always be seen on intraoral films (3)
    • impacted thir molars
    • jaw fracutres
    • large lesions in the posterior mandible
  2. the panoramic radiograph allows the dental professional to view?
    large areas of the maxilla and manible on a single film
  3. film that shows a wide view of the upper and lower jaws
    panoramic film
  4. extraoral film is placed inside or outside the mouth?
  5. Purpose of Panos (5)
    • Evaluate impacted teeth
    • Evaluate eruption patterns, growth, and development
    • Evaluate trauma
    • Detect diseases, lesions, and conditions of the jaws
    • Examine the extent of large lesions
  6. Imagaes are not as defined or sharp on which films?
  7. panos should not be used to evaluate (3)
    • caries
    • periodantal disease
    • periapical lesions
  8. film rotates in which direction
    opposite the tubehead
  9. the term tomo means
  10. a radiographic technique that allows the imaging of one layer or section of the body while blurring images from structures in other planes
  11. in panoramic radiography, the image conforms to the shape of the?
    dental arches
  12. pivotal point, or axis, around which the cassette carrier and x-ray tubehead rotate is termed?
    rotation center
  13. Three basic rotation centers
    • Double-center rotation
    • triple-center rotation
    • moving-center rotation
  14. why does the center of rotation change as the film and tubehead rotate around the patient?
    allows the layer to conform to the elloptical shape of the dental arches.
  15. the location and number of rotational centers influence?
    the size and shape of the focal trough
  16. a theoretical concept used to determine where the dental arches must be postitioned to achieve the clearest image
    focal trough
  17. other name for focal trough
    image layer
  18. three-dimentional curved zone in which structures are clearly demonstrated on a panoramic radiograph
    focal trough
  19. structures located within the focal trough appear?
    resonably well defined
  20. structures located inside or outside the focal trough appear
    blurred or indistinct
  21. The closer the rotation center is to the teeth?
    the narrower the focal trough
  22. in most panoramic x-ray machines, the focal trough is
    narrow in the anterior region and wide in the posterior region
  23. the quality of the resulting panoramic radiograph depends on the
    postioning of the patient's teeth within the focal trough and how closely the patient's jaws conform to the focal trough designed for the average jaw
  24. equipment (4)
    • panoramic x-ray unit
    • screen film
    • intensifying screens
    • cassette
  25. panoramic units may differ in
    • the number of rotation centers
    • size and shape of the focal trough
    • type of film used
  26. main components of the panoramic unit(3)
    • x-ray tubehead
    • head positioner
    • exposure controls
  27. how is the tubehead in the panoramic x-ray machine?
    each has a filament used to produce electrons and a target used to produce x-rays
  28. how is the collimator in an intra-oral machine vs a panoramic x-ray machine
    • Intraoral:
    • lead plate with a small round or rectangular opening in the middle
    • collimator trestricts the size and shape of the x-ray beam

    • Extraoral:
    • lead plate with an opening in the shape of a narrow vertical slit
    • x-ray beam emerges from teh panoramic tubehead through the collimator as a narrow band
    • the beam passes through the patient and then exposes the film through another vertical slit in the cassette carrier
  29. is the verical angulation of the pano tubehead varied?
  30. the x-ray beam is directed slightly...
  31. the tubehead of the panoramic unit always rotes
    behind the patient's head as the film rotates in front of the patient
  32. the typical head postioner consists of
    • chin rest
    • notched bite-block
    • forehead rest
    • lateral head supports or guides
  33. which exposure factors are adjustable
    • milliamperage
    • kilovoltage
  34. which exposure factor is not adjustable
    exposure time
  35. What kind of film is used for panos?
    screen film
  36. where is screen film placed?
    between two intensifying screens in the cassette holder
  37. what happens when the cassette holder is exposed to x-rays?
    the screens convert the x-ray energy into light wich exposes the screen film
  38. size of film used for panos
    • 5x12
    • 6x12
  39. two types of intensifying screens
    • rare earth (emit green light)
    • calcium tungstate (emit blue light)
  40. which are faster adn require less x-ray exposure
    rare earth screens
  41. device that is used to hold teh extraoral film and intensifying screens
  42. cassette may be (4)
    • rigid
    • flexible
    • curved
    • straight
  43. to protect the film from exposure, all cassettes must be
    light tight
  44. What must be marked before exposure
    • R
    • L
    • patient's name
    • dentist name
    • date
  45. Step-by-step procedures
    • equipment prep
    • patient prep
    • patient positioning
  46. Equipment prep (3)
    • load panoramic cassette in the darkroom under safelight conditions. one extraoral film and two intensifying screens must be placed in teh cassette and teh cassette msut be securely closed
    • cover the bite-block with a disposable plastic coverslip. If not covered; sterilize
    • set exposure factores. adjust machine to accommodate height of patient. align all movable parts properly. cassette msut be loaded in teh cassette carrier of the panoramic unit
  47. patient prep
    • explain procedures
    • place the lead apron without thyroid collar adn secure it. double sided apron is recommended
    • rove all objects form the head and neck area that may interfere with film exposure
  48. patient postioning (7)
    • instruct patient to sit or stand as tall as possible
    • instruct patient to bite on teh plastic bite block.
    • position the midsaggittal plane perpendicular to the floor
    • positon the Frankfort plane (imaginary plane that passes thru the top of the ear canal and the bottom of the eye socket) parallel to the floor
    • instruct the patient to position the tongue on the roof of the mouth
    • instruct patient to remain still while the machine is rotated during exposure
    • expose the film and proceed with film processing
  49. Patient preparation errors (2)
    • ghost images
    • lead apron artifact
  50. radiopaque artifact seen on a panoramic film that is produced when a radiodense object is penetrated twice by the x-ray beam
    ghost image
  51. ghost images (9)
    • eyeglasses
    • earrings
    • necklaces
    • hairpins
    • removable and partial dentures
    • complete dentures
    • orthodontic retainers
    • hearing aids
    • napkin chains
  52. a ghost image resembles its real counterpart and is found where?
    how does it look?
    • on the opposite side and higher
    • appears indistinct and larger
  53. cone-shaped artifact
    lead apron artifact
  54. Postitioning of the lips and tongue
    • lips closed around the bite block
    • tongue raised up to the palate
  55. if lips are not closed?
    obscures the anterior teeth
  56. if tongue is not on palate?
    a dark radiolucent shadow results that obsures the apices of the maxillary teeth
  57. problems with postioning of Frankfort Plane upward (chin tipped too high) (4)
    • hard palate and floor of nasal cavity appear superimposed over the roots of the maxillary teeth
    • loss of detail in the maxillary incisor region
    • maxillary incisors appear blurred and magnified
    • reverse smile line (curved downward)
  58. To prevent postioning of frankfort plane upward
    frankfort plane is parallel with the floor
  59. positioning of frankfort plane downward (4)
    • mandibular incisors appear blurred
    • loss of detail in the anterior apical regions
    • mandibular condyles may not be visible
    • exaggerated smile line
  60. how to prevent frankfort plane downward
    make sure frankfort plane is parellel with the floor
  61. problem with postioning of teeth anterior to focal trough
    How to fix?
    • teeth appear blurred
    • anterior teeth appear skinny and out of focus

    position patient so that teeth are placed in an end-to-end position in the groove of the bite-block
  62. problem with postioning of the midsagittal plane

    • patient's head is not centered and ramus and posterior teeth appear unequally magnified on the panoramic radiograph
    • side farthest from the film appears magnified
    • side closest to the film appears smaller

    position the patient's head so that the midsagittal plaen is perpendicular to teh floor while the midline is centered on the bite-block
  63. problems with positioning of the spine

    patient is not standing or sitting with a staight spine then the cervical spine appears as a radiopacity in the center of the film

    instruct patient to sit as tall as possible with a straight back
  64. Advantages of panoramic radiography (4)
    • field size
    • simplicity
    • patient cooperation
    • minimal exposure
  65. disadvantages of panoramic radiography (4)
    • image quality
    • focal trough limitaions
    • distortion
    • equipment cost
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ch 22 radiography exam III