ch 22 radiography exam III
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what cannot always be seen on intraoral films (3)
- impacted thir molars
- jaw fracutres
- large lesions in the posterior mandible
the panoramic radiograph allows the dental professional to view?
large areas of the maxilla and manible on a single film
film that shows a wide view of the upper and lower jaws
extraoral film is placed inside or outside the mouth?
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
Imagaes are not as defined or sharp on which films?
panos should not be used to evaluate (3)
- periodantal disease
- periapical lesions
film rotates in which direction
opposite the tubehead
the term tomo means
a radiographic technique that allows the imaging of one layer or section of the body while blurring images from structures in other planes
in panoramic radiography, the image conforms to the shape of the?
pivotal point, or axis, around which the cassette carrier and x-ray tubehead rotate is termed?
Three basic rotation centers
- Double-center rotation
- triple-center rotation
- moving-center rotation
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.
the location and number of rotational centers influence?
the size and shape of the focal trough
a theoretical concept used to determine where the dental arches must be postitioned to achieve the clearest image
other name for focal trough
three-dimentional curved zone in which structures are clearly demonstrated on a panoramic radiograph
structures located within the focal trough appear?
resonably well defined
structures located inside or outside the focal trough appear
blurred or indistinct
The closer the rotation center is to the teeth?
the narrower the focal trough
in most panoramic x-ray machines, the focal trough is
narrow in the anterior region and wide in the posterior region
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
- panoramic x-ray unit
- screen film
- intensifying screens
panoramic units may differ in
- the number of rotation centers
- size and shape of the focal trough
- type of film used
main components of the panoramic unit(3)
- x-ray tubehead
- head positioner
- exposure controls
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
how is the collimator in an intra-oral machine vs a panoramic x-ray machine
- lead plate with a small round or rectangular opening in the middle
- collimator trestricts the size and shape of the x-ray beam
- 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
is the verical angulation of the pano tubehead varied?
the x-ray beam is directed slightly...
the tubehead of the panoramic unit always rotes
behind the patient's head as the film rotates in front of the patient
the typical head postioner consists of
- chin rest
- notched bite-block
- forehead rest
- lateral head supports or guides
which exposure factors are adjustable
which exposure factor is not adjustable
What kind of film is used for panos?
where is screen film placed?
between two intensifying screens in the cassette holder
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
size of film used for panos
two types of intensifying screens
- rare earth (emit green light)
- calcium tungstate (emit blue light)
which are faster adn require less x-ray exposure
rare earth screens
device that is used to hold teh extraoral film and intensifying screens
cassette may be (4)
to protect the film from exposure, all cassettes must be
What must be marked before exposure
- patient's name
- dentist name
- equipment prep
- patient prep
- patient positioning
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
- 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
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
Patient preparation errors (2)
- ghost images
- lead apron artifact
radiopaque artifact seen on a panoramic film that is produced when a radiodense object is penetrated twice by the x-ray beam
ghost images (9)
- removable and partial dentures
- complete dentures
- orthodontic retainers
- hearing aids
- napkin chains
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
lead apron artifact
Postitioning of the lips and tongue
- lips closed around the bite block
- tongue raised up to the palate
if lips are not closed?
obscures the anterior teeth
if tongue is not on palate?
a dark radiolucent shadow results that obsures the apices of the maxillary teeth
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)
To prevent postioning of frankfort plane upward
frankfort plane is parallel with the floor
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
how to prevent frankfort plane downward
make sure frankfort plane is parellel with the floor
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
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
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
Advantages of panoramic radiography (4)
- field size
- patient cooperation
- minimal exposure
disadvantages of panoramic radiography (4)
- image quality
- focal trough limitaions
- equipment cost
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