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Chapter 42
Extraoral and Digital
Radiography
Copyright 2003, Elsevier Science (USA).
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Produced in the United States of America
ISBN 0-7216-9770-4
Introduction
Extraoral radiographs (outside the mouth) are taken
when large areas of the skull or jaw must be examined
or when patients are unable to open their mouths for
film placement.
Extraoral radiographs do not show the details as well
as intraoral films.
Extraoral radiographs are very useful for evaluating
large areas of the skull and jaws but are not adequate
for detection of subtle changes such as the early
stages of dental caries or periodontal disease.
There are many type of extraoral radiographs. Some
types are used to view the entire skull, whereas other
types focus on the maxilla and mandible.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Panoramic Radiography
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Panoramic radiographs show the entire dentition and
related structures on a single film.
Some types of panoramic units operate with the
patient in a seated position, and other types require
the patient to be in a standing position.
Regardless of the type of machine, you must follow the
manufacturer’s instructions carefully.
Because the images on a panoramic film are not as
clear or as well defined as the images on intraoral
films, bite-wing films are used to supplement a
panoramic film to detect dental caries or periapical
lesions.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Basic Concepts
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In panoramic radiography the film and tubehead
rotate around the patient, and it produces a series
of individual images.
The term panorama means “an unobstructed
view of a region in any direction.” When the series
of images are combined onto a single film, an
overall view (panorama) of the maxilla and
mandible is created.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Fig 42-2 The film and x-ray tubehead move around the patient in opposite
directions in panoramic radiography.
Fig. 42-2
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Focal Trough
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An imaginary, three-dimensional curved area that
is horseshoe shaped.
This is a very important concept because many
technique errors are caused by improper
positioning of the patient’s jaws within the focal
trough.
When the jaws are positioned within this area, the
radiograph will be clear.
When the jaws are positioned outside of this area,
the images on the radiograph will appear blurred
or indistinct.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Fig. 42-3 An example of an image layer, or “focal trough.”
Fig. 42-3
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Components of the Panoramic Unit
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Panoramic x-ray tubehead
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Head positioner
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Exposure controls
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Fig. 42-4 The main components of a panoramic unit.
Fig. 42-4
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The Head Positioner
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Each panoramic unit has a head positioner used
to align the patient’s teeth as accurately as
possible.
Each head positioner consists of a chin rest,
notched bite-block, forehead rest, and lateral head
supports or guides.
Each panoramic unit is different, and the operator
must follow the manufacturer’s instructions on how
to position the patient in the focal trough.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Fig. 42-5 The head positioner is used to align the patient’s teeth in the focal
trough.
Fig. 42-5
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Common Errors
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Patient preparation errors
• Ghost images: A ghost image looks like the real
object except that it appears on the opposite side of
the film.
• Lead apron artifact: If the lead apron is placed
too high, or if a lead apron with a thyroid collar is
used, a cone-shaped radiopaque artifact results.
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Patient seating errors
• Chin too high
• Chin too low
Copyright 2003, Elsevier Science (USA). All rights reserved.
Fig. 42-13 Large hoop earrings (A) and ghost images (B). The ghost image
of the earring appears on the opposite side of the film.
Fig. 42-13
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Fig. 42-14 On a panoramic radiograph, a lead apron artifact appears as a
large cone-shaped radiopacity obscuring the mandible.
Fig. 42-14
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Fig. 42-16 The patient’s head is tipped too far upward.
Fig. 42-16
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Fig. 42-18 The patient’s head is incorrectly positioned; the chin is tipped
downward.
Fig. 42-18
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Positioning of the Teeth
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Posterior to focal trough
• If the patient’s anterior teeth are not positioned
in the groove on the bite-block and are either
too far back on the bite-block or posterior to the
focal trough, the anterior teeth appear “fat” and
out of focus on the radiograph.
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Anterior to focal trough
• If the patient’s anterior teeth are not positioned
in the groove on the bite-block and are either
too far forward or anterior to the focal trough,
the teeth will appear “skinny” and out of focus.
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Fig. 42-21 The patient is biting too far back on the bite-block.
Fig. 42-21
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Fig. 42-22 The anterior teeth appear widened and blurred on a panoramic
film when the patient is positioned too far back on the bite-block.
Fig. 42-22
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Fig. 42-23 The anterior teeth appear narrowed and blurred on a panoramic
film when the patient is positioned too far forward on the bite-block.
Fig. 42-23
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Fig. 42-24 If the patient is not standing erect, superimposition of the cervical
spine (arrows) may be seen on the center of the panoramic film.
Fig. 42-24
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Positioning of the Spine
 If the patient’s spine is not straight, the cervical
spine will appear as a radiopaque artifact in the
center of the film and obscure diagnostic
information.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Extraoral Radiography
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Extraoral radiographs provide images of larger areas
such as the skull and jaws.
In some instances, an extraoral film may be necessary
for handicapped patients who cannot open their
mouths for film placement, or because a patient has
swelling or severe pain and is unable to tolerate the
placement of intraoral films.
Extraoral films are also very useful for patients who are
uncooperative and may refuse to open their mouths.
Images seen on an extraoral film are not as clear or as
well defined as the images seen on an intraoral
radiograph.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Equipment
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Extraoral radiographs may be taken with a
standard intraoral x-ray machine.
To aid in patient positioning, special head
positioning and beam alignment devices can be
added to the standard x-ray unit.
In addition, panoramic x-ray units may also be
fitted with a special device known as a cephalostat.
The cephalostat includes a film holder and head
positioner that allow the operator to easily position
the patient.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Grid
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A device used to decrease film fog and increase
the contrast of the radiographic image.
It does this by reducing the amount of scatter
radiation that reaches an extraoral film during
exposure.
Scatter radiation causes film fog and reduces film
contrast.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Fig. 42-27 A grid decreases the amount of scatter radiation that reaches the
extraoral film.
Fig. 42-27
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Lateral Jaw Projection
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Used to view the posterior region of the mandible.
This type of projection is very useful for patients
with a limited jaw opening and in patients who
cannot or will not tolerate intraoral film placement.
A lateral jaw projection does not provide as much
diagnostic information as a panoramic radiograph.
The advantage is that the lateral jaw projection
can be taken with a standard x-ray unit.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Lateral Jaw Projection Techniques
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Body of mandible projection
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Ramus of mandible projection
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Fig. 42-28 A, The body of the mandible; proper patient and film positioning is shown
as viewed from the front and side of the patient. B, The body of the mandible.
Fig. 42-28
Copyright 2003, Elsevier Science (USA). All rights reserved.
Ramus of the Mandible
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This film is used to evaluate impacted third molars,
large lesions, and fractures that extend into the
ramus of the mandible.
The ramus from the angle of the mandible to the
condyle is visible in this projection.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Fig. 42-29 A, Ramus of the mandible; proper patient and film positioning is shown as
viewed from the front and side of the patient. B, An example of a lateral jaw
radiograph; the ramus of the mandible.
Fig. 42-29
Copyright 2003, Elsevier Science (USA). All rights reserved.
Skull Radiography
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Lateral cephalometric projection
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Posteroanterior projection
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Water’s projection
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Submentovertex projection
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Reverse Towne’s projection
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Fig. 42-30 B, An example of a lateral cephalometric radiograph.
Fig. 42-30 B
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Fig. 42-31 B, An example of a posteroanterior skull radiograph.
Fig. 42-31 B
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Fig. 42-33 B, An example of a submentovertex radiograph.
Fig. 42-33 B
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Fig. 42-34 B, An example of a reverse Towne’s radiograph.
Fig. 42-34 B
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Temporomandibular Joint Radiography
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Radiographs of the temporomandibular joint (TMJ)
can be very difficult to examine because of the
multiple adjacent bony structures.
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The articular disc and other soft tissues of the TMJ
cannot be examined by radiographs.
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Special imaging techniques (e.g., arthrography,
magnetic resonance imaging) must be used.
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Radiographic projections of the TMJ can be used to
show the bone and the relationship of the jaw
joint.
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Fig. 42-36 Patient positioned for a transcranial radiograph of the
temporomandibular joint.
Fig. 42-36
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Digital Radiography
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Advances in digital technology have led to a unique
“filmless” imaging system known as digital
radiography.
Introduced in 1987, digital radiography has
influenced both how dental disease is recognized
and how it is diagnosed.
In the last 2 years, the use of digital radiography is
rapidly increasing in both general and specialty
dental practices.
Numerous companies are producing digital
radiography systems.
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The Basics of Digital Radiography
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Digital radiography uses a sensor to capture a
radiographic image, breaking it into electronic
pieces and storing the image in a computer.
The patient is exposed to less x-radiation than with
conventional radiography.
The image is displayed on a computer screen
rather than on film.
The term image (not radiograph) is used to
describe the pictures that are produced.
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The Basics of Digital Radiography- cont’d
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The x-ray beam strikes the sensor.
An electronic charge is produced on the surface of
the sensor, and this electronic signal is digitized.
The digital sensor in turn transmits this information
to the computer.
Software in the computer is used to store the
image electronically.
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Fig. 42-38 The size of the electronic sensor is compared with sizes 0, 1, and 2
of traditional intraoral film.
Fig. 42-38
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Fig. 42-39 All types of radiographs may be produced in digital format.
Fig. 42-39
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Radiation Exposure
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Digital radiography requires much less x-radiation
than conventional radiography because the sensor
is more sensitive to x-rays than to conventional
film.
Exposure times for digital radiography are 50% to
80% less than that required for radiography using
conventional film.
With less radiation, the absorbed dose to the
patient is significantly lower.
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Equipment
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For digital radiography, special equipment is
required. The essential components include:
• Dental x-ray unit
• Intraoral sensor
• Computer
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Types of Digital Imaging
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Direct digital imaging
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Indirect digital imaging
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Storage phosphor imaging
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The difference between each method is in how the
image is obtained and in what size the receptor
plates are available (e.g., panoramic).
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Fig. 42-40 Computer with modified image.
Fig. 42-40
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Fig. 42-15: If the tongue is not placed on the roof of the mouth, a radiolucent shadow
will be superimposed over the apices of the maxillary teeth.
Fig. 42-15
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