Extra Oral Imaging Flashcards
Where is the receptor placed for extra oral radiology? What is it used for? When?
Receptor placed outside of the mouth.
Used to view larger surface area, such as the skull or jaw.
They are generally used in conjunction with an FMS
Why are extra oral radiographs used in conjunction with an FMS?
Exposures do not show clarity of teeth and bone levels for inter-proximal decay and fine diagnostic problems. Not as defined or as sharp as an intra oral image
When are extra oral exposures used that are not supplemental to an FMS?
When swelling or injury mix receptor placement impossible
When a child cannot tolerate receptors intra-orally
What specific things are extra oral exposures used for?
- To evaluate large areas of the school and jaw
- growth and development
- impacted teeth
- to detect diseases, lesions, conditions of the jaw
- to examine the extent of large lesions
- to evaluate trauma
- to evaluate the TMJ
Which dental professionals are extra oral radiographs most valuable to?
Oral surgeons, orthodontists and prosthodontist
What are two of the special attachments called for a panoramic unit that are used to stabilize the patient’s head parallel to the receptor at right angles to the direction of the beam of radiation?
Cephalostat
Craniostat
What are the two types of intensifying screens?
- Calcium tungstate screen
- Rare earth screen
What color light does the calcium tungstate screen emit?
Blue light
What color light does the rare earth intensifying screen emit?
Greenlight
Provides less radiation to the patient, is more efficient
Most typical size of an extra oral receptor
8x10
Can use an occlusal size 4 but requires more radiation and does not cover a large area
What holds the intensifying screen and the film tight together?
Cassettes
Which side of the cassette his face toward the tube?
Plastic side toward the tube
Metal side reduces scatter radiation
What is a grid used for?
Reduces scatter which reduces fog
Has led strips so radiation scatters after it hits the skin, lead absorbs it
Receptor placement for the lateral jaw technique: body of the mandible
Receptor flat against cheek, centered over body of mandible. Also parallel with body of mandible, patient holds in position with thumb under bottom edge
Head position for the lateral jaw technique: body of the mandible
Head is tipped 15° toward the side being imaged. The chin is extended and elevated slightly
Beam alignment for the lateral jaw technique: body of the mandible
Central ray directed to a point just below the inferior border of the mandible on the side opposite the receptor. Beam is directed upward and centered on the body of the mandible. Beam must be directed perpendicular to the receptor
Receptor placement for the lateral jaw technique: ramus of the mandible
Receptor flat against patients cheek, centered over the ramus. Receptors also positioned parallel with the ramus. Patient must hold receptor in position with some under edge and palm placed against outer surface surface
Head position for the lateral jaw technique: ramus of the mandible
Head tipped approximately 15° toward side being imaged. Chin is extended and elevated slightly
Beam alignment for the lateral jaw technique: ramus of the mandible
Central ray directed to a point posterior to the third molar region on the side opposite the receptor. Beam is directed upward and centered on the ramus of the mandible. Beam must be directed perpendicular to the receptor
What does the posterioanterior skull view evaluate?
Facial growth and development, trauma, developmental abnormalities. Can also see frontal and ethmoid sinuses, Orbits and nasal cavity
How are the receptor, head and central ray positioned for a Posterioanterior skull view?
Receptor placed perpendicular to the floor, and vertically
Patient face is receptor. For head and nose touch receptor, mid sagittal plane perpendicular to the floor
Central ray aligned perpendicular to the receptor
What does the lateral cephalemetric skull view evaluate? What can we see?
Facial growth and development, trauma, developmental abnormalities
We see bones of the face and skull, shows soft tissue profile
What does the waters technique evaluate?
Maxillary sinuses. Can also see frontal and ethmoid sinuses, Orbits and nasal cavity
What does the submentovertex projection evaluate
Position of condyles, base of skull, zygomatic arch. Also can see sphenoid/ethmoid sinus and lateral wall of maxillary sinus
What does a reverse towne projection evaluate?
Fx of condyle neck and ramus
What does the trans cranial image of the TMJ evaluate?
Superior surface of condyle/articular eminence. Can also compare bilateral joint spaces
What does TMJ tomography evaluate?
The TMJ. Shows structures while blurring other structures. We move x-ray and receptor in opposite directions around a fixed rotation
What is the image in TMJ tomography called?
Tomogram.
What are cephalometric radiographs used for?
Reliable for lateral growth of the skull and face. Skull and soft tissue measurement. Skull radiographs are used for making skull measurements, must be viewed for pathology prior to tracing
What are the two most common radiographic views?
Lateral (most common)
Frontal colon indicated when asymmetry is suspected. Frontal Posterionterior ( used for further study of cranial growth patterns)
What do cephalometric radiographs help determine?
Help determine because of malocclusion: can be skeletal, dental, or skeletodental
What is anthropometry
The science that deals with measurements of the size, weight and proportions of the human body
Disadvantages of panoramic exposures
Cannot detect height of alveolar bone and inter-proximal decay
Varying degrees of magnification, distortion and definition. As well as overlapping because it is exposed outside of the patient’s mouth
Advantages of panoramic exposures
To detect pathology that cannot be seen on intra oral radiographs
Radiation dose is relatively low

What are indications for using panoramic exposures?
Orthodontics: exhibit spacing and crowding of teeth, growth of both jaws and development of teeth
Surgery: impacted third molar, fractures, outline of pathologic lesions
Periodontics: exhibit condition of bone supporting the teeth
Miscellaneous: absence of teeth, impacted or unerupted Teeth and foreign bodies
What is the image size of a panoramic exposure?
5 to 6 inches wide and 12 inches long
What is the principal that the panoramic machine operates on?
Principle of curved surface laminography (tomography)
What is tomography?
Recording of selected layers of body tissue on a radiograph
What is seen on a panoramic image
Entire Dentition, surrounding alveolar bone, sinuses and TMJ
What is the exposure time for a panoramic image? How does it compare to an FMS
Three minutes compared to 15 minutes for an FMS. Actual exposure time is 10 to 30 seconds
What is the definition of fundamental of rotational panoramic radiography?
Technique for making radiographic projections by utilizing a narrow beam of x-rays to image a curved layer. X-ray beam is directed toward the moving cassette to record a selected plane of dental anatomy
What is the rotational center?
The axis on which the tube head and cassette rotate, is the functional focus of the projection
What does it mean if an x-ray beam is collimated?
 narrow opening in the tube head means less tissue is irradiated
What is the focal trough
Theoretical concept, zone of sharpness.
A plane extends through the trough with objects in that plane are recorded with diagnostic sharpness. Objects are located at various distances from the plane which become less sharp as they get farther from the plane
Outside FT= blurry
Inside FT= clear
What is the main factor that determines the width of the focal trough?
Distance from the function center of rotation to the object (structure to be radiographed)
What is a real image?
When a structure is between the rotation center and receptor
What is a double image?
Structure behind the rotation center, penetrated twice by the beam
What is a Ghost image
Outside of the focal plane, close to x-ray source, blurred/magnified, On opposite side of the image and higher up
What is the Frankfort plane?
Horizontal plane between porion with orbitale
What is the porion?
Mid portion of the upper edge of the external auditory meatus
What is the orbitale?
Lowest point on the contour of the bony orbit
Where most of the Frankfurt plane be?
Parallel to the lines on the head stabilizer
Where should the sagittal plane be?
Perpendicular to the floor; position at midline or mid sagittal plane
Where should the teeth be positioned?
In the focal trough
Where should the tongue be during a panoramic exposure
On the roof of the patient’s mouth. Then ask them to swallow. Closes palatoglossal air space
Common errors in panoramic imaging
- Artifacts
- ghost image
- lead apron
Positioning errors in panoramic imaging
- Lips not closed on bite block cause a dark shadow that it scares front teeth
- tongue not in contact with pallet causes a dark shadow that it scares the apices of the maxillary teeth
- Frankfurt plane up or down
- teeth Anterior or Posterior to focal trough
- mid sagittal plane not perpendicular to the floor
- Slumped spine
Why do we need to use descriptive term analogy when documenting interpretations?
We need to communicate using a common language: patient may be referred to a specialist. Document lesions in patient record
What will show up as radiolucent on a radiograph?
Air spaces, soft tissue, pulp, periodontal ligament, carries and loss of bone
Ex. Soft tissue cyst, abscess, granuloma, tumor, neoplasms, carcinoma, sarcomas, lymphoma
What does it mean when a lesion has a unilocular corticated border?
Is a space with a well defined radiopaque border indicative of a benign, slow growing process
What does it mean when a lesion has a unilocular non-corticated border?
Is a space with fuzzy, non-defined water. Benign or malignant
What does it mean when a lesion is multilocular?
Resembles soap bubbles, usually well-defined borders. Large and expansive, displaces lingual and buccal plates of bone. Benign with aggressive growth
What will show up as radiopaque on a radiograph?
Dense tissue or materials.
Ex. Hard tissue osteitis, sclerotic bone, odontoma, hard tissue tumors, fibroma, sarcoma‘s, carcinoma, calcified glands and nodes, foreign bodies, ossification etc.
What describes a focal opacity?
Well defined in the localized
What describes a target Lesion?
Well defined, localized, but surrounded by a radiolucent halo
What describes multifocal confluent?
Multiple radiopacities that overlap or flow together
What is described as irregular?
Poorly defined pattern
What is described as ground glass?
Granular or pebbled
What is described as mixed lucent opaque
Mixed radiopaque and radiolucent
What is described as soft tissue opacity?
Well defined, located in soft tissue
What does inter-radicular mean
Between roots of adjacent teeth
What is an edentous zone
Location without teeth
What does pericoronal mean?
Around the crown of an impacted tooth
