Only region that will be in focus
Narrower in anterior, wider in posterior
-Critical that patient's teeth be located in focal trough
-Placement of anterior teeth particularly important
Panoramic Radiograph: Narrow Beam
Beam of very narrow width is allowed to rotate about the point where the X-ray source was previously located.
In the vertical dimension, the magnification is calculated by dividing the distance from the X-ray source to the film by the distance from the X-ray source to the object.
In the horizontal dimension, since the focus is different, it is calculated by dividing the distance from the intraoral rotation center to the film by the distance from the rotation center to the object.
This makes the magnification factor much greater in the horizontal than in the vertical dimension and leads to the peculiar image.
Critical steps for producing radiograph of diagnostic quality
Position patient properly
Expose film properly
Process film properly
-Disinfect all parts touched by patient
-Place sterile bite-pin or plastic bag over non-removable bite-pin
-Load cassette with film and position appropriately in cassette holder
-Adjust height of machine
-Select exposure factors
-Ask patient to remove all jewelry in the head and neck (earrings, lip and tongue rings, necklaces), as well as dental appliances, hearing aids, etc
-Drape patient with leaded apron
-Tell patient what to expect during procedure
Remove All Metal Jewelry and Appliances
Images of metal objects show up as "ghosts" on opposite side of image
Drape patient with leaded apron
Two-sided aprons frequently used
Thyroid collars are not used because they interfere with image
Position Patient Correctly
Cervical Spine straight
Tongue to roof (palate) of mouth
-Machine manufacturers try to make this simple and repeatable
-Lights shine on face to guide position
-Must check details for specific machines in owner's manual
-Basic principles same for all machines
3 Positioning Lights
1. Frankfort (horizontal)
2. Midline (midsagittal; look at whole face not just nose)
3. Focal trough (anterior-posterior)
Frankfort (Occlusal) Plane
- From floor of orbit (eye socket) to external auditory meatus (ear canal)
- Must be parallel to floor
- Can also use ala (wing) of nose to tragus (triangle) of ear at 5 degrees downward
- Move chin up or down to adjust
-Radiograph shows a gentle smile if occlusal plane correct
-Keeps roots of maxillary teeth away from shadow of hard palate
Midline, from forehead through nose to chin
Must be perpendicular to floor
Must be in midline of x-ray machine (head not rotated)
Focal trough (anterior-posterior position)
Must put teeth in focal trough
Patient bites in groove of bite-pin
Midsagittal plane vertical
No rotation of head
Chin support for edentulous patients
Panoramic Positioning Errors
Too Far Anterior
Teeth in front of focal trough are shrunken
More of a problem in anterior than posterior
Too Far Posterior
Teeth behind focal trough are enlarged
More of a problem in anterior than posterior
Incorrect Occlusal Plane: Beam Too Far Down
Patient's head tipped down too much
Image is distorted
An "exaggerated smile line" is seen on a panoramic film when the patients chin is tipped down.
Incorrect Occlusal Plane: Beam Too Far Up
Patient's head not tipped far enough
Occlusal plane too flat
Image is distorted
Maxillary roots covered by palate
A "reverse smile line" is seen on a panoramic film when the patients chin is tipped up.
Positioning: Spine Straight
-Normal cervical spine is curved
-Spine must be straight to minimize shadow on radiograph
-Ask patient to move feet forward so spine will straighten
-Must hold on to handles on machine to avoid falling
-No unwanted spine shadow
-Anterior teeth seen clearly
Positioning: Spine Not Straight
Unwanted white shadow covering anterior teeth
May be a problem for patients with short or stiff neck or patient in wheelchair
The more non-straight the larger the ghost image
If the patient is not standing erect, superimposition of the ghost image of the cervical spine (arrows) may be seen on the center of the panoramic film.
Tongue to roof of mouth
Squeeze air out between tongue and palate
"Like peanut butter is holding your tongue up there"
Have the _entire_ tongue on the roof of the mouth for the entire exposure
Tongue not to roof of mouth
Black air shadow above tongue covers roots of teeth
Air spaces will be displayed as black shadows on film
Proper Panoramic Exposure
Correct machine settings based on patient size
Verify patient positioning
Ask patient to swallow and put tongue to roof of mouth
Caution patient to hold still
Depress exposure switch for entire cycle (15-20 seconds)
Cannot change the exposure time.
What we can change is the kVP and Ma.
Closer to the midline
Incorrect Lead Apron Block
On a panoramic radiograph, a lead apron artifact appears as a large cone-shaped radiopacity obscuring the mandible.
Incorrect Tongue Placement
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.
Patient Positioning: Too Far Forward
The anterior teeth appear narrowed and blurred on a panoramic film when the patient is positioned too far forward on the bite-block.
Patient Positioning: Too Far Back
The anterior teeth appear widened and blurred on a panoramic film when the patient is positioned too far back on the bite-block.
Patient Positioning: Head Not Centered
The patients posterior teeth and ramus appear to be magnified on a panoramic film when the head is not centered.
Panoramic Concepts: Midline
Midline structures may be projected as single and/or double images
Diamond shaped midline area that produces double images
Real vs. Ghost Image
Real: located between film, center of rotation
Ghost: located between center of rotation, x-ray source
Soft Tissue in Panoramics
Between tongue and hard palate
--May not be symmetrical if patient swallows during scan!
Anatomic Variants: Medial sigmoid depression
Osseous depression in medial portion of ramus at sigmoid notch
May be unilateral or bilateral
Anatomic Variants: Hyperplastic Tonsils
Soft palate looks much larger than normal elliptical shape
Anatomic Variants: Panoramic anterior median radiolucent pseudolesion
Prominent midline depression located in focal trough
Anatomic Variants: Spine of sphenoid bone
Special TMJ program seen here
Radiopacity on top of condyle
Anatomic Variants: Ear Canal & Condyles
Ear canal superimposed over condyles
Verified with open mouth view
Condyle moved, "lesion" did not
Condyle has air in it so will show a radioleucency
TMJ Gross Changes Can Be Observed
Asymmetry (hypo- or hyperplasia)
Maxillary sinus findings
Cloudiness / opacification (sinusitis)
Mucous retention pseudocysts
Polyps (may even erode the floor of sinus walls)
Sinus pneumatization (floor scallops between roots)
Look for symmetry, follow the floor of the sinus!