Panoramic imaging principles Flashcards
What are the indications for panoramic radiographs?
(7)
▪ Overall evaluation of dentition
▪ Intraosseous pathology (cysts, tumors, infections,
etc)
▪ Gross evaluation of the temporomandibular joints
▪ Evaluation of position of impacted teeth (3rd molars)
▪ Evaluation of dental development and eruption
▪ Dentomaxillofacial trauma
▪ Developmental disturbances of the maxillofacial
skeleton
Advantages of panoramic over FMS
(6)
- Relatively low radiation dose
- Broad coverage of facial bones and teeth
- Easier technique
- Can be used in patients with trismus or in
patients who cannot tolerate intraoral
radiographs - Quick and convenient radiographic
technique - Useful visual aid in patient education
Disadvantages of panoramic over FMS
(6)
- Lower-resolution images (no possible
to detect small carious lesions or early
periapical disease) - Overlap in the premolar area
- Magnification across image is unequal,
making linear measurements unreliable - Image is superimposition of real,
double, and ghost images - Requires accurate patient positioning to
avoid positioning errors and artifacts - Difficult to image both jaws when
patient has severe maxillomandibular
discrepancy
How does panoramic radiograph work?
Continuous movement of panoramic
Source starts on the R side –> continues behind head –> ends up on the L side
When the source is on the ____ side, the left side of the mandible is being imaged.
right
Is the panoramic sensor ever in the back of the patient?
never
Is the panoramic xray tubehead ever in front of the patient?
never
What is the focal trough?
a 3D curved zone in which structures are reasonably well defined
Where should dental arches be positioned to achieve sharpest images?
focal trough
Objects outside the focal trough are…
blurred, magnified, or reduced in size and are sometimes distorted to the extent of not being recognizable
Structures positioned in the center of the focal trough are…
the clearest
Getting progressively farther from the focal trough structures become….
progressively less clear
How many centers of rotation for panoramic?
not just ONE center of rotation
(multiple and constantly moving centers of rotations)
Objects closer to the receptor will be ______
narrowed
Objects closer to the source will be _____
widened
Buccal objects will be projected _____
lower
Lingual objects will be projected _____
higher
What should the beam angulation be for panoramic?
-4 degrees to avoid projection of the occipital bone
Structures closer to the source are projected _________ on the image, relative to structures that are positioned farther away from the source
higher
Distance between the root apex and the ____________ can be misrepresented on a panoramic radiograph
mandibular canal
___________ magnification is determined by the position of the object within the focal trough.
Horizontal
Lingual to the focal trough → closer to the source→ Appears ________
wider
Buccal to the focal trough→ Appear _______
narrow
The _____________ of the horizontal distortion depends on the distance of the object from the center of the focal trough
magnitude
The magnitude of ____________
distortion varies between the anterior and posterior regions of the jaws.
horizontal
In the ____________ region, horizontal magnification increases markedly as the object moves away from the center of the focal trough
anterior
Where is the degree of the magnification greater: posterior or anterior region?
anterior
Horizontal measurements made on panoramic radiographs are…
unreliable
What are real images?
Every anatomical structure positioned between the center of rotation and the receptor.
What are ghost images?
Created by objects located between the x-ray source and the center of rotation.
Where do ghost images appear in relation to the real image?
Appear on the opposite side, at a higher level, blurred and magnified.
Anatomical structures that cast a ghost image include:
- Inferior border of the mandible
- angle
- ramus
- hyoid
- cervical spine
- jewelry (earrings, hairpins, necklace)(this would not be an anatomical feature tho)
- palate
What are the characteristics of ghost shadows?
▪ Appears on the opposite side
▪ Positioned higher than real structure
▪ More blurred than the real structure
▪ Vertical component is highly magnified
What are double images?
Objects that lie posterior to the center of rotation and that are intercepted twice by the x-ray beam
What are examples of structures that can have double images?
- hyoid bone
- epiglottis
- cervical spine
- all of which cast images on both the right and left side of the image.
Are double images real or ghost?
real
What are the steps for positioning for a pano?
- Remove jewelry, glasses and dentures
- Place lead apron
- Bite in bite block groove
- Stand patient upright
- Align the center laser line
- Align the Frankfurt horizontal plane
- Close side guides
- Have the Pt. close their lips, swallow & keep tongue on the palate and hold still
- Expose the radiograph
When do you use the chin rest during a pano?
The chin rest if used if the patient has no or only a few anterior teeth.
