Panoramic radiography

Question 1

What is the process of panoramic radiography?

Answer 1

X-rays are generated by the tube head, X-rays are directed towards patient. Some X-rays are stopped by the patient and some pass through dependent on material.
Pulp - less dense so X-rays pass through, are radiolucent
Amalgam - more dense so not much of the receptor is exposed to that area - radiopaque
Those that pass through reach the image receptor and produce a grayscale image

Question 2

What is a panoramic radiograph?

Answer 2

Where an X-ray source and image receptor rotating around the patient produces a radiograph.

Question 3

Where is the patient positioned?

Answer 3

Placed between image receptor and X-ray source, patient should be placed properly in the focal trough to avoid malpositioning.
Patient should be positioned so that the anatomy of interest coincide with the focal trough.

Question 4

What is the principle of tomography?

Answer 4

Tube and image receptor both move at the same time generating an in focus slice of anatomy - anything outside of this are blurred.

Question 5

What degree of incline is the image produced at?

Answer 5

8 degree upward incline

Question 6

What produces ghost images?

Answer 6

Produced when object to image receptor distance is long or anything between the centre of rotation and X-ray source.

Question 7

Compared to the object that generates them ghost images are:

Answer 7

Larger - beam divergence
Higher - upward angle of beam
Blurred - more vertically than horizontally - vertical more exposed to image receptor.
Can happen with earrings and studs, ask patient to remove

Question 8

How does anatomy produce ghost images?

Answer 8

Normal anatomy falls between X ray source and centre of rotation during image of opposite side.
Anatomy is imaged twice once when receptor is close enough to side of interest - real image and second on the opposite side - ghost

Question 9

What are positioning errors?

Answer 9

Chin up, chin down
Too far forward, back
Patient rotated/off-centre

Question 10

What is the chin down error?

Answer 10

Pronounced downward inclination of occlusal plane - smiley face produced.
Lower incisors become too far back

Question 11

What is the chin up error?

Answer 11

Pronounced upward inclination of occlusal plane - U shaped.

Upper incisors become too far back

Question 12

If teeth are too close to X ray source how do they appear on a radiograph?

Answer 12

Appear bigger

Question 13

What is the too far forward error?

Answer 13

Too close to image receptor - narrow out of focus teeth, see too much spine

Question 14

What is the too far back error?

Answer 14

Too close to X ray source - magnified out of focus teeth, cut off spine

Question 15

What is a rotational error?

Answer 15

One side too far back one too far forward

Question 16

What is the off centre error?

Answer 16

Rotated to left too close to the image receptor, smaller out of focus to the right molars are further away from the image receptor and appear enlarged.

Question 17

Advantages of panoramic radiography

Answer 17

Shows entire dentition on one film
Time efficient
Lower dose than full mouth periapicals
Well tolerated by patients 
Can be used when a patient can't fully open their mouth

Question 18

Disadvantages of panoramic radiography

Answer 18

Only focal trough structures in focus
Overlapping teeth in some areas (caries sensitive)
Careful patient positioning
Superimposition of soft tissue and air shadows cause misinterpretation
Image can be distorted/magnified
Resolution not as good as intra oral

Question 19

Indications of panoramic radiography

Answer 19

Bony lesion not demonstrated on intra orals
Grossly neglected dentition prior to GA
Assessment of wisdom teeth prior to surgery
Orthodontic assessment
In hospital - mandibular fractures, see condyle
Assess periodontal bone support

Question 20

Check for these four anatomical indicators of pathology

Answer 20

Zygomatic buttress
Hard palate
Posterior wall of maxillary sinus
Floor of maxillary sinus