panoramic radiograph

Question 1

indications for DPT(8)

Answer 1

1. overall evaluation of dentition
2. impacted tooth (eg. wisdom tooth)
3. extensive caries or periodontal disease
4. dentomaxillary trauma (eg. fracture)
5. gross evaluation of TMJ (eg rheumatoid arthritis)
6. growth and development or dental eruption (sequence of max: 61245378, mand: 61234578, ectopic location)
7. intraosseous pathology (eg. cysts, tumor etc)
8. developmental disturbances (eg. fibrous dysplasia)

Question 2

technique for DPT

Answer 2

1. patient preparation
   - remove jewellery, hair pins, earrings, removable prosthodontic appliances
   - explain procedure to pt
   - ask female pt if pregnant
   - use lead apron not thyroid collar (artefeact)
2. equipment preparation
   - set exposure factors
   - place plastic barrier over incisor bite stick
3. patient positioning
   - patient hold onto handles
   - bite upper and lower incisors edge to edge into bite block and rest chin on chin support
   - immobolise head with temple support
   - light beam markers to ensure that :
   frankfurt plane is horizontal
   mid-sagittal plane is vertical
   canine light is at correct position
   -ask pt to close lips, and tongue to the roof of their mouth
   - dont move for 15-18 seconds during procedure
   - release temple support
   - ask patient to remove plastic barrier on incisor bite stick
   - wipe down equipment

Question 3

principles of dpt

Answer 3

Principles of tomography
- x ray source and image receptor rotate simultaneously about a fixed centre of rotation, hence objects in this layer will be clearly depicted
- objects above or below centre of rotation will appear blurred or distorted.
in panoramic radiograph,
- x ray source and image receptor are located across each other, patient in the centre
- x ray source and image receptor rotate synchronously in opposite directions
- x ray source is collimated to form a narrow beam that will only expose a part of image receptor at one time
- x ray source and image receptor rotates about a centre of rotation that moves, not a fixed centre of rotation –> forming a horseshoe shape image layer –> objects within this layer will be clearly depicted. objects outside image layer will be blur distorted
- x ray source and image receptor does not rotate about a fixed point –> will form circular image layer –> does not conform to jaw shape

Question 4

criteria for a diagnostic dpt (8)

Answer 4

1. all upper and lower and supporting alveolar ridges seen clearly
2. magnification horizontally and vertically are equal
3. molars of R and L teeth equal width and rami equal width
4. no palatoglossal air space
5. hard palate at apices of maxillary teeth
6. no artefacts
7. minimal ghost of cervical spine and mandible
8. marked R/L to indicate R/L sides

Question 5

common imaging errors of DPT –> modifications

Answer 5

inherent error
1. magnification and distortion
- magnification and distortion worse in anterior region than posterior region
- horizontal magnification: objects outside of image layer appear blurred and distorted
- vertical magification: objects located more lingually will be projected higher on image VS objects located buccally will be projected lower
2. ghost and double image
- ghost image: objects appears in opp side, magnified, blurry, large, same morphology
- double image: always mirrored

patient preparation
1. artefacts –> remove
2. palatoglossal air space –> place tongue at roof of mouth

patient positioning
1. magnification –> patient never bite in the notches of incisor bite stick –> patient closer to x ray source
- anterior teeth blurry, wider, larger
- condyles at edge of image
- increase ghosting of mandible
2. minification –> pt nvr bite… –> patient further to x ray source
- anterior teeth blurry, small narrow
- spine visible on both sides

3. chin tilting downwards –> frankfurt plane not correct
   - v shape mandible
   - blurry lower incisors
4. chin tilting upwards –> frankfurt plane
   - occlusal plane flat
   - mandible flat/broad
   - blurry max incisors
   - condyles at edge of image
5. tilted –> mid sagittal plane not correct
   - molar or rami on one side wider than other side
6. movement
   - step defect on inferior border of mandible
   - motion artefacts appear at region that was being exposed when pt move

Question 6

advantage of dpt (6)

Answer 6

1. overview of upper and lower jaws and all teeth
2. compare left and right at same time
3. easy to use, quick convenient
4. patient education tool
5. lesser radiation than fmx of intra-oral film
6. for pt who cant tolerate intra oral radiographs

Question 7

disadvantage of dpt (7)

Answer 7

1. distortion and magnification –> measurements unreliable
2. ghost and double images –> hard interpretation
3. structures outside image layer blur and distorted
4. lower resolution –> only for extensive caries or gross evaluation of TMJ
5. not for children –> cannot stay still for duration
6. not for skeletal discrepancies patient
7. accurate patient positioning to avoid image errors