RAD02 - Lecture 4 - Panoramic (DPTs)

Question 1

What does DPT stand for?

Answer 1

Dental panoramic tomography (radiography)

Question 2

What are the common clinical indications for DPTs? (6)

Answer 2

Bony lesion or unerupted tooth is a size or in a position that precludes (prevents) its complete demonstration on intra-oral radiographs

Grossly neglected mouth

Orthodontic assessment

Third molar assessment (to planned intervention)

Mandibular fractures

Periodontal assessment if pocketing >6mm in >1 quadrant

Question 3

Give 4 examples of other indications for DPTs

Answer 3

Prior to surgery under GA

Assess multiple sites for implants on ajaw

Patients who cannot tolerate intra-oral radiography

TMJ assessment (to exclude bone disease)

Question 4

Give 2 examples of where DPTs cannot be justified

Answer 4

No clinical signs or symptoms

For review at arbitary (personal) time intervals

Question 5

What should you consider first prior to DPTs - why?

Answer 5

Intra-oral radiographs -> lower dose and better detail

Question 6

How is a simple linear (flat) tomograph produced?

Answer 6

Moving the X-ray tube in one direction and the film in the opposite direction (on either side of the patient)

Question 7

What is the shape of the panoramic focal trough (or in focus layer)? (1)

Answer 7

3D horse-shoe shape

Question 8

What determines the precise shape and positon of the “in focuse” horse-shoe layer? (2)

Answer 8

Its predetermined by the manufacturer

Thus - positioning of the patient correctly within the machine is crucial

Question 9

What happens to any teeth that lies outside the focal trough? (1)

Answer 9

Appear burred and out of focus (on the film)

This happens when you have abnormal incisior position -> it will be impossible for patient to bite both U and L incisiors into the peg at the same time

Question 10

How would the image differ if the object is inside or outside the horseshoe?

Answer 10

Inside horseshoe = object is further from image receptor -> ↑ distance (d) -> appears bigger + wider

Outside horseshoe = object is closer to image receptor -> appears smaller + narrower

Question 11

How long does it take for the machine to orbit around the head?

Answer 11

15-18 seconds

Question 12

Does the X-ray machine move behind the patients head? (1)

Answer 12

Yes

Question 13

What is the beam of X-rays shape? (1)

Answer 13

Narrow vertical slit

Question 14

What is the angulation of the X-ray beam? 91)

Answer 14

~8^o upwards

Question 15

What is the equipment needed to take a DPT? (2)

Answer 15

X-ray tube head

Cassette + phosphor plate

Question 16

How is the image formed (with regarding the film/phosphor plate)? (2)

Answer 16

The film/phosphor plate is exposed bit by bit throughout the movement

As the vertical beam traverses across the image receptor

Question 17

With regard to the distance between the focus layer + film - what is the magnification of DPTs?

Answer 17

x1.3 magnification

Question 18

What should you do to reduce radiation dose when taking DPTs? (2)

Answer 18

The smallest field size compatible with obtaining the required information should be used

This ensures that only pre-selected parts of the patients are exposed and imaged ont he final film

Question 19

What are the 6 typical field size options?

Answer 19

Full field

Dentition only (doesnt include condyles or upper part of maxilla)

Maxilla only

Mandible only

Additional subdivisions (i.e. right/left side or specific quadrants)

TMJ (condyles can be image with mouth close and open)

Question 20

If you just choose the field size for dentition (only) - how much does the radiation dose decrease by from a full field?

Answer 20

50% reduction in effective dose

Question 21

What are ghost shadows? (1)

Answer 21

Shadows of structures on the opposite side of the jaw

Question 22

How can you spot ghost shadows? (3)

Answer 22

Out of focus (not in the focal trough)

Magnified (further away form the film than focal trough)

Projected higher (upward angulation of x-ray beam)

Question 23

Describe how you would prepare a patient for a DPT (12)

Answer 23

1) Confirm patients identity

2) Remove anything radio-opaque between -> top of ears and shoulders (i.e. earings, necklace, nose studs, tongue studs, hair slides, glasses, hearing aids)

3) Remove denture and orthodontic appliances

4) Explain procedure and equipment

5) Position patient in the machine -> hold handles

6) Ensure patient spine is straight (if standing or seated)

7) Get patient to bite their upper and lower incisiors edge-to-edge on the bite peg

8) Ensure chin is in good contact with chin support

9) Immobilise the head using the temple supports

10) Use the light beam markers as a guide to adjust head position (mid saggital, frankfurt, canine line) and keep straight w/ no rotation

11) Ask patient to remain still

12) Press exposure button

Question 24

GIve examples of patients that are not suitable for DPTs

Answer 24

Unable to keep still (physical or mental disabilities)

Unable to support themselves

Physical deformity (i.e. kyphosis)

Small children

Question 25

What is the 3 planes on the DPT - explain how the light beam markers should be used to adjust position of the head?

Answer 25

Midline saggital plane -> vertical and head is straight with no rotation (middle of face)

Frankfort plane -> line joining the lower border of the orbit and the tragus of the ear (head up or down)

Canine plane -> centre between the upper left lateral incsior and canine (ensures mandible is in focal trough)

Question 26

How would you modify the DPT technique for edentulous patients? (3)

Answer 26

Do not use bite-peg

Rest chin on chin support (usually a special one for edentulous patients)

Centre canine positioning light beam on the corner of the mouth

Question 27

What are the advantages of DPTs? (7)

Answer 27

A large area imaged and all tissues in the focus layer -> displayed on one image (even if patient cant open their mouth -> useful after trauma)

Positioning relatively simple

Image is a useful teaching aid for patients

Patient movement in the vertical plane only distorts part of the image (thats produced that instant)

Evaluate perio status and orthodontic assessment

TMJ programmes available to image condyles

Relatively low dose examination

Question 28

What are the disadvantages of DPTs? (4)

Answer 28

Soft tissue, ghost and air shadows

Not suitable for children <6yrs

Not suitable for patients with some physical or mental disabilities

Some jaws do not conform to the shape of the “in focus layer or focal trough”

Question 29

What is the quality criteria for DPTs? (10)

Answer 29

Image correctly labelled with patients details and anatomical markers

Upper occlusal plane parallel to floor (slight smiley appearance)

Teeth should be in focal trough

All upper and lower teeth w/ supporting alveolar bone in that area required/selected must be clearly demonstrated

Hard palate must be projected clear of the apices of the upper teeth

Whole mandible in required area must be included

Maginification in the vertical and horizontal plane must be -> equal

No overlap of premolars or molars

No distortion of the right and left molar teeth

Uniform density across image -> no air shadow (black radiolucency) above tongue

Minimal ghost shadows -> only contralateral angle of mandible and C-spine visible

All jewlrey should be removed as far as possible

Question 30

Give examples of distortions of DPTs and cause (4)

Answer 30

Exaggerated smile appearance -> chin too down

Frowning appearance -> chin too up

Thin and needle like teeth (no bone levels) -> too foward

Wide teeth (unclear apices) -> too back