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Radiology > Dental Panoramic Tomography (DPT) > Flashcards

Dental Panoramic Tomography (DPT) Flashcards

1
Q

what is a tomogram?

A

A radiograph showing a slice or section of tissue in focus

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2
Q

What is a form of tomography used in dentistry?

A

DPT

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3
Q

Only structures within what area/slice are sharp on a DPT image?

A

The focal trough

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4
Q

what shape is the focal trough?

A

Horse-shoe shaped

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5
Q

what are the three disadvantages of intensifying screens within conventional film cassettes?

A

Light is emitted in all directions
Light affects larger area of film than a single photon
Image quality (fine detail) is not as good as direct action film

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6
Q

When taking a DPT, what does use of a bite peg do?

A

Forces patient into edge-to-edge occlusion
positions both arches in focal trough

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7
Q

what are the main advantages to taking a DPT over a periapical?

A

Can capture entire dentition in once image
Able to image non-dental areas
Lack of intra-oral holders benefits some patients

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8
Q

What are some key clinical indications for taking a DPT?

A

orthodontic assessment
mandibular fractures
degenerate disease of TMJ
implant planning or review
symptomatic third molars

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9
Q

What are the main disadvantages of taking a DPT over a periapical?

A

lack of fine detail
superimposition
more artefacts
patient co-operation required
exposure time up to 16 seconds
higher radiation dose per image

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10
Q

describe the patients position when taking a DPT

A

Stands with spine straight, holding handles
Bites incisors edge to edge on bite block
Head immobilised
Tongue to roof of mouth
Stand still
Do not talk or swallow

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11
Q

Why should we not routinely use lead aprons in dental radiography?

A

Because they do not protect from internal scatter and they interfere with image as can be projected onto image and may also catch the tube as it rotates

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12
Q

What is an example dose of radiation from a DPT?

A

3.85-30 micro Sv

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13
Q

what are ghost images?

A

Images of a structure on one side which are projected onto other side

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14
Q

why are ghost images always seen at a higher level than the real structure?

A

Because the x-ray beam is pointing upwards at an angle of 8 degrees to the horizontal

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15
Q

what incisors relationship does not allow for a patient to correctly bite upon a bite block?

A

Class III incisal relationship- where mandibular incisor is anterior to maxillary incisor

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16
Q

What does ‘collimated’ mean?

A

To make parallel

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17
Q

When a patient has a strong gag reflex, what radiograph is most likely to be taken?

A

DPT

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18
Q

Why is superimposition not as bad in intra-oral x-rays compared to extra-oral x-rays?

A

As intra-oral x-ray source and receptor can both be placed close to area of interest ( therefore fewer structures are captured, less superimposition)

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19
Q

What form of radiography try to counteract superimposition?

A

Tomography

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20
Q

what type of tomography, involving multiple slices is commonly used in medicine?

A

Computed tomography

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21
Q

What type of tomography is a Panoramic radiograph?

A

Conventional tomography

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22
Q

Where is the x-ray source in comparison to the patient during a DPT?

A

Behind

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23
Q

Where is the receptor in comparison to the patient during a DPT?

A

In front

24
Q

Describe the characteristics of an x-ray beam used for DPT

A

Narrow, vertical, “fan-shaped”

25
Q

why is it common for the incisor region to appear blurry on a DPT?

A

Because the focal trough is thinner in this region

26
Q

What does “orthogonal” view mean?

A

A 90 degree view horizontally or vertically

27
Q

What are the advantages of the x-ray beam angulation being changed to a more orthogonal view in order to visualise teeth?

A

reduces overlap of the teeth to aid assessment of approximal caries (particularly improves premolars)
improves angulation to better represent interdental periodontal bone levels

28
Q

What are the disadvantages of the x-ray beam angulation being changed to a more orthogonal view in order to visualise teeth?

A

distorts the rest of skeleton
typically a narrower field of view so may miss condyles on edge of image

29
Q

How much is the image within the focal trough magnifies by?

A

Around 25%

30
Q

Which structures in relation to the focal trough are more magnified?

Lingual or buccal

A

Lingual

31
Q

Which structures in relation to the focal trough are less magnified?

Lingual or buccal

A

Buccal

32
Q

How do teeth positioned buccal to the focal trough appear on an image?

A

Narrower (vertical magnification)

33
Q

How do teeth positioned lingual l to the focal trough appear on an image?

A

Broader (horizontal magnification)

34
Q

Why are structures within the focal trough not distorted?

A

Because the degree of horizontal magnification matches that vertically

35
Q

Where is the x-ray source positioned in comparison to the focal trough?

A

Lingually

36
Q

By how many times is the radiation dose greater per DPT image compared to periapical image?

A

5 times

37
Q

What is the ‘field limitation’?

A

Changing size of x-ray field to reduce radiation does

38
Q

What are the three light beam markers used to take DPT?

A

horizontal line: Frankfort plane
vertical mid-line: mid-sagittal plane
vertical canine lines

39
Q

If the Frankfort plane is out of position due to the chin of the patient being down, how will this reflect on the image?

A

The occlusal plane will appear ‘smiling’

40
Q

If the Frankfort plane is out of position due to the chin of the patient being up, how will this reflect on the image?

A

“Flat” occlusal plane

41
Q

If the mid-sagittal plane is not centered, how will this reflect on the image?

A

Distortion of one/both sides of image

42
Q

If the mid-sagittal plane is out of position due to incorrect vertical alignment, how will this reflect on the image?

A

Distortion and occlusal plane cant

43
Q

If the mid-sagittal plane is out of position due to the patient being slumped over, how will this reflect on the image?

A

Excessive cervical spine shadow

44
Q

If patient does not press tongue against palate while DPT is being taken, how will this reflect on the image and why?

A

A black radiolucent band across the maxilla will appear as an air gap has been created between the tongue and roof of mouth

45
Q

What are the 6 different structures that make up the mandible and can be seen clearly on a DPT?

A

condyle
coronoid process
sigmoid notch
ramus
angle
body

46
Q

How does the submandibular fossa present on a radiograph?

A

As a depression on the lingual aspect of the body of the mandible

47
Q

Why does the mastoid process sometimes appear as having a ‘honeycomb’ pattern on a radiograph?

A

Because it is filled with trabecular bone

48
Q

What is the purpose of the articular eminence?

A

Stops condylar head from moving forward out of the glenoid fossa

49
Q

Why are misleading shadows created on DPT’s?

A

Due to the rotational technique, the resulting panoramic image also exhibits abnormal structures

50
Q

What are the two types of misleading shadow?

A

Double shadows
Ghost shadows

51
Q

What are double shadows and how are they created?

A

Created by structures located near the centre of rotation which, due to their central position, are captured twice (i.e. x-ray machine passes through them twice as it spins round head)

52
Q

what three anatomical structures commonly have a double shadow?

A

Hyoid bone
Soft palate
Cervical spine

53
Q

What are ghost shadows and why are they created?

A

Structures on one side are projected onto the other side. Created by structures between the x-ray source and the centre of rotation

54
Q

Why do ghost shadows always appear higher than where the structure should actually be?

A

Due to the inclination of the x-ray beam and that it is transposed on to the opposite side of the true anatomical position

55
Q

Why are DPT’s poor for showing anterior fractures of the mandible?

A

Due to superimposition of ghost shadow of cervical spine

55
Q

Why are DPT’s poor for showing anterior fractures of the mandible?

A

Due to superimposition of ghost shadow of cervical spine

Radiology (12 decks)

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