Dental Panoramic Tomography (DPT)

Question 1

what is a tomogram?

Answer 1

A radiograph showing a slice or section of tissue in focus

Question 2

What is a form of tomography used in dentistry?

Answer 2

DPT

Question 3

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

Answer 3

The focal trough

Question 4

what shape is the focal trough?

Answer 4

Horse-shoe shaped

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What are some key clinical indications for taking a DPT?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

describe the patients position when taking a DPT

Answer 10

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

Question 11

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

Answer 11

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

Question 12

What is an example dose of radiation from a DPT?

Answer 12

3.85-30 micro Sv

Question 13

what are ghost images?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

What does ‘collimated’ mean?

Answer 16

To make parallel

Question 17

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

Answer 17

DPT

Question 18

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

Answer 18

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

Question 19

What form of radiography try to counteract superimposition?

Answer 19

Tomography

Question 20

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

Answer 20

Computed tomography

Question 21

What type of tomography is a Panoramic radiograph?

Answer 21

Conventional tomography

Question 22

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

Answer 22

Behind

Question 23

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

Answer 23

In front

Question 24

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

Answer 24

Narrow, vertical, “fan-shaped”

Question 25

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

Answer 25

Because the focal trough is thinner in this region

Question 26

What does “orthogonal” view mean?

Answer 26

A 90 degree view horizontally or vertically

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

Around 25%

Question 30

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

Answer 30

Lingual

Question 31

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

Answer 31

Buccal

Question 32

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

Answer 32

Narrower (vertical magnification)

Question 33

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

Answer 33

Broader (horizontal magnification)

Question 34

Why are structures within the focal trough not distorted?

Answer 34

Because the degree of horizontal magnification matches that vertically

Question 35

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

Answer 35

Lingually

Question 36

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

Answer 36

5 times

Question 37

What is the ‘field limitation’?

Answer 37

Changing size of x-ray field to reduce radiation does

Question 38

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

Answer 38

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

Question 39

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

Answer 39

The occlusal plane will appear ‘smiling’

Question 40

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

Answer 40

“Flat” occlusal plane

Question 41

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

Answer 41

Distortion of one/both sides of image

Question 42

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

Answer 42

Distortion and occlusal plane cant

Question 43

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

Answer 43

Excessive cervical spine shadow

Question 44

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

Answer 44

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

Question 45

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

Answer 45

condyle coronoid process sigmoid notch ramus angle body

Question 46

How does the submandibular fossa present on a radiograph?

Answer 46

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

Question 47

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

Answer 47

Because it is filled with trabecular bone

Question 48

What is the purpose of the articular eminence?

Answer 48

Stops condylar head from moving forward out of the glenoid fossa

Question 49

Why are misleading shadows created on DPT’s?

Answer 49

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

Question 50

What are the two types of misleading shadow?

Answer 50

Double shadows Ghost shadows

Question 51

What are double shadows and how are they created?

Answer 51

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)

Question 52

what three anatomical structures commonly have a double shadow?

Answer 52

Hyoid bone Soft palate Cervical spine

Question 53

What are ghost shadows and why are they created?

Answer 53

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

Question 54

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

Answer 54

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

Question 55

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

Answer 55

Due to superimposition of ghost shadow of cervical spine

Question 55

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

Answer 55

Due to superimposition of ghost shadow of cervical spine