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BDS4 Orthodontics > Orthodontic Radiology > Flashcards

Orthodontic Radiology Flashcards

1
Q

How is dose kept ALARP?

A

Equipment – correct operation and maintenance

Adequate staff training

Justification – only take radiographs when required and select the most appropriate view

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2
Q

What is the effective dose in mSv for different dental radiographs?

A

IO = 0.0003-0.022
OPT = 0.0028-0.038
Upper standard occlusal = 0.008
Lateral Ceph = 0.0022-0.0056
Mandible/maxilla CT = 0.25-1.4
Dentoalveolar CBCT = 0.01-0.67
Craniofacial CBCT = 0.03-1.1

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3
Q

What is the estimated risk of developing fatal cancer for different dental radiographs?

A

IO- 1 in 10,000,000
OPT- 1 in 1,000,000
Upper standard occlusal- 1 in 2,500,000
Lateral Ceph- 1 in 5,000,000
Mandible and maxilla CT- 1 in 14,300 to 80,000
Dentoalveolar CBCT- 1 in 30,000 to 2,000,000
Craniofacial CBCT- 1 in 18,200 to 670,000

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4
Q

What can be done to limit dose?

A

70kV

Rectangular collimation

F speed film/digital receptors

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5
Q

What are the reasons for taking an OPT in new orthodontic patients at the assessment?

A
  • State of development - presence or absence of permanent teeth
  • Presence and position of ectopic or supernumerary teeth
  • The stage of development of individual teeth
  • The morphology of unerupted teeth
  • State of the alveolar bone ( Periodontal disease )
  • State of the teeth- Size of restorations, gross caries, periapical infection, other pathology
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6
Q

What are the other indications for an OPT?

A

Oral surgery
- pathological jaw lesions
- surgery
- evaluation and review
- trauma /fractures

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7
Q

What are the stages in reporting an OPT?

A

Check patient details and check orientation of film

Chart teeth : start from the back of mouth
-> Identify erupted teeth/ unerupted teeth/ any missing teeth/ any extra teeth

Check roots of teeth – apical pathology/ root resorption

Check state of tooth crowns Any obvious caries? /large restorations/ hypoplasia

Check for any alveolar bone loss

Any other findings- cysts

Lastly focussing on reason you took radiograph

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8
Q

What are the causes of faults when taking an OPT?

A

Due to the limitations in the width of the focal trough – particularly at the front of the mouth

Faults in patient positioning- use guidelines

Movement of patient- exposure takes 18-20 secs, patient may not remain still

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9
Q

What happens if structure is outwit the focal trough?

A

It will be blurred or not visible at all

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10
Q

What is the issue with focal trough and malocclusions?

A

When a patient’s malocclusion does not permit them to bite Edge to Edge within the groove on the bite block either the whole tooth, or roots of teeth, may end up outwith the focal trough

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11
Q

How do different malocclusions affect image? (teeth are outwith focal trough)

A

Class II div I - Roots of one or both upper and lower incisors may be blurred or not visible

Class III – roots of upper incisors may be blurred

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12
Q

What happens if patient is too far forward in OPT machine?

A

The teeth will look narrower on the film (in anterior region)
- this is because the teeth are further from the centre of rotation and the x-ray beam therefore passed more quickly through these teeth relative to the speed of the image receptor

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13
Q

What happens if patient is too far back in OPT machine?

A

The teeth will look wider on the film
- this is because the teeth are closer to the centre of rotation and the x-ray beam therefore passed more slowly through these teeth relative to the speed of the image receptor.

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14
Q

What is required to produce a clear image?

A

The speed of the x-ray beam through the teeth and the speed of the receptor through the x-ray beam need to be synchronised

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15
Q

Why are ghost images always higher up?

A

They are always seen at a higher level on the opposite side of the mouth because the x-ray beam of the machine is angled upwards by 8 degrees

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16
Q

What objects can appear as ghost images?

A

Metal objects

Restorations

Earrings

Normal anatomic features

17
Q

What happens if patient moves during OPT exposure?

A

Gross distortion

18
Q

What happens if we take an OPT with Frankfort plane angles down?

A

Smiley face appearance

19
Q

What are the reasons for taking a standard upper occlusal?

A

 To look for pathology in the upper anterior region of the maxilla
 To confirm the presence of unerupted teeth
 Root resorption – but periapical view better for assessment
 To aid localisation of unerupted teeth in combination with another radiographic view (parallax)

20
Q

What are the reasons for taking a periapical radiograph?

A

 To assess for root resorption
 To look for evidence of periapical infection
 To assess if a tooth might be ankylosed
 To aid localisation of unerupted teeth in combination with another radiographic view (parallax)

21
Q

What are the reasons for taking bitewings?

A

 To assess caries status
 To provide more information on tooth prognosis
 To get more information on alveolar bone levels

22
Q

What are the types of parallax and how are they achieved?

A

Vertical- OPT and Upper maxillary occlusal

Horizontal- 2 PAs

23
Q

How is parallax applied?

A

Objects furthest away from the x-ray beam will move in the same direction as the beam moves.

Objects closer to the x-ray beam will move in the opposite direction to which the x-ray beam

24
Q

What are the indications for taking a lateral ceph?

A

To aid diagnosis
-> Skeletal class II or III (marked AP discrepancy)
-> Vertical discrepancy

Treatment planning
-> Help clarify the tooth movements to be achieved
-> To decide orthodontics only or orthognathic surgery
-> Orthognathic planning

Progress monitoring
-> Fixed appliance treatment
-> Functional appliance treatment
-> Monitoring facial growth
-> Predict future growth?

25
Q

What is position is Lateral Ceph taken in?

A

Cephalostat

Frankfort plane- horizontal

Teeth in RCP

26
Q

What are the important reference lines for lateral ceph?

A

 Sella-nasion (and how it relates to A and B point)
 Frankfort plane
 Maxillary plane
 Occlusal line
 Mandibular plane

27
Q

What are examples of different analysis forms in lateral ceph radiographs?

A

Eastman

Downs

Rickets

Jacobson

28
Q

What are the different ANB (AP discrepancy) values for different severity of malocculsion?

A

> 8- severe class II

6-8- Moderate class II

4-6- mild class II

2-4- Class I

0-2- Mild class III

-3-0- Moderate class III

<-3- Severe class III

29
Q

What should the angle of upper incisors to maxillary plane be on a ceph? (Ui/MxP)

A

109 +/- 6

30
Q

What should angle of lower incisors to maxillary plane be on a ceph? (Li/MnP)

A

93 +/-6

31
Q

What should the angle created by relationship of upper and lower incisors be? (Ui/Li)

A

135 +/- 10

32
Q

What are the different values of MMPA for different types of vertical discrepancy?

A

> 37- severely increased face height

32-37- moderately increased face height

27-32- mildly increased face height

27- average

22-27- mildly decreased

17-22- moderately decreased

<17- severely decreased

33
Q

What errors can occur in cephalometry?

A

Radiographic projection errors
-> magnification
-> distortion

Errors within the measuring system
-> non-linear fields

Errors in landmark identification
-> quality of image
-> landmark definition and location
-> operator and registration procedure

34
Q

What structures may be superimposed on ceph image?

A

Anterior wall of sella

Middle cranial fossa

Anterior surface of zygomatic process

Outline of IAN canal

Anterior border of chin

Inner cortical plate at mandibular symphysis

35
Q

What are the uses of cone beam computer tomography?

A

Localisation of teeth- if we need more info on proximity to adjacent teeth/structures (may cause resorption)

To get better view of structural anamolies
-> Gemination
-> fusion
-> supernumeraries

Some orthognathic cases

Some cleft palate cases

36
Q

Why is CBCT not used often in ortho?

A

Radiation dose is much higher than plain films

Longer exposure/Patient set up time takes longer than OPTs

Additional training needed to report on CBCT

Cost

BDS4 Orthodontics (14 decks)

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