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Ortho > Radiography in orthodontics > Flashcards

Radiography in orthodontics Flashcards

1
Q

What is cephalometry?

A

Cephalometry is the analysis and interpretation of standardised radiographs of the facial bones.

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2
Q

What view are cephalographs taking?

A

True lateral view

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3
Q

How are the radiographs standardised?

A
  • Fixed position of ear posts that sit into the external acoustic meatus (central beam of X-ray is to the ear post)
  • Head is in the vertical position by ensuring frankfort plane is horizontal
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4
Q

What cannot be standardised? How does this affect the magnification?

A
  • distance from the beam to the patient
  • distance from the film to the patient
  • Causes around 7-8% magnification
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5
Q

Approximate standard dose of a lateral ceph

A

6 usv (microsiverts)

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6
Q

When are lateral cephs indicated? (5)

A
  • Skeletal discrepancies
  • When treatment involves movement of the incisors
  • When treatment will cause movement in three planes
  • Sometimes: to monitor changes during tx and to locate displaced unerupted teeth
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7
Q

Define: A point

A

Point of deepest concavity on the anterior profile of the maxilla

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8
Q

What is the A point also called?

A

Subspinale

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9
Q

What does the A point represent?

A

Anterior limit of the maxilla

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10
Q

What is the ANS (anterior nasal spine)

A

Tip of the anterior process of the maxilla, found at the lower margin of the nasal aperture

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11
Q

Define: B point

A

Deepest concavity of the anterior surface of the mandibular symphysis

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12
Q

Define: Gonion (Go)

A

Most posterior inferior point on the angle of the mandible

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13
Q

How can Gonion be determined?

A

Bisect angle from tangents from the posterior border of the ramus and the inferior border of the mandible

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14
Q

Define: Menton (Me)

A

Lowest point of the mandibular symphysis

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15
Q

Define: Pogonion (Pog)

A

Most anterior point on the mandibular symphysis

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16
Q

Define: Nasion (N)

A

Most anterior point on the frontonasal suture

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17
Q

What can be used if nasion cannot be found?

A

Deepest concavity at the intersection of the frontal and nasal bones

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18
Q

Define Orbitale (Or)

A

Most inferior anterior point of the margin of the orbit

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19
Q

Which orbit should be used by definition? What is done instead?

A
  • Left orbit

- Average of both orbits taken

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20
Q

Define: Porion (Po)

A

Uppermost outermost point on the bony external auditory meatus

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21
Q

Why may Porion be difficult to find? What do you use instead?

A
  • Blocked by ear post

- Use uppermost surface of condylar head

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22
Q

Define PNS (posterior nasal spine)

A

Tip of the posterior nasal spine of the maxilla

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23
Q

Where can you find the PNS if its blocked on the film? What usually blocks it?

A
  • Directly below pterygomaxillary fissure

- Unerupted 8s block it

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24
Q

Define Sella (S)

A

Midpoint of the sella turcica

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25
Q

What is the SN line

A

Connects Sella with Nasion

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26
Q

What does the SN line represent

A

Cranial base

27
Q

What landmarks make up the Frankfort plane

A

Connects Porion to Orbitale

28
Q

What landmarks make up the maxillary plane

A

ANS to the PNS

Or line parallel to nasal floor

29
Q

What landmarks make up the mandibular plane

A

Gonion to Menton

30
Q

What is the functional occlusal plane

A

Line between cusp tips of permanent molars or premolars

31
Q

Why isn’t the functional occlusal plane useful? (2)

A
  • Difficult to locate

- Subject to change with growth and change in tooth position

32
Q

What is cephalometric interpretation?

A

Comparing values obtained from the radiographs to the average values for the population (e.g. race)

33
Q

What does the ANB angle represent?

A

Relationship between the maxilla and mandible to the cranial base

34
Q

How to get the ANB angle?

A

Calculate SNA angle and SNB angle

The difference between them is the ANB angle

35
Q

How does ANB relate to skeletal class?

A 
2-4 degrees = Class I 
>4 degrees = Class II 
<2 degrees = class III
36
Q

What are the limitations to the ANB angle?

A

It can vary with vertical or horizontal positioning of sella or nasion in the skull

37
Q

How to overcome limitations of ANB angle?

A

If the SN to maxillary plane is 8 +/- 3 degrees

  • for every degree ANB is >81 subtract 0.5 degrees from ANB
  • For every degree ANB <81 add 0.5 degrees to ANB
38
Q

What is the MMPA angle

A

Maxillary-mandibular plane angle

extend tangents on paper until they meet

39
Q

What is the average MMPA?

A

27 +/- 4 degrees

40
Q

What MMPA indicates lower anterior facial height is reduced?

A

if MMPA is <23 degrees

41
Q

What MMPA indicates lower anterior facial height is increased?

A

MMPA >32 degrees

42
Q

What should the lower facial height % be?

A

55%

43
Q

How to measure angulation of the incisors

A

Angle between the long axis of the most prominent upper or lower incisors to their respective maxillary or mandibular planes

44
Q

What is the average maxillary incisor angulation

A

109 +/- 6 degrees

45
Q

What is the average mandibular incisor angulation

A

93 +/- 6 degrees

46
Q

What can the incisor angulation tell us?

A

If the angle is greatly increased = incisors are proclined

If the angles are reduced = incisors are retroclined

47
Q

What is the interincisal angle?

A

Intersection between long axes of the upper and lower incisors

48
Q

What is the average incisal angle

A

133-135 degrees

49
Q

What does the wits analysis assess?

A

Compares relationship of mandible and maxilla to the occlusal plane

50
Q

How to do wits analysis

A
  • Measure distance from where A and B points meet the functional occlusal plane (this is AO and BO)
51
Q

What are the values for Wits analysis?

A 
AO and BO within 1mm = Class I 
AO is >1mm ahead of BO = class II 
BO is >1mm ahead of AO = class III
52
Q

What does the Ballards conversion assess?

A

Positions of incisors relative to the mandible and maxilla

53
Q

What is the outcome of Ballards conversion>

A

The relationship between the line through the lower incisors and where it meets the upper incisor along the long axis = skeletal class

54
Q

What type of radiographic views are used in ortho?

A 
Bitewings 
PAs 
Occlusals 
DPT 
CBCT 
lateral cephs
55
Q

What indications would you take periapical radiographs in orthodontic assessment?

A

Assess risk of root resorption as a side effect

Used for parallax technique

56
Q

What indications would you take occlusal radiographs in orthodontic assessment?

A

Assess displaced/unerupted teeth using parallax

57
Q

Why would you take DPT radiographs in orthodontic assessment?

A

Assess presence, position and pathology of successors

Used in the parallax technique

58
Q

When would you use CBCT in orthodontics?

A

Determine position of unerupted teeth that require surgical removable
Accurate assessment of root resorption risk

59
Q

What is the parallax technique?

A

Use of two radiographs at different views, whereby there is movement of the tube head

60
Q

What is horizontal parallax

A

Two radiographs at a different horizontal angle, but within the same vertical angulation

61
Q

What is vertical parallax

A

Two radiographs taken at different vertical angulations

62
Q

List examples of horizontal parallax

A

Two PAs at different positions horizontally

USO and ULO

63
Q

List examples of vertical parallax

A

PA and USO
DPT and USO
DPT and PA?

Ortho (20 decks)

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