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Radiography in orthodontics Flashcards

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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
What is the SN line
Connects Sella with Nasion
26
What does the SN line represent
Cranial base
27
What landmarks make up the Frankfort plane
Connects Porion to Orbitale
28
What landmarks make up the maxillary plane
ANS to the PNS | Or line parallel to nasal floor
29
What landmarks make up the mandibular plane
Gonion to Menton
30
What is the functional occlusal plane
Line between cusp tips of permanent molars or premolars
31
Why isn't the functional occlusal plane useful? (2)
- Difficult to locate | - Subject to change with growth and change in tooth position
32
What is cephalometric interpretation?
Comparing values obtained from the radiographs to the average values for the population (e.g. race)
33
What does the ANB angle represent?
Relationship between the maxilla and mandible to the cranial base
34
How to get the ANB angle?
Calculate SNA angle and SNB angle | The difference between them is the ANB angle
35
How does ANB relate to skeletal class?
``` 2-4 degrees = Class I >4 degrees = Class II <2 degrees = class III ```
36
What are the limitations to the ANB angle?
It can vary with vertical or horizontal positioning of sella or nasion in the skull
37
How to overcome limitations of ANB angle?
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
What is the MMPA angle
Maxillary-mandibular plane angle | extend tangents on paper until they meet
39
What is the average MMPA?
27 +/- 4 degrees
40
What MMPA indicates lower anterior facial height is reduced?
if MMPA is <23 degrees
41
What MMPA indicates lower anterior facial height is increased?
MMPA >32 degrees
42
What should the lower facial height % be?
55%
43
How to measure angulation of the incisors
Angle between the long axis of the most prominent upper or lower incisors to their respective maxillary or mandibular planes
44
What is the average maxillary incisor angulation
109 +/- 6 degrees
45
What is the average mandibular incisor angulation
93 +/- 6 degrees
46
What can the incisor angulation tell us?
If the angle is greatly increased = incisors are proclined | If the angles are reduced = incisors are retroclined
47
What is the interincisal angle?
Intersection between long axes of the upper and lower incisors
48
What is the average incisal angle
133-135 degrees
49
What does the wits analysis assess?
Compares relationship of mandible and maxilla to the occlusal plane
50
How to do wits analysis
- Measure distance from where A and B points meet the functional occlusal plane (this is AO and BO)
51
What are the values for Wits analysis?
``` AO and BO within 1mm = Class I AO is >1mm ahead of BO = class II BO is >1mm ahead of AO = class III ```
52
What does the Ballards conversion assess?
Positions of incisors relative to the mandible and maxilla
53
What is the outcome of Ballards conversion>
The relationship between the line through the lower incisors and where it meets the upper incisor along the long axis = skeletal class
54
What type of radiographic views are used in ortho?
``` Bitewings PAs Occlusals DPT CBCT lateral cephs ```
55
What indications would you take periapical radiographs in orthodontic assessment?
Assess risk of root resorption as a side effect | Used for parallax technique
56
What indications would you take occlusal radiographs in orthodontic assessment?
Assess displaced/unerupted teeth using parallax
57
Why would you take DPT radiographs in orthodontic assessment?
Assess presence, position and pathology of successors | Used in the parallax technique
58
When would you use CBCT in orthodontics?
Determine position of unerupted teeth that require surgical removable Accurate assessment of root resorption risk
59
What is the parallax technique?
Use of two radiographs at different views, whereby there is movement of the tube head
60
What is horizontal parallax
Two radiographs at a different horizontal angle, but within the same vertical angulation
61
What is vertical parallax
Two radiographs taken at different vertical angulations
62
List examples of horizontal parallax
Two PAs at different positions horizontally | USO and ULO
63
List examples of vertical parallax
PA and USO DPT and USO DPT and PA?

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