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My BDS3 > Orthodontics - Atieology of Malocclusion > Flashcards

Orthodontics - Atieology of Malocclusion Flashcards

1
Q

what are the general aetiological factors of malocclusion?

A

Skeletal - size, shape and positions of the upper and lower jaws

Muscular - Form and function of muscles surrounding the teeth i.e. lips, cheeks, tongue

Dentoalveolar - Size of the teeth in relation to size of the jaw

(genetically and environmentally influenced too)

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2
Q

name the 3 skeletal planes.

A

Antero-postero
Vertical
Transverse

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3
Q

list the cephalometrics for a class I antero-postero relationship.

A

SNA relates maxilla to the anterior cranial base
Average value is 81 degrees ( +/- 3)

SNB relates mandible to the anterior cranial base
Average value is 78 degrees ( +/- 3)

ANB relates the mandible to the maxilla
Average value is 3 degrees ( +/- 2)

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4
Q

what causes a class II antero-postero relationship? (3)

A

Class II = maxilla >3mm in front

Mandible is too small (common) or maxilla is too large or both

obtuse cranial base = Mandible can be normal sized but placed too far back

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5
Q

list the cephalometrics for a class II antero-postero relationship.

A

SNA relates maxilla to the anterior cranial base
Average value is 81 degrees ( +/- 3)
For class II its usually average but can be increased if the maxilla is prognathic

SNB relates mandible to the anterior rnaial base
Value usually decreased ( < 78 degrees)

ANB relates the mandible to the maxilla
> 5 degrees (increase from average)

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6
Q

what causes a class III antero-postero relationship? (3)

A

Class III = maxilla < 2-3mm in front (behind the mandible)

Maxilla is too small (common) or mandible is too large or both

acute cranial base = Normal sized jaws but placed too far forward due to an

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7
Q

list the cephalometrics for a class III antero-postero relationship.

A

SNA = < 81 decreased if the maxilla is deficient

SNB = Value usually average (78 degrees) but can be increased if the mandible is prognathic

ANB relates the mandible to the maxilla
< 1 degrees or negative

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8
Q

what is dento-alveolar compensation?

A

where the surrounding dente-alveolar structures disguise the underlying discrepancy

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9
Q

name the planes used to assess the vertical jaw relationship. (2)

A

Frankfort plane

mandibular plane

(Both used to Create the Frankfort mandibular plane angle)

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10
Q

what is the average clinical value of the frankfort mandibualr plane angle?

A

27 degrees (+/- 4)

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11
Q

what is the clinical value of the frankfort mandibualr plane angle in an individual with a long face?

A

31 degrees

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12
Q

what kind of occlusion does an individual with a long face commonly have?

A

AOB

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13
Q

what is the clinical value of the frankfort mandibualr plane angle in an individual with a short face?

A

< 23 degrees

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14
Q

what kind of bite does an individual with a short face commonly have?

A

deep overbite (and parallelism of jaws)

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15
Q

what is the lower anterior face height to total anterior face height proportion in an individual with a long face?

A

55%

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16
Q

what is the lower anterior face height to total anterior face height proportion in an individual with a short face?

A

< 55%

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17
Q

when does mandibular displacement occur?

A

When there is inter-arch width discrepancies that cause the upper and lower cusps to meet
- mandible has to deviate to one side to avoid this

Associated with TMJ disease

18
Q

what are dental causes of facial asymmetry?

A

Displacement of the mandible due to unilateral cross-bites

19
Q

how do we measure the vertical plane?

A

FMPA - Frankfort mandibular plane angle

20
Q

what can cause inter-arch width discrepancies, mandibular deviation and consequently unilateral posterior crossbites?

A

digit sucking

21
Q

list the local causes of malocclusion. (5)

A

variation in tooth number
- supernumerary and hypodontia

variation in tooth size and from
- macrodontia and microdontia

variation in tooth position
- ectopic

abnormalities of the surrounding soft tissues
- tongue thrust, digit sucking, frenum attachments

local pathology

22
Q

list the types of supernumerary teeth (4)

A

conical

odontome

supplementary

tuberculate

23
Q

where are supernumary teeth more common?

A

anterior maxilla

24
Q

What gender are more prone to supernumerary teeth?

A

males

25
Q

which supernumerary tooth is the main cause of failure of the permanent tooth to erupt?

A

tuberculate

26
Q

What supernumerary teeth are known as mesiodents?

A

Conical - erupt near the midline

27
Q

what supernumerary teeth have normal tooth morphology?

A

Supplemental

28
Q

what teeth are commonly affected by hypodontia? (2)

A

upper laterals

upper second premolars

29
Q

what is the causes of retained baby teeth

= malocclusion)? (7

A

Absent successor

Ectopic successor

dilacerated successor

Ankylosed primary molars

Dentally delayed development

Pathology

supernumerary

30
Q

What is an infra-occluded tooth?

What is this caused by?

A

The process where a tooth fails to achieve or maintain its occlusal relationship with adjacent teeth

Temporary ankylosis - Root is fused to the bone

31
Q

How long should there be between shedding of the tooth and the contra-lateral tooth?

A

6 months

32
Q

when primary teeth are lost prematurely what is crowding dependant on? (3)

A

Which tooth was extracted

When the tooth was extracted

Crowding at present

33
Q

what is a balancing extraction?

A

By extracting a tooth from the other side of the same arch

i.e. if u take out a right canine remove a left canine

34
Q

what is a compensating extraction?

A

By extracting a tooth from the opposing arch of the same side
i.e. if you remove an upper 6 remove the lower 6

35
Q

Which teeth require balancing/compensating extractions and why? (2)

A

Canines = balancing extraction as unilateral loss can cause centreline shifts
(if upper right is lost, remove the upper left)

Molars = only lower molars need compensation

36
Q

when is it acceptable for 6’s to be lost (in mandible specifically)?

A

6s are ideally lost by the time the bi-furcation if the 7’s have developed

37
Q

at what age do we check for a palpable canine bulge?

A

9 years old

38
Q

what do we assess for on a radiograph of a delayed/missing/ectopic C? (3)

A

presence, position and pathology

39
Q

How do we clinically assess ectopic 3’s? (4)

A

Visualisation/palpation of the labial bulge
assess Inclination of the 2
Mobility or the C or 2 - from root resorption
Colour of the C or 2 - from root resorption

40
Q

Wha are the impact of digit sucking? (4)

A

Proclined upper incisors

Retroclined lower incisors

Localised Anterior open bits

Unilateral posterior cross bite from the Constriction/prevention of transverse growth of the maxilla

41
Q

describe the 2 types of tongue thrust.

A

Endogenous - medical issues i.e. downs syndrome, macroglossia

Exogenous - habit (must be stopped before treatment is done)

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