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BDS3 Orthodontics > Aetiology of Malocclusion - Skeletal Elements > Flashcards

Aetiology of Malocclusion - Skeletal Elements Flashcards

1
Q

where is malocclusion most common

A

western developed countries - mix of gene pools from different populations

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2
Q

what are the general factors to malocclusion

A

skeletal
muscular
dento-alveolar

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3
Q

what does the skeletal aspect of malocclusion mean

A

size, shape and relative positions of the upper and lower jaws

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4
Q

what does the muscular aspect of malocclusion mean

A

form and function of the muscles that surround the teeth - lips, cheeks and tongue

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5
Q

what does dentoalveolar aspects of malocclusion mean

A

size of the teeth in relation to the size of the jaws

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6
Q

what are the components of the facial skeleton

A

maxilla (attached to anterior cranial base)
mandible (articulates with posterior cranial base)
maxillary and mandibular alveolar processes

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7
Q

what aspects affect the transverse facial variation

A

width of the jaws
width of cranial base

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8
Q

what causes variation in facial skeleton

A

genetic and environmental factors
hereditary

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9
Q

what occlusion class is hereditary

A

class III

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10
Q

what are possible environmental factors of skeletal facial variation

A

masticatory muscles
mouth breathing
head posture

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11
Q

what are the three planes of space for facial skeletal examination

A

AP
transverse
vertical

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12
Q

what is a class I AP relationship

A

mandible related normal to maxilla such that the teeth erupt in class I - slight convex profile

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13
Q

what are lateral cephalograms

A

standardised radiographs of the face and base of skull
they are reproducible

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14
Q

what is the technique for a lateral cephalogram

A

frankfort plane horizontal

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15
Q

what is the eastman analysis

A

AP and vertical values from a lateral cephalostat that is recorded

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16
Q

what is the SNA angle of a lateral cephalogram

A

the SNA is the angle between the sella turcica (S), the (A) maxi concavity above upper incisor (B) is max concavity below bottom incisor

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17
Q

what is the SNA of a normal occlusion

A

3

18
Q

what are reasons for a class II jaw relationship

A

mandible too small or maxilla too large
mandible normal sized but placed too far back due to obtuse angle of cranial base

19
Q

what are the values usually for a class II

A

SNA close to normal
SNB decreased

20
Q

what are reasons for the jaws to be in class III occlusion

A

maxilla too small or mandible too large
normal sized jaws but mandible placed too far forwards

21
Q

what are the values for a class III relationship

A

SNA decreased if maxilla deficient
SNB normal or increased if mandible prognathic

22
Q

what is dento-alveolar compensation

A

soft tissues disguise skeletal discrepancies by tilting teeth towards one another

23
Q

what reference planes do you need to look at vertical relationship of jaws

A

Frankfort plane (lower orbital rum to superior border of EAM)
mandibular plane

24
Q

where does the Frankfort plane and mandibular plane ususally meet

A

external occipital protuberance

25
Q

what proportional measurements do you look at in vertical jaw relationship

A

upper anterior face height
lower anterior face height

26
Q

what should the ratio of UAFH to LAFH be

A

equal (50-50)

27
Q

what is the gonion

A

angle of mandible

28
Q

what should be the angle between the Frankfort plane and mandibular plane in a normal jaw relationship

A

27 degree

29
Q

what would happen to the frankfort plane - mandibular plane angle in a long face

A

increased

30
Q

what would happen to the frankfort plane - mandibular plane angle in a reduced face

A

decreased

31
Q

what does transverse jaw relationship look at

A

disproportion of maxillary and mandibular arch sizes - deals with crossbites

32
Q

what is posterior cross bite most often associated with

A

class III malocclusion

33
Q

what is mandibular displacement

A

occurs when inter-arch width discrepancies causes upper and lower teeth to meet cusp to cusp and the mandible is forced to deviate to achieve position of inter-cuspation

34
Q

what is dento-alveolar compensation in transverse plane

A

eg upper molars flare out and lower molars roll in due to small maxilla

35
Q

what are causes of asymmetry

A

dental
true mandibular asymmetry

36
Q

what is dental cause of asymmetry

A

displacement of normal mandible due to unilateral cross bite

37
Q

what are causes of true mandibular asymmetry

A

hemi-mandibular hyperplasia/ elongation
condylar hyperlasia

38
Q

what is dento-alveolar disproportion

A

discrepancy between size of teeth and jaws

39
Q

what can cause crowding

A

large teeth and small jaws

40
Q

what can cause spacing

A

large arch and small teeth

BDS3 Orthodontics (9 decks)

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