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BDS3 CLINICAL Ortho > Etiology of Malocclusion 1 > Flashcards

Etiology of Malocclusion 1 Flashcards

1
Q

What are the 3 tissue types that we need to consider when thinking of malocclusions

A

skeletal
muscular
dentoalveolar

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2
Q

What are the general skeletal etiological factors

A

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

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3
Q

What are the general muscular etiological factors

A

form and function of the muscles that surround the teeth i.e lips, cheeks and tongue

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4
Q

What are the general dentoalveolar aetiolgoical factors

A

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

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5
Q

What are the components of the facial skeleton

A

maxillary & mandibular bases

maxillary and mandibular alveolar processes (carry teeth)

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6
Q

What is the maxillary complex attached to

A

anterior cranial base

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7
Q

What is the mandibular complex articulating with

A

glenoid fossa of the posterior cranial base

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8
Q

What does facial variation result in

A

differences in the size, shape of the maxilla, mandibular and alveolar processes and their relationship to each other in all 3 planes of space

variation in the size and angle of the cranial base causing a difference in the relative position of the mandible

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9
Q

What does malocclusion result from

A

disharmony between the components of the facial skeleton

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10
Q

What are the 3 planes that facial variation can occur

A

antero-posterior
vertical
transverse

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11
Q

What is the etiology of skeletal variation

A

genetic and environmental factors

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12
Q

What features of malocclusion are hereditary

A

class 3

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13
Q

What are possible environmental factors that can result in malocclusion

A

masticatory muscles
mouth breathing
head posture

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14
Q

What is a class 1 antero-posterior relationship

A 
mandible related normally to maxilla such the teeth erupt into class 1 occlusion 
jaws usually correctly sized but may have bimaxillary protrusion or recursion
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15
Q

What is the normal cranial base angle

A

130-135 degrees

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16
Q

What is lateral cephalometry

A

standardized lateral radiographs of the face and base of the skull

reproducible - patient is positioned in a cephalostat a set distance from the one and the film

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17
Q

What is cephalometry

A

analysis and interpretation of these radiographs

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18
Q

What is the radiographic technique

A 
ALARA - soft tissue filter
thyroid collar
triangular collimation
rare earth screen
lanes screen
fastest film possible
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19
Q

How is cephalometry analysis done

A

hand traced onto paper

digitized using a computer

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20
Q

What is the SNA

A

relates maxilla to anterior cranial base

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21
Q

What is the SNB

A

relates mandible to anterior cranial base

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22
Q

What is the ANB

A

relates mandible to maxilla

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23
Q

In class 1 what is the SNA

A

avg 81 degrees

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24
Q

In class 1 what is the SNB

A

avg 78

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25
Q

In class 1 what is the ANB

A

avg 3

26
Q

What is the class II antero-posterior relationship

A 
mandible placed posteriorly relative to maxilla
teeth erupt into post-normal class II occlusion
27
Q

What are causes of class II

A

mandible too small (most commonly) or maxilla too large or combo
mandible normally sized but placed too far back due to obtuse cranial base angle

28
Q

What is the SNA in class II

A

usually average but may be increased if the maxilla is prognathic

29
Q

What is the SNB in class II

A

usually decreased as mandible is further back

30
Q

What is the ANB in class II

A

> 5 so outside of the standard deviation

31
Q

What is a class III anterior posterior relationship

A

mandible placed anteriorly relative to maxilla

tooth rust into pre-normal occlusion (class III)

32
Q

What is the cause of class III

A

maxilla is too smalll (most commonly, mandible is too large or combination of both

normally sized jaws but mandible positioned too far forward due to acute cranial base angle

33
Q

What is the SNA in class III

A

decreased if maxilla is deficient

34
Q

What is the SNB in class III

A

often average but may be increased if mandible is prognathic

35
Q

What is the ANB

A

<1 or negative

36
Q

What is dentoalveoalr compensation

A

the dents-alveolar structures underlying discrepancy

forces from the lips, cheeks and tongue tend to incline teeth towards a position of soft tissue balance

37
Q

What are the clinical values we look at when looking at the vertical jaw relationship

A

Frankfurt and mandibular plane

the two normally meet at the external occipital protuberance

38
Q

What is the frankfurt plane

A

lower orbital rim to superior border of external auditory meatus

39
Q

What is the mandibular plane

A

lower border of the mandible

40
Q

What is the upper anterior face height

A

brow ridge (glabella) to base of nose

41
Q

What is the lower anterior face height

A

base of nose (sub nasal) to inferior aspect of the chin

42
Q

What is the average ratio of LAFH to TAFH

A

50%

43
Q

What is the average value of FMPA

A

27 degrees

44
Q

On a lateral ceph where is the frankfurt plane

A

(orbitale to porion)

45
Q

On a lateral ceph where is the mandibular plane

A

(menton to gonion)

46
Q

What is the upper anterior face height on the lateral ceph

A

nasion to anterior nasal spine

47
Q

What is the lateral anterior faec height on the lateral ceph

A

anterior nasal spine to mention

48
Q

What is the average value of LAFH to TAFH

A

55%

49
Q

What is the LAFH to TAFH proportion for a long facial type

A

> 55%

50
Q

What is the FMPA for a long facial type

A

<31 degrees

51
Q

What is a long facial type

A

steeply inclined mandibular plane

backward mandible growth rotation

anterior open bite tendency

52
Q

What is a short facial type

A

tendency to parallelism of jaws
forward mandibular growth rotation
deep overbite tendency

53
Q

What is the LAFH to TAFH proportion in short facial type

A

<55%

54
Q

What is the TAFH proportion in in short facial type

A

<23 degrees

55
Q

What can arch width discrepancies (transverse) result from

A

disproportion of maxillary and mandibular dental arches
causes unilateral or bilateral buccal segment cross bitse
often exaggerated by anteroposterior discrepancies

56
Q

How does mandibular displacement occur

A

occurs where inter-arch width discrepancy causes upper and lower posterior teeth to meet cusp to cusp
mandible forced to deviate to one side to achieve position of inter-cuspation
possible association with TMD

57
Q

What are dental causes of facial asymmetries

A

displacement of normal mandible due to unilateral cross bite

58
Q

What is a true mandibular asymmetry

A

hemi mandibular hyperplasia/elongation

condylar hyperplasia

59
Q

What is dentoalveolar disproportion

A

discrepancy between size of teeth and jaws

60
Q

What is crowding caused by

A

small jaws and normally sized teeth

large teeth - macrodontia

61
Q

What is spacing caused by

A 
large jaws, normally sized teeth
small teeth (microdontia)

BDS3 CLINICAL Ortho (11 decks)

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