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BDS3 Orthodontics > Aetiology of Malocclusion > Flashcards

Aetiology of Malocclusion Flashcards

1
Q

What are the components of the facial skeleton?

A
  • maxillary base
  • mandibular base
  • mandibular and maxillary alveolar processes
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2
Q

Malocclusion aetiological factors

A
  • skeletal: size, shape and relatively positions of upper and lower jaws
  • muscular: form and function of muscles that surround the teeth e.g. lips, cheeks and tongue
  • dentoalveolar: size of the teeth in relation to the size of the jaws
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3
Q

components of the facial skeleton

A
  • mandibular base
  • maxillary base
  • maxillary and alveolar processes
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4
Q

aetiology of skeletal variation

A

genetic factors
environmental factors
- masticatory muscles
- mouth breathing
- head posture

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5
Q

Class 1 AP definition

A
  • mandible related normally to maxilla
  • jaws are correctly sized
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6
Q

What is a class II occlusion?

A
  • anteroposterior relationship
  • mandible placed posteriorly relative to maxilla
  • mandible too small (most common) or maxilla too large or both
    OR
  • mandible normally sized but placed too far back due to obtuse cranial base angle
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7
Q

What is the SNA?

A

-sella-nasion A point angle
-relates the maxilla to anterior cranial base
avg value 81 +/- 3 degrees

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8
Q

What is the SNB?

A

-Sella-nasion B point angle
-relates the mandible to the anterior cranial base
avg value 78 +/- 3 degrees

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9
Q

What is the ANB

A
  • A-point-nasion B-point angle
  • relates the mandible to maxilla
    avg value 3 degrees +/- 2
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10
Q

What are the cephalometric of a class II occlusion?

A
  • SNA usually average
  • SNB usually decreased
  • ANB> 5 degrees
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11
Q

What are the features of a class III occlusion?

A
  • mandible placed anteriorly relative to maxilla
  • maxilla too small (most common) or mandible too large or both
  • or normally sized jaws but mandible positioned too far forwards as a result of acute cranial base angle
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12
Q

outline the cephalometrics of a class III occlusion

A
  • expect SNA to be decreased
  • SNB often average
  • ANB <1 degrees or negative
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13
Q

In what ways does the facial skeleton vary?

A
  • antero-posterior
  • vertical
  • transverse
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14
Q

What are the planes looked at when assessing the vertical jaw relationship?

A

Frankfort plane
- lower orbital rim to superior border of external auditory meatus

Mandibular plane
- lower border of mandible

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15
Q

where do the mandibular and Frankfort planes usually meet at?

A

the external occipital protuberance

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16
Q

What are the borders for the upper and lower anterior face heights?

A

Upper anterior face height
- brow ridge to base of nose

Lower anterior face height
- base of nose to inferior aspect of chin

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17
Q

What is the average ratio of the lower anterior face height to the total anterior face height?

A

55%

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18
Q

What is the average value of the FMPA (Frankfort-mandibular plane angles)?

A

27 +/- 4 degrees

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19
Q

What are the features of a short facial type?

A
  • LAFH to TAFH <55%
  • FMPA < 23 degrees
  • deep overbite tendency
  • tendency to parallelism of jaws
20
Q

What is meant by the term ‘arched width discreptancies’?

A
  • disproportional mandibular and maxillary dental arches
  • leads to unilateral or bilateral buccal segment cross-bites
  • often exaggerated by anteroposterior discreptancies
21
Q

What is mandibular displacement?

A
  • occurs where inter-arch width discrepancy causes upper and lower posterior teeth to meet cusp to cusp
  • mandible forced to deviate from one side to achieve position of inter-cuspatiion or centric occlusion
  • may be associated with TMD
22
Q

What is dento-alveolar disproportion?

A

Discrepancy between size of teeth and jaws

23
Q

What causes crowding?

A
  • small jaw, normal sized teeth
    OR
  • large teeth (macrodontia)
24
Q

what causes spacing in the dentition?

A
  • Large jaws, normal sized teeth
    OR
  • small teeth (microdontia)
25
Q

What is the prevalence of malocclusion?

A

68%

26
Q

What is meant by a ‘local’ cause of malocclusion?

A

a localised problem or abnormality within either arch, usually confined to one, two or several teeth producing a malocclusion.
- tend to get worse with time

27
Q

Give some examples of local causes of malocclusion

A
  • variation in tooth number
  • variation in tooth size or form
  • abnormalities of tooth position
  • local abnormalities of soft tissues
  • local pathology
28
Q

What is a supernumerary tooth?

A
  • a tooth or tooth-like entity which is additional to the normal series
  • most common in anterior maxilla
  • more common in males
29
Q

what is the prevalence of a supernumerary tooth?

A
  • 1% in primary dentition
  • 2% in permanent dentition
30
Q

What is an ectopic tooth?

A

A tooth that is not located at the dental arch

31
Q

What is the prevalence of an ectopic maxillary canine?

A

1-3% of population
80% palatal

32
Q

How to do you check for an ectopic maxillary canine?

A
  • check for palpable buccal canine bulge from age 9 onwards
33
Q

what radiographs can be used to asses a possible ectopic canine?

A
  • OPT
  • Upper anterior oblique occlusal
34
Q

hypodontia definition

A

developmental absence of one or more teeth

35
Q

Factors causing a variation in tooth number

A
  • supernumerary teeth
  • hypodontia
  • retained primary teeth
  • early loss of primary teeth
  • unscheduled loss of permanent teeth
36
Q

Why might a primary tooth be retained?

A

absent successor
ectopic or dilacerated successor
ankylosed primary molars
dentally delayed in terms of development
pathology/supernumerary

37
Q

absent successor - management

A
  • maintain primary tooth as long as possible if good prognosis
    OR
  • extract deciduous tooth early to encourage spontaneous space closure in crowding cases

early orthodontic referral for advice

38
Q

early loss of primary teeth - possible causes

A

trauma
periapical pathology
caries
resorption by successor

39
Q

Balancing extraction - what does this mean?

A
  • extracting a tooth from the opposite side of the same arch
  • in order to minimise midline shift
40
Q

compensating extraction - what does this mean?

A
  • extracting a tooth from the same side of the opposing arch
  • in order to maintain occlusal relationship
41
Q

early loss of canines - management

A
  • consider balancing extraction
  • early loss in crowded arch can give centre line shift
  • some mesial drift of buccal segments
42
Q

early loss of molars - management

A
  • more space loss with Es than ds
  • more space loss in uppers
  • 6s can drift mesially and steal 5 space
43
Q

Factors influencing impact of loss of 6s

A

age at loss
crowding
malocclusion

44
Q

Age at loss of 6s - significance

A

upper arch = less important

lower arch:
- if 7s erupted (late) = poor space closure likely
- if extraction too early = distal drift of 5s, especially if Es lost at the same time as 6s

45
Q

unscheduled loss of central incisors - effect

A
  • depends on timing
  • early = drift of adjacent teeth
  • late = long term space
46
Q

unscheduled loss of central incisors - management

A
  • ideally maintain space
  • re implant
  • simple denture
    definitive prosthesis to deal with space long term
47
Q

POA if lateral incisor drifts to fill space from loss of upper incisor

A
  • reopen space for prosthesis
  • or build up lateral

BDS3 Orthodontics (10 decks)

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