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Ortho > Aetiology of malocclusion > Flashcards

Aetiology of malocclusion Flashcards

1
Q

What are the three main factors that contribute to occlusal development

A

Skeletal factors
Soft tissue factors
Dentoalvolar factors

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2
Q

Environmental factors affecting occlusion

A

Habits

Early loss or trauma of primary tooth

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3
Q

What are the three planes

A

Anteroposterior
Vertical
Transverse

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4
Q

Describe class I skeletal anteroposterior pattern

A

Maxilla and mandible are in the correct position with respect to the cranial base

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5
Q

Describe class II skeletal anteroposterior pattern

A

Mandible positioned more posteriorly than ideal

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6
Q

What can contribute to a class II skeletal AP pattern

A
  • Mandibular retrognathia or a small mandible

- Maxillary prognathia

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7
Q

Describe class III anteroposterior skeletal pattern

A

Mandible in occlusion is positioned more anteriorly relative to the maxilla

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8
Q

What contributes to a class III skeletal anteroposterior pattern

A

Retrognathia maxilla
Large mandible
Prognathic mandible
Combination

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9
Q

What causes increased vertical dimensions of the face

A

High gonial angle
Posterior (clockwise) growth of the mandible
Vertical maxillary excess

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10
Q

What occlusal discrepancies can occur due to an increased facial height

A

Incomplete overbite

AOB

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11
Q

What causes decreased vertical dimensions of the face

A

Low gonial angle

Anterior (anti-clockwise) growth of the mandible

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12
Q

What does vertical maxillary excess lead to

A

Increased facial height and chin point retrusion

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13
Q

What is the ideal transverse skeletal relationship

A

Maxilla slightly larger than mandible allowing for the normal buccal overjet of 2-4mm

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14
Q

Describe the two transverse discrepancies and their causes

A

Buccal posterior crossbite due to narrow maxilla or wide mandible
Lingual crossbite due to wide maxilla or narrow mandible

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15
Q

Describe the equilibrium between teeth and muscles

A

The muscular forces acting directly on the teeth must be in balance in order to maintain a stable position

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16
Q

What is the neutral zone

A

Where the forces of the lips and cheeks (outside) are balanced by the forces of the tongue (inside)

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17
Q

What are the soft tissues that affect the occlusal development

A

Lips, tongue, adenoids and PDL

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18
Q

What features of the lips can influence occlusion

A

Size
Form / fullness
Seal
Lip line

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19
Q

Occlusion associated with full, everted lips

A

Bimaxillary proclination

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20
Q

What type of lip form results in retroclined lower incisors

A

Tense lips

Strap like lips

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21
Q

Describe the cause of strap like lips

A

Hyperactive mentalis muscle

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22
Q

What is lip incompetence

A

Lips do not meet at rest

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23
Q

What are potentially competent lips

A

Lips who are able to come together with slight circumoral muscle activity

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24
Q

What are the types of adaptive swallowing mechanisms in incompetent lips

A

Circumoral lip to lip
Tongue to lip
Lower lip to palate

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25
Q

What does lip incompetence result in

A

Proclination of the incisors due to tongue positioned anteriorly

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26
Q

What type of adaptive seal is associated with class III

A

Tongue to upper lip

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27
Q

Define lip line

A

The level at which the lower lip meets the upper incisors in normal function

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28
Q

What is the ideal lip line

A

Lower lip should cover the lower incisal 1/3rd of the labial surface of the upper incisors at rest

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29
Q

What is a lip trap?

What malocclusion is it associated with?

A

Lower lip is positioned behind the upper incisors at rest (CLASS2/1)

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30
Q

How does macroglossia influence occlusion

A

Large tongues rest on the front teeth causing bimaxillary proclination which can cause AOB or incomplete overbite

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31
Q

How does loss of PDL influence tooth position

A

Loss of PDL in perio disease results in loss of equilibrium resulting in spacing, extrusion, tilting, incr OJ

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32
Q

How do large adenoids affect breathing

A

Obstructed nasal breathing resulting in mouth breathing

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33
Q

What can large adenoids/mouth breathing influence

A

It can affect skeletal pattern

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34
Q

How does mouth breathing affect occlusion?

A

Head tilts upwards slightly therefore tongue position drops and cheek pressure is unopposed

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35
Q

What are the typical features of adenoid facies?

A 
Increased vertical dimension 
Backward rotation of the mandible 
Narrow maxilla / posterior crossbite 
Reduced overbite 
Narrow nose
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36
Q

What effect can digit sucking have on the dentition

A
  • Proclined upper incisors with increased overjet
  • +/- Retroclined lower incisors
  • Asymmetrical AOB or incomplete overbite
  • Narrow maxilla with a unilateral buccal crossbite
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37
Q

How does digit sucking narrow the maxilla

A

Increased buccal pressure on the buccal aspects of the teeth resulting in lateral displacement of the mandible into ICP (buccal xbite)

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38
Q

What does the effect of digit sucking on occlusion depend on

A

Age of patient
Frequency during the day
Manner in which the digit is sucked

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39
Q

How many hours a day is digit sucking required to have a significant effect

A

> 6 hours a day

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40
Q

What is an example of an iatrogenic environmental factor affecting occlusion

A

Poorly designed mouth gaurds allowing 7s to over erupt forming an AOB

41
Q

List local dental aetiological factors of malocclusion

A
  • Abnormal tooth number
  • Abnormal tooth size
  • Abnormal tooth position
  • Abnormalities in local soft tissue
  • Habits
42
Q

List factors affecting tooth number

A

Hypodontia
Premature primary tooth loss causing impaction
Supernumerary teeth

43
Q

What are the potential effects of supernumerary teeth

A
  • Failure of eruption
  • Displacement of unerupted tooth
  • Crowding with supplementals
  • No effect if unerupted
  • Cystic transformation
  • Root resorption
44
Q

Management of a supernumerary tooth preventing eruption of a permanent tooth

A

Surgical removal of the supernumerary tooth

Exposure of the permanent tooth with gold chain placement to move it into position

45
Q

Management of supplemental teeth causing crowding

A

Removal the tooth which is most poorly formed or displaced

46
Q

Why should unerupted supernumeraries be monitored

A

Resorption of roots

They have potential for cystic formation (monitor for radiographic signs of follicular enlargement)

47
Q

What dental anomalies are associated with hypodontia

A
  • Impacted upper canines
  • Delayed dental development
  • Microdontia
  • Retained primary teeth
  • Reduced LFH and incr overbite
  • Ectodermal dysplasia (anodontia)
48
Q

Significance of hypodontia in class III patients

A

Space closure in a labial segment may compromise the incisor relationship further

49
Q

Significance of hypodontia in class II div 1

A

Space closure in the labial segment may aid overjet reduction

50
Q

Tx options for hypodontia

A
  • Do nothing
  • Maintain or redistribute space and place restoration
  • Ortho space closure and disguise adjacent teeth
51
Q

What is Kesling’s trial set up used for

A
  • Assess feasibility for treatment options in hypodontia

- Show teeth after ortho tx

52
Q

In which instances does premature loss of a primary tooth have a greater effect?

A
  • Crowded dentitions
  • Maxillary tooth
  • Younger patients
  • the type of tooth lost
53
Q

In general, when is more space lost when a primary tooth is lost prematurely

A

Maxilla > mandible

E > D

54
Q

Effect of early loss of primary incisors

A

Minimal impact on occlusion

Possibly some space loss in crowded dentitions

55
Q

Effect of early loss of primary canine

A

If unilateral loss = centre line shift to affected side in crowded dentitions
- Space loss for permanent canines

56
Q

Management of early loss of primary canines

A
  • Balanced extractions in crowded dentitions to avoid loss of centreline
57
Q

Effect of premature loss of primary first molar (Ds)

A
  • Small centre line shift in crowded dentitions
  • Mesial movement of E and 6 without rotation or tilting
  • Space loss for canines in the maxilla
  • Space loss for canines or 4s in the mandible
58
Q

Management of premature loss of Ds

A
  • Balancing extractions

- Space maintainers

59
Q

Effects of premature loss of second primary molar (Es)

A
  • Little effect on centreline
  • Mesial drift of molars with space loss
  • If 6s unerupted, they will erupt anteriorly
  • If 6s erupted - there is mesial tipping, rotation and impaction of 5s
60
Q

Management of premature loss of Es

A

Space maintainers in all but spaced arches

61
Q

List causes of abnormally placed teeth

A

Abnormal position of crypts
Infraoccluded teeth
Transposition
Displaced (e.g. due to crowding)

62
Q

What would indicate an abnormal position of crypts

A

Displaced or rotated crypts

63
Q

What are the occlusal complications of infraoccluded teeth

A

Tipping of adjacent teeth
Deviation of dental centreline to affected side due to stretching of transseptal fibres
Inhibition of vertical development of adjacent teeth

64
Q

What is transposition

A

Position of the teeth are interchanged

65
Q

Which teeth are commonly transposed

A

Maxillary canines and first premolars

66
Q

Which teeth are commonly impacted

A

Maxillary canines
Second premolars (upper and lower)
Maxillary central incisors

67
Q

What is the aetiology of displaced/impacted teeth

A
  • Abnormal position of tooth germ
  • Crowding
  • Retention of primary tooth
  • Presence of supernumerary
  • Presence of pathology e.g. cyst
68
Q

Management of a displaced tooth

A

If mild - extract primary + space maintain, surgical exposure of displaced tooth with traction
If severe - extract tooth

69
Q

Which teeth become displaced if crowding is the aetiology

A

The last tooth in the series - upper 2s, upper 3s, 5s and 8s

70
Q

Management of displaced teeth due to crowding

A

Relief of crowding and active tooth movement

If severe, extract

71
Q

What is the prevalence of ectopic upper canines

A

2%

72
Q

Where can a canine be deflected in severe displacement

A

Horizontally near the floor of the nose

73
Q

What are ectopic canines associated with

A

Small or absent lateral incisors

74
Q

Management for ectopic canines

A
  • Remove retained C for spontaneous repositioning
  • if mild - extract upper 4s to provide space
  • If severe - surgical exposure and traction OR surgical transplantation OR surgical extraction
  • Leave it
75
Q

Describe surgical transplantation of ectopic canines

A

The displaced canine is surgically removed and splinted in position for 2-3 weeks

76
Q

Disadvantages of surgical transplantation of ectopic canines

A

Space needs to be present in the arch

There is 50% risk of root resorption

77
Q

When is extraction of ectopic canines indicated

A

Poor prognosis e.g. poorly formed crown or root

No other option is feasible

78
Q

DELETE

A

Microdontia
Macrodontia
Crowding
Spacing

79
Q

What is microdontia linked to

A

Hypodontia

Microdontia upper lateral with ectopic upper canine

80
Q

What is macrodontia linked to

A

Supernumerary teeth

81
Q

What is crowding a manifestation of

A

Dentoalveolar disproportion (mismatch between tooth size and jaw)

82
Q

What is the aetiology of crowding

A
  • Genetics determining dentoalveolar proportions

- Environmental factors/local - early loss of primary teeth, supernumerary teeth, megadontia

83
Q

What are the types of crowding

A

Primary - inherent discrepancy in tooth size to jaw size
Secondary - to environmental factors
Tertiary - late lower incisor crowding

84
Q

What is the severity classification of crowding

A

Mild <4mm
Moderate 5-9mm
Severe >9mm

85
Q

Tx options for mild crowding

A
  • Arch expansion using a fixed appliance (common)
  • Interproximal stripping
  • Molar distalisation with headgear (not common)
  • NO EXTRACTIONS
86
Q

Tx options for moderate-severe crowding

A
  • Extractions to relieve crowding
87
Q

What influences extraction pattern in treatment of moderate-severe crowding

A
  • Quality/prognosis of teeth
  • Severity and location crowding
  • Anchorage requirements
88
Q

Anchorage requirements in extraction basis for crowded teeth

A
  • If more space required anteriorly - extract 4s

- If space required posteriorly - extract 5s

89
Q

What are the best conditions allowing for spontaneous movement of teeth following relief from crowding (Extractions)

A
  • Growing child
  • Extractions occured just prior to eruption of adjacent tooth
  • Adjacent teeth are positioned favourably (upright)
  • No occlusal interferences
90
Q

Aetiology of spacing

A
  • Tooth missing in a well developed arch due to hypodontia, premature loss, displacement
  • Microdontia is a well developed arch
  • Midline diastema
  • Dentoalveolar disproportion (rare)
91
Q

Treatment of spacing

A
  • Orthodontic space closure

- Redistribute spacing posteriorly and restore with bridges

92
Q

Where is the labial frenum attached in infancy

A

To the crest of the alveolar ridge in the midline between the central incisors

93
Q

What happens to the labial frenal attachment with dentoalveolar growth

A

Attachment becomes higher with no influence on tooth position

94
Q

How do diastemas close in children

A

Eruption of canines as the attachment migrates labially to the attached mucosa

95
Q

What will indicate frenal aetiology of a midline diastema

A
  • Blanching of incisive papilla if tension applied to frenum
  • Radiograph showing V shaped notch at the crest in the alveolar bone
96
Q

Tx options for midline diastema

A
  • Wait for canines to erupt
  • Accept diastema
  • Fixed appliance +/- frenectomy and permanent retention
97
Q

Why does late lower incisor crowding occur

A

Intercanine width increases up until 12-13 and then starts to decrease gradually throughout adulthood thus incr any pre-existing labial crowding or producing new crowding

98
Q

Factors causing tertiary crowding

A
  • Forward growth of the mandible
  • Maturation of soft tissues
  • Mesial migration of posterior teeth due to interseptal fibres
  • Presence of erupting 8s pushing teeth anteriorly
  • 8s preventing anterior pressure being dissipated distally around the arch

Ortho (20 decks)

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