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Ortho > Class III > Flashcards

Class III Flashcards

1
Q

What is the prevalence of class III in the UK population?

A

<5%

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2
Q

What is the AP skeletal relationship in class III?

A
  • Majority have a class III skeletal base

- Most important aetiology

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3
Q

List the causes of the class III AP skeletal pattern

A
  • Increased mandibular length / acute cranial base angle due to anteriorly positioned glenoid fossa
  • Reduced maxillary length (maxillary retrusion)
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4
Q

How does an acute cranial base angle / incr mandibular length result in a class III malocclusion

A

Glenoid fossa is placed anteriorly = condylar head is placed anteriorly
Therefore mandible is prognathic relative to the maxilla

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5
Q

Describe the vertical skeletal pattern in class III

A

Ranges - LFH can be increased, normal or reduced

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6
Q

What does forward rotation of the jaw lead to in class III patients

A

Chin prominence

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7
Q

Soft tissue factors in class III

A
  • Very small role in aetiology
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8
Q

How can soft tissues impact the severity of class III malocclusions?

A
  • Tend to reduce severity via DAC
  • With competent lips - they procline the ULS and retrocline LLS to produce a less severe occlusion in comparison to the skeletal pattern
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9
Q

Explain the role of soft tissues on class III malocclusions with increased vertical proportions

A
  • Lips tend to be incompetent with incr vertical proportions (oral seal via tongue to lower lip)
  • No DAC seen
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10
Q

Describe the dental factors in class III malocclusions

A
  • Maxilla narrow and often crowded

- Mandible broader and can be well aligned or even spaced

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11
Q

Summarise the occlusal features in class III

A
  • Anterior cross bite (Reverse OJ)
  • Buccal cross bite
  • Varied molar and incisor relationship
  • Upper jaw crowding, lower jaw aligned/spaced
  • Varied vertical - deep overbite, normal or AOB
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12
Q

How does buccal cross bite occur in class III

A
  • Size discrepancy between jaws

- Position of mandible relative to the maxilla

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13
Q

What are the different incisor relationships that may be seen in class III malocclusion?

A
  • Edge to edge
  • Edge to edge with forward displacement
  • Frank reverse overjet
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14
Q

Describe edge to edge incisor relationship with forward displacement in class III patients

A

Edge to edge is achieved in RCP and the mandible is postured forward to achieve ICP (Essentially causing a reverse OJ and exaggerating severity of occlusion)

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15
Q

What factors influence tx options for class III patients

A
  • Severity of skeletal pattern
  • Patient expectations
  • Growth pattern (amount and type)
  • Age
  • Degree of alveolar compensation
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16
Q

What type of growth is seen in class III patients? What is the significance?

A
  • Forward growth of the mandible

- This is unfavourable as it worsens the malocclusion

17
Q

What are good prognostic factors for class III correction?

A
  • Class I or mild III skeletal base
  • Pt can achieve edge to edge which displaces anteriorly
  • No/minimal DAC
  • Normal or increased overbite
18
Q

Describe the relevance of extractions in class III tx

A
  • Extractions in upper arch alone will worsen incisal relationship
  • If extractions are necessary in, then extract further forward in lower arch = 55/44
19
Q

List the tx options for class III

A
  • Accept
  • Early interceptive tx or URA
  • Orthodontic camouflage
  • FA + surgery
20
Q

Describe the use of URA in class III patients - indications and design of appliance

A
  • Class I or mild III only

- Design - URA with Z springs and adams on Ds and 6s with posterior capping

21
Q

Describe the movement in orthodontic camouflage in class III patients

A
  • Procline ULS and/or retrocline LLS to correct incisor relationship
  • +/- elastics
22
Q

What is the limitation of using elastic traction in class III patients

A
  • May cause extrusion of molars which would reduce overbite
23
Q

What demonstrates good stability for class III patients treated with orthodontic camouflage?

A
  • Adequate overbite

- Further growth is not unfavourable

24
Q

What are the indications for surgery (for class III)

A

Non growing
ANB <4
Inclination of lower incisors to mandibular plane is <80

25
Q

Describe the correction of class III patients with FA and surgery as a tx

A
  • Fixed appliance removes/reduces any DAC and aligns

- Surgery corrects skeletal relationship

26
Q

Why does DAC need to be reduced/removed before surgery of class III patients

A

Vital to achieve a satisfactory occlusal and facial result post surgery

27
Q

What are the aims of camouflage for class III patients?

A
  • Utilise DAC to camouflage skeletal pattern
28
Q

How to make space in class III patients?

A
  • Extractions

- Expansion of the arch

29
Q

Aims of early interceptive treatment in class III

A
  • enhance maxillary growth and restrain/redirect mandibular growth
30
Q

Methods of early interceptive treatment in class III

A

Protraction face mask
Bone anchored maxillary protraction
Chin cup

31
Q

Options for mild-moderate class III pattern

A

Accept or camouflage

Ortho (20 decks)

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