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BDS4 Orthodontics > 2 - Class III malocclusion > Flashcards

2 - Class III malocclusion Flashcards

1
Q

Define a class III malocclusion.

A

Lower incisor edge occludes anterior to the cingulum plateau of the upper incisor central incisor, the overjet is reduced or reversed

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2
Q

What is the UK incidence of class III malocclusion?

A

3-7%

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3
Q

Describe the aetiology of class III malocclusion.

A
  • strong genetic link (parents may have class III)
  • environmental factors ie CLP or acromegaly
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4
Q

What are the common skeletal features of a class III malocclusion?

A
  • usually present with class III skeletal base
  • can be due to small maxilla and/or large mandible
  • associated with variety of vertical proportions
  • commonly associated with crossbites
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5
Q

How does the vertical relationship impact treatment of a class III malocclusion?

A

Increased FMPA and an AOB are more complex to treat

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6
Q

How does the AP relationship impact treatment of a class III malocclusion?

A

The greater the discrepancy the more complex treatment is

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7
Q

Why are bilateral crossbites commonly seen in class III malocclusions?

A

Retrusive maxilla sits on wider part of mandible

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8
Q

What are the common dental features seen in a class III malocclusion?

A
  • often class III incisor and molar relationships
  • tendency to reverse overjet
  • reduced overbite common, AOB
  • crossbites, posterior and anterior common
  • maxilla is often crowded with spacing in mandible
  • dentoalveolar compensation
  • displacement on closing
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9
Q

What dentoalveolar compensation is seen in class III malocclusion?

A
  • proclined upper incisors
  • retroclined lower incisors
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10
Q

How are soft tissues involved in class III malocclusion?

A
  • not involved in aetiology
  • encourage dentoalveolar compensation as tongue prolines upper incisors and lower lip retroclines lower incisors
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11
Q

Why do you treat a class III malocclusion?

A
  • aesthetics (dental and profile)
  • dental health (attrition, gingival recession, mandibular displacement)
  • function (speech and mastication)
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12
Q

What factors increased the complexity of treatment of class III malocclusions?

A
  • number of teeth in crossbite
  • skeletal elements
  • increased AP discrepancy
  • AOB
  • facial growth
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13
Q

How does facial growth impact treatment of class III malocclusion?

A
  • growth is unfavourable
  • mandibular growth continues for longer than maxillary
  • potential for growth to continue and worsen malocclusion
  • nothing irreversible should be completed until growth has stopped
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14
Q

How do you determine growth status of the patient?

A
  • height and weight charts
  • when the feet stop growing, height continues for small time after
  • if in doubt, watch and wait
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15
Q

What are the management options of a class III malocclusion?

A
  • accept/monitor
  • intercept early with URA
  • growth modification
  • camouflage
  • combined orthognathic/orthodontic treatment
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16
Q

When is it appropriate to accept/monitor a class III malocclusion?

A
  • no concerns
  • no dental health implications (no attrition or displacements)
  • mild cases
17
Q

When is appropriate to use early interceptive treatment in a class III malocclusion?

A
  • if class III incisors developed due to early contact on permanent incisors
  • correction of anterior crossbite may slow mandibular growth by dentoalveolar compensation (increased overbite maintains tooth position)
  • only suitable if patient can achieve edge to edge occlusion
18
Q

What active components can be used in a URA to correct an anterior crossbite?

A
  • Z spring
  • screw
19
Q

When is it appropriate to use growth modification in a class III malocclusion?

A
  • in the growing patient, 10-14 years
  • aimed to reduce and or redirect mandibular growth and encourage maxillary growth
20
Q

What can be used in growth modification of class III malocclusions?

A
  • functional appliances (chin cup, reverse twin block, Frankel III)
  • protraction headgear ± RME
21
Q

Describe the chin cup.

A
  • historic
  • lingual tipping of lower incisors
  • rotates mandible down and back
22
Q

Describe the Frankel III.

A
  • single piece appliance
  • labial shield to hold lips away from teeth
  • palatal arch to procline upper incisors
  • lower labial bow to retrocline lower incisors
23
Q

Describe the reverse twin block.

A
  • used in mild class III (edge to edge required)
  • harnesses growth of mandible to encourage maxillary growth/movement of upper teeth
24
Q

Describe protraction headgear.

A
  • can be removable or fixed with RME
  • requires cooperative patient as must be worn for >14 hours a day
  • 400g force applied each side
  • best results in early mixed dentition 8-10 years
  • RME disrupts circum-maxillary sutures
25
Q

What are bollard implants?

A
  • used in late mixed/permanent dentition
  • requires mucoperiosteal flap to be raised to insertion and removal
  • class III elastics are placed on implants
26
Q

What are class III elastics?

A

Elastics run from distal in the upper to mesial in the lower

27
Q

When is it appropriate to use orthodontic camouflage in class III malocclusion?

A
  • accept underlying skeletal base
  • once growth has stopped, mild to moderate class III where ANB > 0
  • average or increased overbite
  • able to achieve edge to edge relationship
  • no dentoalveolar compensation (uppers not proclined and vice versa)
28
Q

What are the aims of orthodontic camouflage of class III malocclusion?

A
  • procline upper incisors
  • retrocline lower incisors
  • correct overjet
29
Q

What is the ideal extraction pattern for orthodontic camouflage of class III malocclusion?

A
  • extract further back in upper arch
  • extract further forward in lower arch
  • classic pattern is upper 5s, lower 4s
  • may be dictated by dental health
30
Q

Define orthognathic surgery.

A

Surgical manipulation of mandible and/or maxilla to produce optimal dentofacial aesthetics and function

31
Q

When is it appropriate to use orthognathic surgery and orthodontic treatment in class III malocclusion?

A
  • patient has aesthetic (profile) or functional concerns
  • growth in completed
  • moderate to severe skeletal discrepancy
32
Q

What is maxillary advancement surgery?

A
  • maxilla is brought forward surgically
  • mandible not involved in surgery but will autorotate to accommodate new position of maxilla
33
Q

What orthodontic treatment is involved in orthognathic surgery?

A
  • 18 months pre-surgical orthodontics
  • level, align, coordinate and decompensated incisors (remove curve of spee)
  • post-surgical orthodontics for 6 months
34
Q

What is the GDP role in class III malocclusion?

A
  • identify and refer to appropriate service
  • possible URA treatment of anterior crossbite

BDS4 Orthodontics (14 decks)

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