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BDS4 Orthodontics > Class III Malocclusion > Flashcards

Class III Malocclusion Flashcards

1
Q

What is the BSI incisor classification of a class III malocclusion?

A
  • lower incisor edge occludes anterior to the cingulum plateau of the upper central incisor
  • the overjet is reduced or reversed
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2
Q

What is the incidence of class III malocclusion?

A
  • geographical variation
    • UK - 3-7%
      • higher in west of Scotland
    • higher incidence in Asia
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3
Q

What is the aetiology of class III malocclusion?

A
  • strong genetic link
  • cleft lip/palate
  • acromegaly
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4
Q

What is the skeletal aetiology of a class III malocclusion?

A
  • small maxilla
    • most common
  • large mandible
  • combination of both
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5
Q

Describe the antero-posterior skeletal features of a class III malocclusion

A
  • usually present on a class III skeletal
    • can present on class I
    • rarely class II
  • the greater the A-P discrepancy, the more complex the malocclusion is to treat
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6
Q

Describe the vertical skeletal features of a class III malocclusion

A
  • can be associated with average, increased or reduced vertical proportions
  • reference points
    • FMPA
    • facial height proportions
    • lateral cephalometry
  • increased FMPA and anterior open bite is more challenging to treat
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7
Q

Describe the transverse skeletal features of a class III malocclusion

A
  • A-P and transverse relationship linked
  • bilateral crossbiyes
    • retrusive maxilla
    • wider part of mandible
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8
Q

Describe the dental features of a class II malocclusion

A
  • variable
  • Class III incisor relationship
  • Class III molar relationship
    • sometimes
  • tendency to reverse overjet
  • reduced overbite
    • possible anterior open bit
  • crossbites
    • anterior
    • buccal
  • alignment
    • crowded maxilla
      • narrow, v-shaped arch
    • aligned or spaced mandible
  • dentoalveolar compensation
    • proclined upper incisors
    • retroclined lower incisors
  • tendency for displacement on closing
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9
Q

Describe the soft tissue features of a class III malocclusion

A
  • not usually involved in aetiology
  • can contribute to dentoalveolar compensation
    • upper incisors proclined by tongue
    • lower incisors retroclined by lip
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10
Q

Why might a class III malocclusion require treatment?

A
  • aesthetics
    • dental
    • profile concerns
  • dental health reasons
    • attrition
    • gingival recession
    • mandibular displacement
  • function
    • speech
    • mastication
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11
Q

What factors in a class III malocclusion increase the complexity of treatment?

A
  • greater number of teeth in anterior cross bite
  • skeletal element in aetiology
  • greater the anteroom-posterior discrepancy
  • presence of an anterior open bite
  • facial growth
    • tends to be unfavourable
    • mandible grows for longer
    • potential for class III to get worse
    • no irreversible treatment until complete
      • can affect further treatment
      • especially if surgery required
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12
Q

How can the growth status of a child be determined?

A
  • onset of pubertal growth spurt coincides with support of jaw growth
    • difficult to predict
  • height and weight charts
  • cervical vertebrae maturation
    • requires lateral cephalogram
    • bodies of vertebrae change
    • not particularly reliable
  • once feet stop growing, height stops shortly after
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13
Q

What are the treatment options for a class III malocclusion?

A
  • accept/monitor
  • intercept with early URA
  • growth modification
  • camouflage
  • orthognathic surgery and orthodontics
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14
Q

When can a class III malocclusion be accepted and monitored?

A
  • no concerns
  • no dental health indications
    • no displacements
    • no attrition
  • mild cases
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15
Q

How can a class III malocclusion be treated with interceptive URA?

A
  • suitable if class III incisors have developed due to early contact on permanent incisors
    • mandibular displacement
  • correction of anterior cross bite in mixed dentition
    • advantage
      • further forward mandibular growth
      • may be counter-balanced
      • dento-alveolar compensation
  • only suitable for correcting a lateral incisor cross bite if permanent canines are high above lateral roots
    • delay if canines are in buccal position
    • risk of resorption to lateral incisor
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16
Q

What can be used to indicate whether appliance alone can be used to treat a class III malocclusion?

A

if the patient can achieve edge-to-edge bite

17
Q

What does interceptive treatment with a URA aim to do for a class III malocclusion?

A
  • proclination of incisors over the bite
    • overbite maintains stability
    • z-spring
    • screw section
18
Q

How can growth modification be used to treat a class III malocclusion

A
  • used for a growing patient
  • reduces or redirects mandibular growth
    • encourages maxillary growth
19
Q

What are the different appliances that can be used for growth modification of a class III malocclusion?

A
  • chin cup
  • reverse twin block
  • Frankel III
  • protraction headgear +/- RME
20
Q

How does a chin cup function to treat a class III malocclusion?

A
  • mainly a historic form of treatment
  • lingual tipping of lower incisors
  • rotates mandible down and back
20
Q

How is a Frankel III used to treat a class III malocclusion?

A
  • pellotes labial to upper incisors to hold lip away
  • palatal arch to procaine upper incisors
  • lower labial bow to retrocline lower incisors
  • not commonly used now as patient function is greatly reduced
21
Q

How does a reverse twin block work for treating class III malocclusion?

A
  • opposite to class II div 1 twin block
    • mandible postured backwards
  • only works for mild class III
    • patient can achieve edge to edge
22
Q

How can protraction headgear be used to treat a class III malocclusion?

A
  • rapid maxillary expansion device
  • requires a cooperative patient
    • 14 hours daily wear
    • 400g force applied to each side
  • 8-10 years old
    • before maxillary sutures start to fuse
23
Q

What are bollard implants used for?

A
  • correction of class III malocclusion
    • bollard implants
      • like TADs
      • infrazygomatic and canine regions
    • class III elastics
  • mucoperiosteal flap must be raised
    • insertion and removal
  • can be successful but not popular
24
Q

How can a class III malocclusion be camouflaged?

A
  • accept underlying skeletal base relationship
    • aim for class I incisors
  • proclination of upper incisors
  • retroclination of lower incisors
  • correct overjet
25
Q

What are favourable features for camouflage for a class III malocclusion?

A
  • growth stopped
  • mild to moderate class III skeletal base
    • ANB not below 0 degrees
  • average or increased overbite
  • able to reach edge to edge incisor relationship
  • little or no dentoalveolar compensation
26
Q

What extraction pattern may be used for correction of a class III malocclusion through camouflage?

A
  • extract further back in the upper arch
  • extract further forward in the lower arch
  • classic extraction pattern
    • upper 5s
    • lower 4s
  • dental health ultimately dictates extraction pattern
27
Q

Write a potential treatment plan for camouflage of a class III malocclusion

A
  1. extraction of upper 5s
  2. extraction of lower 4s
  3. upper and lower fixed - class I
  4. lifelong retention
28
Q

What is orthognathic surgery?

A

surgical manipulation of the mandible and/or maxilla to produce optimal dent-facial aesthetics and function

29
Q

When might orthognathic surgery be considered for a class III malocclusion?

A
  • pt has aesthetic or functional concerns
  • growth completed
  • moderate/severe skeletal discrepancy
    • A-P
    • transverse
    • vertical
30
Q

What does orthognathic surgery to correct a class III malocclusion involve?

A
  • pre-surgical orthodontics
    • approximately 18 months
    • level, align, coordinate, decompensate
      • uppers (109 degrees)
      • lowers (90 degrees)
      • rotations
      • curve of Spee
  • orthognathic surgery
    • reposition the jaws
      • mandible
      • mandible +/- maxilla
  • post-surgical orthodontics
    • approximately 6 months
31
Q

What is the role of the GDP for treatment of class III malocclusion?

A
  • identify class III malocclusion
  • refer to hospital service or orthodontist
  • anterior crossbite correction with URA

BDS4 Orthodontics (8 decks)

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