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BDS4 Orthodontics > Class III Malocclusion > Flashcards

Class III Malocclusion Flashcards

1
Q

What is the definition 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 3 in the UK?

A

3-5%

-> higher in Asia

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3
Q

What are the aetiological factors contributing to class III malocclusion?

A

Strong genetic link- runs in families (autosomal with unknown cause)

Environmental
-> CLP- surgery early in life restricts growth in maxilla
-> Acromegaly- excess GH from pituitary

Skeletal, dental, ST

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4
Q

What are the skeletal causes of Class III malocclusions?

A

Small maxilla

Large mandible

-> combination

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5
Q

What are the AP skeletal features of class III malocclusions?

A

Usually present with a Class 3 skeletal base relationship
-> Can present with a Class 1 and rarely a Class 2 skeletal base relationship

The greater the A-P discrepancy the more complex the malocclusion is to treat

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6
Q

Which vertical skeletal features make Class III malocclusions difficult to treat?

A

High FMPA and AOB

-> likely requires orthognathic surgery

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7
Q

What aspect of the transverse skeletal relationship can result in bilateral cross bites?

A

Retrusive maxilla (associated with AP relationship too) sits on wider part of the mandible

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8
Q

What are the typical dental features of class III maloculsions?

A

Class III incisor relationship

Class III molar relationship (not always)

Tendency to reverse overjet (can be edge to edge)

Reduced overbite, anterior open bite may be present

Crossbites- Anterior/Buccal

Tendency for displacement on closing

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9
Q

What are the typical features of alignment within the arches in patients with class III malocclusion?

A

Maxilla (often narrow and v-shaped)- crowded

Mandible- aligned or spaced

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10
Q

What are the results of dentoalveolar compensation in Class III patients?

A

Proclined upper incisors

Retroclined lower incisors

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11
Q

How do the ST encourage dentoaleolar compensation?

A

Tongue prolines upper incisors

Lower lip retroclines lower incisors

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12
Q

What factors make class III relationships harder to treat?

A

> 1-2 teeth in anterior cross bite

Skeletal cause

Greater AP discrepancies

Presence of an AOB

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13
Q

What are the reasons for treating Class III malocclusions?

A

Aesthetics- dental, profile

Dental health reasons
-> attrition
-> recession- roots can be pushed through buccal plate
-> mandibular displacement

Function- speech/mastication

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14
Q

What are the issues with facial growth and Class III relationships?

A

Tends to be unfavourable as mandibular growth continues for longer
-> Class III often gets worse

Do not do anything irreversible until growth has stopped

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15
Q

What can be used to predict the onset of the pubertal growth spurt reliably? (coincides with jaw growth)

A

Height and weight charts

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16
Q

What are examples of unreliable means of predicting growth and why?

A

Cervical vertebral maturation (CVM) on lateral ceph
-> Evaluates the shape changes in the bodies of cervical vertebrae C2, C3 and C4 (difficult to reproduce, poor reliability and validity)

Hand wrist radiographs - low reliability and risks of repeated radiography (not justified)

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17
Q

What are the treatment options for Class III malocclusions?

A

Accept/monitor

Intercept early with URA to correct incisor relationship

Growth Modification- functional appliances, head gear, TADs

Camouflage- accept skeletal, correct incisors to Class I

Combined orthognathic and Orthodontics- if functional or profile issues

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18
Q

When may the decision to accept a class III malocclusion be opted for?

A

If mild class III and no concerns

If no dental health indications- no displacement or attrition

If unsure how growth and development will progress

19
Q

When can interceptive treatment for Class III relationships be considered?

A

If Class III incisors have developed due to early contact on permanent incisors (i.e. mandibular displacement)

Correction of anterior crossbite in mixed dentition has the advantage that further forward mandibular growth may be counter-balanced by some dento-alveolar compensation.

  • Only suitable for correcting a lateral incisor crossbite if permanent canines are high above lateral roots
    -> Delay if canines have dropped down into buccal position as risk of resorption to lateral incisor
20
Q

Why is a good OB helpful when using a URA to treat class III?

A

Maintains stability- prevents relapse

21
Q

What is used to correct crossbites in class III malocclusions in URA treatment?

A

Z-spring- moves tooth out of crossbite
-> proclines

PBP- allows anterior disclusion

22
Q

What is the aims of growth modification in Class III patients?

A

Reducing or redirecting mandibular growth

Encouraging maxillary growth

23
Q

What are the types of orthodontic appliances used in growth modification for class 3 patients?

A

Functional
-> chin cup
-> reverse twin block
-> Frankel 3

Protraction headgear (with RME)

24
Q

What are the effects of a chin cup? (historic)

A

Lingual tipping of lower incisors

Rotates mandible down and back

-> limited skeletal change

25
Q

How does a Frankel 3 operate?

A

Labial pellotes (shields) hold lip away from upper incisors

Palatal arch causes upper incisors to procline

Lower labial bow retroclines lower incisors

26
Q

What are the issues with Frankel 3?

A

One piece- difficult to tolerate

Trauma from acrylic components

Prone to breakage

27
Q

What are the issues with producing reverse twin blocks?

A

Patient must bite on wax in desired occlusion
-> difficult to guide the patient into or get them to posture into

28
Q

When is a reverse twin block indicated?

A

Class III with edge to edge relationship

29
Q

What is the function of protraction headgear with screw?

A

Protraction headgear- pulls maxilla forward (anchorage provided by face mask)

Hitac screw (turned twice per day)
-> splits palatal sutures
-> works in combination with facemask to pull forward as circumaxillary sutures are freed

30
Q

What are the drawbacks of Protraction head gear?

A

Not well tolerated- require cooperative patient

Must be worn 14 hours per day

High levels of force applied- 400g per side

31
Q

When do the best results for fixing class III with protraction headgear occur?

A

In early mixed dentition (age 8-10)

32
Q

When are bollard implants used? (anchorage device)

A

Used in late mixed dentition
-> placed at infrazygomatic crest and lower canine region (done under GA as mucoperiosteal flaps raised)

33
Q

What are the favourable features of a Class III patient for treatment using camouflage?

A

Growth stopped

Mild to moderate Class III
-> ANB not <0

Average or increased OB

Able to reach edge to edge incisor relationship

Little or no alveolar compensation

34
Q

What is the typical extraction pattern in camouflage orthodontic treatment of Class 3 malocclusion?

A

Upper 5s, lower 4s (further back in upper, further forward in lower)

-> not always possible- dental health influences

35
Q

What are the aims of camouflage treatment for Class III relationships?

A

Procline upper incisors

Retrocline lower incisors

-> correct OJ

36
Q

What is the main drawback of camouflage treatment?

A

Life long retention required

37
Q

What can be done as an early compromise treatment in patients with class III who have not stopped growing?

A

Upper arch alignment only
-> do not extract in lower arch as this can effect future options (can reopen extraction spaces)

38
Q

What is the orthognathic approach to treatment of Class 3 patients?

A

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

39
Q

What are the indications for orthognathic treatment?

A

Patient has functional or aesthetic concerns

Growth completed

Moderate/severe skeletal discrepancy- AP/T/V

40
Q

Who are the members of the MDT required for orthognathic surgery?

A

 Orthodontist
 Maxillofacial surgeon
 Technician- specilaist
 Psychologist

41
Q

What can be used to show the patient what the results of their orthognathic surgery may look like?

A

Prediction planning software

42
Q

What are the stages in orthognathic treatment of class 3 malocclusions?

A

Presurgical Ortho (18 months)
-> align, coordinate arch width, decompensate (move uppers to 109 and lowers to 90 degrees)
-> remove curve of spee

Orthognathic surgery to reposition jaws
-> mandible or maxilla and mandible

Post-surgical ortho (6 months)

43
Q

What is the GDP role in treating Class 3 malocclusions?

A

 Identify Class III malocclusion

 Refer to hospital service or specialist practitioner

 URA Treatment- potentially if anterior cross-bite correction required

BDS4 Orthodontics (14 decks)

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