Class III Malocclusion Flashcards by Janine Hoonjan

The diagnosis of class III malocclusion is based on

The incisor relationship

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What is the definition of class III malocclusion

Lower incisor edges are
anterior to the cingulum
plateau of the upper incisors

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What is the significance of class III malocclusion?

Appearance?
Associated with?

 Poor dental appearance
 May be associated with an anterior mandibular displacement

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Class III

Facial profile?
Growth?

Facial profile often poor

Growth usually unfavourable (i.e. Mandible grows forward more than maxilla)

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What is the incidence of class III malocclusion?

relatively uncommon malocclusion
 3-5% (UK)
Relatively common in some ethnic groups

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Aetiology of class III malocclusion

 Genetic – due to skeletal pattern

 Most are due to an AP skeletal discrepancy
(mandibular excess, maxillary hypoplasia or
both)

 May be a result of a mandibular
displacement

Cleft lip and palate patients

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Skeletal Class III: maxillary hypoplasia would look like…

Mandible in normal position and maxilla looks retruded

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Skeletal class III mandibular excess would look like

Maxilla in normal position and mandible protruded

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Class III mandibular displacement- describe

Patient initially bites edge to edge then displaces forwards

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Genetic background of class III mandibular displacement?
Mother?
Father?
Siblings?

 13% of patients have an affected sibling
 13% have a Class III mother
 20% have a Class III father

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Family history can be useful in

Helping to predict future growth patterns for skeletal class III

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Ceph tracing… what is the ANB

<2 degrees

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What is the percentage of class III patients with a skeletal III pattern? (<2 degrees)?

> 70% have a skeletal III pattern (ANB < 2
degrees)

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Skeletal pattern may be the result of

Small maxilla and/or large mandible

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The maxilla is often … resulting in …

Narrow
Crossbite

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Dental features of class III
Incisors?
…
Arch
Arch

 Class III incisors (mild cases are edge-edge,
severe cases may have a large reverse
overjet)

 Dentoalveolar compensation (i.e. upper
incisors proclined & lowers retroclined)

 Upper arch often narrow & crowded,
crossbites

Mandibular arch may be spaced

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Why treat class III?

 Improve dentofacial appearance
 Psychosocial - teasing
 Eliminate mandibular forward displacement if present

Treatment of class III- aims? (4)

 Produce a positive overjet
 Relieve crowding and align arches
 Improve facial profile
Produce a stable result

Treatment options?

 Accept the incisor relationship
 Procline the upper incisors
 Retrocline the lower incisors
 Orthognathic Surgery (correct skeletal problems)

Class III Skeletal Discrepancy and
Treatment

None/mild
Moderate
Severe

 None / Mild: Orthodontic appliances only
 Moderate: +/- Orthognathic Surgery
 Severe: Orthognathic Surgery

Timing of treatment-
Growth?

Is often unfavourable and lasts longer in Class III cases (ie. Class III tends to get worse

Timing of treatment- displacements?

can often be treated early using appliances to procline the upper incisors, often in the mixed dentition

Timing of treatment-

Appliance treatment is…

usually carried out at a later age than in other types of malocclusion

Age 15-16 when growth has stopped

Favourable factors for patients suitable for appliance treatment only?

pre-treatment overbite

ability to bite edge-edge

anterior displacement

Small or no skeletal discrepancy

Favourable factors for patients suitable for appliance treatment only? (4)

pre-treatment overbite ability to bite edge-edge anterior displacement Small or no skeletal discrepancy

Favourable factors for treatment with fixed appliances? (2)

Mild to moderate skeletal discrepancies with acceptable facial profile  Crowded lower (and/or upper) arches

Fixed appliance treatment - the aim is ...

To produce dentoalveolar compensation

Dentoalveolar compensation provided by fixed appliance treatment for class III is done by ...

Extracting lower premolars to allow retroclination of lower incisors

What other appliance can you have?

Class III elastics

Surgery for class III? Patients suitable

 severe skeletal discrepancies and poor facial profile / appearance  Vertical problems and anterior open bites

Class III surgery- clinical procedure-

- Fixed appliances to align individual arches & produce “decompensation”  Surgical mandibular setback and / or Maxillary advancement

What is the prognosis of class III? Growth?

Is often unfavourable and continues longer. Incisor relationship often gets worse during teens

Prognosis of class III Stability?

of incisor correction depends on the presence of a positive overbite  Surgically treated cases are usually stable

Aim for treatment of class III is

positive overjet and acceptable facial profile

Mild cases may be treated with

early with URA – to eliminate displacements and push upper incisors “over the bite”

Most cases are treated with

fixed appliance treatment which is often carried out later than Class II or Class I cases

What are NOT used in treatment of class III?

Functional appliances

What is common with class III

Displacements (Forwards)

What is favourable for treating with appliances only in class III?

Pre- treatment presence of a positive overbite and the ability to bite edge-edge

What is unfavourable for treating in class III

The pre-treatment presence of dentoalveolar compensation or a skeletal problem

What is often a problem in treating class III

Growth