Class III Malocclusion Flashcards
The diagnosis of class III malocclusion is based on
The incisor relationship
What is the definition of class III malocclusion
Lower incisor edges are
anterior to the cingulum
plateau of the upper incisors
What is the significance of class III malocclusion?
Appearance?
Associated with?
Poor dental appearance
May be associated with an anterior mandibular displacement
Class III
Facial profile?
Growth?
Facial profile often poor
Growth usually unfavourable (i.e. Mandible grows forward more than maxilla)
What is the incidence of class III malocclusion?
relatively uncommon malocclusion
3-5% (UK)
Relatively common in some ethnic groups
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
Skeletal Class III: maxillary hypoplasia would look like…
Mandible in normal position and maxilla looks retruded
Skeletal class III mandibular excess would look like
Maxilla in normal position and mandible protruded
Class III mandibular displacement- describe
Patient initially bites edge to edge then displaces forwards
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
Family history can be useful in
Helping to predict future growth patterns for skeletal class III
Ceph tracing… what is the ANB
<2 degrees
What is the percentage of class III patients with a skeletal III pattern? (<2 degrees)?
> 70% have a skeletal III pattern (ANB < 2
degrees)
Skeletal pattern may be the result of
Small maxilla and/or large mandible
The maxilla is often … resulting in …
Narrow
Crossbite
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
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
