Class III malocclusions Flashcards
What is the BSI definition of a class III incisor relationship?
Lower incisor edge occludes anterior to the cingulum plateau of the upper central incisor
Overjet is reduced or reversed
What is the incidence of a class III malocclusion in the UK?
3-7%
What is the definition of a class III skeletal relationship?
Mandible in front of maxilla.
What is the aetiology for class III relationship?
Strong genetic link
CLP, acromegaly, Down’s syndrome
Retrognathic maxilla - hypoplastic maxilla most common reason
Large mandible
Combination of both
What features make a class III malocclusion difficult to treat?
Increased FMPA
Presence of AOB
The greater the AP discrepancy > number of teeth in anterior crossbite
Facial growth
What are the dental features of a class III malocclusion?
Variable
- HAVE TO HAVE - class III incisor relationship by definition
- Tendency to reverse overjet - not always
- Tend to be spaced in the lower and crowded in the upper
- Reduced OB or AOB may be present
- Crossbites are common (anterior and posterior)
- Dentoalveolar compensation - proclined UA, retro-clined LA
- Tendency to displacement on closing
What is alignment of teeth usually like in a class III?
Maxilla often crowded
Mandible often spaced
General rule of thumb as maxilla is usually hypoplastic
How do the soft tissues encourage dentoalveolar compensation in a class III?
Tongue position proclines the upper incisors
Lower lip retroclines the lower incisors
If you detect a crossbite O/E, what should you do?
Check to see if the patient is displacing the mandible on closing
How does facial growth affect treatability of a class III malocclusion?
Facial growth tends to be unfavourable towards class III treatment.
Those with class III malocclusions tend to have a longer pubertal growth spurt leading to longer time for mandible to grow - potential for class III to get worse.
Cannot do anything irreversible until growth has stopped - can affect future treatment if surgery required.
What is a good prognostic indicator in class III that patient is unlikely to relapse in URA only treatment?
If there is a deep/ good amount of overbite before treatment.
Will prevent upper incisors from retroclining.
When is a patient with a class III suitable for interceptive treatment only (URA)?
Suitable if class III incisor developed due to early contact on permanent incisors - sliding to allow posteriors to meet
Only suitable for correcting lateral incisors crossbite if permanent canines are HIGH above lateral roots
How does a reverse twin block work to treat a class III?
Promotes maxillary growth and restricts mandibular growth and tips upper incisors forward
What features are favourable for orthodontic camouflage?
Growth stopped
Mild to moderate class III skeletal base
Average or increased overbite
Able to reach edge-to-edge incisor relationship
Little or no dentoalveolar compensation
What is the classic extraction pattern (if possible) for class III in orthodontic camouflage?
Upper 5’s and lower 4’s
