2 - Class III malocclusion Flashcards
Define a class III malocclusion.
Lower incisor edge occludes anterior to the cingulum plateau of the upper incisor central incisor, the overjet is reduced or reversed
What is the UK incidence of class III malocclusion?
3-7%
Describe the aetiology of class III malocclusion.
- strong genetic link (parents may have class III)
- environmental factors ie CLP or acromegaly
What are the common skeletal features of a class III malocclusion?
- usually present with class III skeletal base
- can be due to small maxilla and/or large mandible
- associated with variety of vertical proportions
- commonly associated with crossbites
How does the vertical relationship impact treatment of a class III malocclusion?
Increased FMPA and an AOB are more complex to treat
How does the AP relationship impact treatment of a class III malocclusion?
The greater the discrepancy the more complex treatment is
Why are bilateral crossbites commonly seen in class III malocclusions?
Retrusive maxilla sits on wider part of mandible
What are the common dental features seen in a class III malocclusion?
- often class III incisor and molar relationships
- tendency to reverse overjet
- reduced overbite common, AOB
- crossbites, posterior and anterior common
- maxilla is often crowded with spacing in mandible
- dentoalveolar compensation
- displacement on closing
What dentoalveolar compensation is seen in class III malocclusion?
- proclined upper incisors
- retroclined lower incisors
How are soft tissues involved in class III malocclusion?
- not involved in aetiology
- encourage dentoalveolar compensation as tongue prolines upper incisors and lower lip retroclines lower incisors
Why do you treat a class III malocclusion?
- aesthetics (dental and profile)
- dental health (attrition, gingival recession, mandibular displacement)
- function (speech and mastication)
What factors increased the complexity of treatment of class III malocclusions?
- number of teeth in crossbite
- skeletal elements
- increased AP discrepancy
- AOB
- facial growth
How does facial growth impact treatment of class III malocclusion?
- growth is unfavourable
- mandibular growth continues for longer than maxillary
- potential for growth to continue and worsen malocclusion
- nothing irreversible should be completed until growth has stopped
How do you determine growth status of the patient?
- height and weight charts
- when the feet stop growing, height continues for small time after
- if in doubt, watch and wait
What are the management options of a class III malocclusion?
- accept/monitor
- intercept early with URA
- growth modification
- camouflage
- combined orthognathic/orthodontic treatment
When is it appropriate to accept/monitor a class III malocclusion?
- no concerns
- no dental health implications (no attrition or displacements)
- mild cases
When is appropriate to use early interceptive treatment in a class III malocclusion?
- if class III incisors developed due to early contact on permanent incisors
- correction of anterior crossbite may slow mandibular growth by dentoalveolar compensation (increased overbite maintains tooth position)
- only suitable if patient can achieve edge to edge occlusion
What active components can be used in a URA to correct an anterior crossbite?
- Z spring
- screw
When is it appropriate to use growth modification in a class III malocclusion?
- in the growing patient, 10-14 years
- aimed to reduce and or redirect mandibular growth and encourage maxillary growth
What can be used in growth modification of class III malocclusions?
- functional appliances (chin cup, reverse twin block, Frankel III)
- protraction headgear ± RME
Describe the chin cup.
- historic
- lingual tipping of lower incisors
- rotates mandible down and back
Describe the Frankel III.
- single piece appliance
- labial shield to hold lips away from teeth
- palatal arch to procline upper incisors
- lower labial bow to retrocline lower incisors
Describe the reverse twin block.
- used in mild class III (edge to edge required)
- harnesses growth of mandible to encourage maxillary growth/movement of upper teeth
Describe protraction headgear.
- can be removable or fixed with RME
- requires cooperative patient as must be worn for >14 hours a day
- 400g force applied each side
- best results in early mixed dentition 8-10 years
- RME disrupts circum-maxillary sutures
