Class III Malocclusion Flashcards
What is the BSI incisor classification of a class III malocclusion?
- lower incisor edge occludes anterior to the cingulum plateau of the upper central incisor
- the overjet is reduced or reversed
What is the incidence of class III malocclusion?
- geographical variation
- UK - 3-7%
- higher in west of Scotland
- higher incidence in Asia
- UK - 3-7%
What is the aetiology of class III malocclusion?
- strong genetic link
- cleft lip/palate
- acromegaly
What is the skeletal aetiology of a class III malocclusion?
- small maxilla
- most common
- large mandible
- combination of both
Describe the antero-posterior skeletal features of a class III malocclusion
- usually present on a class III skeletal
- can present on class I
- rarely class II
- the greater the A-P discrepancy, the more complex the malocclusion is to treat
Describe the vertical skeletal features of a class III malocclusion
- can be associated with average, increased or reduced vertical proportions
- reference points
- FMPA
- facial height proportions
- lateral cephalometry
- increased FMPA and anterior open bite is more challenging to treat
Describe the transverse skeletal features of a class III malocclusion
- A-P and transverse relationship linked
- bilateral crossbiyes
- retrusive maxilla
- wider part of mandible
Describe the dental features of a class II malocclusion
- variable
- Class III incisor relationship
- Class III molar relationship
- sometimes
- tendency to reverse overjet
- reduced overbite
- possible anterior open bit
- crossbites
- anterior
- buccal
- alignment
- crowded maxilla
- narrow, v-shaped arch
- aligned or spaced mandible
- crowded maxilla
- dentoalveolar compensation
- proclined upper incisors
- retroclined lower incisors
- tendency for displacement on closing
Describe the soft tissue features of a class III malocclusion
- not usually involved in aetiology
- can contribute to dentoalveolar compensation
- upper incisors proclined by tongue
- lower incisors retroclined by lip
Why might a class III malocclusion require treatment?
- aesthetics
- dental
- profile concerns
- dental health reasons
- attrition
- gingival recession
- mandibular displacement
- function
- speech
- mastication
What factors in a class III malocclusion increase the complexity of treatment?
- greater number of teeth in anterior cross bite
- skeletal element in aetiology
- greater the anteroom-posterior discrepancy
- presence of an anterior open bite
- facial growth
- tends to be unfavourable
- mandible grows for longer
- potential for class III to get worse
- no irreversible treatment until complete
- can affect further treatment
- especially if surgery required
How can the growth status of a child be determined?
- onset of pubertal growth spurt coincides with support of jaw growth
- difficult to predict
- height and weight charts
- cervical vertebrae maturation
- requires lateral cephalogram
- bodies of vertebrae change
- not particularly reliable
- once feet stop growing, height stops shortly after
What are the treatment options for a class III malocclusion?
- accept/monitor
- intercept with early URA
- growth modification
- camouflage
- orthognathic surgery and orthodontics
When can a class III malocclusion be accepted and monitored?
- no concerns
- no dental health indications
- no displacements
- no attrition
- mild cases
How can a class III malocclusion be treated with interceptive URA?
- suitable if class III incisors have developed due to early contact on permanent incisors
- mandibular displacement
- correction of anterior cross bite in mixed dentition
- advantage
- further forward mandibular growth
- may be counter-balanced
- dento-alveolar compensation
- advantage
- only suitable for correcting a lateral incisor cross bite if permanent canines are high above lateral roots
- delay if canines are in buccal position
- risk of resorption to lateral incisor
What can be used to indicate whether appliance alone can be used to treat a class III malocclusion?
if the patient can achieve edge-to-edge bite
What does interceptive treatment with a URA aim to do for a class III malocclusion?
- proclination of incisors over the bite
- overbite maintains stability
- z-spring
- screw section
How can growth modification be used to treat a class III malocclusion
- used for a growing patient
- reduces or redirects mandibular growth
- encourages maxillary growth
What are the different appliances that can be used for growth modification of a class III malocclusion?
- chin cup
- reverse twin block
- Frankel III
- protraction headgear +/- RME
How does a chin cup function to treat a class III malocclusion?
- mainly a historic form of treatment
- lingual tipping of lower incisors
- rotates mandible down and back
How is a Frankel III used to treat a class III malocclusion?
- pellotes labial to upper incisors to hold lip away
- palatal arch to procaine upper incisors
- lower labial bow to retrocline lower incisors
- not commonly used now as patient function is greatly reduced
How does a reverse twin block work for treating class III malocclusion?
- opposite to class II div 1 twin block
- mandible postured backwards
- only works for mild class III
- patient can achieve edge to edge
How can protraction headgear be used to treat a class III malocclusion?
- rapid maxillary expansion device
- requires a cooperative patient
- 14 hours daily wear
- 400g force applied to each side
- 8-10 years old
- before maxillary sutures start to fuse
What are bollard implants used for?
- correction of class III malocclusion
- bollard implants
- like TADs
- infrazygomatic and canine regions
- class III elastics
- bollard implants
- mucoperiosteal flap must be raised
- insertion and removal
- can be successful but not popular
How can a class III malocclusion be camouflaged?
- accept underlying skeletal base relationship
- aim for class I incisors
- proclination of upper incisors
- retroclination of lower incisors
- correct overjet
What are favourable features for camouflage for a class III malocclusion?
- growth stopped
- mild to moderate class III skeletal base
- ANB not below 0 degrees
- average or increased overbite
- able to reach edge to edge incisor relationship
- little or no dentoalveolar compensation
What extraction pattern may be used for correction of a class III malocclusion through camouflage?
- extract further back in the upper arch
- extract further forward in the lower arch
- classic extraction pattern
- upper 5s
- lower 4s
- dental health ultimately dictates extraction pattern
Write a potential treatment plan for camouflage of a class III malocclusion
- extraction of upper 5s
- extraction of lower 4s
- upper and lower fixed - class I
- lifelong retention
What is orthognathic surgery?
surgical manipulation of the mandible and/or maxilla to produce optimal dent-facial aesthetics and function
When might orthognathic surgery be considered for a class III malocclusion?
- pt has aesthetic or functional concerns
- growth completed
- moderate/severe skeletal discrepancy
- A-P
- transverse
- vertical
What does orthognathic surgery to correct a class III malocclusion involve?
- pre-surgical orthodontics
- approximately 18 months
- level, align, coordinate, decompensate
- uppers (109 degrees)
- lowers (90 degrees)
- rotations
- curve of Spee
- orthognathic surgery
- reposition the jaws
- mandible
- mandible +/- maxilla
- reposition the jaws
- post-surgical orthodontics
- approximately 6 months
What is the role of the GDP for treatment of class III malocclusion?
- identify class III malocclusion
- refer to hospital service or orthodontist
- anterior crossbite correction with URA
