Class III Malocclusion

Question 1

Define Class III incisal relatioship.

Answer 1

• Lower incisal edge occludes anterior to the cingulum plateau of the upper incisors.
• OJ is reduced or revewrsed

Question 2

What is the incidence of Class III malocclusion?

Answer 2

3-5%

Question 3

What medical conditions are related to Class III malocclusion?

(2)

Answer 3

cleft lip and palate
acromegaly

Question 4

What is the skeletal aetiology for Class III malocclusion?

Answer 4

• commonly underlying class III skeletal relationship
• increased mandibular length
• more anteriorly placed glenoid fossa so that the condylar head is positioned more anteriorly leading to mandibular prognathism
• reduced maxillary lengthh
• more retruded position of the maxilla leadinng to maxillary retrognathia
• reduced overbite
• increased LAFH

Question 5

What is the soft tissue aetiology for Class III malocclusion?

Answer 5

Dentoalveolar compensation
Soft tissues tend to tilt the upper and lower incisors towards each other so that the incisor relatonnship is less severe than the underlying skeletal pattern.
* tongue proclines the upper incisors
* lower lip retroclines lower incisors

Question 6

What is the dental aetiology for Class III malocclusion?

Answer 6

• narrow upper arch (more crowding)
• broad lower arch

Question 7

What are the common features of Class III malocclusion?

Answer 7

• anterior crossbite (if patient is able to achieve an edge-to-edge incisor position, prognosis for correction is more favourable)
• buccal crossbite (due to discrepancy in arch widths)
• proclination of upper incisors
• retroclination of lower incisors

Question 8

What makes treatment more difficult for class III malocclusions?

Answer 8

• > number of teeth in anterior crossbite
• skeletal element in aetiology
• > the A-P discrepancy
• presence of anterior open bite

Question 9

What are the treatment options for class III malocclusions?

Answer 9

Accept and monitor
* for mild class III or unsure how growth and development will progress

Intercept early with URA
* early correction of incisor relationship
* correction of anterior open bite
* correction of lateral incisor crossbite if permanent canines are high above lateral roots

Growth modification
* functional appliances (protraction face-mask, chin-cup, reverse twin block, frankel III)
* head gear
* TADs

Camouflage
* accept underlying skeletal relationship
* correct incisors to class I (able to reach edge-to-edge incisor relationship)
* average or increased OB
* growth has stopped

Combined orthognathic/orthodontic treatment
* functional/masticatory/profile concerns
* pre-surgical orthodontics 18mos
* orthognathic surgery
* post-surgical orthodontics 6mos