Orthodontic class III

Question 1

aetiology of class III skeletal class

Answer 1

1. genetic (small maxilla or large mandible or both)
2. acromegally (env)
3. cleft lip and palate (env)

Question 2

what are the anteroposterior, vertical and transverse effects of class III skeletal bases

Answer 2

AP - protrusive mandible

V - average, increased or decreased (AOB and >FMPA make more complicated)

T - Bilateral crossbite (due to retrusive maxilla sitting on wider part of mandible) - linked with AOB and >FMPA

Question 3

growth modification tx for class III skeletal class (4)

Answer 3

1. chin cup (historic)
2. reverse twin block (hard tissue - tooth born)
3. frankel III - soft tissue born version
4. bollard implants

Question 4

treatment options for a class III skeletal individual

Answer 4

1. Accept and monitor
2. interceptive tx (anterior cross bite can be treated in mixed dentition)
3. growth modification before or during pubertal growth spurt
4. camouflage (accept underlying skletal cause)
   * only if mild skeletal discrepancy
   * stopped growing
   * try and make teeth in class I relationships
   * extractions - remove from further back in upper and more mesial in lower
5. orthognathic surgery

Question 5

dental implications of a class III skeletal base

Answer 5

reverse overjet

crowded maxilla

normal or spaced mandible

reverse OJ

reduced overbite / AOB

cross bites

displacement on biting

dentoalveolar compensation - proclined upper and retro lowers

Question 6

class III skeletal pattern soft tissue effect on dentition

Answer 6

dentoalveolar compensation

• upper protruded by tongue and lowers retroclined by lower lip

Question 7

why treat a class 3 skeletal base

Answer 7

aesthetics (teeth and face)

dentition health
- attrition
- gingival recession
- mandibular displacement

function
- speech and mastication

Question 8

Camouflage tx for class III treatment

• favourable features
• XLA pattern
• aim

Answer 8

favourable
- growth stopped
- mild to moderate class III (ANB not <0)
- able to get edge to edge incisors
- little dentoalveolar compensation

XLA
- XLA further back in maxilla
- V.V. lowers - 5s upper and 4s lower

aims
- procline upers, retro lowers and reduce reverse OJ

Question 9

golden rule in treating a class III individual when they are stil growing

Answer 9

DONT do anything irreversible as limits options for when they have stopped growing

Question 10

what orthodontic work should have already been carried out prior to orthognathic surgery for a class III patient

Answer 10

uppers at 109 degrees

lowers at 90 degrees

eliminate crowding, rotations, favourable curve of spee

warn patient will get worse before gets better