Class III

Question 1

What is the prevalence of class III in the UK population?

Answer 1

<5%

Question 2

What is the AP skeletal relationship in class III?

Answer 2

• Majority have a class III skeletal base

- Most important aetiology

Question 3

List the causes of the class III AP skeletal pattern

Answer 3

• Increased mandibular length / acute cranial base angle due to anteriorly positioned glenoid fossa
• Reduced maxillary length (maxillary retrusion)

Question 4

How does an acute cranial base angle / incr mandibular length result in a class III malocclusion

Answer 4

Glenoid fossa is placed anteriorly = condylar head is placed anteriorly
Therefore mandible is prognathic relative to the maxilla

Question 5

Describe the vertical skeletal pattern in class III

Answer 5

Ranges - LFH can be increased, normal or reduced

Question 6

What does forward rotation of the jaw lead to in class III patients

Answer 6

Chin prominence

Question 7

Soft tissue factors in class III

Answer 7

• Very small role in aetiology

Question 8

How can soft tissues impact the severity of class III malocclusions?

Answer 8

• Tend to reduce severity via DAC
• With competent lips - they procline the ULS and retrocline LLS to produce a less severe occlusion in comparison to the skeletal pattern

Question 9

Explain the role of soft tissues on class III malocclusions with increased vertical proportions

Answer 9

• Lips tend to be incompetent with incr vertical proportions (oral seal via tongue to lower lip)
• No DAC seen

Question 10

Describe the dental factors in class III malocclusions

Answer 10

• Maxilla narrow and often crowded

- Mandible broader and can be well aligned or even spaced

Question 11

Summarise the occlusal features in class III

Answer 11

• Anterior cross bite (Reverse OJ)
• Buccal cross bite
• Varied molar and incisor relationship
• Upper jaw crowding, lower jaw aligned/spaced
• Varied vertical - deep overbite, normal or AOB

Question 12

How does buccal cross bite occur in class III

Answer 12

• Size discrepancy between jaws

- Position of mandible relative to the maxilla

Question 13

What are the different incisor relationships that may be seen in class III malocclusion?

Answer 13

• Edge to edge
• Edge to edge with forward displacement
• Frank reverse overjet

Question 14

Describe edge to edge incisor relationship with forward displacement in class III patients

Answer 14

Edge to edge is achieved in RCP and the mandible is postured forward to achieve ICP (Essentially causing a reverse OJ and exaggerating severity of occlusion)

Question 15

What factors influence tx options for class III patients

Answer 15

• Severity of skeletal pattern
• Patient expectations
• Growth pattern (amount and type)
• Age
• Degree of alveolar compensation

Question 16

What type of growth is seen in class III patients? What is the significance?

Answer 16

• Forward growth of the mandible

- This is unfavourable as it worsens the malocclusion

Question 17

What are good prognostic factors for class III correction?

Answer 17

• Class I or mild III skeletal base
• Pt can achieve edge to edge which displaces anteriorly
• No/minimal DAC
• Normal or increased overbite

Question 18

Describe the relevance of extractions in class III tx

Answer 18

• Extractions in upper arch alone will worsen incisal relationship
• If extractions are necessary in, then extract further forward in lower arch = 55/44

Question 19

List the tx options for class III

Answer 19

• Accept
• Early interceptive tx or URA
• Orthodontic camouflage
• FA + surgery

Question 20

Describe the use of URA in class III patients - indications and design of appliance

Answer 20

• Class I or mild III only

- Design - URA with Z springs and adams on Ds and 6s with posterior capping

Question 21

Describe the movement in orthodontic camouflage in class III patients

Answer 21

• Procline ULS and/or retrocline LLS to correct incisor relationship
• +/- elastics

Question 22

What is the limitation of using elastic traction in class III patients

Answer 22

• May cause extrusion of molars which would reduce overbite

Question 23

What demonstrates good stability for class III patients treated with orthodontic camouflage?

Answer 23

• Adequate overbite

- Further growth is not unfavourable

Question 24

What are the indications for surgery (for class III)

Answer 24

Non growing
ANB <4
Inclination of lower incisors to mandibular plane is <80

Question 25

Describe the correction of class III patients with FA and surgery as a tx

Answer 25

- Fixed appliance removes/reduces any DAC and aligns | - Surgery corrects skeletal relationship

Question 26

Why does DAC need to be reduced/removed before surgery of class III patients

Answer 26

Vital to achieve a satisfactory occlusal and facial result post surgery

Question 27

What are the aims of camouflage for class III patients?

Answer 27

- Utilise DAC to camouflage skeletal pattern

Question 28

How to make space in class III patients?

Answer 28

- Extractions | - Expansion of the arch

Question 29

Aims of early interceptive treatment in class III

Answer 29

- enhance maxillary growth and restrain/redirect mandibular growth

Question 30

Methods of early interceptive treatment in class III

Answer 30

Protraction face mask Bone anchored maxillary protraction Chin cup

Question 31

Options for mild-moderate class III pattern

Answer 31

Accept or camouflage