Class III Malocclusions

Question 1

What is the definition of a class III malocclusion?

Answer 1

The lower edges occlude anterior the cingulum plateau of the upper central incisor.The overjet is reduced or revered.

Question 2

Explain the aetiology of a class III skeletal base.

Answer 2

Retrognathic/underdeveloped maxillaPrognathic/well developed mandibleOr a combination of both.

Question 3

What vertical skeletal features are commonly associated with a class III?

Answer 3

Average, increased, or reduced verticle proportions of:- FMPA angle- Facial height proportionsAnd has been associated with a tranverse relationship, due to bilateral crossbites.

Question 4

What are the dental features of a class III?

Answer 4

Class III incisor relationshipClass III molar relationship (but not always)Tendency to reverse overjetReduced overbite, AOB may be presentAnterior/buccal crossbitesMaxilla often crowded, but mandible often spaced/aligned

Question 5

By what mechanism do proclined upper incisors, and retroclined incisors occur in a class III?

Answer 5

Dentoalveolar displacement

Question 6

How do the soft tissue impact the aetiology of a class III?

Answer 6

Normally not involved, however the soft tissues can cause:- The tongue to procline the upper incisors- The lower lip the retrocline the lower incisors

Question 7

What is the justification for treating a class III malocclusion?

Answer 7

Aesthetics (dental, profile concerns)Dental health (arttition, gingival recession, mandibular displacement)Functional (speech, mastication)

Question 8

WWhich factors make it difficult to treat class III malocclusions?

Answer 8

More teeth in anterior crossbitesAP discrepancyAnterior open bite often presentFacial growth can be unfavourable for orthodontic treatment

Question 9

What management options are there for class III malocclusions?

Answer 9

Accept/monitorIntercept early with a URAGrowth modication (functionals, headgear)Camouflage (accept skeletal, but correct incisors to class I)Orthodontics and orthognathic surgery

Question 10

When can growth modifcation for a class III case be considered?

Answer 10

In a growing patient, where accepting the skeletal relationship is undesirable.

Question 11

What appliances can be used for modifying growth?

Answer 11

Reverse twin blockFrankel IIIProtraction headgear

Question 12

When can orthodontic camouflage be considered for a class III case?

Answer 12

Growth has stoppedMild-moderate skeletal baseANB not <0 degreesAverage or increased overbiteAble to reach edge to edge incisor relationship

Question 13

What 4 special investigations can be done for class III patients?

Answer 13

OPTlateral cephCBCT Clinical photographs Study models

Question 14

What is ANB for class III patients?

Answer 14

Class III = <2 degrees

Question 15

What are the indications for orthognathic surgery?

Answer 15

When growth is complete in severe Skeletal A/P discrepancy or vertical direction in class II cases In cleft lip and palate 18-20 year olds as part of treatment plan Used in class III malocclusions when there is functional, mastication and profile concerns

Question 16

What special tests should be carried out before orthognathic surgey?

Answer 16

Radiographs – lateral ceph; OPT; CBCTClinical photographs Study models

Question 17

Give two examples of maxillary orthognathic surgery.

Answer 17

Bilateral saggital split osteotomy (BSSO)Vertical subsigmoid osteotomy (VSSO)

Question 18

Give two examples of mandibular orthognathic surgery.

Answer 18

LeFort 1Anterior maxillary osteotomy

Question 19

What is dentoalveolar compensation?

Answer 19

The body’s attempt at creating a ‘normal’ relationship between upper and lower arches when not occurring naturally. E.g. proclination and retroclination of incisors.