Class III Malocclusion

Question 1

How can skeletal pattern cause Class III malocclusion?

Answer 1

• Majority of Class III incisal relationships due to Class III skeletal base - most important aetiological factor
• Can be seen with increased vertical proportion or reduced lower face heights
  1. increased mandibular length
  2. more anteriorly placed glenoid fossa so that condylar head is positioned more anteriorly leading to mandibular prognathism
  3. reduced maxillary length
  4. more maxillary retrusion

Question 2

How can dental factors cause Class III malocclusion?

Answer 2

May have narrow upper arch and lower broad arch resulting in upper arch crowded and lower well aligned leading to upper incisors retroclined and lower incisors may be proclined

Question 3

What needs to be considered when treatment planning for Class III cases?

Answer 3

• Severity of skeletal pattern
• Expected pattern of future growth (average growth will tend to worsen the relationship)
• If already dentoalveolar compensated? check upper and lower incisor inclinations
• Normal or increased OB is an advantage
• Check if can achieve edge-to-edge and if anterior displacement occurs
• Crowding in each arch

Question 4

When is the prognosis for correction of Class III cases increased?

Answer 4

• Skeletal I or mild class III
• Pt can achieve edge-to-edge then displaces anteriorly
• Lower incisors proclined and upper incisors retroclined (i.e. no dentoalveolar compensation has occurred)
• Normal or increased OB

Question 5

What needs to be considered when extracting teeth in Class III cases?

Answer 5

• Although maxilla crowded frequently, should resist xla in upper arch only
• This will lead to worsening of incisal relationship
• If need to xla on top, then xla further forwards on bottom arch

Question 6

Is headgear used to treat Class III?

Answer 6

Do not distalise the upper buccal segments with headgear in Class III as this will restrain maxillary growth

Question 7

How can the incisor relationship be corrected in class III cases?

Answer 7

• Can be achieved by proclination of upper incisors or retroclination of lower incisors or a combination
• Using fixed appliance and Class III elastic traction

Question 8

How is Class III treated when pt is skeletal I or mild III?

Answer 8

• Procline upper incisors
• Depends on prognostic factors (OB, Mand deviation etc.)
• Best carried out in mixed dentition
• URA with z springs and cribs on Ds and 6s and posterior capping

Question 9

How is Class III treated when pt is mild to moderate skeletal III?

Answer 9

• Camouflage treatment - combination of proclination of upper incisors and retroclination of lower incisors can correct incisor relationship
• Provided there is adequate OB and further growth not unfavourable then the end result should be stable
• Using fixed appliance and Class III elastic traction
• Management of Class III by orthodontics alone involved dento-alveolar compensation for the underlying skeletal discrepancy i.e. camouflage
• When unsure about future growth pattern better to postpone tx until growth pattern established

Question 10

How is Class III treated when pt is moderate to severe skeletal III?

Answer 10

• During pubertal growth could attempt face mask but may relapse with further growth
• If later then combination of fixed appliance and surgery to correct skeletal problem once growth completed
• Surgery relies on removing existing dentoalveolar compensation first with pre-surgical fixed appliance followed by surgical correction of the jaw