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Orthodontics > Class III Malocclusion > Flashcards

Class III Malocclusion Flashcards

1
Q

Prevalence of Class III Malocclusion compared to Class I and II + in ethnic groups

A

Less frequently observed
Higher freq in Asians

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2
Q

Angles classification of Class III

A

Mesiobuccal cusp of the upper first permanent molar occludes distal to the mesiobuccal groove of the lower first permanent molar

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3
Q

Dental causes of Class III malocclusion

A
  1. Localised crowding/displacement
    - Retroclined upper incisors
    - Proctrusive lower incisors
  2. Functional shift - Pseudo Class III
  3. Missing lower 2nd premolar - mesial tilt or drift of lower 1st molar
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4
Q

Skeletal causes of Class III malocclusion

A
  1. Maxilla too small (decreased SNA)
  2. Mandible too large (Increased SNB)
  3. Maxilla retropositioned (decreased SNA)
  4. Mandible positioned anteriorly (Increased SNB)

Ultimately = Decreased ANB + More negative WITS

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5
Q

What skeletal causes EXACERBATES Class III Malocclusion

A
  • Forward mandibular rotation
  • Reduced LAFH
  • More protrusive chin point
  • Vertically deficient maxilla
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6
Q

What skeletal cause is most common

A

BOTH maxilla retrusion and mandibular protrusion

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7
Q

What family history is important for class III patients

A

Family history of Mandibular prognathia! Hereditary!

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8
Q

What are other causes of mandibular prognathia

A
  • Latent mandibular growth (beyond puberty)
  • Mandibular asymmetry
  • (Environmental) Mandibular posture - constant distraction of condyle from fossa results in growth stimulus –> Functional shift pseudo class III - should seek early intervention
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9
Q

Definition of DAC

A

Physiological adaptation of the dento-alveolar components (teeth) in response to skeletal discrepancies, to maintain a reasonable occlusion (all 3 planes)

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10
Q

DAC in class III

A

Proclined Maxillary Incisors
Retroclined Mandibular Incisors

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11
Q

Class III Soft Tissue Characteristics
Esp max retrusion
6+4

A
  • Straight/Convex facial profile
  • Steep mandibular plane
  • Long lower facial height
  • Lip incompetence
  • Increased nasolabial angle
  • Increased throat length

Max retrusion
- Deep orbital rims
- Deficient cheekbones
- Straight or concave contour at maxilla point
- Interrupted nasal base lip contour

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12
Q

Where is the soft tissue profile measured from

A

Glabella to Subnasale to Pogonian

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13
Q

What other factors may affect the soft tissue profile

A
  • Soft Tissue thickness
  • Steep mandibular plane masks a long man
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14
Q

CR-MI slide of a Pseudo-Class III Malocclusion

A

Premature contact between incisors at CR, resulting in a forward displacement of the mandible to disengage the incisors and permit further closure into posterior occlusion (in MI)

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15
Q

Skeletal, Dental and Soft Tissue Characteristics of a Pseudo-Class III Malocclusion (including in primary dentition)

A

Skeletal:
- Decreased midface length
- Forward position of the mandible with normal mandibular length
Dental:
- Mesial step at MI and flush terminal plane at CR (75% of Primary molars)
- Retroclined maxillary incisors with proclined/nomal mandibular incisors (opposite of skeletal class III)
Soft tissue:
- Retrusive upper lip

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16
Q

Causes of a Pseudo-Class III Malocclusion

A

No familial history (72%)
Dental interference leading to anterior crossbite:
- Local environmental factors eg. retained primary teeth or odontomas, trauma - change the normal path of eruption
- Upper incisors erupt palatally and lower incisors erupt labially

17
Q

Clinical Significance of Pseudo Class III Malocclusion
4

A
  • Anterior crossbite limits maxillary growth - self corrects after 3 years
  • Teeth in traumatic occlusion may become mobile over time and/or present with gingival recession (lower incisors)
  • Functional malocclusion develops into a true mandibular skeletal asymmetry/prognathia overtime via adaptive remodelling
  • Dental asymmetry due to DAC
18
Q

Tx goal for children with pseudo class III malocclusion

A

Eliminate the shift as early as possible

19
Q

Can Class III malocclusions be predicted?

A

Yes! They are present at an early age.
Mesial step molar relationship primary teeth are at risk of developing Class III malocclusion,
This is because it usually worsens with maturity as:
1. There is molar shift into leeway space (size difference between primary molars and premolars)
2. Growth of mandible>maxilla

20
Q

Phase 1 treatment options for Class III malocclusions (in mixed dentition phase)

A
  1. Growth modification (before suture fusion)
    - Reverse-pull headgear (8-10 years old - circummaxillary sutures have not fused yet) –> connected to intra-oral componenet by rubber bands to pull maxilla forward (retruded maxilla)
    - Chin cup
  2. Dental correction
21
Q

Is the success rate of growth modification for retruded maxilla same as prognathic mandible?

A

No, prognosis for retruded maxilla>prognathic mandible.
Tx directed at mandible: relapse during pubertal growth period
Tx directed at maxilla: More promising results - stable 2 years post treatment, 25% reverted to negative overjet 4 years later due to excess horizontal mandibular growth

22
Q

Phase 1 treatment appliances for correction of dental crossbites

A
  • Removable appliance with auxillary springs
  • Maxillary lingual arch with finger springs
  • Sectional fixed appliances (braces on specific teeth) –> not dependent on patient compliance
23
Q

What orthodontic camouflage tactics are used for Class III malocclusion patients?

A
  • Upper incisor proclination and lower incisor retroclination
  • Class III elastics to pull the max forward and man backwards
  • Extraction of upper 5s (prevent upper incisors from falling back) and lower 4s (decrease risk of back teeth moving forward to worsen class III)
24
Q

What are the indications for orthognathic surgical treatment for Class III patients

A
  • Non-growing
  • Severe skeletal problems
25
Q

What are the orthognathic surgical treatment options for Class III patients

A

Maxillary advancement or mandibular setback

26
Q

What 2 factors affect treatment options

A

Aetiology and age

Orthodontics (18 decks)

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