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Ortho > class 3 malocclusion > Flashcards

class 3 malocclusion Flashcards

1
Q

definition of class 3 malocclusion

A

L incisor edge occludes anterior to the cingulum plateau of the U central incisor
OJ reduced or reversed (doesn’t always mean a reverse OJ)

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2
Q

incidence

A

3-8%

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3
Q

which continent has a higher incidence?

A

Asia

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4
Q

aetiology

A 
strong genetic link
 - autosomal dominant
 - Habsburg family
CLP
 - restricted growth of maxilla
acromegaly
 - increased growth of mandible
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5
Q

aetiology/features

A

skeletal (predominantly)
dental
STs

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6
Q

skeletal AP

A

aetiology could be due to

  • small maxilla
  • large mandible
  • combination of both
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7
Q

what skeletal base do pts normally present with?

A

class 3 but not always

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8
Q

what does a greater AP discrepancy mean in terms of tx?

A

more complex malocclusion to treat

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9
Q

what is pseudo class 3?

A

pt may have edge to edge but then displace to class 3 to get posterior tooth contact
check for displacement of mandible on closing
often have underlying C1 skeletal relationship

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10
Q

skeletal vertical

A

may be associated with average, increased or reduced vertical proportions

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11
Q

what vertical skeletal features make the malocclusion more complex to tx?

A

increased FMPA and AOB

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12
Q

skeletal - transverse

A

AP and transverse relationship linked
retrusive maxilla sits on wider part of mandible
- bilateral crossbites

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13
Q

dental features

A 
vary
class 3 incisors
class 3 molars (not always)
tendency to reverse OJ
reduced OB, AOB may be present
crossbites
alignment
 - maxilla often crowded (as small)
 - mandible often aligned/spaced
dentoalveolar compensation
 - retroclined L incisors
 - proclined U incisors
tendency for displacements on closing
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14
Q

dentoalveolar compensation

A

incisors have altered their alignment to compensate for the skeletal base discrepancy

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15
Q

estimating tx difficulty (in general)

A

> no of teeth in anterior CB
skeletal element in aetiology
AP discrepancy
presence of AOB

= more complex case

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16
Q

soft tissues

A

not usually involved in aetiology
do encourage dentoalveolar compensation
- tongue prolines U incisors
- L lip retroclines L incisors

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17
Q

why treat? - broad categories

A

aesthetics
dental health reasons
fct

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18
Q

why treat - aesthetics?

A

dental - pt may call it “underbite”, crowded upper teeth

profile concerns

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19
Q

why treat - dental health reasons?

A

attrition - if displace to get posterior contact can get wear facets on labial of U incisors and lingual of L incisors
gingival recession
mandibular displacement

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20
Q

why treat - fct?

A

esp if severe
speech - but warn pt that correcting their incisor relationship won’t necessarily fix their speech
mastication - AOB - difficulty incising food

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21
Q

facial growth

A 
tends to be unfavourable
mandibular growth continues for longer (teenage years)
potential for class 3 to get worse
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22
Q

why shouldn’t you do anything irreversible until growth has stopped?

A

could affect future tx if surgery required

cannot predict growth changes

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23
Q

growth status

A

difficult to predict
can use height and weight charts
individual variation
if in doubt watch and wait

24
Q

what shouldn’t you use to predict growth status?

A

cervical vertebral maturation (CVM) ceph

hand wrist radiographs

25
Q

class 3 management options

A 
accept/monitor
intercept early with URA
growth modification
camouflage
combined orthognathic/orthodontic tx
26
Q

which tx options can be used while pt still growing and in mixed dentition?

A

accept/monitor
intercept early with URAs
growth modification

27
Q

which tx options are for the permanent dentition?

A

accept/monitor
camouflage
combined orthognathic/orthodontic tx

28
Q

indications for accept/monitor

A

mild cases
unsure how growth and development will progress
no dental health indications - no displacement or attrition
no concerns

29
Q

when is interceptive tx indicated?

A 
pt growing, mixed dentition
if class 3 incisors have developed due to early contact on permanent incisors
30
Q

what is the advantage of interceptive tx of the anterior CB in mixed dentition?

A

further forward mandibular growth may be counterbalanced by some dento-alveolar compensation

31
Q

when is interceptive tx only suitable for correcting a lateral incisor CB?

A

if permanent canines are high above lateral roots

delay if canines have dropped down into buccal position as risk of resorption to lateral incisor

32
Q

URA as interceptive tx

A

procline incisors over the bite

z spring or screw section

33
Q

what feature will help to maintain long-term stability from interceptive URA tx?

A

good OB

34
Q

what is the aim of growth modification and what appliances are used?

A

aim to reduce and/or redirect mandibular growth and encourage maxillary growth
functional appliances

35
Q

chin cup

A 
mainly historic form of tx
lingual tipping of L incisors
rotates mandible down and back
not all pts need mandibular growth restricted 
long-term effects not great
36
Q

when is a reverse twin block best and why?

A

if can achieve edge to edge as can record bite to make a registration

37
Q

how do reverse twin blocks work?

A

the angle the blocks are cut at

  • inhibit mandibular growth
  • enhance maxillary growth
38
Q

Frankel 3

A

pellotes (shields) labial to U incisors to hold lip away
palatal arch to procline U incisors
lower labial bow to retrocline L incisors
works on STs to an extent

39
Q

why do you need a compliant patient for protraction headgear?

A

need to wear the facemark for at least 14hours per day to have effect

40
Q

protraction headgear

A

fix with GIC
hyrax screw
- turn x2 per day to encourage circum-maxillary sutures to separate
allows us to move maxilla forward
apply fairly heavy forces to maxilla - 400g/side

+/- RME - disrupts circum-maxillary sutures

41
Q

what age group does protraction headgear work best in?

A

8-10 yr olds but in theory could work up to about 16 years. - until pts mid palatal suture has fused

42
Q

bollard implants

A

submucosal implants
plates attached to zygoma and symphysis of mandible
but need surgery to place - often GA
- will also need removed at end of tx

43
Q

principles of camouflage

A 
accept underlying skeletal base relationship
aim for class 1 incisors
44
Q

favourable features for camouflage

A

growth stopped
mild to mod class 3 skeletal base ANB not <0
average or increased OB (enhance post-tx stability)
able to reach edge to edge incisor relationship
little or no dentoalveolar compensation

45
Q

camouflage general ext principles

A

extract further back in U arch

extract further forward in L arch

46
Q

camouflage classic extraction

A

U5s, L4s

but not always possible - dental health may dictate ext pattern

47
Q

aim of camouflage

A

procline U incisors 120 max
retrocline L incisors 80 max
correct OJ

48
Q

if pt is still growing what corrective tx is ok?

A

upper arch alignment only
don’t XLA in L arch as this could affect future tx options - if pt grows unfavourably and you have already interfered and extracted - bad

49
Q

orthognathic surgery definition

A

surgical manipulation of the mandible and/or maxilla to produce optimal dentofacial aesthetics and function

50
Q

indications for orthognathic approach

A

fct/profile concerns
growth completed
moderate/severe skeletal discrepancy

51
Q

MDT approach for orthognathic surgery

A

orthodontist
MF surgeon
technician
psychologist

52
Q

risk of bimaxillary surgery

A

increased risk to patient and recovery time

53
Q

orthognathic tx stages

A

pre-tx ortho
surgery
post-surgical ortho

54
Q

orthognathic tx stages - pre-tx ortho

A

about 18m
level, align, co-ordinate, decompensate
Uppers 109, lowers 90
appearance often looks worse at this stage

55
Q

orthognathic tx stages - post-surgical ortho

A

about 6 months

56
Q

GDP role

A

identify class 3 malocclusion
refer - surgery referral 16years but can refer earlier if unsure
URA tx? - anterior CB reduction

Ortho (21 decks)

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