aetiology could be due to - small maxilla - large mandible - combination of both

class 3 malocclusion Flashcards by Becky Wall

definition of class 3 malocclusion

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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incidence

3-8%

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which continent has a higher incidence?

Asia

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aetiology

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

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aetiology/features

skeletal (predominantly)
dental
STs

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skeletal AP

aetiology could be due to

small maxilla
large mandible
combination of both

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what skeletal base do pts normally present with?

class 3 but not always

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

more complex malocclusion to treat

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what is pseudo class 3?

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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skeletal vertical

may be associated with average, increased or reduced vertical proportions

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

increased FMPA and AOB

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skeletal - transverse

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

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dental features

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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dentoalveolar compensation

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

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estimating tx difficulty (in general)

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

= more complex case

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soft tissues

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

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why treat? - broad categories

aesthetics
dental health reasons
fct

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why treat - aesthetics?

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

profile concerns

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why treat - dental health reasons?

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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why treat - fct?

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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facial growth

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

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

could affect future tx if surgery required

cannot predict growth changes

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growth status

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

what shouldn’t you use to predict growth status?

cervical vertebral maturation (CVM) ceph

hand wrist radiographs

class 3 management options

``` accept/monitor intercept early with URA growth modification camouflage combined orthognathic/orthodontic tx ```

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

accept/monitor intercept early with URAs growth modification

which tx options are for the permanent dentition?

accept/monitor camouflage combined orthognathic/orthodontic tx

indications for accept/monitor

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

when is interceptive tx indicated?

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

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

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

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

if permanent canines are high above lateral roots | delay if canines have dropped down into buccal position as risk of resorption to lateral incisor

URA as interceptive tx

procline incisors over the bite | z spring or screw section

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

good OB

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

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

chin cup

``` 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 ```

when is a reverse twin block best and why?

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

how do reverse twin blocks work?

the angle the blocks are cut at - inhibit mandibular growth - enhance maxillary growth

Frankel 3

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

why do you need a compliant patient for protraction headgear?

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

protraction headgear

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

what age group does protraction headgear work best in?

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

bollard implants

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

principles of camouflage

``` accept underlying skeletal base relationship aim for class 1 incisors ```

favourable features for camouflage

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

camouflage general ext principles

extract further back in U arch | extract further forward in L arch

camouflage classic extraction

U5s, L4s | but not always possible - dental health may dictate ext pattern

aim of camouflage

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

if pt is still growing what corrective tx is ok?

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

orthognathic surgery definition

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

indications for orthognathic approach

fct/profile concerns growth completed moderate/severe skeletal discrepancy

MDT approach for orthognathic surgery

orthodontist MF surgeon technician psychologist

risk of bimaxillary surgery

increased risk to patient and recovery time

orthognathic tx stages

pre-tx ortho surgery post-surgical ortho

orthognathic tx stages - pre-tx ortho

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

orthognathic tx stages - post-surgical ortho

about 6 months

GDP role

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