class III malocclusion Flashcards
definition of class III malocclusion BSI
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)
incidence
3-8%
which continent has a higher incidence?
Asia
aetiology
strong genetic link - autosomal dominant - Habsburg family CLP - restricted growth of maxilla acromegaly - increased growth of mandible - pituitary adenoma increased release of GH
aetiology/features
skeletal (predominantly)
dental
STs
skeletal AP
aetiology could be due to
- small maxilla (majority)
- large mandible
- combination of both
what skeletal base do pts normally present with?
class 3 but not always
what does a greater AP discrepancy mean in terms of tx?
more complex malocclusion to treat
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
skeletal vertical
may be associated with average, increased or reduced vertical proportions
what vertical skeletal features make the malocclusion more complex to tx?
increased FMPA and AOB
skeletal - transverse
AP and transverse relationship linked
retrusive maxilla sits on wider part of mandible
- bilateral crossbites
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
dentoalveolar compensation
incisors have altered their alignment to compensate for the skeletal base discrepancy
estimating tx difficulty (in general)
> no of teeth in anterior CB
skeletal element in aetiology
AP discrepancy
presence of AOB
= more complex case
soft tissues role in dentoalveolar compensation
not usually involved in aetiology
do encourage dentoalveolar compensation
- tongue prolines U incisors
- L lip retroclines L incisors
why treat? - broad categories
aesthetics
dental health reasons
fct
why treat - aesthetics?
dental - pt may call it “underbite”, crowded upper teeth
profile concerns
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
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
Effect of facial growth
tends to be unfavourable mandibular growth continues for longer (teenage years) potential for class 3 to get worse
why shouldn’t you do anything irreversible until growth has stopped?
could affect future tx if surgery required
cannot predict growth changes
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
Not reliable
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 design 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
Growth modification for class III examples
- protraction head gear +/- rapid maxillary expansion
- functional appliance
- chin cup
- modified twin block
- Franker III
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 facemask 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 infrazygomatic crest and lower canine region
but need surgery for insertion and removal - mucoperiosteal flap - often GA
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 <-3
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
how long is 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
