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
URA design as interceptive tx
procline incisors over the bite
z spring or screw section
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
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
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
bollard implants
submucosal implants
plates attached to infrazygomatic crest and lower canine region
but need surgery for insertion and removal - mucoperiosteal flap - often GA
