Class III Flashcards
all malocclusions are classed by
incisor relationship
definition of class III malocclusion
lower incisor edge occludes anterior to the cingulum plateau of the upper central incisor
3 presentations of class III,Not necessary for reverse OJ or ant Xbite
incidence of class III
Geographical variation
UK 3-5%
* Higher incidence in west of Scotland
* Higher incidence in Asia
aetiology of class III
**Strong genetic link **
* Patter of transmission controversial (unknown)
* Run in families
Environmental factors
* Cleft lip and palate - Restricted growth of maxilla due to cleft surgery
* Acromegaly - Inc production of growth hormone from pit gland will inc size mandible
3 aspects to consider when assessing malocclusion
features
skeletal
dental
soft tissues
skeletal - consider in
3 planes
* antero-posterior
* vertical
* transverse
antero-posterior skeletal relationship for class III
*All have class III incisor relationship
Left is class I skeletal
Middle is moderate class III
Right is class III skeletal with OB *
Aetiology could be due to
* Small maxilla
* Large mandible
* Combination of both (most)
vertical class III skeletal relationship
may be associated with average, increased or reduced vertical proportions
* Frankfort Mandibular Planes Angle
* Facial Height proportions
* Lateral Cephalometry
↑FMPA and anterior open bite more complex to treat –* likely need orthognathic*
transverse relationship of class III
A-P and transverse relationship linked
Retrusive maxilla sits on wider part of mandible
* Bilateral Crossbites - Narrow maxilla against wide mandible
dental features of class III
8
Vary
- Class III incisor relationship
- Class III molar relationship (not always)
- Tendency to reverse overjet
- Reduced overbite, anterior open bite may be present
- Crossbites sometimes: Anterior or Buccal
Alignment
* Maxilla often crowded common;
* Mandible often aligned or spaced
Dentoalveolar compensation
* Proclined upper inicors
* Retroclined lower incisors
* teeth erupt towards despite underlying skeletal discrepancy
Tendency for displacements on closing
* Mandible displacement to achieve posterior teeth contact
alignment in class III
- Maxilla often crowded common;
- Mandible often aligned or spaced
dentoalveolar compensation in class III
Proclined upper inicors
Retroclined lower incisors
teeth erupt towards despite underlying skeletal discrepancy
tendency for displacement on closing for class III
Mandible displacement to achieve posterior teeth contact
in general tx difficulty for class III malocclusion
estimate
.> number of teeth in anterior crossbite (more than 1-2)
Skeletal element in aetiology
.> the A-P discrepancy (vertical issues e.g. AOB)
Presence of anterior open bite
= more complex case
soft tissues in class III
Not usually involved in aetiology
Do encourage dentoalveolar compensation
* Tongue proclines the upper incisors
* Lower lip retroclines lower incisors
why tx class III malocclusions
3
aesthetics
dental health reasons
function
tx class III malocclusion for aeshtetics
dental
profile concerns
tx class III malocclusion for dental health reasons
attrition - wear on labial of UI and lingual face of LI
gingival recession - occlude healvily on LI, press root through buccal plate
mandibular displacement
tx class III malocclusion for function
speech - warn improve malocclusion, won’t necessarily alter speech
mastication
facial growth for class III malocclusions
Tends to be unfavourable
Mandibular growth continues for longer
Potential for Class III to get worse
Do not do anything irreversible until growth has stopped
* Could affect future treatment if surgery required
facial growth for class III malocclusions
Tends to be unfavourable
Mandibular growth continues for longer
Potential for Class III to get worse
Do not do anything irreversible until growth has stopped
* Could affect future treatment if surgery required
how to predict growth status
Difficult to predict
Height and weight charts
* ? Cervical vertebral maturation (CVM) on lateral ceph
* Evaluates the shape changes in the bodies of cervical vertebrae C2, C3 and C4 – already taking lat ceph to assess skeletal pattern
* difficult to reproduce, poor reliability and valid
DONT USE - Hand wrist radiographs - low reliability and risks of repeated radiography so not justified
Individual variation - If in doubt watch and wait
onset of pubertal growht spurs coincides with spurt in growth
class III management guide
5 options
accept and monitor
intercept early with URA
growth modification
camouflage
combined orthognathic/orthodontic tx
when to accept and monitor class III
no concerns
no dental heatlh indicatins - displacements/attrtion
mild cases
interceptive tx for class III malocclusion
when
Suitable if Class III incisors have developed due to early contact on permanent incisors (i.e. mandibular displacement)
Correction of anterior crossbite in mixed dentition has the advantage that further forward mandibular growth may be counter-balanced by some dento-alveolar compensation.
* Can achieve edge to edge, but displacing into anterior crossbite
* If pt continues to grow, mandible grows, dentoalveolar compensation teeth adapt to new position
Only suitable for correcting a lateral incisor crossbite 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 for interceptive ortho tx
URA procline incisors over the bite
* Z spring
* Screw section
* Need to disclose occlusion – molar capping over buccal segments
Good OB will maintain stability
growth modification for class III
when and options (4)
growing pt
* Aimed at reducing and / or redirecting mandibular growth and encourage maxillary growth
Functional appliances
* Chin cup
* Reverse Twin Block
* Frankel III
* Protraction headgear ± Rapid Maxillary Expansion
chin cup
doesn’t have large skeletal effect
Mainly historic form of treatment
Lingual tipping of lower incisors
Rotates mandible down and back
frankel III
Outdated now – sometimes used
* One piece appliance – hard to wear all the time
* Acrylic heavy - buccal flange, labial culottes - trauma and break easily
* Largely dentoalveolar effect
Pellotes (Shields) labial to upper incisors to hold lip away
Palatal arch to procline the upper incisors
Lower labial bow to retrocline the lower incisors
reverse twin block
Slope the opposite way to twin block
Hard to get pt to bite into wax correctly
* Need mandible in most retruded position
Best in pt who can have edge to edge at start of tx
Mainly dentoalveolar
protraction headgear
Co-operative patient
14 hour/day protraction facemask wear
400g/side – large force
Best results when used in early mixed dentition ( 8-10 years)
* Young pt – co-operation needed
± Rapid maxillary Expansion
* Pt needs to turn screw 2x daily – split mid palatal suture
* Attach to head gear – theory is disrupts circum-maxillary sutures as well
bollard implants
Used in late mixed and permanent dentition
Infrazygomatic crest and lower canine region
* Mucoperiosteal flaps need to be raised for insertion and removal
* GA maybe needed
Can be used in conjunction with facemask
what is orthodontic camoflauge for class III
accept underlying skeletal base relationship, aim for class 1 incisors
3 aims of camoflauge ortho tx
procline upper incisors
retrocline lower incisors
correct OJ
aim for class 1 incisors
favourable features for camoflage tx
5
Growth stopped
Mild to moderate Class III Skeletal base ANB not <0o
Average or inc OB
Able to reach edge to edge incisor relationship (Ask pt)
Little or no dentoalveolar compensation
* Don’t want pt to start tx with UI proclined and LI retroclined
extractions pattern for camoflage tx of class III
Extract further back in the upper arch
Extract further forward in the lower arch
Classic pattern - Upper 5’s , lower 4’s
* However not always possible
* Dental health may dictate extraction pattern
example tx plan for class III camoflage
- XLA all first permanent molars
- Surgically remove LL8 and LR8
- Upper and lower fixed appliances to treat to Class I
- Life long retention
what is good to have pre tx for retention of movement post camo tx (class III)
good overbite proportion
if pt still growing
do not embark on full correction - can get worse, pt undo results due to growth
* Cannot predict growth changes
* Consider upper arch alignment only - Keep pt happy until able to deal with underlying jaw relationship
Do not XLA in lower arch as this could affect future treatment options
* Risk reopen extraction sites in lower arch -> need pros tx
orthognathic surgery
def
surgical manipulation of the mandibule and/or maxilla to produce optimal dentofacial aesthetics and function
when would orthognathic/ortho tx approach be taken for class III
3
pt has aesthetic or functional concerns
growth completed
moderate/severe skeletal discrepanacy
* A-P
* transverse
* vertical
orthognathic surgical tx planning
Careful planning
Multidisciplinary team approach
* Orthodontist
* Maxillofacial surgeon
* Orthognathic Technician
* Psychologist
Prediction planning software
* Make image up of what pt is expected to look like post surgery
3 stages in orthognathic/orthodontic tx for class III
Presurgical orthodontics (approx. 18 months)
* Level, align, co-ordinate and decompensate
* Rid of curve of spee - want teeth to interdigitate when move jaws, as will make lateral OB
* Un-rorate teeth
* Coordinate width of arches- avoid lateral discrepancies
Uppers 109˚
Lowers 90˚
Orthognathic surgery to reposition the jaws
* Mandible
* Mandible ± Maxilla
Post surgical Orthodontics (approx. 6 months)
* settle bite in, with full time intermaxillary elastics usually
sometimes sugery first - want interdigitation after surgeryA
GDP role in class III management
identify class III malocclusion - refer to hosp or specialist
URA tx? - anterior cross bite correction
summary of class III malocclusion management
Challenging malocclusion to treat
Complicated by unpredictable growth
Careful assessment of aetiology important
* Purely dental? Or skeletal involvement?
* Is it treatable with orthodontics only?
