Class 3 Flashcards
What is class 3 defined as
Lower incisor edge occludes anterior to the cingulum plateau of the upper central incisor
Overjet is reduced or reversed
Least common incisor classification
What is the aetiology of class 3 split into
genetics
environmental factors
skeletal
dental
soft tissues
What is the genetic aetiology for class 3
Strong genetic link but pattern of transmission is controversial
What is the environmental aetiology for class 3
Higher incidence in those with cleft lip/palate & acromegaly
What is the most common skeletal AP relationship in class 3
Class 3 skeletal relationship most common but can occur on class 1 or class 2 base
The greater the AP discrepancy, the harder it is to treat
What can the class 3 ap skeletal base be due to
Small maxilla
Large mandible
Combination of both
What is the vertical skeletal features that can contribute to the aetiology
Can present with average, increased or reduced FMPA & facial height proportions
If the patient has increased FMPA angle, increased vertical facial proportions and particularly if they have an anterior open bite then it makes the class III malocclusion much more difficult to manage
What are the transverse skeletal features that may be seen with class 3
The AP and transverse relationship are linked
It is common to have a small maxilla and if it is then the narrower part of the maxilla sits against the wider part of the mandible resulting in buccal bilateral crossbites
What dental features contribute to the aetiology
class III molar relationship (not always)
tendency for reverse overjet
reduced overbite, anterior open bite may be present
may see anterior or buccal crossbites
alignment - maxilla is often crowded and mandible is often aligned or spaced
dentoalveolar compensation
mandibular displacement is common on closing especially with milder class 3 malocclusion
What is the dentoalveolar compensation seen in class 3
Proclined upper incisors
Retroclined lower incisors
Do soft tissues have any involvement in aetiology
o Not usually involved in aetiology
o However they do encourage dentoalveolar compensation:
Tongue prolines the upper incisors
Lower lip retroclines lower incisors
When is a class 3 case complex
if these features present
> number of teeth in anterior xbite
Skeletal element in aetiology
> the AP discrepancy
Presence of AOB
What are treatment considerations we need to think off
treatment difficulty
facial growth
growth status
What should we consider regarding facial growth prior to tx
o Unfavourable
o Mandibular growth continues for longer so potential for it to get worse
o Do not do anything irreversible until growth has stopped as it could effect future tx if surgery is required
What should we consider regarding growth status prior to tx
o The onset of pubertal growth spurt coincides with a spurt in the jaw so it is helpful if we can predict when pubertal growth spurt is going to occur
o Most reliable method is using height and weight charts
o If in doubt, watch and wait, as there is individual variation
What are the reasons for treating class 3
aesthetics
dental health reasons
function
What are the aesthetic concerns
dental
profile
What are the dental health reasons for tx
attrition
gingival recession
mandibular displacement
Why are class 3 prone to attrition
Can cause wear on labial face of upper incisors and lingual face of lower incisors
Why are class 3 prone to gingival recession
If upper incisors occluding heavily on inside of lower incisors as it can push the roots of the lower incisors through the buccal plate
Why is mandibular displacement problematic
Long term TMJ problems
What are the treatment options for class 3
accept
interceptive
growth modification
camouflage
orthognathic surgery
When is it a good idea to accept
no aesthetic concerns
no dental health indications
mild cases
When is interceptive treatment suitable
if class III incisors have developed due to early contact on the permanent incisors – edge to edge (i.e mandibular displacement) – can treat early on
Why is correction of anterior crossbite early on advantageous
that further forward mandibular growth may be counter balanced by some dentoalveolar compensation
What device would be used for treatment of anterior xbite
URA
z spring used
What makes a patient suitable for growth modification
must be growing
What is the aim of growth modification
to reduce/redirect mandibular growth and encourage maxillary growth
What are the different functional appliances
chin cup
frankel 3
reverse twin block
protraction headgear
bollard implants
What is frankel 3
Labial shield holds upper lip away from incisors to let them procline
Palatal arch pushes against the upper incisors
Labial bow used to retrocline
Not favoured anymore
What is reverse twin block
Blocks slope in opposite direction of the class 2 traditional twin block
Hard to construct
Works best for patients who are edge to edge at the start of tx
Mainly has a dentoalveolar effect on the teeth
What is protraction headgear
- Only for the cooperative patient
- Best results in early mixed dentition
- Can be used with or without RME
What are 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
What is camouflage
o Accepting underlying skeletal base relationship and aiming for class 1 incisors
What are the favourable features for camouflage
Growth stopped
Mild to moderate class 3 skeletal base (ANB not <0)
Average/increased overbite
Able to reach edge to edge incisor relationship
Little or no dentoalveolar compensation
What is the extraction pattern for class 3
Extract further back in upper arch and further forward in lower arch
Classic pattern = upper 5s/lower 4s
However dental health may dictate extractions
What are the aims of camouflage in class 3
Procline upper incisors
Retrocline lower incisors
Correct OJ
Why should you not do camouflage in a growing patient
Can not predict growth changes, px may require surgery in future and extraction/tooth movements may cause problems and require to be undone
Consider upper arch aligment only
Do not XLA in the lower arch as this could affect future tx options
What is orthognathic surgery
Surgical manipulation of the mandible and/or maxilla to produce optimal dentofacial aesthetics and function
What are the indications for orthognathic surgery
Px usually has aesthetic or functional concerns
Growth is completed
Moderate/severe skeletal discrepancy often with increased vertical dimension
What is done in the presurgical orthodontics
Level, align, coordinate and decompensate (getting rid of curve of spee)
Uppers 109 degrees
Lower 90 degrees
