Class III malocclusions Flashcards
What defines malocclusions?
the incisor relationship
Define a class III malocclusion?
Lower incisor edge occludes anterior to the cingulum plateau of the upper central incisor
The overjet is (usually) reduced or reversed
Do all C3 malocclusions have reversed/reduced overjets?
no
- can have the lower incisors occluding just slightly anterior to the upper cingulum
- can have edge to edge bite
What causes class III malocclusions? (3)
- Strong genetic link
Environmental factors;
* Cleft lip and palate – surgery early on = restricted growth of maxilla from scarring
* Acromegaly – increased growth hormone affects mandible
What skeletal features do patients with a C3 malocclusion usually present with?
What are these caused by?
usually have a class 3 antero-postero relationship however can also be class 1 (rarely class 2)
Caused by;
Small maxilla, large mandible, or both
What vertical skeletal pattern/features do patients with a C3 malocclusion usually present with?
how is the vertical skeletal pattern measured?
Can be associated with Average, increased or reduced vertical proportions
Assess;
- FMPA
- Facial height proportions
(Lateral ceph useful to assess)
what are the dental features of a C3 malocclusion? (5)
- Class III incisors
- Often but not always C3 molars
- Often reversed overjet
- Reduced overbites or AOB present
- Crossbites (Ant or post)
Describe the alignment of the upper and lower arches in px’s with C3 malocclusion. (4)
- Crowded maxilla
- Aligned or spaced mandible
- Dentoalveolar compensation commonly seen = proclined upper incisors ad retroclined lower incisors
- Tendency for displacement to achieve posterior contact
What dental features indicate that a C3 patient is more difficult to treat? (4)
- More than 1-2 teeth in anterior crossbites
- Skeletal element aetiology
- A greater A-P discrepancy
- Presence of anterior openbite
What is the relevance of soft tissues in terms of C3 malocclusions?
Not usually associated with cause however it does encourage dentoalvolar compensation
- Tongue proclines upper incisors
- Lower lip retroclines the lower incisors
Why should we treat class 3 malocclusions? (5)
- Aesthetics
- appearance of teeth
- Profile concerns
- Dental health:
- Attrition: Displacing jaw = wear of the labial face of upper and palatal face of the lowers
- Gingival recession
- Mandibular displacement = long term TMJ problems
- Function
- Speech: advise px that Correcting the malocclusion doesn’t always fix the speech
- Mastication
If a C3 malocclusion is corrected will the patients speech sound like someone without a C3 malocclusion?
not always - advise px that Correcting the malocclusion doesn’t always fix the speech
what are the implications of long term mandibular displacement?
TMJ dysfunction/pain
Why do we not carry out major/irreversible treatment on patients when they are still growing?
Growth is unfavourable as mandible growth continues longer than maxillary growth = worsens C3 incisor relationship/undo treatment
During which period of growth do the jaws undergo a growth spurt?
during the pubertal growth spurt
(large variation of when this occurs in patients)
how can we predict a px’s pubertal growth spurt?
Height and weight charts
What do we do if we are unsure if a patient is in their pubertal growth spurt?
do nothing and wait
list the treatment options for a C3 malocclusion. (5)
accept and monitor
interceptive treatment
growth modifications
orthodontic camouflage
orthodontics + orthognathic surgery
In what C3 patients is accept and monitor indicated? (3)
Mild cases
- Used when Px has n concerns
- Used when px has no Dental health indications (displacement or attrition)
In what C3 patients is interceptive tx indicated? (3)
- when Class III incisors have developed due to early contact on permanent incisors (i.e. mandibular displacement)
- In correction of anterior crossbite in mixed dentition has the advantage that further forward mandibular growth may be counter-balanced by some dento-alveolar compensation.
- Only suitable for correcting a lateral incisor crossbite if permanent canines are high above lateral roots
- Delay if canines have dropped down into the buccal position as this is a risk of resorption to lateral incisor
what dental feature indicates stability of the dentition post treatment?
the presence of a desired/good overbite before treatment
In what C3 patients are growth modifications indicated? (1)
those who are still growing
What does growth modification treatment aim to do?
Reducing/redirecting mandibular growth and encourage maxillary growth
How can we modify growth? (5)
Functional appliances;
* Chin cup (historic)
* Frankel III (not as commonly used)
* Reverse Twin block
- Protraction headgear +/- rapid maxillary expansion
- Protraction headgear +/- bollard implants
Why are frankel III’s not as commonly used to modify the growth of a C3 malocclusion? (3)
- it’s a one-piece appliance which is hard to wear all the time
- has lots of acrylic/wire = trauma to mucosa
- is prone to breakage
in what age of patient does Protraction headgear +/- rapid maxillary expansion have the best effects in growth modification?
mixed dentition - 8-10 years
What are the aims of Protraction headgear +/- rapid maxillary expansion in growth modification? (2)
Pulls maxilla forward with anchorage to the facemask
When used alongside rapid maxillary expansion = splits midpalatal and the circummaxillary suture = easier to pull maxilla forward
how many hours per day should Protraction headgear +/- rapid maxillary expansion be used?
minimum 14 hours
where are upper bollard implants placed?
infrazygomatic region
where are lower bollard implants placed?
region of lower canines
Describe what the aims of orthodontic camo of a C3 malocclusion are.
accept the underlying skeletal base relationship and aim for class 1 incisor relationships (Achieved with fixed appliances only)
In what C3 patients is orthodontic camo indicated? (5)
Px’s which have;
- Stopped growing
- Mild/moderate C3 (ANB>0 degrees)
- Increased/average overbite at start of tx
- Can edge to edge bite at start of tx
- Little/no DA comp (don’t want px to start tx with v proclined upper incisors and retroclined lowers)
Describe the usual extraction pattern for orthodontic camouflage treatment. (2)
what other factor influences this?
- Extract further back in uppers e.g. 5’s
- Extract further forward in lowers e.g. 4’s
Dental health can dictate pattern e.g. XLA teeth with poorer prognosis (heavily filled, carious etc)
what tx can we offer to a C3 patient who is unhappy with the appearance of their teeth however cannot have definitive tx since they are still growing?
Can align the upper arch only before px stops growing to satisfy complaints
- once px stopped growing you can correct the jaw relationship
what is orthognathic surgery?
Orthognathic surgery is surgical manipulation of the mandible and / or maxilla to produce optimal dentofacial aesthetics and function
In what C3 patients is orthognathic surgery indicated? (3)
- Pt with aesthetic or functional concerns
- Growth completed
- Moderate/Severe skeletal discrepancy
- A-P
- Transverse
- Vertical
List the treatment steps for a c3 patient undergoing orthognathic surgery and orthodontic tx. (3)
- Presurgical orthodontics
- Level, align, coordinate and decompensate
- Eliminate rotation and crowding
- correct angulation
upper incisors = 109 degree angulation
lower incisors = 90 degree angulation - Orthognathic surgery to reposition the jaws
- Mandible or Mandible ± Maxilla
- Post surgical Orthodontics (approx. 6 months)
What angulation of upper and lower incisors do we aim for in pre-surgical orthodontics prior to orthognathic surgery?
upper incisors = 109 degree angulation
lower incisors = 90 degree angulation
How long is orthodontic treatment post orthogathic surgery?
approx 6 months
