Class III malocclusions

Question 1

What defines malocclusions?

Answer 1

the incisor relationship

Question 2

Define a class III malocclusion?

Answer 2

Lower incisor edge occludes anterior to the cingulum plateau of the upper central incisor

The overjet is (usually) reduced or reversed

Question 3

Do all C3 malocclusions have reversed/reduced overjets?

Answer 3

no
- can have the lower incisors occluding just slightly anterior to the upper cingulum

• can have edge to edge bite

Question 4

What causes class III malocclusions? (3)

Answer 4

• Strong genetic link

Environmental factors;
* Cleft lip and palate – surgery early on = restricted growth of maxilla from scarring
* Acromegaly – increased growth hormone affects mandible

Question 5

What skeletal features do patients with a C3 malocclusion usually present with?

What are these caused by?

Answer 5

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

Question 6

What vertical skeletal pattern/features do patients with a C3 malocclusion usually present with?

how is the vertical skeletal pattern measured?

Answer 6

Can be associated with Average, increased or reduced vertical proportions

Assess;
- FMPA
- Facial height proportions
(Lateral ceph useful to assess)

Question 7

what are the dental features of a C3 malocclusion? (5)

Answer 7

• Class III incisors
• Often but not always C3 molars
• Often reversed overjet
• Reduced overbites or AOB present
• Crossbites (Ant or post)

Question 8

Describe the alignment of the upper and lower arches in px’s with C3 malocclusion. (4)

Answer 8

• Crowded maxilla
• Aligned or spaced mandible
• Dentoalveolar compensation commonly seen = proclined upper incisors ad retroclined lower incisors
• Tendency for displacement to achieve posterior contact

Question 9

What dental features indicate that a C3 patient is more difficult to treat? (4)

Answer 9

• More than 1-2 teeth in anterior crossbites
• Skeletal element aetiology
• A greater A-P discrepancy
• Presence of anterior openbite

Question 10

What is the relevance of soft tissues in terms of C3 malocclusions?

Answer 10

Not usually associated with cause however it does encourage dentoalvolar compensation
- Tongue proclines upper incisors
- Lower lip retroclines the lower incisors

Question 11

Why should we treat class 3 malocclusions? (5)

Answer 11

• 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

Question 12

If a C3 malocclusion is corrected will the patients speech sound like someone without a C3 malocclusion?

Answer 12

not always - advise px that Correcting the malocclusion doesn’t always fix the speech

Question 13

what are the implications of long term mandibular displacement?

Answer 13

TMJ dysfunction/pain

Question 14

Why do we not carry out major/irreversible treatment on patients when they are still growing?

Answer 14

Growth is unfavourable as mandible growth continues longer than maxillary growth = worsens C3 incisor relationship/undo treatment

Question 15

During which period of growth do the jaws undergo a growth spurt?

Answer 15

during the pubertal growth spurt
(large variation of when this occurs in patients)

Question 16

how can we predict a px’s pubertal growth spurt?

Answer 16

Height and weight charts

Question 17

What do we do if we are unsure if a patient is in their pubertal growth spurt?

Answer 17

do nothing and wait

Question 18

list the treatment options for a C3 malocclusion. (5)

Answer 18

accept and monitor

interceptive treatment

growth modifications

orthodontic camouflage

orthodontics + orthognathic surgery

Question 19

In what C3 patients is accept and monitor indicated? (3)

Answer 19

Mild cases
- Used when Px has n concerns
- Used when px has no Dental health indications (displacement or attrition)

Question 20

In what C3 patients is interceptive tx indicated? (3)

Answer 20

• 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

Question 21

what dental feature indicates stability of the dentition post treatment?

Answer 21

the presence of a desired/good overbite before treatment

Question 22

In what C3 patients are growth modifications indicated? (1)

Answer 22

those who are still growing

Question 23

What does growth modification treatment aim to do?

Answer 23

Reducing/redirecting mandibular growth and encourage maxillary growth

Question 24

How can we modify growth? (5)

Answer 24

Functional appliances;
* Chin cup (historic)
* Frankel III (not as commonly used)
* Reverse Twin block

• Protraction headgear +/- rapid maxillary expansion
• Protraction headgear +/- bollard implants

Question 25

Why are frankel III's not as commonly used to modify the growth of a C3 malocclusion? (3)

Answer 25

- 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

Question 26

in what age of patient does Protraction headgear +/- rapid maxillary expansion have the best effects in growth modification?

Answer 26

mixed dentition - 8-10 years

Question 27

What are the aims of Protraction headgear +/- rapid maxillary expansion in growth modification? (2)

Answer 27

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

Question 28

how many hours per day should Protraction headgear +/- rapid maxillary expansion be used?

Answer 28

minimum 14 hours

Question 29

where are upper bollard implants placed?

Answer 29

infrazygomatic region

Question 30

where are lower bollard implants placed?

Answer 30

region of lower canines

Question 31

Describe what the aims of orthodontic camo of a C3 malocclusion are.

Answer 31

accept the underlying skeletal base relationship and aim for class 1 incisor relationships (Achieved with fixed appliances only)

Question 32

In what C3 patients is orthodontic camo indicated? (5)

Answer 32

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)

Question 33

Describe the usual extraction pattern for orthodontic camouflage treatment. (2) what other factor influences this?

Answer 33

* 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)

Question 34

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?

Answer 34

Can align the upper arch only before px stops growing to satisfy complaints - once px stopped growing you can correct the jaw relationship

Question 35

what is orthognathic surgery?

Answer 35

Orthognathic surgery is surgical manipulation of the mandible and / or maxilla to produce optimal dentofacial aesthetics and function

Question 36

In what C3 patients is orthognathic surgery indicated? (3)

Answer 36

* Pt with aesthetic or functional concerns * Growth completed * Moderate/Severe skeletal discrepancy - A-P - Transverse - Vertical

Question 37

List the treatment steps for a c3 patient undergoing orthognathic surgery and orthodontic tx. (3)

Answer 37

* 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)

Question 38

What angulation of upper and lower incisors do we aim for in pre-surgical orthodontics prior to orthognathic surgery?

Answer 38

upper incisors = 109 degree angulation lower incisors = 90 degree angulation

Question 39

How long is orthodontic treatment post orthogathic surgery?

Answer 39

approx 6 months