class III malocclusion

Question 1

what is the definition of a class 3 malocclusion?

Answer 1

> Lower incisor edges are anterior to the cingulum plateau of the upper incisors

> The diagnosis of a Class III malocclusion is based on the incisor relationship

> reversed overjet or edge to edge

Question 2

what is the significance of a class III malocclusion?

Answer 2

> Poor dental appearance

> May be associated with an anterior mandibular displacement

> Facial profile often poor

> Growth usually unfavourable (i.e. Mandible grows forward more than maxilla)

Question 3

what is the incidence of a class III malocclusion?

Answer 3

> Class III is a relatively uncommon malocclusion

> 3-5% (UK)

> more common in some ethnic groups (Far Eastern, Northern European)

Question 4

what is the aetiology of a class III malocclusion?

Answer 4

> Genetic – due to skeletal pattern

> Most are due to an AP skeletal discrepancy (mandibular excess, maxillary hypoplasia or both)

> May be a result of a mandibular displacement

> Cleft lip & palate patients

Question 5

what is the genetic background of a class III malocclusion?

Answer 5

> 13% of patients have an affected sibling

> 13% have a Class III mother

> 20% have a Class III father

> Family history can be useful in helping to predict future growth pattern

Question 6

what is the cephalometric tracing of a skeletal class III discrepancy?

Answer 6

ANB < 2 degrees

Question 7

what are the skeletal features for a class III malocclusion?

Answer 7

> 70% have a skeletal III pattern (ANB < 2 degrees)

> Skeletal pattern may be as a result of small maxilla and / or large mandible

> Maxilla is often narrow, resulting in crossbite

Question 8

what are the dental features of a class III malocclusion?

Answer 8

> Class III incisors (mild cases are edge-edge, severe cases may have a large reverse overjet)

> Dentoalveolar compensation (i.e. upper incisors proclined & lowers retroclined) - limits tx options

> Upper arch often narrow & crowded, crossbites

> Mandibular arch may be spaced or well aligned

Question 9

what is mandibular displacement?

Answer 9

> patient initially bites edge to edge then displaces forwards

> making the incisor relationship seem worse than it is in order for posterior teeth to be in occlusion

Question 10

what are the typical intraoral features of a class III malocclusion?

Answer 10

> +/- reverse overjet

> +/- increased overbite

> +/- hypodontia

Question 11

what is dentoalveolar compensation?

Answer 11

> occurs naturally with no tx

> upper incisors proclined
lower incisors retroclined

> caused by soft tissue

> restricts how much more orthodontic tooth movement can be carried out

Question 12

why do we treat class III malocclusions?

Answer 12

> Improve dentofacial appearance - reverse overjet, class III skeletal

> Psychosocial - teasing, can’t be carried out until the end of facial growth - end of teens

> Eliminate mandibular forward displacement if present

Question 13

what are the aims of class III malocclusion treatment?

Answer 13

> Produce a positive overjet

> Relieve crowding and align arches

> Improve facial profile

> Produce a stable result

Question 14

what are the treatment options for class III malocclusion ?

Answer 14

> Accept the incisor relationship

> Procline the upper incisors

> Retrocline the lower incisors

> procline the uppers and retrocline the lowers

> Orthognathic Surgery (correct skeletal problems)

Question 15

what are the treatment options for class III skeletal discrepancies?

Answer 15

> None / Mild: Orthodontic appliances only
(usually fixed)

> Moderate: +/- Orthognathic Surgery

> Severe: Orthognathic Surgery
(jaw surgery)

Question 16

what is the unique timing of treatment for class III malocclusion?

Answer 16

> Growth: often unfavourable and lasts longer in Class III cases (ie. Class III tends to get worse)

> Displacements can often be treated early using appliances to procline the upper incisors
- often in the mixed dentition

> Appliance treatment is usually carried out at a later age than in other types of malocclusion
- Age 15-16 when growth has stopped

> Severe upper arch crowding may require earlier treatment for psychological reasons

Question 17

what are the favourable factors for patients indicated for appliance treatment only in class III malocclusion?

Answer 17

> pre-treatment overbite

> ability to bite edge-edge

> anterior displacement

> Small or no skeletal discrepancy

> URA

Question 18

what patients are suitable with class III malocclusion are suitable for fixed appliance treatment?

Answer 18

> Mild to moderate skeletal discrepancies with acceptable facial profile

> Crowded lower (and/or upper) arches

Question 19

what is the aim of fixed appliance treatment for class III malocclusion?

Answer 19

> Aim is to produce dentoalveolar compensation

> retocline lowers, procline the uppers

Question 20

what teeth are extracted to allow for retorclinatiion of lower incisors in class III malocclusion treatment with fixed appliances?

Answer 20

> lower premolars

> often lower 4s if there is crowding of the lower incisors = gives space to retract canines and retrocline incisors

> if there isn’t as much crowding, lower 5s are removed to allow retraction of the canines and retroclination of lower incisors

> quite often upper arch is crowded too however it is best to try and not extract from the upper arch in order to keep it as large as possible

Question 21

how do you increase anchorage in class III malocclusion treatment?

Answer 21

> ask patient to wear inter arch elastics

> produce and distal force on the lower arch and a forward force on the upper arch

> helps correct a class III relationship

Question 22

which class III patients are suitable for surgery as a treatment option?

Answer 22

> severe skeletal discrepancies and poor facial profile / appearance

> Vertical problems and anterior open bites

Question 23

what are the stages of treatment for class III patients undergoing surgery as a treatment option?

Answer 23

1. fixed appliances to align individual arches and produce decompensation - allows us to make a better facial profile once surgery is complete
2. surgical mandibular setback
3. maxillary advancement

Question 24

what is the prognosis of class III malocclusion treatment?

Answer 24

> Growth is often unfavourable and continues longer. Incisor relationship often gets worse during teens

> Stability of incisor correction depends on the presence of a positive overbite

> Surgically treated cases are usually stable

Question 25

what type of appliances are not used for treatment of class III malocclusions?

Answer 25

> functional appliances