class III malocclusion Flashcards
what is the definition of a class 3 malocclusion?
> 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
what is the significance of a class III malocclusion?
> 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)
what is the incidence of a class III malocclusion?
> Class III is a relatively uncommon malocclusion
> 3-5% (UK)
> more common in some ethnic groups (Far Eastern, Northern European)
what is the aetiology of a class III malocclusion?
> 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
what is the genetic background of a class III malocclusion?
> 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
what is the cephalometric tracing of a skeletal class III discrepancy?
ANB < 2 degrees
what are the skeletal features for a class III malocclusion?
> 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
what are the dental features of a class III malocclusion?
> 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
what is mandibular displacement?
> 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
what are the typical intraoral features of a class III malocclusion?
> +/- reverse overjet
> +/- increased overbite
> +/- hypodontia
what is dentoalveolar compensation?
> 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
why do we treat class III malocclusions?
> 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
what are the aims of class III malocclusion treatment?
> Produce a positive overjet
> Relieve crowding and align arches
> Improve facial profile
> Produce a stable result
what are the treatment options for class III malocclusion ?
> Accept the incisor relationship
> Procline the upper incisors
> Retrocline the lower incisors
> procline the uppers and retrocline the lowers
> Orthognathic Surgery (correct skeletal problems)
what are the treatment options for class III skeletal discrepancies?
> None / Mild: Orthodontic appliances only
(usually fixed)
> Moderate: +/- Orthognathic Surgery
> Severe: Orthognathic Surgery
(jaw surgery)
what is the unique timing of treatment for class III malocclusion?
> 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
what are the favourable factors for patients indicated for appliance treatment only in class III malocclusion?
> pre-treatment overbite
> ability to bite edge-edge
> anterior displacement
> Small or no skeletal discrepancy
> URA
what patients are suitable with class III malocclusion are suitable for fixed appliance treatment?
> Mild to moderate skeletal discrepancies with acceptable facial profile
> Crowded lower (and/or upper) arches
what is the aim of fixed appliance treatment for class III malocclusion?
> Aim is to produce dentoalveolar compensation
> retocline lowers, procline the uppers
what teeth are extracted to allow for retorclinatiion of lower incisors in class III malocclusion treatment with fixed appliances?
> 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
how do you increase anchorage in class III malocclusion treatment?
> 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
which class III patients are suitable for surgery as a treatment option?
> severe skeletal discrepancies and poor facial profile / appearance
> Vertical problems and anterior open bites
what are the stages of treatment for class III patients undergoing surgery as a treatment option?
- fixed appliances to align individual arches and produce decompensation - allows us to make a better facial profile once surgery is complete
- surgical mandibular setback
- maxillary advancement
what is the prognosis of class III malocclusion treatment?
> 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
what type of appliances are not used for treatment of class III malocclusions?
> functional appliances
