Class III Flashcards
What is the prevalence of class III in the UK population?
<5%
What is the AP skeletal relationship in class III?
- Majority have a class III skeletal base
- Most important aetiology
List the causes of the class III AP skeletal pattern
- Increased mandibular length / acute cranial base angle due to anteriorly positioned glenoid fossa
- Reduced maxillary length (maxillary retrusion)
How does an acute cranial base angle / incr mandibular length result in a class III malocclusion
Glenoid fossa is placed anteriorly = condylar head is placed anteriorly
Therefore mandible is prognathic relative to the maxilla
Describe the vertical skeletal pattern in class III
Ranges - LFH can be increased, normal or reduced
What does forward rotation of the jaw lead to in class III patients
Chin prominence
Soft tissue factors in class III
- Very small role in aetiology
How can soft tissues impact the severity of class III malocclusions?
- Tend to reduce severity via DAC
- With competent lips - they procline the ULS and retrocline LLS to produce a less severe occlusion in comparison to the skeletal pattern
Explain the role of soft tissues on class III malocclusions with increased vertical proportions
- Lips tend to be incompetent with incr vertical proportions (oral seal via tongue to lower lip)
- No DAC seen
Describe the dental factors in class III malocclusions
- Maxilla narrow and often crowded
- Mandible broader and can be well aligned or even spaced
Summarise the occlusal features in class III
- Anterior cross bite (Reverse OJ)
- Buccal cross bite
- Varied molar and incisor relationship
- Upper jaw crowding, lower jaw aligned/spaced
- Varied vertical - deep overbite, normal or AOB
How does buccal cross bite occur in class III
- Size discrepancy between jaws
- Position of mandible relative to the maxilla
What are the different incisor relationships that may be seen in class III malocclusion?
- Edge to edge
- Edge to edge with forward displacement
- Frank reverse overjet
Describe edge to edge incisor relationship with forward displacement in class III patients
Edge to edge is achieved in RCP and the mandible is postured forward to achieve ICP (Essentially causing a reverse OJ and exaggerating severity of occlusion)
What factors influence tx options for class III patients
- Severity of skeletal pattern
- Patient expectations
- Growth pattern (amount and type)
- Age
- Degree of alveolar compensation
What type of growth is seen in class III patients? What is the significance?
- Forward growth of the mandible
- This is unfavourable as it worsens the malocclusion
What are good prognostic factors for class III correction?
- Class I or mild III skeletal base
- Pt can achieve edge to edge which displaces anteriorly
- No/minimal DAC
- Normal or increased overbite
Describe the relevance of extractions in class III tx
- Extractions in upper arch alone will worsen incisal relationship
- If extractions are necessary in, then extract further forward in lower arch = 55/44
List the tx options for class III
- Accept
- Early interceptive tx or URA
- Orthodontic camouflage
- FA + surgery
Describe the use of URA in class III patients - indications and design of appliance
- Class I or mild III only
- Design - URA with Z springs and adams on Ds and 6s with posterior capping
Describe the movement in orthodontic camouflage in class III patients
- Procline ULS and/or retrocline LLS to correct incisor relationship
- +/- elastics
What is the limitation of using elastic traction in class III patients
- May cause extrusion of molars which would reduce overbite
What demonstrates good stability for class III patients treated with orthodontic camouflage?
- Adequate overbite
- Further growth is not unfavourable
What are the indications for surgery (for class III)
Non growing
ANB <4
Inclination of lower incisors to mandibular plane is <80
Describe the correction of class III patients with FA and surgery as a tx
- Fixed appliance removes/reduces any DAC and aligns
- Surgery corrects skeletal relationship
Why does DAC need to be reduced/removed before surgery of class III patients
Vital to achieve a satisfactory occlusal and facial result post surgery
What are the aims of camouflage for class III patients?
- Utilise DAC to camouflage skeletal pattern
How to make space in class III patients?
- Extractions
- Expansion of the arch
Aims of early interceptive treatment in class III
- enhance maxillary growth and restrain/redirect mandibular growth
Methods of early interceptive treatment in class III
Protraction face mask
Bone anchored maxillary protraction
Chin cup
Options for mild-moderate class III pattern
Accept or camouflage
