Class III Malocclusion Flashcards
Prevalence of Class III Malocclusion compared to Class I and II + in ethnic groups
Less frequently observed
Higher freq in Asians
Angles classification of Class III
Mesiobuccal cusp of the upper first permanent molar occludes distal to the mesiobuccal groove of the lower first permanent molar
Dental causes of Class III malocclusion
- Localised crowding/displacement
- Retroclined upper incisors
- Proctrusive lower incisors - Functional shift - Pseudo Class III
- Missing lower 2nd premolar - mesial tilt or drift of lower 1st molar
Skeletal causes of Class III malocclusion
- Maxilla too small (decreased SNA)
- Mandible too large (Increased SNB)
- Maxilla retropositioned (decreased SNA)
- Mandible positioned anteriorly (Increased SNB)
Ultimately = Decreased ANB + More negative WITS
What skeletal causes EXACERBATES Class III Malocclusion
- Forward mandibular rotation
- Reduced LAFH
- More protrusive chin point
- Vertically deficient maxilla
What skeletal cause is most common
BOTH maxilla retrusion and mandibular protrusion
What family history is important for class III patients
Family history of Mandibular prognathia! Hereditary!
What are other causes of mandibular prognathia
- Latent mandibular growth (beyond puberty)
- Mandibular asymmetry
- (Environmental) Mandibular posture - constant distraction of condyle from fossa results in growth stimulus –> Functional shift pseudo class III - should seek early intervention
Definition of DAC
Physiological adaptation of the dento-alveolar components (teeth) in response to skeletal discrepancies, to maintain a reasonable occlusion (all 3 planes)
DAC in class III
Proclined Maxillary Incisors
Retroclined Mandibular Incisors
Class III Soft Tissue Characteristics
Esp max retrusion
6+4
- Straight/Convex facial profile
- Steep mandibular plane
- Long lower facial height
- Lip incompetence
- Increased nasolabial angle
- Increased throat length
Max retrusion
- Deep orbital rims
- Deficient cheekbones
- Straight or concave contour at maxilla point
- Interrupted nasal base lip contour
Where is the soft tissue profile measured from
Glabella to Subnasale to Pogonian
What other factors may affect the soft tissue profile
- Soft Tissue thickness
- Steep mandibular plane masks a long man
CR-MI slide of a Pseudo-Class III Malocclusion
Premature contact between incisors at CR, resulting in a forward displacement of the mandible to disengage the incisors and permit further closure into posterior occlusion (in MI)
Skeletal, Dental and Soft Tissue Characteristics of a Pseudo-Class III Malocclusion (including in primary dentition)
Skeletal:
- Decreased midface length
- Forward position of the mandible with normal mandibular length
Dental:
- Mesial step at MI and flush terminal plane at CR (75% of Primary molars)
- Retroclined maxillary incisors with proclined/nomal mandibular incisors (opposite of skeletal class III)
Soft tissue:
- Retrusive upper lip
Causes of a Pseudo-Class III Malocclusion
No familial history (72%)
Dental interference leading to anterior crossbite:
- Local environmental factors eg. retained primary teeth or odontomas, trauma - change the normal path of eruption
- Upper incisors erupt palatally and lower incisors erupt labially
Clinical Significance of Pseudo Class III Malocclusion
4
- Anterior crossbite limits maxillary growth - self corrects after 3 years
- Teeth in traumatic occlusion may become mobile over time and/or present with gingival recession (lower incisors)
- Functional malocclusion develops into a true mandibular skeletal asymmetry/prognathia overtime via adaptive remodelling
- Dental asymmetry due to DAC
Tx goal for children with pseudo class III malocclusion
Eliminate the shift as early as possible
Can Class III malocclusions be predicted?
Yes! They are present at an early age.
Mesial step molar relationship primary teeth are at risk of developing Class III malocclusion,
This is because it usually worsens with maturity as:
1. There is molar shift into leeway space (size difference between primary molars and premolars)
2. Growth of mandible>maxilla
Phase 1 treatment options for Class III malocclusions (in mixed dentition phase)
- Growth modification (before suture fusion)
- Reverse-pull headgear (8-10 years old - circummaxillary sutures have not fused yet) –> connected to intra-oral componenet by rubber bands to pull maxilla forward (retruded maxilla)
- Chin cup - Dental correction
Is the success rate of growth modification for retruded maxilla same as prognathic mandible?
No, prognosis for retruded maxilla>prognathic mandible.
Tx directed at mandible: relapse during pubertal growth period
Tx directed at maxilla: More promising results - stable 2 years post treatment, 25% reverted to negative overjet 4 years later due to excess horizontal mandibular growth
Phase 1 treatment appliances for correction of dental crossbites
- Removable appliance with auxillary springs
- Maxillary lingual arch with finger springs
- Sectional fixed appliances (braces on specific teeth) –> not dependent on patient compliance
What orthodontic camouflage tactics are used for Class III malocclusion patients?
- Upper incisor proclination and lower incisor retroclination
- Class III elastics to pull the max forward and man backwards
- Extraction of upper 5s (prevent upper incisors from falling back) and lower 4s (decrease risk of back teeth moving forward to worsen class III)
What are the indications for orthognathic surgical treatment for Class III patients
- Non-growing
- Severe skeletal problems
What are the orthognathic surgical treatment options for Class III patients
Maxillary advancement or mandibular setback
What 2 factors affect treatment options
Aetiology and age
