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Malocclusion class iii
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Definition :
According to British Standards class iii
incisor relationship includes those
malocclusions ::*where the lower incisor edge
occludes anterior to the cingulum plateau of
upper incisors . , *the overjet is reduced or
reversed
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Ashraf 16 yrs old presented with incisor
3 relationship based on class 1 skeletal
relationship with anterior crossbite and
ectopic canines in the upper arch.
His oj=1 mm
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Incidence
-It affects 3% Caucasians
- 2- 5 % Jordanian people
The incidence of this malocclusion rangesbetween 4%and 13% among the Japanese and
4% and 14% among the Chinese
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Skeletal Pattern
eitiology
Features: A-P
vertical
Transverse
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Aetiology :Skeletal Pattern
The most important Factor in producing Class
iii malocclusion : skeletal class iii
A-P: the more adverse the skeletal pattern the
more severe the class iii
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Skeletal iii could result from
1.early closure of the nasomaxillary complex
sutures . 3.collapsed maxilla for cleft lip and palate
patients.
2.hereditary ,small size maxilla and big size
mandible.
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the prognathic mandible of Austrian
royal family
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*Now the class iii skeletal which is associated
with iii malocclusion could result from:
Maxilla : Retrognathic +- growth deficiency
MICROGNATHIA),
Mandible : Prognathic
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Skeletal Pattern Features
A-P: Usually there is Class iii skeletal pattern
It is possible to have class i skeletal
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Ashraf 16 yrs old presented with incisor 3 relationship based on class 1
skeletal relationship with anterior crossbite and ectopic canines in the upper
arch.
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Diagnosis of class III malocclusionPROFILE ASSESSMENT
Evaluate the chin
positionEvaluate midface
concave profile, flattening of the infraorbital rim
the chin is protruded
Convexity in midface
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Now how to determine you A-P skeletal pattern
with the aid of Cephalometics :
it is by determining the values of:
1-SNA: 81 +-2 (maxilla cranial base )
2- SNB:78 +-2 (mandible position )
3-ANB:
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Skeletal Pattern Features
Vertical :
We have wide range of the lower facial height
it could be : Avg , increased or decreased ,, So the overbite maybe normal in amount ,
deep ,reduced,, or we could have open bite
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*Decreased LFH:
Ant /vertical /Acc
growth
low mmpa
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*increased LFH:
Posterior growth
/horizontal /cc/
high mmpa :>27
Infront of occiput
Reduced OB or open bite
AlFH > 0.55
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Soft
tissue
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SOFT TISSUE:
The soft tissue surrounding play a very minor effect
in the etiology of class III malocclusion
Competent lips
This will induse retroclination of the lower incisors
and prolination of the upper incisors
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Incompetent lips
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these cases often have
a skeletal anterior open
bite
with an adaptive
variation of swallowing
behaviour e.g : tongue
to lower lip seal whichmay procline the lower
incisors.
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Dentoalveolar
AetiologyAnd
Occlusal features
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Dentoalveolar Aetiology
A-proclination of lower anterior teeth
B-retroclination of upper anterior teeth.
C-(or both)
mild CL III :
O.J.=(1,0,-1,-2 mm)
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Ashraf
Dental class iii Oj
1mm
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OCCLUSAL FEATURE:
Incisor iii
Overjet : reduced , edge-edge, or reversed
Molar relationship iii , i ,ii
C di
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Crowdingis more common and more severe inthe upper arch
often resulting from the fact that : The upper archis short and narrow compared with a longer and
wider lower arch.
Spacing : lower arch
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Overbite
The overbite may be increased ,average ,or
reduced.
Where the vertical facial proportions are
increased ,there is often an anterior open bite
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Skeletal open bite : symmmetrical , severe increased lower facial ht,beyond canine
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Cross bites
Cross bites of the labial and/or buccal
segments are common,. Cross bite may be
associated with a mandibular displacement
particularly where a unilateral buccal segmentcrossbite exists.
In the case of anterior cross bite, the
possibility of displacement should be assessed
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Diagnosis of class III malocclusionDENTAL ASSESSMENT
(overjet)
Negative overjet Positive overjet or endend
incisal relationship
FUNCTIONAL
ASSESSMENT
True class III
malocclusion
Pseudo class III
malocclusion
Compensated class III
malocclusion
No CR- CO shift CR- CO shift
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PSEUDO CLASS III MALOCCLUSION:
FUNCTIONAL ANALYSIS:
The path of closure is from the postural rest
position to occlusion must be carefully
studied.
The mandible may slide anteriorly into a
forced protrusion because of premature
contact and tooth guidance when the jaw
closes into full occlusion.
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PSEUDO CLASS III MALOCCLUSION:
CLASS III MALOCCLUSION WITH A PSEUDOFORCED BITE OR ANTERIORDISPLACEMENT
1. This condition is partially compensated by the
labial tipping of the upper incisors and the lingualinclination of the lower incisors pt is often withskeletal classi or mild iii
2. This tooth mal position results in additionalanterior guidance of the mandible on the pathfrom postural rest to the habitual occlusion asthe lingual aspect of thelower incisors rides onthe maxillary incisor margins after initial contact