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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