Ch 2 Orthodontics

The aetiology and

classification of

malocclusion

By Cezar Edward

The aetiology of malocclusion

At a basic level, malocclusion can occur as a result of genetically

determined factors, which are inherited, or environmental factors, or

more commonly a combination of both inherited and environmental

factors acting together.

example caries (an environmental factor) has led to early

loss of many of the deciduous teeth then forward drift of the first permanent

molar teeth may also lead to superimposition of the additional

problem of crowding.

Examples of environmental influences include digit-sucking habits

and premature loss of teeth as a result of either caries or trauma. Soft

tissue pressures acting upon the teeth for more than 6 hours per day can

also influence tooth position. However, because the soft tissues including

the lips are by necessity attached to the underlying skeletal framework,

their effect is also mediated by the skeletal pattern.

the main types of malocclusion:

(1) Skeletal pattern – in all three planes of

space

(2) Soft tissues

(3) Dental factors

Functional occlusion

• An occlusion which is free of interferences to smooth

gliding movements of the mandible with no pathology

• Orthodontic treatment should aim to achieve a functional

Occlusion

• BUT lack of evidence to indicate that if an ideal functional

occlusion is not achieved that there are deleterious long-

term effects on the TMJs

Commonly used classifi cations

and indices 1-Angle’s classification

Angle’s classification was based upon the premise that the first permanent

molars erupted into a constant position within the facial skeleton,

which could be used to assess the anteroposterior relationship of the arches.

Angle described three groups:

• Class I or neutrocclusion — the mesiobuccal cusp of the upper first

molar occludes with the mesiobuccal groove of the lower first molar.

In practice discrepancies of up to half a cusp width either way were

also included in this category.

• Class II or distocclusion — the mesiobuccal cusp of the lower first

molar occludes distal to the Class I position. This is also known as a

postnormal relationship.

• Class III or mesiocclusion — the mesiobuccal cusp of the lower first

molar occludes mesial to the Class I position. This is also known as a

prenormal relationship.

2-British Standards Institute classification

based upon incisor relationship and is the most widely used

descriptive classification.

Some workers have suggested introducing a Class II intermediate

category for those cases where the upper incisors are upright and the

overjet increased to between 4 and 6 mm. However, this suggestion has

not gained widespread acceptance.

3-Summers occlusal index

It is popular in America, particularly for

research purposes.

The index scores nine defined parameters including molar relationship,

overbite, overjet, posterior crossbite, posterior open bite, tooth

displacement, midline relation, maxillary median diastema, and absent

upper incisors.

4-Index of Orthodontic Treatment Need

(IOTN)

The purpose of the index was to help determine

the likely impact of a malocclusion on an individual’s dental health

and psychosocial well-being. It comprises two elements.

Dental health component

five grades reflecting need for treatment :

• Grade 1 — no need

• Grade 2 — little need

• Grade 3 — moderate need

• Grade 4 — great need

• Grade 5 — very great need

an alternative approach is to look consecutively for the following features (known as

MOCDO):

• Missing teeth

• Overjet

• Crossbite

• Displacement (contact point)

• Overbite

Aesthetic component

The scores are categorized according to need for treatment as follows:

• score 1 or 2 — none “most aesthetic

• score 3 or 4 — slight

• score 5, 6, or 7 — moderate/borderline

• score 8, 9, or 10 — definite

5-Peer Assessment Rating (PAR)

The PAR index was developed primarily to measure the success (or otherwise)

of treatment. Scores are recorded for a number of parameters

Obviously it is difficult to achieve a significant reduction in PAR

in cases with a low pretreatment score.

A high standard of treatment is indicated by a mean percentage

reduction of greater than 70 per cent.

6-Index of Complexity, Outcome and Need

(ICON)

This new index incorporates features of both the Index of Orthodontic

Need (IOTN) and the Peer Assessment Rating (PAR).

Improvement grade = pre-treatment score – (4 × post-treatment score)

This ambitious index has been criticized for the large weighting

given to the aesthetic component and has not yet gained widespread

acceptability.

The total sum gives a pretreatment score, which is said to reflect the

need for, and likely complexity of, the treatment required. A score of

more than 43 is said to indicate a demonstrable need for treatment.

Reference