This chapter discusses the classification and etiology of malocclusion. Malocclusion can result from genetic factors, environmental factors, or a combination. Environmental influences include habits like digit-sucking and premature tooth loss from caries or trauma. Several commonly used classification systems are described, including Angle's classification (Classes I, II, III based on molar relationship), the British Standards Institute classification (based on incisor relationship), and the Index of Orthodontic Treatment Need (IOTN) which evaluates dental health and psychosocial impacts. The goal of orthodontic treatment is a functional occlusion without interference or pathology, though lack of an ideal occlusion may not cause long-term issues.

1. Ch 2 Orthodontics
The aetiology and
classification of
malocclusion
By Cezar Edward

2. 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.

3. the main types of malocclusion:
 (1) Skeletal pattern – in all three planes of
space
 (2) Soft tissues
 (3) Dental factors

4. 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

5. 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.

7. 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.

9.  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.

10.  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

11. 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

12.  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.

13.  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.

14. Reference