Evolution 1

Evolution
and
Epidemiology of
malocclusion
www.indiandentalacademy.com

Introduction:
While dental caries has been
regarded as the major dental disease
throughout the world, Malocclusion
is a close runnerup.

With fluoridation, there is a good
chance for significant reduction or
even elimination of caries as a
problem.

The morphogenetic nature of most
malocclusions assures us that this
dentofacial problem will continue to
demand the best that dentistry can
offer for a long time, indeed.

Classification of malocclusion:
Purpose of classification:
1. Traditional reasons,
2. Ease of self communication,
3. Purpose of comparison,
4. Case references .

Various systems of classification ;
Angle’s system.
Dewey’s modifications.
Bennett’s classification.
Simon system.

Ackerman and Proffit system..
Lischer’s classification,
Ballarard’s incisor classification
Etc.

Angle’s system:
Edward H.Angle in 1899.
The first molar is the key to
occlusion.

Class I (Neutroclusion):
Mesiobuccal cusp of the maxillary first
molar occludes with the mesiobuccal
groove of the mandibular first molar.

The bony base supporting the
mandibular dentition is directly
beneath the maxillary dentition.
Malocclusion is confined to the mal
position of the teeth.

Normal anteroposterior relation
b/w the maxilla and mandible.

Class II ( Distoclusion):
The distobuccal cusp of the maxillary
first molar occludes with the mesio
buccal groove of the mandibular first
molar .

Distal relationship of the mandible
to the maxilla.
Two divisions of Class II.
Class II Division 1.
Class II Division 2.

Class II Division 1:
Protrusion or Labio
version of the maxillary
incisors.
‘U’ ‘V’

Class II Division 2:
Lingual inclination
of the maxillary
centrals and
labial inclination of
the maxillary
laterals.

Subdivision :
When the distoclusion occurs on one
side of the dental arch only the
unilaterality is referred to as the
subdivision of its division.

Class III ( Mesioclusion):
The mesiobuccal cusp of the
maxillary first molar occludes in the
interdental space b/w the
mandibular first molar and second
molar.

Pseudo Class III:
A habitual occlusion.

Class IV:
Angle Class IV occurs when the
subject has ,
A unilateral Class II accompanied
with a unilateral Class III.

Simon classification:
Malocclusion occurs in all three
planes.
Related the dental arches to the
anthropometric planes based on the
cranial landmarks.

Anteroposterior relation The
Orbital plane:
Should pass through the distal
third of the upper canine.
Ahead = Protraction.
Behind = retraction.

Transverse relation the Midsagittal
plane.
Distraction .
Contraction.

Vertical relation- Frankfurt horizontal
plane:
Abstraction.
Attraction .

Evolution of malocclusion:

Facial structures
Functional activity
Failure of certain genetically
determined features to reach their
full development rather than their
suppression.

Factors influencing this evolutionary
changes are:
1. Intrinsic genetic factors.
2. Local epigenetic factors.
3. General epigenetic factors.
4. Local environmental factors.
5. General environmental factors.

Intrinsic genetic factors:
Genetic factors inherent to the skull
tissue.

Local epigenetic factors:
Genetically determined influence
originating from adjacent
structures and spaces, e.g. brain ,
eyes, etc.

General epigenetic factors:
Genetically determined influences
originating from distant structures
e.g. hormones, etc.

Local environmental factors:
Local non genetic influences
originating from the external
environmental, e.g. local external
pressures, muscle forces,etc.

General environmental factors:
General non-genetic influence
originating from the external
environment, e.g. food, oxygen
supply.

Malocclusion has often been referred
to as a ''disease of civilization,"
The prevalence of malocclusion is
higher in developed countries. AJO, Volume
1981 Mar (250 - 262): Occlusal variation in a rural Kentucky community - Corruccini

There are three basic theories to explain genetic increase in prevalence of occlusal variation in modern urbanized
populations:
There are three basic theories to
explain genetic increase in
prevalence of occlusal variation in
modern urbanized populations:

1. Genetic admixture causes
independent assortment and
disharmonious mixing of various
shapes and sizes of tooth and jaw
attributes that no longer fit one
another.

One weakness of this theory is that
mismatches leading to dental spacing
would be expected to be as frequent
as dental crowding, whereas the
latter is much more prevalent.

2. Genetic inbreeding allows
normally rare traits to find
expression in the homozygous state .

The fact that malocclusion appears
rapidly (within one generation) in
some aboriginal peoples, once they
are contacted by Western cultures,
also calls this explanation into
question.

3. Natural selection pressures have
been relaxed for man because of
technology.
Hence, genetic mutations allowing
irregular occlusion are no longer
selected out and accumulate in the
population over many successive
generations.

Again, as with the inbreeding theory,
a major drawback to this explanation
is the fact that aboriginal populations
develop a significant incidence of
malocclusion within one generation
after contact with Western technology
and food products.

Although crowding, psychological
stress, environmental noise, or prenatal
disturbances might contribute to such
rapid changes in occlusion,

The key altered variable in these
circumstances was the diet and the
associated stress of mastication.
.

Ahlgren and colleagues found
lessened electromyographic activity
recorded for masticatory muscles in
boys with Class II malocclusion

Moyers also found variable muscle
function in persons with
malocclusion.

Watt and Williams and later
investigators have shown that the
maxillary dental arch becomes
narrower in rats fed a water-
softened diet as opposed to a hard
form of food.

Variation in size, shape, form ,
number and position of teeth.

Size and shape of teeth:
Most common and most obvious
possibility.
Large teeth and small jaws/ small
teeth large jaws can create
malocclusion.

Change in number of teeth:
Congenitally / Extracted.
Third molars.
Upper Lateral incisors. Incidence is
3 out of every 100.
Garn et al noted that the more distal
tooth in each morphologic class,
more likely it is subjected to
variations. www.indiandentalacademy.com

Epidemiology of malocclusion:

Epidemiology :
Epi- Among , demos- people, logos-
study.
The study of the distribution and
determinants of health related states
and events in the population.

Aims:
To describe the distribution and the
size of the problem in the population.
To identify the etiological factor.

To provide the data essential to the
planning, implementation,
evaluation of the services for the
prevention, control, treatment and to
the setting up of priorities among
those services.

The ultimate aim:
To eliminate or reduce health
problems or its consequences and
promote health and well being.

Prevalence:
The term prevalence is used to
indicate what proportion of a given
population is affected by a
condition at a given point of time.

Types of studies :
Cross sectional studies:
Longitudinal studies:

Cross sectional studies:
The simplest in concept and
execution is the cross sectional
study.
Individuals are chosen who may
be representative of a population
or of people in a particular
community.

Longitudinal studies:
In simple terms it as cross sectional
studies done for a longer duration by
repeating periodically.
Time consuming and difficult to
organize.

Occlusal indices:

An index is an expression of clinical observation in numerical values and is used to describe the status of the
individual or group with respect to a condition being measured. Indices have been developed to compare the
extent and severity of diseases
An index is an expression of clinical
observation in numerical values and
is used to describe the status of the
individual or group with respect to
a condition being measured.

Indices have been developed to
compare the extent and severity of
diseases.

Uses of occlusal indices:
•Diagnostic classification.
•Epidemiological data collection.
•Patient counseling.
•To record treatment priority needs.
•To assess treatment success .

•To record treatment need.
•To record treatment difficulty.
•To record malocclusion severity.
•To record desire.
•To record the amount of deviation
from ideal tooth relationship.

Different types of occlusal indices:
•Treatment priority index. ( TPI)
•Dental esthetic index ( DAI)
•Index of treatment need (IOTN)

•Handicapping malocclusion
assessment record.
•Treatment stability index.
•Treatment desire index ( TDI)
•Index for amount of deviation.

Prevalence of malocclusion:

The prevalence of malocclusion is
higher in developed countries.

Distoclusion in India is comparatively
low,
USA- 34%whites and 15% blacks.
Europe- 29%

Indians have more tendency towards
class II relation compared to the
Africans ( 4.26%)
Class III is less prevalent in India

Between 1930 and 1965 the
prevalence of malocclusion in US
was estimated to be 35%-95%.
Disparity was because of
investigators different criteria for
normal.

By 1970 two large surveys were
carried out.
Division of health statistics (USPHS)
6-11yrs b/w 1963-1965.
12-17yrs b/w 1969-1970.

1989-1994, NHANES III ( National
Health And Nutrition Estimates
Survey III).
The irregularity index,
Prevalence of midline diastema >
2mm,
Prevalence of posterior crossbite.

Overjet and overbite/open bite
were also measured.

Inference:
Over half of children b/w 8-11yrs
had well aligned incisors.
Percentage with excellent alignment
decreases by age 12-17yrs.
34% of population had well aligned
lower anteriors.

Nearly 15% of adolescents and adults
had severe irregularity of lower
incisors.

Midline diastema often present in
childhood 26%,
6% adolescents and adults have
midline diastema,
Blacks are more than twice as likely
to have a midline diastema.

Overjet of 5mm or more occurs in
23% 0f children, 15% in youth and
13% in adults.
Reverse overjet indicative of classIII
is less frequent 1% in children and
increases in adults slightly.

Severe deep bite >5mm occurs in
20% of children and 13% of adults.
Openbite occurs less frequently
about 1%.
Racial difference; deepbite is more
prevalent in whites than blacks.
Open bite is more prevalent in blacks
than whites.

Prevalence of malocclusion in India:

Prevalence of malocclusion in india has
been reported to be 19.6%-96.05%.
Some variation can be explained due to
the multi ethnic population.
Seven ethnic groups based on the
anthropometric measurements.

•Indo-Aryans occupy the estern
punjab and Kashmir.
•Sytho-Dravidans inhibit hilly tracts
of Madhya pradesh.
•Manglo-Dravidans seen in Bengal
and Orissa.
•Mongoloids are distributed in a belt
along the Himalayan region.

•Dravidans inhibit the southern India,
southern Bihar and costal Orissa.
•Aryo-Dravidans are mainly confined
to the Northern India.
•Turko-Iranians the frontier province (
POK)

Factors contributing to the extreme
variations are:
•Lack of demarcation between
prevalence of malocclusion in the
population Vs frequency distribution
of malocclusion among patients
visiting the hospital.
•Sample size and technique.

Inappropriate selection procedures.
Variation in age group , sex , inter and
intra observers, objective criteria.

Evolution 1

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Evolution 1