Genetics and Orthodontics

Genetics is a science
concerned with structure

and function of all genes in
different organisms.
Gregor mendel
Father of genetics
WHY SHOULD A STUDENT OF
ORTHODONTICS BE INTERESTED IN
GENETICS????
• Because they effect growth and
development and function of oral and
facial structure which is important for
an orthodontics.
• It also help us to diagnose ,treat and
subsequently maybe prevent malocclusion
from occurring in next generation.
• Genetic disorders in a general aspect
can be considered to be of two
types:-
 Numerical disorder.
 Structural disorders.
• Numerical disorders:- These are those in which
there is a change in the number of chromosomes
within the cell.
• Eg:-
– Polyploidy
– Monosomy
– Trisomy
– Turner’s syndrome.
– Klinefelter’s syndrome.
• Structural disorders:- Those in which there is
change in basic composition & structure of
chromosomes.
• Eg:-
– Translocation.
– Deletions.
– Ring chromosomes.
MODE OF
TRANSMISSION OF
MALOCCLUSION:-
3. VARIABLE TRAITS :-
• Occurrence of different but related type of
malocclusion within several generation of same
family.
• Traits seen with variable expression
eg,missing teeth,which are commonly seen
feature in some families, but the same teeth
may not be missing in different generations or
within the same generation.
• A diagnosis of genetic malocclusion should be
made on bases of longitudinal studies of
padigree same family.
• Human potentialities are determined by the
genotype, but their manifestation depends on
environment.-also known as epigenetics
• Evidence of genes being responsible for a
particular characteristic in the production of
an anomaly can be masked by environmental
conditions such as climate, economic condition
,oral hygiene.
• Knowledge of human inheritance is possible
only from study of pedigree and not on
experimentation.
• Humen twins can be of 2 types:-
– Monozygotic twins.
– Dizygotic twins.
 MONOZYGOTIC TWINS:- They are
two individuals developed from single
fertilized ovum,which divides into two
at an early stage of development.
 These twins thus have a genetic
make-up identical to each other.
• Dizygotic twins:- They are two
individuals developed fromm two
saperate ova,ovulated & fertilized
by two different sperms.
• These twins are not genetically
identical as they develop from
two different embryos.
• AUTOSOMAL DOMINANT INHERITANCE
• Trait appear in every generation .
• An affected child must have at least one
affected parent.
• About one half of the offspring of an affected
person are affected(reoccurrence risk is 50% at
each conception)
• Both male & female persons are affected.
• Abnormal recessive genes are transmitted through
hetrozygotes.
• Characteristics:
• The trait visible only in siblings but not in their
parents and relatives .
• Parents of an affected person may have been blood
relatives .
• About one fourth of children are
affected;reccurrence risk is 25%.
• Both male and female children have equal chance of
being affected.
• This type of inheritance is mostly X-linked
• Predominantly males are affected
• Heterozygous females are carriers expected to produce
normal & affected sons in ratio of 1:1
• An affected male never produces an affected son (for ex:
hemophilia)
• Characteristic of x-linked recessive inheritance
• males are affected more frequently than females
• When the female parent is carrying the trait then 50% of her
sons are affected & 50% daughter are carriers
• Affected male parent cannot transmit the trait directly to his
sons i.e. trait will skip a generation
• Affected male parent transmit the trait to his
daughter but not to the son
• When affected females are homozygous they
transmit the trait to all children irrespective of
their sex
• When affected females are heterozygous – only
50% of children of both sexes have a chance of
being affected
• The clinical features are due to cummulative effects
of all polygenes as well as other factors
• Other factors may be certain other genes or local or
general environmental factor
• Classical ex – cleft lip & cleft palate
• Developmental hereditary characteristics
are influenced by local and general
environmental factors and their penetrance
and expressivity can be greatly modify by
these influence
• Occlusal variations are polygenic that is
control by many genes and various
environmental factors
• Extreme deviation are due to chromosomal
or single gene effect.
Genetics related to
malocclusions
Class II :- The size ,position & relation of the jaws are
to a large extend by genes.
thus class II malocclusion exibiting skeletal
anomalies such as prognathic maxilla or retrognathic
mandible can be due to hereditary cause.
Class II div 1 malocclusion-Extensive cephalometric
studies have been caried out to determined the
heretibility of certain craniofacial parameter in
class II div. 1 malocclusion.
• These investigation have shown that in the class
II patient the mandible is significantly more
retruded than in class I patients with the body of
mandible smaller & overall mandibular length
reduced.
• These studies also showed a higher correlation
between the patient & his immediate family.
• Class II division 2 malocclusion:- this malocclusion
is a distinct clinical entity & is a more consistent
of definable morphometric features occuring
simultaneously i.e. a syndrome than the other
malocclusion types put forward by angle in early
1900s.
• These malocclusion comprises the unique
combination of deep overbite,retroclined
incisors,class II skeletal discripency.
• Class III :- true class III
malocclusion underlying skeletal
imbalance is usually inherited.
• These are said to have a strong
genetics basis.
• Features include:
– A retrognathic maxilla
– Prognathic mandible or both
Probably the most famous eg.
Of genetic trait in humans
passing through several
generations is the pedgree
of the so called Hapsburg
jaw,
• Hapsburg family line that the mandibular
prognathism was transmitted as an autosomal
dominant trait. This could be regarded as an
exception & in itself does not provide sufficient
information to predict the mode of inheritance of
mand. Prognathism.
1. Micrognathia 10. Downs syndrome.
2. Macrognathia. 11. Bimaxillary protrusion.
3. Cleft lip & palate. 12. Bimaxillary atresia.
4. Gardners syndrome. 13. Retarded eruption of
5. marfan’s syndrome. teeth.
6. Cherubism. 14. Hypodontia,
7. Cleido-cranial dysplasia. anodontia,oligodontia,etc
15. Abnormal overjet &
8. Mandibulo-facial
overbite.
dysplasia.
16. Openbite.
9. Osteogenesis
17. High arched palate.
imperfecta..
18. Abnormal number &
arrangement of teeth

Genetics and Orthodontics

Uploaded by

Copyright:

Available Formats

Genetics and Orthodontics

Uploaded by

Document Information

Original Description:

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Genetics and Orthodontics

Uploaded by

Copyright:

Available Formats

Genetics is a science

concerned with structure

You might also like