genetics in orthodontics

1. PRESENTED BY-
IRA SOLANKI
(FINAL YEAR BDS)

2. CONTENTS
• Introduction
• Molecular basis of inheritance
• Pattern of genetic transmission
• Gene mutation
• Chromosome in man
• Genetic disorders
• Genetics in orthodontic perspective
• Dentofacial disturbances of genetic influence
• Butler’s field theory
• Methods of studying role of genes
• conclusion

3. INTRODUCTION
• Genetics is the science concerned with the
structure & function of genes in different
organisms
• Genetics has a significant influence on the
dentoalveolar and craniofacial development.

4. • Studied of genetic interest were traced back to 6000
B.C.
• Pythagoras, Aristotle, Empedocles, Harvey, Adams,
Darwin etc. were the forerunners of genetics.
• In 1814 Joseph Adams proposed many of the basic
principles of medical genetics & is known as founder of
human genetics.

5. • Gregor Mendel is known as the founder of mordern
genetics.
• Mendel gave the famous “Law of segregation” according
to which every individual possesses two factors that
determine a specific characteristic.
• In 1903 Sulton and Boveri gave the “chromosome theory
of inheritance.
• In 1935 Thomas Hunt Morgan was awarded the noble
prize for the extensive studies on the arrangement of
genes along the chromosones.

6. • Watson and Crick in 1953 demonstrated the structure of
the DNA model.
• Finch and Klung proposed the “Solenoid model” of the
choromosome.

7. MOLECULAR BASIS OF
INHERITANCE
• CELL- basic unit of living body.
- made up of different organelles i.e. the cell wall,
cytoplasm, endoplasmic reticulum , ribosome, mitochondria,
nucleus, etc.

8. • THE CHROMOSOME-
Within the nucleus of each cell are thread like structures of
different lengths and shapes called chromosomes.
-the number of chromosomes present in every cell of an
organism is constant but it changes from one species to
another.

9. • THE DNA-
chromosome are made up of long chains of Deoxyribonucleic acid
(DNA) molecules, twisted and twined in a specific manner.
Each long strand of a DNA molecule is a chain of nucleotides.
The basic nucleotide unit comprises of a deoxyribose sugar, a
phosphate molecule and one protein either purine or pyrimide.
Nucleotides form a pair by a weak hydrogen bond between the
proteins. At the same time sugar molecules on both the sides get
attached to an adjacent pair by means of phosphate bonds
The structure hence resembles a stepladder.

12. • The ladder like structure of
DNA undergoes coiling of the
DNA duplex itself.
• Secondary coiling of these
twisted duplex around
spherical protein beads called
histones, to form
nucleosomes.
• Tertiary coiling of nucleosomes
to form chromatin fibres.
• Quaternary coiling to form the
chromatic loops,
• These loop are then tightly
wound to form the
chromosome

13. • THE GENE-
-Basic unit of inheritance
-Gene consists of a portion of the double stranded DNA
molecule with 300 to 1000 nucleotide pairs.
-Each chromosome consists of hundreds of thousands of
nucleotide pairs which can be considered as a sequence of
genes.

14. • TRANSCRIPTION-
the process by which the information is transmitted from
DNA to messenger RNA at the initial stage of replication.
TRANSLATION-
The process by which the genetic information is actually
converted into protein synthesis.

15. PATTERN OF GENETIC
TRANSMISSION
REPETITIVE DISCONTINUOUS VARIABLE
It is characterized by
recurrence of a dento-facial
deviation within the
immediate family and its
progenitors
It is characterized by the
recurrence of a malocclusion
trait that reappears within the
family background over
several generations but not
continuously
It is characterized by the
occurrence of different but
related types of
malocclusion within
several generations of the
same family

16. GENE MUTATIONS
• A Change induced by certain agents in the composition of
the DNA base pair leading to an altered protein synthesis is
known as a mutations.
• This may result in a gross reduction or even a complete
loss of the biological activity resulting in an altered
expression of certain specific characteristics of the
individuals.
• Gene mutation can be of different types like visible
mutations, detrimental mutation, lethal mutations etc.

17. • Mutagens are the agents that induces genetic mutations.
• They are of different types-
1. Ionizing radiations
2. Certain drugs, chemicals and food additives
3. Certain viruses
4. High temperature

18. CHROMOSOMES IN MAN
• In 1956 , Tjio & Levan , and independently Ford & Hamerton demonstrated
that - the number of chromosomes in man is 46 i.e. 23 pairs.
• Among these 44 (22 pairs) – autosomes
a pair of a sex chromosome.
• The autosomes in male & female cells are identical while the sex
chromosomes are different.
• Males – 2 sex chromosome –one X & one Y chromosome
• Females- 2 X chromosome
• Normal human cell- 46 chromosome
• Gametes- 23 chromosome (haploid cell)
• During fertilization- union of 2 haploid cells from each parents- results in
an offspring with 46 chromosomes

20. GENETIC
DISORDERS
NUMERICAL
DISORDERS
STRUCTURAL
DISORDERS

21. NUMERICAL DISORDERS
POLYPLOIDY
additional full set of
chromosomes
MONOSOMY
where one chromosome is
missing
TRISOMY
KLINEFELTER’S
SYNDROME
an addition of a single
chromosome only
sex chromosome abnormality in
males where there are additional
x chromosome
TURNER’S
SYNDROME
sex chromosome abnormality
in females with one x
chromosome missing

22. STRUCTURAL DISORDERS
TRANSLOCAT
ION
•An exchange of segments between non-homologous chromosomes.
•E.g. acute myelogenous Leukemia.
DELETION
S
•Loss of a segment of the chromosome. E.g. Cri du chat- deletion of small portion of
chromosome 5.
RING
CHROMOSOME
•Deletion at both the ends of the chromosome.
•Later the deleted ends stick together to form a ring

23. GENETICS IN ORTHODONTIC
PERSPECTIVE
• In 1836 Frederick G. Kussel after extensive study
reported that malocclusion, both skeletal and
dental can be transmitted from one generation to
another.

24. DENTOFACIAL DISTURBANCES
OF GENETIC INFLUENCE ARE-
• Micrognatia
• Macrognatia
• Clep lip and palate
• Downs syndrome
• Gardners syndrome
• Marfan’s syndorme
• Cherubism
• Cleido-cranial dysplasia
• Mandibular-facial
dysostosis
• Osteogenesis imperfecta
• Bimaxillary protrusion
• Bimaxillary atresia
• Retarded eruption of teeth
• Hypodontia, anodontia,
oligodontia, etc.
• Abnormal overjet & overbite
• Open bite
• High arched palate
• Abnormal number and
arrangement of teeth.

25. • Relapse, occlusal mannerisms, jaw positioning, and
abnormal pressure habits which induce untoward forces
that tend to move the orthodontically treated teeth back
into malocclusion can also be genetic in origin.

26. BUTLER’S FIELD THEORY
• According to this theory, mammalian dentition can be
divided into several developmental fields.
• The developmental fields include the molar/premola field,
the canine and the incisor field.
• Among the fields, dental variability manifests itself strongly
in the distal than in the mesial direction.
• For example the lateral incisor is more prone to variation
than the central incisor.

27. METHODS OF STUDYING ROLE
OF GENES
I. TWIN STUDIES- these are done by analyzing the
monozygotic and dizygotic twins in a specific manner.
MONOZYGOTIC
TWINS
DIZYGOTIC
TWINS

28. • MONOZYGOTIC TWINS- two individuals developed
from a single fertilized ovum, which divides into two at an
early stage of development.
• They have similar genetic make up, but post natally
some of them have different environment condition.
• This help us to study the expression of the genetic factor
at the same time, the environmental influences on this
genetic expression.

29. • DIZYGOTIC TWINS- two individual developed from two
separate ova, ovulated and fertilized at the same time. The
two ova are fertilized by two different sperms.
• They are not genetically identical as they develop from two
different embryos.
• They have similar developmental environment including
the intra-uterine life.
• The influence of genetic as well as environmental factors
in the expression and development of an individual can be
studied.

30. • LIMITATIONS OF TWIN STUDIES-
Identification of different types of twins as well as their
developmental environment.

31. II. PEDIGREE STUDIES-
• Most common among genetic studies.
• Definite trait of an individual is studied along his “family
tree” so as to find any hereditary influence.
• Many of the family traits like bimaxillary protrusion,
missing teeth, high arched palate etc., can readily be
attributed to hereditary inheritance.
• One should aware of the dominant and recessive traits
and their expressions.

33. III. INBREEDING-
• Mode of transmission of dominant and recessive traits
can be analyzed by studying certain communities where
practices like polygamy and marriages within the family
still exist.

34. CONCLUSION
• Research into genetic influence of the dento-facial complex
has thrown light on the new vistas of thoughts.
• We can hope that the innovative field of genetics in the near
future can help us solve the unanswered questions