This document discusses genetics in orthodontics. It begins by defining genetics and key figures in the field. It then explains how genetics influences growth, development, and malocclusions. The molecular basis of inheritance is described including DNA, genes, and genetic disorders. Different modes of genetic transmission are covered. Finally, specific malocclusions like Class II and Class III are discussed and twin/pedigree studies are summarized that show the genetic influences for different traits.

1. Genetics in orthodontics
Presented by RINCE MOHAMMED
Final B.D.S

2.  Genetics is the science concerned with
the structure and function of all genes in
different organism.
 Founder of human genetics – Joseph
Adams
 Gregor Mendel – Father of modern
genetics.

3. Why genetics in ortho?
 Growth, development and function of oral and facial
structure of an individual depends on his genes.
 An orthodontist should know exactly why or how a
malocclusion occurs, to what extend it express on
next generation, what is its prevelance and how it
react to the treatment plan and mostly if it can be
prevented.
 Genetics shed light on all these questions. It helps to
segregate inherited malocclusions or aberrations of
growth from those due to the effect of
environmental factors.Thus help us to diagnose and
prevent it from occurring in next generation.

4. Molecular basis of inheritence
 The cell - the basic unit of any living body.
 Chromosomes -thread like structures in the
nucleus. made up of DNA.
 D.N.A.- Each strand of DNA molecule is a chain of
nucleotides. Basic nucleotide unit comprise of
deoxyribose sugar, a phosphate molecule and
protein, either purine or pyramidine.
 Gene – Gene forms the basic unit of inheritance by
determining the make up and structure of particular
characteristic in an organism.
 Transcription -the process by which information is
transmitted from the DNA to the messenger RNA.
 Translation is the process by which the genetic
information is actually converted to protein
synthesis.

5. GENETIC DISORDERS - Its of 2 types
 Numerical disorders - are those in which there is a
change in the number of chromosomes within the
cell. Normally it is 46.
Polyploidy – an additional set of chromosome is
present.
Monosomy - one autosome is missing.
Trisomy - there is an addition of a single
chromosome.Eg:Down syndrome -The person has 3
pairs of chromosome 21 rather than 2.
Klinefelters syndrome – 22 A+ XXY
Turner syndrome -22 A + OX -has only one sex
chromosome.

6.  Structural disorders-change in the basic
composition and structure of chromasome.
Deletion – A portion of chromosome is missing /
deleted.
Duplication –A portion of chromosome is duplicated
resulting in extra genetic material.Eg Charcot man
tooth disease by duplication of chromosome 17.
Translocation – When portion of one chromosome is
transferred to another chromosome.
Inversion - A portion of chromosome has broken off
and turned upside down and reattained.There for
the genetic material is inversed.

7. Mode of transmission of Malocclusions
 RepetitiveTraits :The recurrence of a single
dentofacial deviation within the immediate family
and in the progenitors.The same trait is seen
generation after generation.
 Discontinous Traits: It is the recurrence of a
malocclusion that reappears within the family over
several generations but not continuously.
 Variable traits: the occurrence of different but
related types of malocclusions within several
generations.Eg: missing teeth - same teeth may
not be missing in different generations.

8. Genetic influence in orthodontics.
• In 1836 Frederick G.kussel reported malocclusion both
skeletal dental can be transmitted from one generations to
other.
• Dento facial disturbances of genetic origin includes.
Micrognathia,Macrognathia
Down’s syndrome,Gardners syndrome,Marfan’s
syndrome,Cherubism
Cleidocranial dysplasia,Ectodermal dysplasia
Bimaxillary Protrusion,Prognathism
Open bite
High arched palate
Hypodontia, Anodontia
Hypoplasia and discoloration of teeth
Facial Clefts, cleft lip and cleft palate

9.  A study of relapse on treated cases showed
that relapse can be caused by hereditary
factors.
 Occlusal mannerisms,jaw positioning,and
abnormal pressure habits are genetic in origin
and may cause relapse.
 Occlusal variations are determined by both
genetic and environmental factors.

10. Butler’s Field Theory
 Butler divided the mammalian dentition into
several development fields.
 It includes molar/premolar field,canine and
incisor field
 Among the fields the maximum variability
manifests itself in the distal and the least in
the mesial direction.Hence maximum
variability will be seen for the third molars as
compared to the first molars.More variability
in lateral compared to central incisors.

11. Method of studying role of genes
 Twin studies
 Pedigree studies
 Inbreeding

12. Twin studies
 Done to evaluate the role of genetics played in
various traits.
 If both the individuals of the monozygotic twins
(they have identical genetic make up) express a
trait that is seen in the parent,it is a strong
evidence for a very significant role of genetics in
that particular trait.
 In case only one of the monozygotic twins
express the trait and the other is absolutely
normal, then we come to the conclusion that
although there is a genetic component in the
disease, there are some other factors which
control the disease i.e multifactorial trait.

13.  Depending upon the presence or absence of a
particular trait twins can be classified into
concordant and discordant twins.
 If a particular character is seen in both the
members they are said to be concordant.
 if only one member of the pair expresses the
trait they are said to be discordant.

14.  Cleft studies suggest that the concordance
rate in Monozygotic twins for cleft lip was
35% and that for cleft palate was 26%.
 In Dizygotic twins the concordance rate for
cleft lip was 5% and that for cleft palate was
6%.
 This reflects the heritability of the condition;
the higher the monozygotic concordance, the
more important the genetic contribution and
so the higher the heritability.

17.  Twin studies reveales that
 Genetic variation has a major effect on arch
width and length.
 Identical twins were not occlusally identical.
 Greater genetic basis for tooth size and shape
 Known dimensions were largely under
genetic control

18.  Pedigree studies-Most common
 Definite trait of an individual is studied along
his family tree so as to find any hereditory
influence.
 Inbreeding-The mode of transmission of
certain traits can be studied and their
dominant & recessive characteristics are
determined by analyzing certain
communities where practices like polygamy
and marriages within the family still exist.

19. Contribution of genetics in various malocclusions
 Class 2 & class 3 malocclusions have polygenic
mode of inheritance.
 Redman & Shapiro proposed that genes on X
chromosome causes lengthening of mandible
relative to maxilla.
 High % of class 2-(shortened mandible) in XO
subjects (Turner syndrome).

20.  Class II div 1 Malocclusion
 Various investigations show that mandible is
significantly retruded & the overall mandibular
length is reduced in most of the class II div 1
malocclusions. A higher correlation between the
patient and the immediate family members is
found suggesting an obvious genetic etiology.
 Some environmental factors have also been
suggested to play a role in establishing the class
II div 1 pattern.it includes Soft tissue (controls
the position of upper & lower incisors),Digit
sucking,Lip incompetence.

21.  Class II div 2
 Markovic in 1992 after evaluating 48 twin
pairs came to the conclusion that the
concordance rate for this malocclusion in MZ
twins was 100%.Whereas in DZ twins the
concordance rate was only 10% and 90%
were discordant.This is a strong evidence to
quote genetics as a main etiologic factor.

22.  Class III
 One of the famous examples was the
mandibular prognathism that was running in the
Austrian monarchy -The Hapsburg jaw.
Strohmayer in 1937 concluded from detailed
pedigree analysis that the mandibular
prognathism was transmitted as an autosomal
dominant trait. Schulze & Weize in their twin
studies in 1965 concluded that the concordance
rate in MZ twins was 6 times higher than that in
DZ twins. Both of the above studies report a
polygenic hypothesis as the primary cause for
mandibular prognathism.