Genetic factors influencing malocclusion

INFLUENCE OF
GENETICS IN
MALOCCLUSION
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HUGES AND MORE (1941)
•Maxilla and mandible under different
genetic control
•Individual bones such as
Ramus
Body
Symphisis
Under different genetic and
environmental influences.www.indiandentalacademy.com

Hereditary variations in
•Anterior cranial base
•Mandibular body length
•Lower facial height
•Total facial height
HOROWITZ et al (1960)

Ferenex et al (1967)
•Found boys show similarities to their
parents than girls.
•Facial skeleton pattern were more
frequently transmitted from mother to sons
than from mother to daughter.
•Female twins showed greater concordance
in facial features than male twins.

WATNICK (1972)
Genetic predominance
•Lingual symphysis
•Lateral surface of the ramus
•Frontal curvature of the mandible
Environmental influences
•Antigonial notch

Genetic analysis of occlusal variation in twins –
Corruccini- AJO-DO 1980 Aug (140-154):
HERITABILITY COULD NOT BE
DEMONSTRATED FOR
•Overbite
•Overjet
•Buccal segment relation
•Total tooth displacement and
•Occlusal discrepancies in arch shape.
SIGNIFICANT GENETIC VARIANCE
(36%)
•Arch size
•Individual tooth displacement scores
•Cross-bite
Indiana University twin panel,
60 samples
12- to 20-yr

Occlusion and arch widths in families –
Harris and Smith
AJO-DO 1980 Aug (155-163):
------------------------------------------------------------
•Arch Size
•Shape
IS ATTRIBUTABLE TO HEREDITY.
•Overjet
•Overbite
•Crowding
•Tooth rotations and
•Molar relationships
RESULTS FROM NON GENETIC
CAUSES
Northern coast of Bougainville,
Melanesian population

Hereditary factors in craniofacial morphology of Class II and
Class III malocclusions - Nakasima, Ichinose, Nakata, and
Takaham: AJO-DO 1982 Aug (150-156)

.
Nakasima et al 1982

CLASS II DIVISION I MALOCCLUSION
HARRIS (1963, 1975)
Study showed higher correlation
between immediate family than data from
random pairing of unrelated siblings
Environmental factors are also equally
responsible.

CLASS II DIVISION II MALOCCLUSION
MARKOVIC (1992)
Carried out a clinical and cephalometric
study on 48 twin pairs and six sets of
triplets.
100 % Monozygotic twins showed concordance
Almost 90% of dizygotic twins showed
discordant
Unlike div I there is a strong evidence for
genetics as main etiological factor.www.indiandentalacademy.com

CLASS III MALOCCLUSION
Common example is HAPSBURG JAW,
seen in AUSTRIAN DUAL MONARCHY
SUZUKI (1961)
Studied on 1365 persons from 243
Japanese families
Result showed higher incidence of mandibular
prognathism (34.3%) than the families of
individuals with normal occlusion (7.5%)

malformation
General
population
First degree
relatives
third degree
relatives

Butler’s Field Theory
Among the fields the maximum
variability manifests itself in the distal and
least in the mesial direction.

HOMEOBOX GENES
• The genes that control the process of
development are called homeotic genes
or homeobox genes.
• These genes, also known as HOX genes
• These genes contain 180-base pair
sequence
• Each branchial arch exhibits a specific
combination of Hox gene
• These genes were first discovered in the
fruit fly Drosophila melanogaster.

• Disruption of Hox a-2
-Some 2nd arch structures changed to 1st arch
structures
• Stapes missing – 2 malleus’ formed.
• Ectopic expression of Hox d-4
– Occipital bones develop into vertebrae
• Deletion of Hox a-3 and Hox d-3
-Atlas is deleted

Msx -1  involved in the development of
secondary palate and tooth.
Msx- 2  Disruption of this causes
Craniosynostosis
Pax9  for tooth morphogenesis
SHH (Sonic hedgehog gene)  expression
of mid line structures
• Excess expression of SHH results in
Hytertelorism

GENETIC ENGINEERING
Defined as the manipulation or
alteration of the genetic structure of a
single cell or organism.
Recombinant DNA technology
Recombinant DNA science
Gene transfer
Gene splicing
Gene cloning

DISCOVERY OF RESTRICTION
ENZYMES
•
Hamilton Smith was studying how
Haemophilus influenzae defend
themselves from bacteriophage
attack

Ligase
Enzyme used to join
two pieces of DNA

Using Plasmids
• Plasmid is small circle of bacterial DNA
• Foreign DNA can be inserted into plasmid

DNA
ligase recombinant
plasmids
host cells containing
recombinant plasmids

• Identify the entire set of genes & map
them all to their chromosomes
• Determine the nucleotide sequence of
the estimated 3 billion base pairs
• Store this information in databases
• Analyze genetic variation among
humans
Aims and objectives

• 1-2 % codes for protein products
• 24% important for translation
• 75% “junk”
• your DNA is 99.9% the same as any other
human on Earth
Humans & chimpanzees share about
98.5% of their gene
Banana DNA & human DNA are about
50% the same
•Known as “mini” humans
•Very similar physiological systems
•Share 90% of their genes

Genetic factors influencing malocclusion

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