Genetics in orthodontics

2. The relative influence of genetics and
environmental factors in the etiology of
malocclusion has been a matter of
discussion, debate & controversy in
orthodontic literature

3.  Genetic mechanisms are clearly
predominant, but environment is also
thought to influence dentofacuial
morphology post natally.
 The key to determination of etiology of
malocclusion & its treatability lies in the
ability to differentiate the effect of genes
& environment in the cranio facial
skeleton in a particular individual

4.  Our ability to do this is limited by our lack
of knowledge on the genetic
mechanisms, that control growth and
lack of scientific evidence for the
influence of environmental factors on
human cranio facial morphogenesis.

5.  Genotype : The genetic makeup of an organism
 Phenotype : External visible appearance
 Alleles : A pair of genes controlling the same
character and located at the same locus in the
homologous chromosomes
 Homozygote : Individual carrying identical genes for
a particular character
 Heterozygote : Individual carrying non identical
genes for particular character

6.  Dominant : If a trait or disease manifests
itself when the affected person carries
only one copy of the gene responsible,
along with one normal allele
 Recessive : If 2 copies of the defective
gene are required for expression of the
trait

7.  Hypodontia may occur without a family history, although it is
often familial
 It can also occur as part of a syndrome like Ectodermal Dysplasia
 Genetic factors play a major role in this case with autosomal
dominant, autosomal recessive and X-Linked multifactorial
inheritance being reported
 MSX-1 & PAX9 Genes involved in dentition patterening have been
found to be involved in non syndromic autosomal dominant
Hypodontia
 LTBP3 gene which involves short stature, increased bone density
in autosomal recessive hypodontia

8.  Solitary Midline Maxillary Central Incisor
Syndrome :
This heterogenous condition
may include other midline abnormalities
of the brain and other structures, can be
due to mutation in SONIC HEDGEHOG
GENE, SIX3 Gene.

9.  Directional Asymmetery : Occurs when
development on one side is different from
that of the other during normal development,
e.g Human Lung
 Anti Symmetry : Occurs when one side is
larger than the other
 Fluctuating Asymmetry : Observed in primary
and permanent dentition

10.  Degree and severity of EARR associated with orthodontics
is multifactorial.
 It involves host & environmental factors.
 EARR exists in those individuals who have not received
Orthodontic treatment.
 Individuals with bruxism, chronic nail biting, anterior open
bites and tongue thrust, all show increased extent of EARR
before initiating orthodontic treatment.
 EARR is also increased as consequence of orthodontic
mechanical loading

11.  Orthodontic biomechanics has been found to
account for 1/10 to 1/3 of total variation in EARR
 There is considerable variation in EARR associated
with orthodontic treatment, indicating predisposition
& multifactorial etiology
 Retrospective twin study found evidence for both
genetic & environmental factors influencing EARR
 Variation in Interleukin-1B gene in orthodontically
treated individuals accounts for 15% of variation in
EARR
 Although this genetic marker is associated with the
trait, there are patients who have the marker but fail
to present EARR, so the predictive value of this
marker is limited by itself.

12.  Iwasaki et al, found differences in ratio of IL-1B
& IL-1RA in crevicular fluid of patients
undergoing canine retraction.
 This supports the hypothesis that bone
modeling in part by IL-1B can be factor in
EARR
 Evidence suggests TNFRSF11A locus associated
with EARR.
 TNFRSF11A gene codes for RANK, part of
osteoclast activation pathway
 Future estimation of susceptibility to EARR will
likely require the analysis of several genes

13.  TMD classified as somatic & neuropathic
 Genetic factors play role in TMD by influencing variation in pain
perception, production of inflammatory cytokines etc from genes
expressed in TMJ
 Family aggregation studies have failed to identify genetic
influence on TMD
 Zubeitta et al, reported a gene encoding for enzyme catechol-
O-methyl-transferase (COMT) is associated with decreased pain
mechanism in CNS
 Slade et al, TMD onset was 2.5 times greater in subjects who had
HPS or APS haplotypes based on COMT genetic variation

14.  Contrary to the presumption that malocclusions
caused by genetic cause are less amenable to
treatment than those of enviornmental cause
 Change in enviromental factors = change in
polygenic trait
 The capacity of an individual to respond to a
change in environment influenced by genetic
factors is of more importance clinically than the
relative influence of genetic variation has on
phenotypic variation before treatment