1. GOOD MORNING

3. INTRODUCTION :
• A sound knowledge of various etiologies or causes of malocclusion is a basic requirement for
any orthodontic student.
• Malocclusion is an interaction between genetic and environmental factors.
• Malocclusion may result from complex interaction among multiple factors that influence growth
and development.
• Broadly speaking, malocclusions are either caused by genetic or environmental factor
• It is of great value in making preventive and interceptive orthodontic procedures as possible
because malocclusion is prevented or intercepted by timely removal of cause.

4. WHITE AND GARDINER'S CLASSIFICATION :
A. Dental base abnormalities
1. Antero-posterior mal relationship
2. Vertical mal relationship
3. Lateral mal relationship
4. Disproportion of size between teeth
and basal bone
5. Congenital abnormalities.

5. A. Pre eruption abnormalities
1.Abnormalities in position of developing tooth germ
2. Missing teeth
3. Supernumerary teeth and teeth
abnormal in form .
4. Prolonged retention of primary teeth
5. large labial frenum
6. Traumatic injury

6. C. Post-eruption abnormalities
1. Muscular
a. Active muscle force
b. Rest position of musculature
c. Sucking habits
d. Abnormal path of closure
2. Premature loss of deciduous teeth
3. Extraction of permanent teeth

7. MOYER’S CLASSIFICATION :
1.Heredity –
a. Neuromuscular
b. Bone
c. Teeth
d. Soft Parts
2. Developmental defects of unknown origin
3. Trauma
a. Prenatal trauma and birth injuries
b. Postnatal trauma
4. Physical agents
a. Premature extraction of primary teeth
b. Nature of food

8. 5. Habits:
a. Thumb sucking and finger sucking
b. tongue thrusting
c. lip sucking and lip biting
d. posture
e. nail biting
f. abnormal swallowing and other habits

9. 6. Diseases
a. systemic diseases
b. endocrine disorders
c. local diseases
i. Nasopharyngeal diseases and disturbed
respiratory function
ii. Gingival and periodontal diseases
iii. Tumors
iv. Caries
7. Malnutrition

10. GRABER’S CLASSIFICATION:
GENERAL FACTORS
1. Heredity
2. Congenital
3. Environment
a. Prenatal
b. Post natal (birth injury, cerebral palsy, T.M.J. injury)
4.Predisposing Metabolic disease
a. Endocrine imbalance
b .Metabolic disturbances
c. Infectious diseases
5. Dietary problems (nutritional deficiency)

11. 6. Abnormal pressure habits and functional aberrations
a. Abnormal sucking
b. Thumb and finger sucking
c. Tongue thrust and tongue sucking
d. Lip and Nail biting
e. Abnormal swallowing habits
f. Speech defects
g. Respiratory abnormalities
h. Tonsils and adenoids
i. Psychogenic tics and bruxism
7.Posture
8.Trauma and accidents

12. LOCAL FACTORS:
1. Anomalies of number:
Supernumerary teeth,
Missing teeth [congenital absence or loss due to
accidents. caries. etc.]
2. Anomalies of tooth size
3. Anomalies of tooth shape
4. Abnormal labial frenum
5. Premature loss of deciduous teeth

13. 6. Prolonged retention of deciduous teeth
7. Delayed eruption of permanent teeth
8. Abnormal eruptive path
9. Ankylosis
10. Dental caries
11. Improper dental restoration

14. Houston’s classification:
 General Factors:
Discrepancy between tooth size & arch size resulting in crowding or spacing,
skeletal mal relationships and soft tissue factors.
 Local Factors:
1. Anomalies in number of teeth
 Extra teeth
 Missing teeth
 Loss of permanent teeth
 Premature loss of deciduous teeth
 Retained deciduous teeth
2. Anomalies in form & position of teeth
3. Habits
4.Abnormal labial frenum.

15. Proffit’s classification:
Specific causes of malocclusion
A) Disturbance in embryologic development
B) Skeletal growth disturbance
(i) fetal molding and birth injuries
eg: intrauterine molding
:birth trauma to mandible
(ii)childhood fractures of jaws
C)muscle dysfunction
D)acromegaly and hemi mandibular hypertrophy
E)disturbances of dental development

16. F. Genetic influences
G. Environmental influences
a) equilibrium theory and development of dental
occlusion
b) functional influences on dentofacial development

17. GRABER’S CLASSIFICATION:
A. General factors:
1.Heredity
2.Congenital defects
3.Environment
a. prenatal
b. postnatal
4. Predisposing metabolic climate and disease.
a. endocrine imbalance
b. metabolic disorders

18. 5. Nutritional deficiency
6. abnormal pressure habits and functional abrasion
a. tongue thrust and tongue sucking
b. thumb and finger sucking
c. lip and nail biting
Local factors:
1. Abnormalities of number:
supernumerary teeth
missing teeth
2.Anomalies of tooth shape

19. 3.Abnormal labial frenum
4.Premature loss
5.Prolonged retention
6.Delayed eruption of permanent teeth.
7.Abnormal eruptive path
8.Ankylosis
9.Dental caries
10.Improper dental restorations.

20. Basic terms:
 Genetics Branch of biology that deals with heredity and variations.
 Heredity –
transmission of character from one generation to next or from parents to offspring.
 Variation –
forces or influences due to which no two organisms are exactly alike.
 Trait –
An inherited character and its detectable variant.
 Inheritance –
Transmission of characters from parents to offspring.

21.  Alleles or Allomorph:
• Genes like chromosomes are arranged in pair.
• Each pair of gene control a trait or character.
• These pair of gene is called allele.

22. Chromosomes:
Chromatin of the interphase nucleus is closely coiled in the form of rod like basophilic structures called
chromosomes.

23. DNA: (Deoxyribo-nucleic acid)
Chromosomes are made up of two long chains of DNA, intertwined and twisted in a specific sequence.

24. GENES:
• Genes – (from Greek word ‘Gene’- to become)
• It is particular segment of DNA which is responsible
for the inheritance and the expression of the
character.
• These are the structural units of heredity stored in
chromosomes.
• They contain the heredity information encoded in
their chemical structure for transmission from
generation to generation.
• They have ability to determine traits. E. g. tooth
size, shape, arch form etc.

25. Mutation:
• This term is used to denote a physico-chemical change in a gene which
alters the effect on character or trait.
Homozygous:
When two members of pair of genes are alike.
Heterozygous:
When two members of pair of genes are different

26. Dominant:
• It is in allele that represent its trait in presence of
alternative allele i.e. in heterozygous condition
Recessive:
• It is an allele which is not expressed in presence of
alternative allele.

27. HEREDITY:
• Heredity means transfer of characters or traits from parents to
offspring.
• Heredity plays part in the following conditions:
I. Facial asymmetries
II. Micro and macrognathia
III. Micro and macrodontia
IV. Anodontia, Oligodontia, hypodontia.
V. Deep bite
VI. Crowding
VII. Rotations etc.

28. Types of transmission of malocclusion:
Malocclusions are transmitted by three ways:
i)
Repetitive: Recurrence of single dentofacial deviation within immediate family.
i)
Discontinuous : recurrence of tendency for malocclusal trait to reappear after
few generations.
ii) Variable: Expression of different but related types of malocclusion within the
several generations of the same family.

29.  Modes of Inheritance:

Following are the modes of inheritance:
•Autosomal dominant
• Autosomal recessive
• Sex-linked
• Polygenic
•Chromosomal

34. Genetic studies:
 Twin study:
• In this study twins are compared.
• Comparing monozygotic twins with dizygotic twins is the best way to determine the
extent of genetic effect On malocclusion.
Monozygotic twins
•
Happen due to early division of fertilized egg.
•
Both the individuals will have the same DNA
•
They are genetically similar.
•
Also called identical twins
Dizygotic twins
•
Happen when two eggs fuse with two different spermatozoa
•
The twins will have different DNA
•
They are genetically dissimilar
•
Also called fraternal twins.

35.  Procedure:
• The heritability of the malocclusion can be determined by comparing the
monozygotic twins, dizygotic twins and ordinary siblings.
• In monozygotic twins, any change in occlusion or feature could be attributed
to environment factor since both have same DNA.
• In dizygotic twins, interplay of genetic and environmental factor is studied.
 Disadvantages of twin studies:
•
•
Difficulty in identifying identical twins.
Difficulty to establish the same environment for the twins.

36. Family study/pedigree study:
• In this method of study occlusal features and differences between mother- child,
father-child and siblings are analyzed.
• Helps to differentiate between dominant and recessive traits
• Dominant traits will be expressed in all the subsequent generation.

37.  Butlers field theory
 The human dentition is divided into four fields:
(i) incisor
(ii) canine
(iii) premolar
(iv) molar.
• The most distal tooth in each field is the most susceptible to changes or variations.
• The changes include –
 Absence of tooth
 Variation in size
 Shape and structure.

38. •
Accordingly lateral incisors, second premolars and third molars are the
most variable in their group.
•
Canine is the least variable tooth in the arch.
•
Butlers field theory does not apply in lower anterior region, where
mandibular central incisor is more commonly missing than lateral incisor.

39. Advances in genetics:
• Gene mapping:
-Mapping of genes to specific locations
on chromosomes.
• Cloning:
-Clone is a series of identical DNA.
• Gene therapy:
-Insertion of normal genes in the bodies of individuals affected with
genetic disorder.

40. • Lauweryns et al(1993) summarized a number of twin
studies and concluded that 40% of the dental and
skeletal variations that lead to malocclusion can be
attributed to hereditary factors.
The use of twins in dentofacial genetic research
Lauweryn I,Carels C,Vlietinck R
AJODO 1993;103:33-38
• According to Bolton –Brush growth study (1930s to
1970’s) Harris and Johnson concluded that the heritability
of skeletal characteristics was relatively high but that of
dental (occlusal) characteristics was low.

41.  There is a strong influence of inheritance on facial features
Eg: tilt of the nose, the smile, shape of jaw.
 Certain type of malocclusion run in families.
 Mcuigan described the most well known example of inheritance, the Hapsburg
family having the distinct characteristic of prognathic lower jaw known as
Hapsburg jaw of German royal family.
 Litton et al in 1970 concluded that the dental Class III characteristic were
related to genetic inheritance in offspring and siblings.

42. • We can say that there is definite genetic determinant that
influences the ultimate accomplishment of dentofacial
morphology.
• The pattern of accomplishment has a strong hereditary
component.
• Since the offspring is a product of dissimilar heredity, cognizance
must be taken of the inheritance from both the sources.

43. • A child may have resemblance to father or mother or it can be
combination of features from each parent.
• i.e. child may inherit tooth size and shape, jaw size, shape and
relationship from the father or mother.
• But it is equally possible that child may inherit tooth shape and
size characteristic from one parent and jaw size and shape from
other.

44. • In the complex interplay of chromosomes and genes, two
recessive factors may combine to become a dominant
characteristic, or dominant characteristic may be offset by genetic
potential from other parent; and characteristic may then
disappear in the offspring.

45. HEREDITARY RACIAL INFLUENCE:
• DENTAL CHARACTERISTICS, LIKE FACIAL CHARACTERISTICS SHOW RACIAL
INFLUENCE.
• WHERE THERE HAS BEEN MIXTURE OF RACIAL STRAINS
THE INCIDENCE OF
JAW SIZE DISCREPANCIES AND OCCLUSAL DISHARMONIES IS SIGNIFICANTLY
GREATER.

46. • Professor Stockard did his experiments on dogs to show the role of
genetics in development of malocclusion.
 Stockard’s study on cross-bred dogs (1930s)
•Observations:
 Dramatic malocclusions did occur more from jaw discrepancies than
from tooth-size- jaw-size discrepancy.
This seemed to confirm that independent inheritance of facial
characteristics could be a major cause of malocclusion.
Study was misleading as many breeds of small dogs carry genes for
Achondroplasia.

47. HEREDITARY FACIAL TYPE:
• THE FACIAL TYPE OF THE OFFSPRING IS PROBABLY, HEAVILY
INFLUENCED BY HEREDITY.
• HASUND AND SIVERTSEN POINT OUT THE SEX LINKED NATURE OF
FACIAL WIDTH AND DENTAL ARCH SHAPE.
• FEMALES DEMONSTRATE A POSITIVE CORRELATION – THE WIDER
THE FACE THE WIDER THE ARCH.

48. HEREDITARY INFLUENCE ON GROWTH
AND DEVELOPMENTAL PATTERN:
• AS THE MORPHOGENETIC PATTERN HAS A STRONG HEREDITARY
COMPONENT, IT IS REASONABLE TO ASSUME THAT THE
ACCOMPLISHMENT OF THAT PATTERN IS ALSO AT LEAST
PARTIALLY UNDER THE INFLUENCE OF HEREDITY.
• OBVIOUSLY THE ENVIRONMENTAL INFLUENCES ARE IMPORTANT
HERE, TOO, AND THEY CAN AND MODIFY HEREDITARILY
DETERMINED PATTERN.

49. Heredity and specific dento-facial morphologic
characteristic:
• Lundstorm made an intensive analysis of some
characteristics in twins, and he concluded that heredity
could be considered significant in determining the following
characteristics:
Tooth size
Width and length of arch
Height of the palate
Crowding and spacing of the teeth
Degree of sagittal overbite. (overjet)

50.  If heredity influence is present and can be demonstrated in
the enumerated areas, it is logical to assume that heredity
plays a part in the following conditions.










Congenital deformities
Facial asymmetries
Macrognathia and micrognathia
Macrodontia and microdontia
Oligodontia and anodontia
Cleft palate and harelip
Deep overbite
Crowding and rotation of teeth
Mandibular retrusion
Mandibular prognathism

51. Hereditary causes can be those influencing the
• Neuromuscular system
• Dentition
• Skeletal structure
• Soft tissues other than musculature.
:

52. NEUROMUSCULAR SYSTEM:
• The anomalies that have been found to possess some inherited
component include deformities in size, position, tonicity,
contractility, and in the neuromuscular coordination pattern of
facial, oral and tongue musculature.
• Certain tongue & lip habits can be learned by imitation or be
inherited and may be found to reoccur within a family over
generations.

53. DENTITION
• Certain characteristics, especially related to the dentition are definitely
inherited. These include:
A. Size and Shape of the Teeth:
 Studies on twins have proved that the size
and relative shape of the teeth is inherited
e.g. Peg shaped.

54. • Lateral are the most commonly seen and noticed abnormally
shaped teeth encountered clinically.
• To produce a malocclusion the discrepancy should exist
between the basal bone and the teeth size, or the associated
skeletal structures.

55. B. Number of teeth:
• Presence of either more or less no. of teeth can also be inherited.
• This includes condition such as Anodontia, Oligodontia, and Hypodontia.
C. Primary Position of Tooth, Germ and the Path of Eruption is considered to
be inherited. E.g. Cross bites,
Ectopic tooth eruption.
.

56. D. Shedding of Deciduous Teeth & Sequence of Eruption
E. Mineralization of Teeth:
Inherited defects of the tooth structure differ from defects in mineralization as
they are present in both the deciduous dentition as well as permanent
dentition and are localized in the enamel or the dentine.
e.g. hypo plastic teeth

57. SKELETAL STRUCTURES:
Skeletal structures are partially inherited
e.g. Class III skeletal pattern is associated with familial tendency
SKELETAL
CLASS III

58. 
SOFT TISSUES (OTHER THAN THE NEUROMUSCULATURE):
• These generally includes the size & shape of the frenum especially
the maxillary labial frenum.

59. GENES IN MALOCCLUSION
Some of the key genes required for craniofacial morphogenesis
• Polarizing signals: Shh, Bmp2, Bmp4 and Bmp7, Wnt5a, Smad2–4
• Growth factors and receptors : Egf, Egfr, Tgfa, Tgfb1–
3, Fgf1, Fgf2, Fgf8, Fgfr1, Fgfr2
• Transcription factors:
Hoxa2, Irf6, Lhx8, Pax9, Pitx2, Prx1, Msx1, Tbx1, Tbx22
• Cell adhesion molecules: Pvrl1, Connexin43, E-cadherin
• Extracellular matrix: Mmp2, Mmp3, Mmp9,Mmp13, Timp1–3

60.  In humans number of homeobox containing genes are expessed in
maxillary, mandibular arches and the developing facial primordia.
• THESE GENES INCLUDE:





MSX1 AND 2
DLX1-6
BARX-1
PAX
SHH

61.  Homeobox genes:
• Homeobox genes are genes, which are highly conserved through out
evolution of diverse organisms and are now known to play a role in
patterning the embryonic development.
• These can be regarded as master genes of the head and face
controlling patterning, induction, programmed cell death & epithelial
mesenchymal interaction during development.

62. Those of particular interest in cranio facial development include:
• Hox group
• Msx 1 and Msx 2 (muscle segment)
• Dlx ( distalless )
• Otx ( orthodontical )
• Shh ( sonic hedgehog )

63. MSX genes: (Muscle segment homeobox gene)
• Involved in tooth formation.
• This gene has been associated with dental and facial abnormalities.
• MSX-1 genes are expressed in migrating neural crest cells and later
in the mesenchymal cells of dental papilla and follicle.
• MSX-2 genes are involved in signaling interactions, which are
essential for the tooth development.

64.  DLX genes(Distal-less homeobox gene)
• Expressed in migrating neural crest cells and the first branchial arch.
• Expression of DLX-1 and DLX-2 in maxillary and mandibular arch
mesenchyme is restricted to the proximal regions where the future
molar teeth will develop.

65.  BARX genes: (Bar class homeobox genes)
•
BARX genes along with DLX-2.
•
No expression in anterior region.
•
As tooth development proceeds, BARX-1 expression becomes
localized extensively to the mesenchymal region around developing
molars.
•
Mutation of these genes could be associated with facial and dental
anomalies.

66. PAX genes: (paired-box homeotic genes)
•
There are nine PAX genes arranged in 4 groups.(PAX-1 to PAX-9).
•
PAX-9 is associated with development of teeth.
•
Mutation in this gene results in conditions such as Hypodontia,
transposition, etc.
•
Nubuser et al. found that PAX 9 transmission factor is associated with the
genetic mechanism for tooth displacement anomalies, such as palatally
displaced canines and canine transposition.

67.  SHH genes: (Sonic hedgehog genes)
• Expressed in the epithelial thickenings of tooth forming regions.
• SHH along with BMP-4 determine the position of future forming tooth germs.
• SHH is necessary for initiation of tooth development, epithelial signaling and
cuspal morphogenesis.
• GLI Zinc transmission factors are known to act downstream of SHH gene.
• GLI1-3 play a vital role in development of tooth mutation of GLI results in
formation of abnormal tooth.

68.  PTHR gene:
• These genes are included in eruption of teeth.
• Mutation in PTHR 1 causes primary failure of eruption.
• Mutation in PTHR is strongly associated with failure of orthodontically assisted
eruption and tooth movement.
 Primary failure of eruption and PTHR1: the importance of genetic diagnosis for orthodontic planning
Sylvia A. Frazier-Bowers, Darrin Simmons, J. Timothy Wright, William R. Proffit, James L. Ackerman
(American Journal of Orthodontics and Dentofacial Orthopedics, Volume 137, Issue 2, February 2010,
Pages 160-161)

69. TBX22:
These genes play essential roles in early
development and in particular mesoderm
specification
Human Molecular Genetics, 2004, Vol. 13, Review Issue 1

70.  PVRL1:
•
mutations were identified in the cell adhesion molecule PVRL1
(Nectin-1), which is expressed in the developing face and palate
Autosomal recessive CLP with ectodermal dysplasia (CLPED1)
 IRF6:
• In the mouse, Irf6 expression is restricted to the palatal MEE
immediately prior to and during fusion

71. 
MSX1:
• MSX1 first came to prominence as a candidate for CL/P following
the generation of a gene knockout with cleft palate and
Oligodontia.
•
Jezewski et al analysed a large cohort of CL/P patients from a
variety of different ethnic origins and demonstrated that up to 2%
of patients, predominantly with CLP, carried MSX1 mutations
(Human Molecular Genetics, 2004, Vol. 13, Review Issue 1)

72. 
(Kanzaki and colleagues)
• Gene therapy with OPG and RANKL Local RANKL gene transfer
to the periodontal tissue accelerated orthodontic tooth movement
by approximately 150% after 21 days, without eliciting any
systemic effects
•
With OPG gene transfer, there is inhibition of the tooth
movement by 50% after 21 days
(Orthodontics in the year 2047: genetically driven treatment plans, Bruce Havens, Sunil Wadhwa, Ravindra
Nanda, 549 – 56 vol XLI Number 9, JCO/ Sep 2007)

73.  Use of functional appliances ↓ses regulation of
the genes ( PTHrP, Indian Hedgehog, Collagen
typeX and VEGF) in the mandibular condylar
cartilage
(Orthodontics in the year 2047: genetically driven treatment plans, Bruce Havens, Sunil Wadhwa, Ravindra Nanda, 549
56 vol XLI Number 9, JCO/ Sep 2007)

74. • The size of the mandible (as well as that of the maxilla) is partially
regulated by the number of neural crest cells that migrate
successfully into the first pharyngeal arch.
• Mutations in genes such as TREACLE may be responsible for the
milder cases of mandibular retrognathia commonly seen in
orthodontic practice
(Orthodontics in the year 2047: genetically driven treatment plans, Bruce Havens, Sunil Wadhwa, Ravindra
Nanda, 549 – 56 vol XLI Number 9, JCO/ Sep 2007)

75. Contribution of genetics in various malocclusions:

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 family members is found
suggesting an obvious genetic etiology.

76. •
Some environmental factors have also been suggested to play a role
in establishing the class II div 1 pattern. A few are listed below;
1. Soft tissue – controls the position of upper & lower incisors producing
a class II div 1 pattern of incisors.
2. Digit sucking.
3. Lip incompetence.

77.  Bolton & Brush Growth study(conducted on siblings between 1930s &
1970s).
 Harris & Johnson concluded that-heritability of craniofacial characters was
high but dental was low.
 Heritability estimates for skeletal characters increases with age but for
dental characters decreased-indicates environmental contribution.
Heritability of craniometric & occlusal variables: A longitudinal sib analysis
Edward F Harris & Michelle G.Johnson AJO-DO 1991;99:258-68.

78. • Harris has shown that the craniofacial skeletal pattern with class II
malocclusion is heritable & there is high resemblance of skeletal
pattern in their siblings.
• He concluded that the genetic basis for their resemblance is
polygenic.

79. Inheritance of Class II malocclusion in three
brother

80.  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.

81. • Familial occurrence of Class II division 2 has been documented in
several published reports including twin and triplet studies. (E.g.
Kloeppel, 1953: Markovic, 1992) and in family pedigrees from
Korkhaus (1930), Rubbrecht (1930), Trauner (1968) and Peck et al.
(1998).
• Markovic (1992)carried out a clinical and cephalometric study of 114
Class II division 2 malocclusions. 48 twin pairs and six sets of
triplets.

82. •
Intra- and inter- pair comparisons were made to determine concordance/
discordancy rates for monozygotic and dizygotic twins
•
Of the monozygotic twin pairs. 100 per cent demonstrated concordance for
the Class II division 2 malocclusion, whilst almost 90 per cent of the
dizygotic twin pairs were discordant.
•
This is strong evidence for genetics as the main aetilogical factor in
development of class II div 2 malocclusion.

83.  Class III
•
One of the famous examples was the mandibular prognathism that was running in
the Austrian monarchy - The Hapsburg jaw.
HAPSBURSG JAW
CHARLES II
THE BEWITCHED
PHILIP IV
HAMB

84. •
Strohmayer in 1937 concluded from detailed pedigree analysis that
the mandibular prognathism was transmitted as an autosomal
dominant trait.

85. Suzuki (1961) studied 1362 persons from 243 Japanese families
and noted that-
• While the index cases had mandibular prognathism, there was a
significantly higher incidence of this trait in other members of his
family (34.3 per cent) in comparison to families of individuals with
normal occlusion (7.5 per cent).

86. • 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.

87. • A wide range of environmental factors have been
suggested to play a role in class III malocclusions. To
name a few–
1. Enlarged tonsils
2. Nasal blockage
3. Congenital anatomic defects
4. Hormonal disturbances
5. Posture etc.

88.  Genetic influence on tooth no & size
•
Osborne et al (1958) in their twin studies concluded that crown dimensions are
strongly determined by heredity.
• Clinical evidence suggests that congenital absence of teeth and reduction in tooth
size are associated
e.g. hypodontia and hypoplasia of maxillary lateral incisors frequently present simultaneously.
• This implies that they are different expressions of the same disorder.
• It is apparent from the study that tooth size fits the polygenic multi factorial threshold
model.

89.  Supernumerary tooth:
•
Most frequently seen is a mesiodens in the premaxillary region
with a male predilection.
• They are most commonly seen in parents & siblings of patients.
• Sugaku (1963) analysed the data from family studies and
suggested that the genetics of the less prevalent condition of
supernumerary teeth is under the control of a number of
different loci.

90. Hypodontia:
•
Study of children with missing teeth found that up to half of their siblings & parents
also had missing teeth.
•
Markovic in 1982 found a high rate of concordance for hypodontia in MZ twin pairs
whereas the DZ twins that he observed were found to be discordant.
• These and the other previous studies conclude that the mode of inheritance could be
explained by a single autosomal dominant gene with incomplete penetrance.

91. Abnormal tooth shape:
•
Alvesalo & Portin (1969) provided substantial evidence that missing and
malformed laterals may well be the result of a common gene defect.
• Abnormalities in the lateral incisor vary from peg shaped to microdontia
to missing teeth all of which have familial trends, female preponderance
& association with other dental anomalies such as missing teeth, ectopic
canines, transposition suggesting a polygenic etiology.

92. Ectopic maxillary canines:
•
Various studies in the past have suggested a genetic tendency for ectopic maxillary
canines.
• Peck in 1994 concluded that palatally ectopic canines were an inherited trait, being one
of the anomalies in a complex of genetically related dental disturbances, often
occurring in combination with missing teeth, tooth size reduction, supernumerary tooth
and other ectopically positioned tooth.

93. CONCLUSION:
• A PERMANENT INTERACTION BETWEEN GENETIC AND ENVIRONMENTAL
FACTORS, BOTH OF A CONTINUALLY ALTERING NATURE, DETERMINE THE
DENTOFACIAL MORPHOLOGY.
• PREDOMINANCE OF MORPHOGENETIC PATTERN OF MALOCCLUSION
PROFOUNDLY INFLUENCES ORTHODONTIC OBJECTIVES AND THERAPEUTIC
RESULTS.
• THEREFORE MORE HEREDITARY STUDIES ARE IMPORTANT TO EVIDENCE THE
BASE OF GENETICS FOR THE PRACTICE OF ORTHODONTICS.

94. REFRENCES:
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T. M. GRABER- ORTHODONTICS- PRINCIPLES AND PRACTICE
T. C. WHITE, J. H. GARDINER, B. C. LEIGHTON- ORTHODONTICS FOR DENTAL STUDENTS.
S GOWRI SHANKAR - TEXTBOOK OF ORTHODONTICS
SRIDHAR PREMKUMAR –TEXTBOOK OF CRANIOFACIAL GROWTH.
OMPRAKASH KHARBANDA – DIAGNOSIS AND MANAGEMENT OF MALOCCLUSION AND DENTOFACIAL DEFORMITIES
THE USE OF TWINS IN DENTOFACIAL GENETIC RESEARCH . BY LAUWERYN I,CARELS C,VLIETINCK R (AJODO 1993;103:33-381)
HERITABILITY OF CRANIOMETRIC & OCCLUSAL VARIABLES: A LONGITUDINAL SIB ANALYSIS. BY- EDWARD F HARRIS & MICHELLE
G.JOHNSON. (AJO-DO 1991;99:258-68)
HERITABILITY MALOCCLUSION : PART 2. THE INFLUENCE OF GENETICS IN MALOCCLUSION. BY P.A. MOSEY; BRITISH JOURNAL OF
ORTHODONTICS/VOL 26/1999/195-203.
HEREDITARY FACTORS IN TOOTH DIMENSION, A STUDY OF ANTERIOR TEETH OF TWINS. BY- HOROWITZ, OSBORNE AND DEGEORGE
(AJODO, APRIL, 1958/ VOL-28/ NO. 2)

95. THANK YOU