2. Dentition in mammals
• Definition of dentition
• Structure and development of tooth.
• Classification or types of teeth with examples
• Dental formula with examples
• Theories
• Significance of dentition
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3. Dentition in mammals
Definition :- The study of arrangement, structure,
number and types of teeth collectively known as
dentition.
Teeth are present in all mammals except in Spiny ant
eater (entirely absent at any time), whale,
whalebone, Ornithorhynchus (no true teeth in adult
stage).
The hard and usually pointed structures connected to
jaw bones in the buccal cavity of vertebrates are
known as teeth.
The study of the structure, development and the
diseases of the teeth is called odontology. 3
4. Tooth consists three parts such as
1.Crown 2. Neck 3. Root.
Crown is the exposed part of the teeth. Neck is the
Junction place between crown and root. Root is the
part of the tooth inserted into the jaw bone.
The tooth is formed by hard dermal bony substance/
material called dentine.(LS of tooth).
The dentine of crown is covered externally by hard,
thin, shiny white enamel which is hardest part of the
body.
The dentine of root is covered by cement.
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6. Structure and Development of tooth
The socket is lined by the periodontal membrane
formed by dense fibrous connective tissue which is
attached to the socket wall and surface of the root.
Attachment of tooth on the jaw bone is
strengthened. by the gum.
Tooth contains narrow pulp activity, odontoblasts
lines of pulp cavity and these are the tooth forming
cells.
Pulp cavity contains pulp, opening at the base of the
root, through which nerves as well as blood vessels
enter into it.
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8. Structure and Development of tooth
Teeth are formed partly from epidermis and partly
from dermis.
Enamel of the tooth is formed from the epidermis.
The dentine, cement and pulp are formed from
dermis.
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10. According to the
Structure:
A) Homodont :- All the teeth are similar in size and
shape
Ex:- Dolphins, Seals, Walruses.
B) Heterodont :- The teeth differ in size, shape
and activity and are of four different types.
Ex:- Human and most of the mammals.
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12. FOUR TYPES OF HETERODONT
1. Incisors:- These are present on the premaxilla of
the upper jaw and at the tip of the dentary of the
lower jaw, one root, Sharp edge for biting as well as
cutting the food materials. But in elephant tusks are
modified as the two upper incisors with open roots
and in lemurs two incisors of upper jaw are
denticulate like a comb.
2. Canines:-These are sharp pointed crown, long,
conical shape with one root and are present
between the incisor and premolar. Its help in the
tearing of food.
In herbivorous mammals canines are absent. The
gap between incisors and premolars is called
diastema. In carnivorous, these are well developed
for biting and tearing the prey.
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13. FOUR TYPES OF HETERODONT
3. Premolars:- These are called Cheek teeth and
replaced once in life time. They have compressed
crown with one or two cusps. These are used for
grinding and crushing.
4. Molars:- These are also called cheek teeth. They
have more than two roots and cusps. Molars are
used for crushing and mastication.
In carnivore, last Premolars in upper jaw and first
molars in lower jaw are modified into carnasial teeth
which are used for breaking the bones.
In seal – molars modified to filter the plankton.
In man- Molar teeth are wisdom teeth.
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15. :- There are mainly of three
types such as
1. Acrodont:-Attached to the summits of the jaws,
have no roots. Ex:- Fishes, Amphibians, Reptiles.
2. Pleurodont:- Attached to the sides of the
jawbones. Ex:-Lizards.
3. Thecodont:-Placed in the sockets of the
jawbones. Ex:- Human, Mammals
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17. :- There
are divided into three types such as
1. Monophyodont :- Teeth are formed only once in
the life.
Ex:- Platypus (Prototheria), Marsupials
(Metatheria), Moles
2. Diphyodont:- Teeth are formed twice in the life
time. There are Milk/lacteal/Deciduous teeth and
Permanent teeth.
Ex: Most of the mammals, Human.
.
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18. 3. Polyphyodont: -Teeth are formed many times in the
life span.
Ex: Fishes, Amphibians and Reptiles
:- The
following types are there
1. Bunodont:- Teeth have small, separate, rounded
cusps for grinding. Ex:- Man and Monkey.
2. Secodont:- Molar Teeth have pointed cusps forming
sharp cutting crowns for tearing and cutting flesh.
EX:-Carnivorous mammals.
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19. 3. Solenodont:-Teeth are square with vertical crescent
shaped cusps of hard enamel. Ex:- Ruminants animals
(Cattle, Sheep).
4.Hypsodont:- The teeth are having long crown with short
roots and cusps are crescent shaped. Ex:- Horse
5.Brachyodont:- Molar teeth with short crown and the neck
at the surface of the gum and crescent shaped cusps.
Ex:- Dog
6.Lophodont:- The cusps join to form ridges called lophs,
which are intricating folded to form sharp transverse
ridges covered with enamel, between the ridges is
dentine which are used for grinding plants. Ex:- Elephant.
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21. DENTAL FORMULA
Dental formula:-The typical mammalian dental formula is
shown by
The number of teeth in the half of the upper jaw (Numerator) 2
The number of teeth in the half of the lower jaw(Denominator)
Man:- 2 1 2 3 2 8X2=16 16X2 =32
2 1 2 3 *Man= 32
Incisor-2,canine-1,premolar-2,molar-3
Pig, Horse, Mole= 3/3, 1/1, 4/4, 3/3 X 2= 44
Dog = 3/3, 1/1, 4/4, 2/3 X 2 = 42
Cat = 3/3, 1/1, 3/2, 1/1 x 2 = 30
Rabbit= 2/1, 0/0, 3/2, 3/3 X 2 =28
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23. Significance of Dentition
It provides clue to the diet/Food habits of the
mammals.
It is useful in deciding pedigree or ancestry of
certain mammals.
The number of teeth present gives an idea of the
approximate age of the mammal.
It is also having evolutionary significance.
The arrangement and number of teeth is useful for
the classification of mammals.
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