Dentition
in Mammals:
Usually,
heard and pointed structure present into the buccal cavity, attached to the jaw
is called as dentation or teeth. Teeth are found in fishes,
amphibians, and mammals. In birds, teeth are absent and are reported in
ancient/fossil birds.
Structure of tooth
The
typical tooth of mammal shows the following parts.
a. Crown
b. Neck
c. Root.
Crown
: it
is exposed part of the tooth, covered by relatively hard enamel. the enamel is
a white glistening part composed of hydroxyapatite covering dentine. Enamel is
folded with sharp cutting edges. On the basis of cavity or cusp formed by
enamel, teeth are mono-cuspid, di-cuspid, poly-cuspid.
Dentine: Dentine is softer than enamel but harder than bone. dentine encloses the cavity called pulp cavity filled with pulp consist of the blood vessel, lymph vessels, nerve, connective tissue, etc. enervate through the opening of the pulp cavity. The pulp cavity project into numerous treelike branched process called dentine forming odontoblast.
Neck- it is the middle part of tooth surrounded by the fleshy fold of the mucus membrane called gum.
Root:: It is the lower part of the tooth, fitted into the socket of the jaw bone. The incisor and canines have a single root, pre-molar has two roots and molar teeth have two to three roots. The tooth is fitted into the socket or alveolus by cellular cement.
There
are several kinds of dentation which are as follows.
a. Kinds
of teeth on the basis of attachment to the jaw bone
b. Kinds
of teeth on the basis of succession or replacement
c. Kinds
of teeth on the basis of structure.
a. Kinds
of teeth on the basis of attachment to the jaw bone.
On
the basis of attachment following are the kinds of teeth
i) Acrodont
teeth
ii) Pleurodont
teeth
iii) Thecodont
teeth
I. Acrodont
teeth: In this type, the teeth are not directly attached
to the jaw bone. But simply embedded into the socket of jaw bone are present at
the free edge of the jaw bone. eg. Scoliodon
ii. Pleurodont
teeth : in this kind, teeth are present on the inner side
of jaw bone are also embedded into the mucus membrane of the jaw bone. eg.
lizard
iii. Thecodont
teeth: in this kind, the teeth are fitted into the
socket of the jaw bone. e g. Mammals
b. Kinds
of teeth on the basis of succession or replacement
On the basis of succession or replacement of teeth in a lifetime, there are three
kinds of teeth in animals, which are as follows.
i. Polyphyodont
ii. Monophydont
iii. Diphyodont
Polyphyodont
i. Polyphyodont:
In
this type, there are several sets of teeth during a lifetime. If teeth are
destroyed of ware off are replace by new rows of teeth. This condition is known
as polphyodont condition.
Eg.
Lower vertebrates such as fishes, amphibians, reptiles, etc.
ii. Monophyodont: In
some mammals, there is a single set of teeth during a lifetime known as a
monophyodont condition. In duckbill platypus, teeth are present in embryonic
conditions, which are replaced by horny epidermal plate. In spiny
anteater, teeth are absent in all stages of life forms.
Eg.
Duckbill platypus, whales, marsupials, etc.
iii. Diphyodont : in this type, there are two sets of teeth during a lifetime. Such types of teeth are present in mammals. The condition is called as diphyodont. The first set of teeth is called lacteals or milk teeth or deciduous teeth. These teeth are replaced by permanent teeth.
Eg.
Man, monkey, etc.
c. Kinds
of teeth on the basis of structure:
On
the basis of the structure following are the kinds of teeth.
i. Homodont
ii. Heterodont
i.
Homodont:
In
this type, all the teeth are similar in shape and structure, called homodont
dentition of isodont dentition. Such types of teeth are present
lower vertebrates, such as fishes, amphibians, reptiles and in certain mammals
such as whales, dolphins, armadillo, etc.
2.
Heterodont Teeth:
The
presence of heterodont is the characteristics of mammals. In this type, teeth
are dissimilar in shape and structure. The variation in the dentition is on
the basis of food and manner of eating food. The heterodont teeth include four
kinds of teeth which are as follows
1. Incisor
2. Canines
3. Pre-molar
4. Molar
teeth
1. Incisors: These
are front or anterior teeth situated at the tip of the dentary in the upper jaw
and lower jaw. The incisors are with a single root and monocuspid crown. In the
case of rat (Rodents) incisors are open rooted and continue to grow throughout
life. In the case of ox and sheep on the upper jaw, the incisors are absent.
Function:
Incisors are used for cutting and copping.
2. Canines:
Incisors the canines are followed by canines are also single-rooted. The crown
is ling and pointed.. The canines are absent in the jaws of some
herbivores animals leaving the toothless region between incisor and premolar.
This toothless region is called diastema. In carnivore,
canines are long and sharply pointed used for piercing and tearing the animal
flesh.
Functions: To
tear the animal flesh and it acts as an organ of offense and defense.
3. Premolars:
In
the buccal cavity, canines are followed by pre-molars. The premolars
are with a bi-cuspid crown and two roots.
Function: Gridding
or crushing of food particles.
4. Molar: The
molar teeth lie behind pre-molars. The molar tooth has a two to three roots and
enamel is with several cavity or cusps. In humans, the last molar tooth is
called Wisdom tooth.
Function: Gridding or
crushing of food particles.
The pre-molar and molar teeth are together
called cheek teeth.
Cheek
teeth: On the basis of structure and
numberscof the cusp, there are various kinds of cheek teeth are present,
which are as follows,
i. Triconodont- -
Fossil mammals
ii. Tri-tuberculate -
Fossil mammals
iii. Bunodont -Man
Monkey
iv. Selenodont -
Cattles
v. Secodont -
Carnivore
vi. Lophodont -
Elephant
i. Triconodont: In
this type, the crow shows the presence of three conical projections arranged
linearly. Ex. Fossil mammals.
ii. Trituberculate: The
crown shows the presence of three tuberosity arranged separately in the
form of a triangle. Ex. Fossil mammals
iii. Bunodont:
in this type the crow is polycuspid. The cusp are separate and remain rounded,
called bunodont used for grinding of food.
Ex.
Man, Monkey, primate, etc.
iv. Selenodont: The selenodont teeth are
present in cattle. There are two types of selenodont teeth, includes
1. Brachydont:
2. Hypsodont
1. Brachydont:: In
this type, the enamel is poly-cuspid with sharp cutting edges. These teeth are
deeply rooted. Ex. Ruminants (Cow)
2. Hypsodont: The
crown is tall prism-like and low rooted. The enamel is poly-cuspid with sharp
cutting edges. Ex. Horse
Functions:
Selenodont teeth are used for crushing plant material.
v. Secodont: In
this type, the crown is poly-cuspid. The enamel shows the presence of sharp cutting
edges. such types of teeth are used to crack the bones and for cutting sharing
tendons. Such types of teeth are also called carnassial teeth.
Eg. Carnivore.
vi. Lophodont: In
this type of cheek teeth, the enamel is much folded, these folds are called
lophs. Hence, the tooth is called lophodont. Such type
of lophodont is found in elephants, measures about 30X10 cm. such
types of teeth are used for grinding of all kinds of plants and grasses.
Ex.
Elephant.
Dental
formula:
The
method of expressing the total number of teeth in animals according to the
arrangement is termed as the Dental Formula. The dental formula expresses the
number of each type of tooth into the buccal cavity for a given species.
Thus,
the dental formula represents the arrangement of teeth in each half of the
upper and lower jaw multiplied by two, which represents the total number of
teeth in the buccal cavity. The dental formula is represented as follows.
Dental
formula
In
the above formula
I –
Incisor
C-
Canines
Pm-
Pre-molar
M-
Molar
From
half of the upper and lower jaws.
For
Ex.
The
dental formula of Man -2123/2123X2=
32 Teeth
For
instance, a man has 2 incisor, 1 canine, 2 premolars and 3 molars on one side
of the upper jaw and 2 incisor, 1 canine, 2 premolars and 3 molars on one side
of the lower jaw. The number of teeth is multiplied by 2 which gives the total
number of teeth in the buccal cavity that is 32
The
dental formula of Dog =
3142/3143 X 2 =42 Teeth
For
instance, a dog has 3 incisors, 1 canine, 4 premolars and 2 molars on one side
of the upper jaw and 3 incisors, 1 canine, 4 premolars and 3 molars on one side
of the lower jaw. The total number of teeth is 42
The
dental formula of elephant =
1003/0003 X 2 =14
In
elephant, 1 incisors, 0 canine, 3 premolars and 3 molars on one side of the
upper jaw and 0 incisors, 0 canines, 3 premolars and 3 molars on one side of the
lower jaw are present. ‘0’ indicates the absence of
teeth. The Ivory tusk in the elephant are nothing but the modified
incisors of the upper jaw.
Some
dental formulas:
The
dental formula of Rat -1003/1003X2=
14 Teeth
The
dental formula of cattle -0033/4033X2=
32 Teeth
The
dental formula of sheep -0033/3133X2=
32 Teeth
Significance
of Dentition :
1. For the
taxonomic classification of animals.
2. To
calculate the approximate edge of the animal.
3. To
illustrate the pedigree of certain animals.
4. To
understand the diet of the animal.
Functions
of dentition :
In
the life of the animal, dentition performs the following functions
1. Chewing
or crushing of food particles.
2. Teeth
help in the process of speech and pronunciation
3. It acts
as an organ of offense and defense.
4. Tearing
the animal flesh.
Dentition
in Mammals:
By,
Dr. Vidhin Kamble
Sangola
College, Sangola
