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TEETH– BASIC IDEA ABOUT STRUCTURE AND FUNCTION

 

 

INTRODUCTION:- Teeth are the hardest non- bony structure in the vertebrate body,

attached to the jaw bones. In our body, they are used in biting, chewing and

grinding of the food or in catching of prey. In human teeth are responsible for taking food also.

 

TYPES OF TEETH:– Most animals have Teeth in their jaws. Teeth are used to cut and break

the food into smaller parts. The kind, number and arrangement of teeth

in a personal or animal is called. ” dentition “.  It is of two types:

 

a) HOMODONT: All the teeth in the jaws are similar in shape and structure e.g fish and frog.

 

b)HETERODONT: The teeth in the jaws are not similar in shape and

structure e.g. cows and humans.

 

Mammals have heterodont dentition since all the teeth are not alike in them.

There are four types of teeth in mammals; incisors, canines, premolars and molars.

The number, size and shape of the teeth are related to the food the animals consume.

 

 

STRUCTURE OF A HUMAN TOOTH:–

 

The human teeth are enclosed in bony sockets or alveoli in the jaw bones.

These are called ” thecodont”. Each tooth consists of three parts.

* ROOTS— The basal part, embedded in the alveoli.

* NECK— They middle part enclosed in the gum.

* CROWN— They visible part projected beyond the gum.

 

In longitudinal section of a tooth, the following parts are seen:-

a)    Enamel: The white shiny outer covering of the crown is called enamel or ivory.

Ø  It is the hardest substance in the body. It can withstand tremendous pressure

while eating. Enamel wears away with age and dentine is exposed and the

teeth start looking yellow.

 

b) Dentine: It is the yellowish bone- like tissue that lies inside the enamel.

Dentine is not hard like enamel but harder and stronger than a bone.

 

c) Cement: It is a bone like structure that covers and fixes the root of

tooth within the socket of bone.

 

 

d) Pulp cavity and pulp: Pulp cavity is the central space in the tooth and is filled with soft

connective tissue. The pulp is richly supplied with blood capillaries, nerve fibres and

lymph vessels. These enter the pulp through root canal. The narrow part of the pulp

cavity is called root canal.

 

e) Odontoblasts: Dentine contains many canals having dentine producing cells called

Odontoblasts.

 

f) Periodontal fibres: Many fibres connect cement at one end and the jawbone at the other

end and hold the tooth firmly in position which are known as periodontal fibre.

 

CHARACTERISTICS OF HUMAN TEETH: The human teeth are;

a) THECODONT—The teeth are fastened in the socket of jaw bones.

b) DIPHYODONT: In human, two  sets of teeth are developed during lifetime.

These are known as temporary or deciduous teeth and permanent teeth.

The temporary teeth appear first. They are replaced by permanent set of teeth.

The deciduous or milk teeth fall because their roots begin to dissolve making way for

permanent teeth. The total number of teeth in adult is 32 which are permanent, but children

up to age of 12 years have just 20 temporary or milk teeth.

The milk teeth start erupting out of the gums when the child is about 6-8 months old.The entire set of 20 milk teeth is completed by the age of two years. They start falling

out one by one at the age of 7-8 years and are replaced by permanent teeth by the age

of 12 years.

 

c) HETERODONT: Different types of teeth to perform different functions. Based on

their functions they are of four types:

 

b)    INCISORS: These are situated at the front of the buccal cavity. They are flat and

straight with sharp edges which are used for “cutting and biting the food”.

 

ii) CANINES: These are situated one on either side of the incisors in each jaw. These

are sharp and pointed for “holding

and tearing the food”

 

iii) PREMOLARS: There are two premolars situated next to the canines. Each premolar

possesses one or two roots and two cups or projections on the surface of a tooth.

The premolars are specialized for ” crushing and grinding the food”.

 

iv) MOLARS: These are the last three teeth in each jaw. They have more than one root.

Molars in the upper jaw have three roots while those in the lower jaw have two roots.

Each molar has four or five cusps. These types of food helps in crushing and grinding

of hard part of the food..

The last molar of each side  in each jaw is also called the wisdom teeth, because it appears

last, generally at the age of 17-20 years when the body reaches  maturity. However, in some

people this tooth does not appear at all. But this does not mean they have no ” wisdom”.

 

DENTITION AS PER DIET: Dentition in animals is based on their feeding habits:

 

HERBIVORES: Animals like sheep, cow and horse have teeth with broad ridged surfaces

that are suitable for grinding tough plant material. The incisors and canines are generally

modified for biting off pieces of vegetation.

 

 

CARNIVORES: Animals like cat and dog have pointed incisors and canines that can be used

to kill prey and tear off flesh. The premolars and molars are modified for crushing and shredding.

 

OMNIVORES: Animals such as human beings are adapted for eating both vegetation and

meat and have a relatively mixed dentition. There are two incisors for biting and cutting,

one canine for tearing, two premolars for grinding and three molars for crushing.

 

 

                                             DENTAL FORMULA

The number and arrangement of teeth in a mammal is represented by dental formula.

The number of teeth in right and left half of each jaw is the same. The dental formula is

represented as shown below:

(Dental formula: number of teeth in one half of upper jaw÷ number of teeth in one half of lower

jaw) × 2

 

I+C+Pm+M

——————–. × 2/2

I+C+Pm+M

 

Here are some dental formula of various mammals including their dentition.

 

a) Dental formula  of cow ( herbivore)

0+0+3+3.

——————× 2/2= 12/18=30

3+1+2+3

Incisors are chisel shaped .Sometimes canine is absent or less sharp. Vaccant space between

incisors and premolars is called diastema.

 

b) Dental formula of dog ( carnivores)

3+1+4+2

——————×2/2 = 20/22= 42

3+1+4+3

. Incisors are sharp for scraping flesh. Canines are long, curved and sharply pointed for

tearing flesh. Premolars and molars have raised conical and pointed ridges or cups for

shearing off flesh from bones

 

c) Dental formula of human being  (omnivore)

2+1+2+3

————— × 2/2= 16/16 = 32

2+1+2+3

Incisors are chisel shaped and flat adapted for biting and cutting. Canines are short and blunt

used for holding the  the food and tearing the fruits. Premolars and molars have low and blunt

crushing surfaces.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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