Human teeth

Structure and function

The process of mechanical digestion mainly occurs in the mouth through the teeth, through a process called mastication.

There are four types of teeth present in human, and they are specialized for different functions.

Following table is showing the types and the functions of 4 types of teeth present in our mouth.


name /type incisor canine premolar molar
position in mouth front/middle teeth


either side of incisors between canines and molars back/last flat
total number total 8

4upper jaw+

4 lower jaw

total 4

2 upper jaw

2 lower jaw

total 8

4 upper jaw+

4 lower jaw

total 12

6 upper jaw+

6 lower jaw

description chisel-shaped

( sharp edge)

slightly more pointed than incisors have two cusps

have one or two roots

four or five cusps

have two or three roots

function biting the food tearning and biting tearing and grinding chewing and best for grinding


Teeth in human upper jaw

Teeth in human upper jaw


Structure of a Tooth:

Structure of a Tooth

Crown: The part of a tooth that is visible above the gum.

Gum: The gum is a tissue that overlays the jaws.

Root: The rest of the tooth that is embedded in the jaw bone, is called the root.

Enamel: the crown is covered by a hard white layer called Enamel. This layer is replaced by cement in the root, which enables the tooth to grip to its bony socket in the jaw.

Dentine: Below the Enamel is a layer of dentine. Dentine is softer than Enamel.

Pulp cavity: Inside the dentine is a pulp cavity, containing nerves and blood vessels,
enters the tooth through a small hole at the base of the root.

Causes of dental decay

  • We all have germs in our mouth that plays an important part in dental decay.
  • If we do not brush our teeth properly then food deposits and a layer of bacteria form on our teeth called plaque.
  • Bacteria feed on this plaque and also on sugar taken up with sugary food and highly contained carbohydrates food.
  • The germs make acids. This acid cause tooth decay means damages the surface of the tooth. Tooth decay cannot stop itself until it is treated so it can be prevented if it is caught early.

 dental decay

  • And if proper dental care does not take place then over the time, acid will dissolve the enemal and make a hole or cavity and penetrate into dentine.
  • Now if the cavity is not cleaned properly and filled by a dentist, the bacteria will
    get into the pulp cavity.
  • Once this penetration reaches the pulp cavity where nerves and blood vessels are present it will cause toothache and possibly, an abscess (an infectionin the jaw).
  • Often, the only way to treat this is to have the tooth pulled out.

dental decay

Different stages of tooth decay

Gum diseases:


There is usually a layer of saliva and mucus over the teeth. This layer contains bacteria that live on the food residues in the mouth, building up a coating on the teeth called plaque.


Tartar or culcus:

If the plaque is not properly removed, mineral salts of calcium and magnesium are deposited on it, forming a hard layer of ‘tartar’ or calculus. If the bacterial plaque that forms on teeth is not removed regularly, it spreads down the tooth into the narrow gap between the gum and enamel.

tartar’ or calculus


Here it causes inflammation, called gingivitis, which leads to redness and bleeding of the gums and to bad breath. Eventually gums recede and expose the cement.


Periodontitis :

If gingivitis is not treated well, it progresses to periodontitis; the fibres holding the tooth in the jaw are destroyed, so the tooth becomes loose and falls out or has to be pulled out.


Care of teeth:

The graph  below shows how the pH in the mouth falls (i.e. becomes more acid) when a single sweet is sucked. The pH below which the enamel is attacked is called the critical pH. In this case, the enamel is under acid attack for about 10 minutes.

pH in the mouth falls (i.e. becomes more acid) when a single sweet is sucked

The following graph shows the effect of sucking sweets at the rate of four an hour. In this case the teeth are exposed to acid attack almost continually.

effect of sucking sweets at the rate of four an hour

Steps to be taken for dental care:

  • The best way to prevent tooth decay, therefore, is to avoid eating sugar at frequent intervals either in the form of sweets or in sweet drinks such as orange squash or soft (fizzy) drinks.
  • It is advisable also to visit the dentist every 6 months or so for a ‘check-up’ so that any caries or gum disease can be treated at an early stage.
  • Brushing the teeth is very important in the prevention of gum disease. It may not be so effective in preventing caries, although the use of fluoride toothpaste does help to reduce the bacterial population on the teeth and to increase their resistance to decay.
  • Rinsing the mouth regularly with mouthwashes helps reduce the number of bacteria residing in the mouth.
  • Drawing a waxed thread (‘dental floss’) between the teeth, or using interdental brushes, helps to remove plaque in these regions.

Test yourself:

  • How many total teeth an adult has?
  • What is a wisdom tooth? Is it a molar or pre- molar?
  • What is the function of molar and pre-molar?
  • What is the basic cause of tooth decay?
  • How does fluoride help to prevent tooth decay?
  • What is a dental floss?
  • What is the difference between plaque and gingivitis?
  • What is enamel?
  • What is an abscess?
  • In which part of the tooth, nerves and blood vessels are present?