4th Class Science Teeth and Digestion Teeth & Microbes

Teeth & Microbes

Synopsis

• Teeth help us to chew food and to break it into smaller pieces. Without the teeth we would not be able to enjoy food.

• A newborn baby has no teeth. Teeth begin to (appear when the baby is six to seven months old. By the age of three years children have 20 teeth. These are called temporary teeth or milk teeth.

• By the age of six years milk teeth begin to fall off and new teeth appear in their place. These are called permanent teeth. At the age of 12 to 13 years, 28 permanent teeth grow. Four more teeth, called wisdom teeth grow between the age of 20 to 25 years. So, an adult has 32 teeth.

• The portion of the tooth above the gum is called the crown. The portion inside the gum is called the root.

• The upper layer of the tooth which is hard is called enamel. The next layer inside is called dentine. The soft material inside the dentine is called pulp and it has blood vessels and nerves.

• There are four kinds of teeth namely, incisors, canines, premolars and molars. Incisors are also called cutting teeth. These are four in number, present in the front side and have sharp edges. These are used for cutting and biting.

• There are four canines on either side and are called tearing teeth. They are very sharp and pointed.

• Premolars are called cracking teeth. They are broad and flat and are next to the canines.

• Molars are broader than premolar teeth and are used for grinding food. So, they are also called grinding teeth.

• The food stuck between the teeth is converted to plaque by the action of germs and cause tooth decay. Plaque reacts with sugar and produces acids which destroy the enamel of the teeth.

• To prevent the formation of plaque we should brush our teeth properly in the morning and at night.

• Microbes are very small organisms which cannot be seen by our eyes. They live in air, water, land and inside and outside animals.

• The mouth is a suitable place for bacteria to grow and multiply in the crevices between the teeth because it is moist, dark and has the right temperature to grow.

• Harmful microbes that cause diseases are called germs.

• Microbes are of four types:

• Typhoid, tuberculosis, small pox, measles, flu, common cold, dysentery are some of the common diseases caused by germs,                          

• Some microbes are very useful to us. They help us by changing milk into curd, baking bread, making wine, in the decay of dead plants and animals, digesting food and producing vitamins in our body.