The Teeth Chapter Notes | Science Class 4 ICSE PDF Download

Introduction

The Teeth

• Teeth are unique and vital features of humans.
• Babies are born without teeth, but they develop over time.
• Teeth help in biting and chewing food to make it easier to swallow.
• They assist in clear speech and enhance appearance.
• Humans have two sets of teeth in their lifetime: temporary (primary) and permanent teeth.

Temporary Teeth

• First set of teeth that appear in children around 6 months of age.
• Growth can be painful for babies.
• By age 3, children usually have 20 primary teeth.
• Also called milk, baby, or deciduous teeth.

Permanent Teeth

• Second set of teeth that replace primary teeth starting around age 6 or 7.
• Also known as adult teeth.
• Adults typically have 32 permanent teeth.
• These teeth last for a long time in the mouth.

Kinds of Teeth and Their Function

Incisors

• Flat teeth with sharp edges located at the front of the mouth.
• Eight incisors in total: four in the upper jaw and four in the lower jaw.
• Used for biting and cutting food into small pieces.

Canines

• Sharp and pointed teeth next to incisors.
• Four canines in total: two in each jaw.
• Used for tearing and ripping food.

Premolars

• Flat and broad teeth located next to canines.
• Eight premolars in total: four in each jaw (two next to each canine).
• Bigger and stronger with ridges to trap and crush food.
• Help move food to molars for chewing.

Molars

• Large, flat teeth next to premolars.
• Twelve molars in total: six in each jaw (three next to each pair of premolars).
• Bigger and wider with ridges for chewing and grinding food.
• Children have 8 molars (four in each jaw) but no premolars, making 20 primary teeth.
• Adults have all four types of teeth.

Time to Revise (Kinds of Teeth)

• Deciduous teeth: 20 in number.
• Permanent teeth: 32 in number.
• Incisors: Flat teeth with sharp edges at the front of the mouth.
• Canines: Sharp and pointed teeth.
• Premolars: Flat and broad teeth located next to canines.
• Molars: Bigger, wider teeth with ridges, six in each jaw.

A Tooth and Its Parts

• Teeth have two main parts: crown and root.
• Crown is the visible part of the tooth.
• Root is the part inside the gums.
• Gums are soft tissues that surround and hold teeth firmly.
• Teeth have three main layers: enamel, dentine, and pulp.

Enamel

• Outermost layer covering the crown.
• White, shiny, and harder than bone.
• Protects the tooth from decay.
• Made of minerals like calcium and phosphorus.
• Hardest substance in the human body.

Dentine

• Hard yellow layer under the enamel.
• Sensitive part of the tooth.

Pulp

• Central soft part of the tooth.
• Contains blood vessels and nerves to supply nutrients and nourish the tooth.

Time to Revise (Parts of a Tooth)

• Enamel: Harder than bone.
• Dentine: Sensitive part of the tooth.
• Pulp: Central soft part of the tooth.
• Crown: Visible part of the tooth.

Care of Teeth and Gums

• Good oral hygiene is essential for overall health.
• Poor hygiene can lead to dental problems.
• Food particles stuck between teeth can cause germs to grow.
• Germs form a sticky yellow coating called plaque.
• Plaque germs produce acid, damaging enamel and causing tooth decay, cavities, toothache, and bad breath.

Ways to Care for Teeth and Gums

• Brush teeth twice daily: before breakfast and after dinner to prevent plaque.
• Use a soft-bristled brush and fluoride toothpaste to protect enamel.
• Brush teeth properly in the correct manner.
• Rinse mouth with water or fluoride mouthwash after every meal for 30-60 seconds.
• Salt solution can also be used for rinsing.
• Use dental floss to clean between teeth, avoiding sharp objects that may cause injury.
• Clean tongue daily with a tongue cleaner gently to avoid injury.
• Visit the dentist regularly for check-ups to detect and treat dental issues.
• Eat fruits, vegetables, and calcium-rich foods like green leafy vegetables, yogurt, and milk products for strong teeth.
• Avoid sugary foods and drinks like sweets, chocolates, pastries, and soft drinks, as they produce acid that harms teeth.
• Maintain a balanced diet for healthy teeth and gums.

Terms to Know

• Temporary teeth: Also called milk teeth, first set appearing from 6 months.
• Permanent teeth: Also called adult teeth, appear from age 6 or 7.
• Incisors: Front flat teeth with sharp edges.
• Canines: Sharp, pointed teeth next to incisors.
• Premolars: Flat, broad teeth next to canines.
• Molars: Bigger, wider teeth with ridges next to premolars.
• Crown: Visible part of a tooth.
• Root: Part of a tooth inside the gums.
• Enamel: White, shiny outermost layer covering the crown.
• Dentine: Hard yellow substance under the enamel.
• Pulp: Central soft part of the tooth.
• Gums: Soft tissue surrounding and holding teeth firmly.
• Plaque: Sticky yellow coating on teeth caused by germs.