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Teeth and the World of Microbes - Types and Structure of Teeth

Grade 4CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Humans have two sets of teeth during their lifetime: Temporary (Milk) teeth consisting of 2020 teeth, and Permanent teeth consisting of 3232 teeth.

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There are four types of teeth: Incisors (8 total) for cutting, Canines (4 total) for tearing, Premolars (8 total) for crushing, and Molars (12 total) for grinding.

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The structure of a tooth is divided into two main parts: the Crown (the visible part above the gum) and the Root (the part hidden inside the gum).

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The Enamel is the outermost white layer of the tooth and is the hardest substance in the human body.

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Below the enamel lies the Dentin, which is a bone-like hard layer that supports the enamel.

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The innermost part of the tooth is the Pulp, which is soft and contains blood vessels and nerves.

📐Formulae

Total Permanent Teeth=8 (Incisors)+4 (Canines)+8 (Premolars)+12 (Molars)=32\text{Total Permanent Teeth} = 8 \text{ (Incisors)} + 4 \text{ (Canines)} + 8 \text{ (Premolars)} + 12 \text{ (Molars)} = 32

Teeth per Jaw (Permanent)=322=16\text{Teeth per Jaw (Permanent)} = \frac{32}{2} = 16

Number of Milk Teeth=20\text{Number of Milk Teeth} = 20

💡Examples

Problem 1:

Rohan is 9 years old and has a full set of milk teeth. How many teeth does he have in his upper jaw?

Solution:

10 teeth10 \text{ teeth}

Explanation:

A complete set of milk teeth consists of 2020 teeth in total. Since the teeth are distributed equally between the two jaws, the upper jaw contains 20÷2=1020 \div 2 = 10 teeth.

Problem 2:

Calculate the total number of 'Tearing' and 'Grinding' teeth in an adult human.

Solution:

16 teeth16 \text{ teeth}

Explanation:

Tearing teeth are Canines (44 in total) and Grinding teeth are Molars (1212 in total). Therefore, 4+12=164 + 12 = 16 teeth.

Problem 3:

Why does a toothache hurt so much when a cavity reaches the innermost layer?

Solution:

Because the innermost layer is the Pulp.

Explanation:

The Pulp contains nerves. When a cavity or decay reaches the pulp, it stimulates the nerves, which sends pain signals to the brain.