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Human Body - The Human Teeth

Grade 4ICSE

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

🔑Concepts

Humans have two sets of teeth in their lifetime: Milk teeth (Temporary) and Permanent teeth. There are 2020 milk teeth and 3232 permanent teeth.

The tooth consists of three main parts: the Crown (visible part), the Neck (middle part), and the Root (embedded in the jawbone).

Enamel is the white, outermost layer of the tooth and is the hardest substance in the human body, rich in minerals like Calcium (Ca2+Ca^{2+}).

Under the enamel lies the Dentin, and inside the dentin is the Pulp, which contains nerves and blood vessels.

There are four types of teeth: Incisors (88 for cutting), Canines (44 for tearing), Premolars (88 for crushing), and Molars (1212 for grinding).

A Dental Formula is a representation of the number and types of teeth in one half of the upper and lower jaws.

Tooth decay is caused by bacteria reacting with sugar to produce acid, which dissolves the enamel: Sugar+BacteriaAcidSugar + Bacteria \rightarrow Acid.

📐Formulae

Milk Teeth Formula=21022102×2=20\text{Milk Teeth Formula} = \frac{2102}{2102} \times 2 = 20

Permanent Teeth Formula=21232123×2=32\text{Permanent Teeth Formula} = \frac{2123}{2123} \times 2 = 32

Total Teeth=2×(Incisors+Canines+Premolars+Molars)\text{Total Teeth} = 2 \times (\text{Incisors} + \text{Canines} + \text{Premolars} + \text{Molars})

💡Examples

Problem 1:

Calculate the total number of Molars in an adult human mouth if the dental formula for one half of the jaw is 21232123.

Solution:

There are 3×2=63 \times 2 = 6 molars in the upper jaw and 3×2=63 \times 2 = 6 molars in the lower jaw, totaling 1212 molars.

Explanation:

In the dental formula 21232123\frac{2123}{2123}, the last digit '33' represents the number of molars in one quadrant. Since there are 44 quadrants in the mouth, total molars = 3×4=123 \times 4 = 12.

Problem 2:

If a child has 2020 milk teeth, how many premolars do they have compared to an adult?

Solution:

A child has 00 premolars, whereas an adult has 88 premolars.

Explanation:

In the milk teeth dental formula 21022102\frac{2102}{2102}, the third digit is 00, meaning premolars are absent in the temporary set. They only appear in the permanent set.

Problem 3:

A tooth has a total of 88 incisors and 44 canines. If the total number of teeth is 3232, how many 'grinding teeth' (Premolars + Molars) are present?

Solution:

32(8+4)=2032 - (8 + 4) = 20 grinding teeth.

Explanation:

By subtracting the cutting teeth (incisors) and tearing teeth (canines) from the total 3232, we find there are 88 premolars and 1212 molars, which equals 2020 teeth used for grinding and crushing.

The Human Teeth - Revision Notes & Key Formulas | ICSE Class 4 Science