The number of teeth that grow twice in human life is

Options

A. 4
B. 12
C. 20
D. 28

Answer

To solve the question about the number of teeth that grow twice in human life, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Types of Teeth**:
- In humans, there are different types of teeth: incisors, canines, premolars, and molars.
- The teeth that grow twice in a human's life are known as **diphyodont** teeth.

2. **Identifying Diphyodont Teeth**:
- Diphyodonts are organisms that develop two sets of teeth: primary (deciduous) teeth and permanent teeth.
- In humans, the primary teeth are often referred to as baby teeth, which eventually fall out and are replaced by permanent teeth.

3. **Counting the Teeth**:
- The dental formula for primary teeth is typically represented as:
- 2 incisors, 1 canine, 2 premolars, and 3 molars per quadrant.
- Therefore, for one half of the jaw, the count is:
- 2 (incisors) + 1 (canine) + 2 (premolars) + 3 (molars) = 8 teeth.
- Since there are 4 quadrants in the mouth (2 upper and 2 lower), we multiply the count by 4:
- 8 teeth × 4 = 32 teeth in total for permanent teeth.

4. **Final Calculation**:
- The primary teeth (20 in total) are replaced by the permanent teeth (32 in total).
- Therefore, the total number of teeth that grow twice in a human's life is **20** (primary teeth).

### Conclusion:
The number of teeth that grow twice in human life is **20**.

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