If we do not clean our teeth and mouth after eating food, then many harmful micro-organisms called A begin to grow and live on the tooth. These micro-organisms act on the substance B present in the left-over food particles sticking to the tooth to form C. The C eats up the parts D and E of the tooth gradually and ultimately make a hole in the tooth. When this hole reaches part F of the tooth, our tooth becomes painful and we get toothache.
What is E?

Answer

To solve the question step by step, we will identify the components involved in the process of tooth decay as described in the video transcript.

### Step 1: Identify the harmful microorganisms
- The harmful microorganisms that grow on our teeth when we don’t clean them are called **A**. According to the transcript, these are **bacteria**.

**Hint:** Think about what types of microorganisms are commonly associated with dental issues.

### Step 2: Identify the substance in leftover food
- The leftover food particles that stick to our teeth contain **B**. The transcript mentions that the most present substance in food is **sugar**.

**Hint:** Consider what common ingredient in food is a favorite for bacteria to feed on.

### Step 3: Understand what C is
- The bacteria act on the sugar (substance B) to produce **C**, which is **acid**. This acid is harmful to the tooth enamel.

**Hint:** Think about what byproducts are typically produced by bacteria when they metabolize sugars.

### Step 4: Identify parts D and E of the tooth
- The acid produced by the bacteria eats away at parts **D** and **E** of the tooth. The transcript indicates that when the enamel is damaged, it leads to a hole. The first layer affected is the **enamel**, which is part D, and the second layer is **dentine**, which is part E.

**Hint:** Recall the structure of a tooth and the layers that are affected by decay.

### Step 5: Identify part F and the consequence
- When the hole reaches part **F**, which is the **pulp cavity**, it causes pain because the pulp contains blood vessels that signal to the brain when there is damage.

**Hint:** Consider what part of the tooth contains nerves and blood vessels.

### Conclusion
- Based on the above steps, the answer to the question "What is E?" is **dentine**.

**Final Answer:** E is **dentine**.