Based on the passage, here are the evaluations of the statements:

1. **Good teeth help us look nice.** - **True**
2. **The decay quickly spreads inside the tooth.** - **True**
3. **We ought to clean our teeth once a day.** - **False** (The passage suggests at least twice a day.)
4. **We shouldn't eat too much chocolate.** - **True** (The passage indicates that some foods can cause decay if eaten between meals.)

If you have any more questions or need further clarifications, feel free to ask!