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Tooth Decay

Tooth decay is the damage of tooth enamel caused when acids in the mouth lower the pH and slowly dissolve the hard outer layer.

In one line: Sugar feeds bacteria, bacteria make acid, acid harms enamel.

Practice This Concept

Understand it

Bacteria in the mouth feed on sugar left on teeth and produce acids.
These acids lower the mouth pH.
If the pH falls below about 5.5, enamel starts getting damaged.
This is why regular brushing, reduced sugar intake, and fluoride toothpaste are useful habits.

Example

After frequent sweet snacks, the mouth becomes more acidic and the enamel can start weakening.

Rule to remember

When mouth pH falls below about 5.5, enamel begins to dissolve more easily, so decay risk increases.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1If a child eats sweets many times a day and does not brush properly, acid forms repeatedly in the mouth.
2The repeated low pH can weaken enamel and cause decay over time.

Method you can reuse

1First identify the cause, usually sugar and bacteria.
2Then explain acid formation and pH drop.
3Finally state the result: enamel damage and tooth decay.

Visual tip

A simple mouth sketch can show sugar, bacteria, acid, and enamel damage as a sequence.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does the mouth need protection after frequent sugary snacks?

Think first, then show answer

Because bacteria use sugar to make acids, the pH of the mouth falls, and the enamel can slowly get damaged, leading to tooth decay.

Common wrong answer

A common wrong answer is to say sugar directly dissolves teeth.

Why it loses marks: Bacteria make the acid that causes the damage.

Don't mix this up

Students often think tooth decay is only about dirty teeth. The main issue is the acid made by bacteria and the drop in pH.

Exam tip

In exam answers, mention sugar, bacteria, acid formation, pH drop, and enamel damage together.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions often ask why sugar increases decay, why fluoride toothpaste helps, or what happens when mouth pH falls below 5.5.

1
Enough for 1 mark
Tooth decay is the damage of tooth enamel caused when acids in the mouth lower the pH and slowly dissolve the hard outer layer.
2
Add for 2 marks
Example: After frequent sweet snacks, the mouth becomes more acidic and the enamel can start weakening.
3
Add for 3 marks
Bacteria in the mouth feed on sugar left on teeth and produce acids.

MCQ Quiz

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