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How does tooth decay happen?

Medicine & HealthLesson on requestFree to readयह पेज हिंदी में पढ़ें

Quick answer

Tooth decay is caused by acid produced when bacteria in plaque ferment sugars from food. This acid dissolves the mineral in tooth enamel. Saliva normally repairs early damage, but frequent sugar exposure overwhelms that repair. Over time, a hole forms in the enamel, which a dentist must fill.

Tooth decay happens when bacteria in plaque ferment dietary sugars into acids that dissolve tooth enamel. Repeated acid attacks, buffered by saliva, eventually create cavities if minerals are not restored.

Step by step

  1. Bacteria in plaque cling to teeth and feed on sugars from food and drinks.
  2. They ferment these sugars into acids, mainly lactic acid.
  3. Acid drops the pH at the tooth surface below 5.5, dissolving calcium and phosphate from enamel.
  4. Saliva washes acid away and redeposits minerals, but repeated attacks outpace repair.
  5. The enamel weakens and eventually collapses, forming a cavity that reaches deeper layers.

Key things to understand

  1. Bacteria such as Streptococcus mutans live in dental plaque on teeth.
  2. They ferment sugars from food into lactic acid and other organic acids.
  3. Acid lowers plaque pH below 5.5, dissolving calcium and phosphate from enamel.
  4. Saliva normally neutralises acid and redeposits minerals in a repair process called remineralisation.
  5. Frequent sugar intake tips the balance toward mineral loss, forming a cavity.

Labelled diagram

  1. Plaque

    Sticky film of bacteria and food debris builds on tooth surface.

  2. Acid attack

    Bacteria ferment sugar, releasing acid that etches enamel.

  3. Mineral loss

    Enamel loses calcium and phosphate, becoming porous and weak.

  4. Cavity

    Enamel breaks down, exposing softer dentine underneath.

  5. Spread

    Decay reaches pulp, causing pain and possible infection.

How a cavity forms

Real-world examples

  • A person who sips sugary soda throughout the day keeps plaque acidic for hours, causing more decay than drinking it quickly with a meal.
  • Children with bottles of juice at bedtime often develop cavities in front teeth because saliva flow drops during sleep.
  • A dry mouth from medication reduces saliva, so acid stays on teeth longer and decay speeds up.
  • Dental sealants on chewing surfaces of molars block plaque from settling in grooves, preventing decay.

Common mistake

✗ Myth: Sugar directly dissolves tooth enamel.

✓ Fact: Sugar does not dissolve enamel; bacteria in plaque ferment it into acid. That acid is what damages the tooth. Without bacteria, sugar alone would not cause cavities.

People also ask

What causes tooth decay?
Tooth decay is caused by acid produced when bacteria in plaque ferment sugars from food and drinks. This acid dissolves the mineral in tooth enamel. Saliva normally repairs early damage, but frequent sugar exposure overwhelms that repair, leading to a cavity.
How to stop tooth decay from getting worse?
You can slow early decay by removing plaque with brushing and reducing how often you eat sugar. Fluoride toothpaste helps repair enamel. If a hole has formed, a dentist must fill it; hygiene alone cannot close a cavity.
Is tooth decay reversible?
Only early decay, before a hole forms, can be reversed. At that stage, minerals can be restored by saliva and fluoride. Once the enamel surface breaks, the damage is permanent and needs a filling. Regular check-ups catch decay early.
Why does sugar cause cavities?
Sugar itself does not dissolve teeth; bacteria in plaque ferment it into acid. That acid then attacks the enamel. The more often you eat sugar, the longer teeth stay under acid attack, so frequency matters more than total amount.
Can tooth decay be reversed?
Early decay, when only the enamel surface has lost minerals, can be repaired by saliva and fluoride. Once a hole forms in the enamel, it cannot heal itself and a dentist must fill it. Good hygiene can stop it getting worse.
How does fluoride prevent cavities?
Fluoride binds to enamel, making it more resistant to acid. It also speeds up remineralisation, helping repair early damage. That is why fluoride toothpaste reduces cavities.
Why do wisdom teeth often decay?
Wisdom teeth sit far back, making them hard to brush properly. Food and plaque collect there easily. Many people also have them partially erupted, creating a trap for bacteria that is difficult to clean.

Part of the guide: How Your Body Works →