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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# Fluoride

Fluoride hardens tooth enamel and protects it from decay; too much in childhood stains the teeth and harms bone.

Updated 2026-11-01

## Key facts

- It replaces hydroxyl groups of hydroxyapatite to form fluorapatite, which resists bacterial acid better.
- Its main effect is topical: it promotes enamel remineralisation and slows plaque bacteria's metabolism.
- Excess in childhood (while enamel forms): dental fluorosis, with white or brown stains.
- Heavy chronic excess: skeletal fluorosis, with dense but brittle bones and calcified ligaments.

## In detail

- Sources: fluoridated or naturally fluoride-rich water, fluoridated salt (used in Colombia and other Latin American countries), toothpaste, tea, fish eaten with bones.
- Mechanism in the tooth: at the acid pH that follows sugar intake enamel loses mineral; fluoride in saliva helps it redeposit as fluorapatite.
- In the bacterium: fluoride inhibits the glycolytic enzyme enolase (2-phosphoglycerate to phosphoenolpyruvate) and reduces acid production.
- Enolase inhibition by fluoride is why grey-top tubes (sodium fluoride) are used to measure glucose: they stop glycolysis by blood cells.
- Acute poisoning (swallowing a lot of toothpaste or fluoride products): nausea, vomiting, abdominal pain, hypocalcaemia.
- Lab: urine or drinking-water fluoride, in population studies.

**Also called**
F⁻, Fluorine, Fluorapatite

## Clinical notes

- Dental fluorosis becomes a public health problem when water or salt supplies too much fluoride in the first years of life.
- Young children use a small amount of toothpaste and are taught to spit it out, to get the topical effect without swallowing fluoride.
- Fluoride varnishes applied by the dentist reduce caries in high-risk children.

## Related conditions

- [Dental caries](https://durgical.com/en/conditions/dental-caries/)

## Related

- [Calcium and phosphate](https://durgical.com/en/biochemistry/topics/calcium-and-phosphate/)

## Test yourself

Think of the answer, then tap the question to see it.

## How does fluoride protect enamel?

It replaces hydroxyls of hydroxyapatite to form fluorapatite, which dissolves less in acid, and it promotes remineralisation.

## Which glycolytic enzyme does fluoride inhibit?

Enolase (2-phosphoglycerate → phosphoenolpyruvate); this is why fluoride tubes preserve the sample's glucose.

## When does dental fluorosis develop?

When too much fluoride is swallowed in childhood, while the enamel of the permanent teeth is forming.

## Why does fluoride's topical effect matter so much?

It acts on the tooth surface during the daily cycles of demineralisation and remineralisation.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Fluoride in diet: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/002420.htm) (MedlinePlus, US National Library of Medicine, 2026); [Oral health](https://www.who.int/news-room/fact-sheets/detail/oral-health) (World Health Organization, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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