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
Related
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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Fluoride in diet: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); 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).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.