Fluoride: Mechanisms, Products & Safety

How fluoride works

Mainly topical and post-eruptive: fluoride in plaque and saliva slows demineralization and speeds remineralization, forming less soluble fluorohydroxyapatite.
Critical pH: about 5.5 for hydroxyapatite versus about 4.5 for fluorapatite.
Fluoride also inhibits bacterial enolase (glycolysis), lowering acid production.
Community water fluoridation: U.S. Public Health Service recommendation 0.7 mg/L (2015); EPA enforceable maximum 4.0 mg/L and secondary standard 2.0 mg/L (cosmetic fluorosis). Policies are under review in some states and federally, so check current status.

Product	Fluoride (ppm)	Use
5% NaF varnish	About 22,600	In-office, all ages; ADA 2013: at least every 3–6 months for elevated caries risk
1.23% APF gel or foam	12,300	In-office, age 6 and up; avoid on porcelain, composite and titanium (acid etches them)
2% NaF gel	About 9,000	In-office; neutral pH, safe on restorations
1.1% NaF prescription paste or gel	About 5,000	Daily home use for high-risk patients age 6 and up
0.243% NaF or 0.454% SnF₂ toothpaste	About 1,100	Twice-daily brushing
0.05% NaF rinse	About 230	Daily OTC rinse (age 6 and up)

NaF is about 45% fluoride by mass, so ppm F ≈ % NaF × 10,000 × 0.45 (for 5% NaF: 50,000 × 0.45 ≈ 22,600).
Toothpaste amount (ADA): a smear (rice-grain size) under age 3, a pea-size amount ages 3–6.

Age	Water under 0.3 ppm	0.3–0.6 ppm	Over 0.6 ppm
Birth to 6 months	None	None	None
6 months to 3 years	0.25 mg/day	None	None
3 to 6 years	0.50 mg/day	0.25 mg/day	None
6 to 16 years	1.0 mg/day	0.50 mg/day	None

Dental fluorosis comes from excess intake while enamel forms (roughly up to age 8); it is a cosmetic, not a toxic, effect.
Probably toxic dose commonly taught: 5 mg F per kg; acute signs are nausea, vomiting and abdominal pain, then hypocalcemia and cardiac effects.
Example: a 20-kg child's PTD is 5 × 20 = 100 mg F, about 8 mL of 1.23% APF gel (12.3 mg F per mL).
Management of a smaller ingestion: give milk or a calcium product to bind fluoride; at or above the PTD, send to the emergency department.

Using APF gel on a patient with porcelain crowns or composite restorations.
Prescribing supplements when the water already has more than 0.6 ppm, or before 6 months of age.
Calling fluorosis a sign of systemic toxicity.
Thinking pre-eruptive (systemic) fluoride is the main benefit: the effect is mainly topical.

Pick an answer to see right away whether it is correct and why.

Which topical fluoride should be avoided on a patient with porcelain veneers?
About how many ppm fluoride does 5% sodium fluoride varnish contain?
A 4-year-old at high caries risk lives where the water has 0.2 ppm fluoride. The daily supplement is:
Using a probably toxic dose of 5 mg F/kg, what is the PTD for a 20-kg child?
The main way fluoride prevents caries in erupted teeth is by:

0 of 5 answered

Answer key: 1 A · 2 A · 3 C · 4 B · 5 A

Dental School Map · Original study material, written and checked by our team; always confirm clinical decisions against current guidelines.