Toothpastes: fluoride concentration is chosen on caries risk, not on age

Toothpaste is the vehicle through which fluoride reaches enamel every day, and it is the preventive measure with the strongest evidence base in all of dentistry.

Concentrations are expressed in parts per million. A standard adult paste contains 1450 ppm, products for young children drop to 1000 ppm or lower, prescription pastes reach 5000 ppm.

The common error is choosing concentration by age group rather than by caries risk. An adolescent with fixed appliances and mediocre hygiene carries a far higher risk than a healthy adult.

Pastes at 5000 ppm have precise, documented indications: patients with multiple caries, exposed roots, xerostomia, fixed orthodontic appliances, disability compromising hygiene.

In these situations the difference from a 1450 paste is not marginal, and prescribing them is a clinical decision like any other, not a generic recommendation.

The chemical form of fluoride affects bioavailability. Sodium fluoride is the historical reference; stannous fluoride adds a documented antibacterial action on plaque and gingivitis.

Sodium monofluorophosphate requires hydrolysis by salivary enzymes to release fluoride, which makes it less immediately available. It is still used but with lesser advantages.

Abrasivity is the second parameter to know, expressed as RDA. Values below 70 count as low, above 100 as high, and whitening pastes often sit in the upper range.

On exposed roots or already abraded necks, a highly abrasive paste accelerates the damage. This is where the patient's aesthetic wish should be met with a concrete explanation.

Behaviour after brushing affects efficacy more than is generally supposed. Rinsing thoroughly washes fluoride out of the mouth precisely when it should stay in contact with enamel.

The correct instruction is to spit without rinsing, or at most to rinse with very little water. It is a simple change of habit that increases contact time at no cost.

Quantity matters little in adults and a great deal in young children. Below three years a rice-grain amount is used, between three and six a pea, to limit ingestion.

In summary: concentration follows risk, stannous fluoride adds antibacterial action, abrasivity matters on exposed roots, and not rinsing afterwards increases efficacy for free.