Whitening toothpastes: they remove surface stains, they do not change tooth colour

Whitening toothpaste is the category with the widest gap between what patients expect and what the product can do, and clarifying it prevents both disappointment and damage.

Tooth colour derives chiefly from the underlying dentine, seen through translucent enamel. No product acting at the surface can alter it.

What a whitening toothpaste can do is remove extrinsic stains deposited on the surface: coffee, tea, wine, tobacco. It is a real result but limited to the tooth's original colour.

A patient with genetically yellower teeth expecting a change of shade will be disappointed whatever product they use, and it is worth saying so beforehand rather than afterwards.

The prevailing mechanism is abrasion. These are products with above-average RDA, and this explains both their effectiveness on stains and their risk.

Prolonged use on intact enamel is tolerated; on exposed necks, dentine or composite it accelerates permanent loss of substance.

The resulting paradox is that continued use can make teeth appear yellower. By thinning the enamel, more of the underlying and darker dentine shows through.

Some formulations add chemical agents, typically hydrogen or carbamide peroxide at very low concentrations, or sodium hexametaphosphate, which acts against stain redeposition.

Peroxide concentrations permitted in over-the-counter products are an order of magnitude below those used in professional whitening, and contact time is two minutes against hours.

The chemical effect is therefore modest. It is not nil, but it is not comparable to a whitening treatment, and presenting it as such is the main reason expectations go unmet.

Activated charcoal deserves a separate note, because its spread has outpaced the evidence. Abrasivity in many formulations is high, and several contain no fluoride.

A highly abrasive, fluoride-free product used daily is the worst combination for a caries-prone patient, and should be actively discouraged when it emerges in the history.

In summary: they remove extrinsic stains and do not alter tooth colour, they act by abrasion with the attendant risks, the over-the-counter chemical effect is modest, and fluoride-free charcoal products should be discouraged.