Teeth whitening: what actually works, and what only looks like it does

Teeth darken for two quite different reasons, and confusing them is why so many people spend money without a result. Surface staining sits on the outside of the enamel — tea, coffee, red wine, tobacco. Intrinsic colour comes from the dentine underneath, which yellows naturally with age and no amount of scrubbing will touch.

Polishing, Airflow and whitening toothpastes deal with the first. Only peroxide-based whitening deals with the second.

Why professional whitening is different

In the UK it is illegal for anyone other than a registered dental professional to carry out tooth whitening. Products sold direct to the public are limited to 0.1% hydrogen peroxide — far too weak to change intrinsic colour. That is the whole explanation for why a high street kit disappoints.

Dentist-supervised whitening uses custom trays made from a scan of your teeth, so the gel sits on the tooth and not on the gum. Worn at home over two to three weeks, it lightens gradually and predictably, and the trays are yours to top up with years later.

The things that will not work

• Charcoal powders — abrasive, and abrading enamel exposes more yellow dentine over time
• Purple toothpastes — a blue-violet dye that cancels yellow for an hour or two, nothing more
• Unregulated salon whitening — often chlorine dioxide, which etches enamel
• Whitening a tooth that is dark because it is root-treated, dead or crowned

Sensitivity, honestly

Most people get some short, sharp sensitivity during whitening. It is temporary, it is managed by spacing the nights out and using a desensitising gel, and it stops when treatment stops. It is not damage.

A word on timing

Whitening goes before bonding, veneers and crowns, never after — restorative materials do not lighten, so they are matched to your final shade. If alignment is planned, that comes first of all.

And before any of it: a hygiene visit. Whitening a stained tooth gives you a lighter stained tooth.