Teeth whitening: what actually works, and what does not

Whitening is the most requested cosmetic dental treatment and the one surrounded by the most misinformation. This guide explains the mechanism, the realistic outcome, and when whitening is the wrong answer.

How whitening actually works

Whitening gels use hydrogen peroxide or carbamide peroxide. The peroxide diffuses through enamel into the dentine beneath and breaks the chemical bonds of the pigment molecules causing discolouration. Smaller molecules reflect more light, so the tooth appears lighter.

Critically, whitening does not remove a layer of tooth. Nothing is stripped away. That is why supervised whitening does not weaken enamel.

Why the type of staining matters

Not all discolouration responds equally.

Extrinsic staining sits on the surface — coffee, tea, red wine, tobacco. This responds very well, and much of it can be removed by Guided Biofilm Therapy before whitening is even considered.

Intrinsic staining is within the tooth structure — ageing, trauma, or tetracycline exposure during development. This responds more slowly and less predictably. Tetracycline banding in particular often needs veneers rather than whitening.

Fluorosis produces white mottling. Whitening lightens the surrounding tooth but the mottling can become more obvious, not less. This needs assessment first.

This is why an examination precedes whitening. Applying a universal treatment to a condition it does not address wastes your money.

In-clinic versus home whitening

In-clinic uses higher concentrations under direct supervision, with the gums isolated by a protective barrier. Results are immediate and it takes roughly an hour. Our clinical protocol references brightening of up to eight shades in a single safe session.

Custom home trays use lower concentrations in trays moulded precisely to your teeth, worn for a set period daily over one to two weeks. Slower, but excellent for maintenance and often gentler on sensitive teeth.

Over-the-counter strips and generic trays deliver low concentrations in a poorly fitting carrier. They produce modest results, and the ill-fitting tray leaks gel onto the gums, which causes most of the burning people report.

The strongest approach is usually combined: an in-clinic session for the initial lift, then custom trays for top-ups.

What to avoid

Charcoal toothpaste is abrasive. It removes surface stain by scratching enamel, and over time that abrasion exposes the yellower dentine underneath — the opposite of the intended effect.

“Whitening” pens and unregulated online gels have unpredictable concentrations and no gum protection.

Whitening over untreated decay or gum disease drives peroxide into places it should not go and can cause significant pain. Health first, cosmetics second.

Managing sensitivity

Transient sensitivity is the most common side effect and usually resolves within 24 to 48 hours. It happens because peroxide temporarily increases fluid movement in the dentinal tubules.

To reduce it:

• Use a desensitising toothpaste containing potassium nitrate for two weeks before treatment
• Avoid very hot and very cold foods for the first day
• Space sessions rather than stacking them
• Tell us if you already have sensitivity — the protocol is adjusted rather than abandoned

Where whitening fits in a bigger plan

If you are considering a Hollywood Smile or veneers, sequence matters enormously. Whitening comes first, so the ceramic can be matched to your newly lightened natural teeth. Whitening afterwards would lighten only the natural teeth and leave the restorations looking dark by comparison.

For many patients, whitening plus professional cleaning achieves what they actually wanted — and costs a fraction of veneers. We will tell you when that is the case.

The first step

A short assessment establishes what is causing your discolouration and whether whitening will address it. That conversation prevents most of the disappointment associated with this treatment.