Teeth whitening: which stains lift, and which do not

Whitening is the most requested cosmetic treatment in dentistry and the most frequently misunderstood. Almost all the disappointment comes from one of two places: the discolouration was never the kind that bleaching addresses, or part of the smile was never going to change colour at all.

Two completely different kinds of stain

Extrinsic: on the outside

Your teeth are coated in a thin protein film from saliva called the acquired pellicle, and pigmented molecules bind to it. Tea, coffee, red wine, tobacco, paan and supari, and dark spices all deposit colour there. This is surface staining. It sits on the tooth rather than in it.

Extrinsic stain is the easy category. A professional clean and polish removes a good deal of it mechanically, and bleaching handles the rest. If your teeth were once noticeably lighter and have darkened over years of tea, this is very likely what you have.

Intrinsic: inside the tooth

Colour within the tooth structure itself is a different problem. The main causes are:

• Age. Enamel thins over decades while dentin, which is naturally yellow, thickens underneath and shows through more. This is normal and it responds reasonably well to bleaching.
• Fluorosis, from too much fluoride while the teeth were forming. Produces white flecking through to brown mottling.
• Tetracycline staining, from certain antibiotics taken during tooth development. Produces grey or brown horizontal bands, and it is the hardest of all to treat.
• A single dark tooth after trauma. The nerve died, blood products entered the dentin, and the tooth darkened from the inside. This one has its own specific treatment.
• Developmental defects in the enamel itself.

How bleaching actually works

It is oxidation, not abrasion. Hydrogen peroxide, or carbamide peroxide which breaks down into it, diffuses through the enamel and into the dentin. There it breaks apart the large pigmented molecules into smaller, less coloured ones. Nothing is sanded off and no enamel is removed.

Because it works by diffusion into the tooth, bleaching reaches intrinsic stain as well as extrinsic. How well depends on the cause: age-related yellowing responds well, mild fluorosis responds moderately, tetracycline banding responds slowly and often incompletely and may need veneers or composite bonding instead.

The thing that catches people out

This is one of the strongest arguments for having whitening assessed rather than bought off a shelf. Ten minutes of looking at which surfaces are natural tooth and which are not will tell you whether the result you are imagining is achievable.

Professional trays, in-clinic sessions and strips

• Custom trays made from impressions of your teeth, worn at home with a prescribed gel. The gel stays where it is meant to and off the gums. This is the workhorse of whitening and gives the most controllable result.
• In-clinic treatment at higher concentration with the gums protected. Faster, more supervised, useful when time matters.
• Over-the-counter strips and generic trays. These can work on mild surface staining, at lower concentration, but a one-size tray leaks gel onto the gums and does not adapt to crowded teeth. Results are patchier.
• Whitening toothpastes. Almost all of these are abrasive rather than bleaching. They remove some surface stain and cannot change the underlying shade at all.

Sensitivity, and why it happens

Transient sensitivity during whitening is common and expected. Peroxide passes down the dentinal tubules and irritates the pulp; the result is the familiar sharp response to cold. It is dose-related, it settles within a few days of stopping, and it does not indicate damage.

It can usually be managed by using a desensitising toothpaste for a couple of weeks beforehand, by shortening each wear period, or by leaving a day between applications rather than pushing through.

A word on charcoal

Charcoal toothpastes remove stain by being abrasive. That does lift some surface discolouration, but abrasion is a one-way process: enamel does not grow back, and the exposed root surface near the gum is far softer than enamel and wears much faster. There is no evidence that charcoal changes intrinsic shade, and reasonable concern about long-term wear and increased sensitivity.

Before you start

Untreated decay, a leaking filling, exposed root surfaces or active gum inflammation all make whitening more uncomfortable and can make the result uneven. A check-up first is not a formality; it is what makes the treatment predictable. Whitening is also not recommended during pregnancy or breastfeeding, and not for children whose teeth are still developing.