Why Teeth Go Yellow — and Why Whitening Does Not Always Work

Before spending money on whitening, it is worth knowing which of two problems you have. They look similar in the mirror and behave completely differently.

Extrinsic: stains on the surface

These sit on the outside of the enamel and come from tea, coffee, red wine, turmeric and other strong spices, tobacco and areca nut, and some mouthwashes — chlorhexidine in particular stains noticeably with long use. Extrinsic stains respond well to a professional cleaning, and respond well to whitening. This is the easy category.

Intrinsic: colour inside the tooth

This is the colour of the dentine showing through the enamel, and it cannot be scrubbed off. Causes include:

• Ageing. Enamel thins over decades and dentine, which is naturally yellow, shows through more. This is the single commonest reason and it is not a hygiene failure.
• Genetics. Natural enamel shade varies. Some people's teeth are simply more yellow.
• Tetracycline taken during tooth development, producing grey or banded discolouration that is notoriously resistant to whitening.
• Fluorosis — excess fluoride during development, giving white flecks through to brown mottling. Relevant in parts of India with high fluoride groundwater.
• Trauma. A single tooth turning grey after a knock usually means the nerve has died.
• Root canal treatment, which can darken a tooth over years.

Why whitening sometimes disappoints

Whitening gel works on organic staining within enamel and dentine. It does nothing to fillings, crowns or veneers — so if you have a white filling in a front tooth, the tooth will lighten around it and the filling will stand out, and it will need replacing afterwards to match. Tetracycline staining improves only partially and slowly. Fluorosis mottling can look more obvious once the surrounding tooth lightens.

A single dark tooth from a dead nerve does not respond to external whitening at all. It needs internal bleaching after root canal treatment, or a crown or veneer.

The options, in order of invasiveness

• Scaling and polishing — removes extrinsic stain. Surprisingly often, this alone is what people actually needed.
• Professional whitening — in-clinic, or custom trays for home use. Predictable, and the concentration and contact time are controlled.
• Internal bleaching for a single dead tooth.
• Composite bonding or veneers where the discolouration will not bleach.

A word on whitening toothpastes: they work by abrasion and remove surface stain only. They cannot change the natural colour of your teeth, and highly abrasive ones can wear enamel, which over time makes teeth look more yellow as more dentine shows through. Charcoal pastes are the worst offenders on this count.

Keeping the result

Rinse with water after tea, coffee or turmeric-heavy food, use a straw for cold staining drinks, do not brush for an hour after anything acidic, and have the stain professionally removed twice a year. Whitening is not permanent — expect to top up periodically, sooner if you smoke or drink a lot of tea.

Frequently asked questions

Does whitening damage enamel?

Professionally supervised whitening at controlled concentrations does not damage enamel. Temporary sensitivity is common and resolves. The risks come from unsupervised high-concentration products and from abrasive home remedies.

Will whitening work on my crowns and fillings?

No. Whitening only affects natural tooth structure. If you have visible fillings or crowns, plan to have them replaced after whitening so they match the new shade.

Do baking soda or charcoal whiten teeth?

They abrade surface stain, which can look like whitening at first. Used regularly they wear enamel, and thinner enamel shows more of the yellow dentine underneath — the opposite of what you wanted.

Why has one tooth gone grey?

Almost always a nerve that died after an old injury, sometimes years earlier. External whitening will not fix it. It needs assessment, usually root canal treatment followed by internal bleaching or a crown.

Talk to a dentist in Dehradun