Why Teeth Turn Yellow

Most people assume yellow teeth mean the surface has not been brushed clean, but the colour of a tooth comes mainly from the dentine underneath — the enamel on the outside is translucent, and what shows through it is the yellower layer within. No amount of hard brushing changes that underlying colour. Tea, coffee and tobacco deposits clinging to the surface can indeed be removed; that is extrinsic staining. The colour of the dentine itself, the changes that come with age, and discolouration caused by medication all need to be approached differently.

更新日期：2026-08-22 資料來源：本頁末列出

Cross-section diagram of the translucent outer enamel and the yellower inner dentine of a tooth — Enamel is translucent, so the colour we see comes mainly from the dentine showing through it. Illustrative diagram, not an image of any particular patient.

First, tell them apart

Extrinsic staining and intrinsic discolouration are handled in completely different ways

Extrinsic staining is pigment sitting on the surface of the tooth, from coffee, tea, red wine, curry, tobacco and the like. It accumulates on the surface and on plaque and calculus, and it can be dealt with by cleaning. If that is all there is, a thorough clean may improve the colour on its own, and whitening may not be needed at all.

Intrinsic discolouration is the colour of the tooth structure itself. Dentine is naturally yellower, and with age it gradually thickens and darkens while the enamel thins with wear; together these make teeth look yellower than they did in youth. Discolouration after trauma, the darkening of a single tooth after root canal treatment, and discolouration caused by medicines such as tetracycline during tooth development all belong to this category too.

This distinction matters because it determines what should actually be done. Extrinsic staining is addressed by cleaning; intrinsic discolouration by a whitening agent penetrating the tooth and altering the colour; and for some severe intrinsic discolouration, whitening achieves only limited change and a restorative approach may need to be considered. Work out which one it is first, then decide what to do — skipping this step is how people end up spending money and feeling that nothing happened.

Comparative cross-section diagram of extrinsic surface staining and intrinsic discolouration of the dentine — On the left, extrinsic staining sitting on the surface; on the right, intrinsic discolouration where the dentine itself is darker. The two are handled differently. Illustrative diagram, not an image of any particular patient.

Comparing the options

How in-office whitening, at-home whitening and whitening toothpaste differ

The differences between the three lie mainly in the concentration of the agent and the contact time, and those two determine how deep and how fast the effect is.

	In-office whitening	At-home whitening	Whitening toothpaste
How it works	A high-concentration peroxide acting for a short time under professional supervision	A low-concentration agent held in a custom tray and worn for a set period each day	Mainly abrasives removing what is stuck to the surface
What it addresses	Mainly intrinsic discolouration	Mainly intrinsic discolouration	Mainly extrinsic staining
Time required	A single session is relatively short	Continued over days to weeks	Long-term use
Professional supervision	Carried out throughout by clinical staff	Impressions taken for a tray first, then used as the dentist directs	None
Common reactions	Tooth sensitivity, gingival irritation	Tooth sensitivity, usually milder	Overly harsh abrasives may cause wear

Whichever route is taken, the result varies with the original colour, the cause of the discolouration and individual conditions; no particular shade can be promised in advance. Which one suits you needs to be assessed by a dentist after an examination.

The most easily overlooked point: crowns and fillings do not whiten with the teeth

A whitening agent acts on natural tooth structure. Porcelain veneers, ceramic crowns, composite fillings and other artificial materials do not change colour because of whitening.

That means that if a front tooth already has a composite filling or a crown, then once the natural teeth have lightened, those restorations will look comparatively darker and the mismatch becomes more noticeable, not less. The literature also notes that whitening may cause degradation of existing restorations.

So where restorations are already present, the usual order is: whiten first, wait for the colour to stabilise, then remake the restorations to match the new colour. This sequence has to be planned before starting; otherwise the mismatch is discovered only after the work is done, and the cost of redoing it falls on you.

Risks

Reactions and limitations worth knowing beforehand

On current research, whitening based on hydrogen peroxide or carbamide peroxide is considered safe and effective when carried out as directed and under professional supervision, but there are risks that need to be understood.

Tooth sensitivity and gingival irritation are the most common reactions, and in most cases they subside once the course is finished. Research also indicates that whitening may cause temporary roughening and softening of the tooth surface, increase the potential for demineralisation, and — as noted above — degrade existing restorations and leave the colour mismatched.

Not every discolouration is suitable for whitening, either. Decay, cracks, inflamed gums or periodontal problems should be dealt with first: applying a whitening agent to a compromised tooth allows it to penetrate more readily and cause discomfort. Whether to proceed during pregnancy or breastfeeding, or in those under the age of majority, also requires separate assessment.

The literature likewise recommends that anyone undergoing whitening should be informed of the associated risks and told which situations warrant returning to the clinic. This is also why even at-home whitening is best preceded by an examination and carried out on a dentist's instructions, rather than bought and used on one's own.

Keeping it up afterwards

How long the effect lasts depends mostly on these three things

Whitening is not permanent. The colour gradually returns over time, and how fast varies from person to person.

01

Diet

Coffee, tea, red wine and dark sauces continue to cause extrinsic staining. Cutting down the frequency, or rinsing soon after, slows the rate at which the colour comes back.

02

Tobacco

Tobacco deposits are a particularly stubborn source of extrinsic staining, with a marked effect on how well the result holds — and they affect periodontal health at the same time.

03

Daily cleaning and professional cleaning

If surface pigment keeps building up, teeth start looking yellow again sooner. Keeping up the quality of daily cleaning, and scheduling scaling at the interval National Health Insurance covers, helps the clean appearance last longer.

其他人也問

常見問題

Are yellow teeth a sign of not brushing properly?

Not necessarily. The colour of a tooth comes mainly from the dentine underneath, and the enamel outside it is translucent, so the underlying colour remains even when the surface is cleaned thoroughly. Tea and tobacco deposits on the surface are extrinsic staining and can be removed; the colour of the dentine itself is not something cleaning can change.

Does whitening toothpaste work?

Whitening toothpaste mainly uses abrasives to remove pigment stuck to the surface, which helps with extrinsic staining, but it does not change the colour of the dentine itself. If what you expect is an overall lightening, toothpaste cannot deliver it; and abrasives that are too harsh, or brushing too hard, may cause wear of the tooth structure over the long term.

Does whitening damage the teeth?

On current research it is considered safe when carried out as directed and under professional supervision. The common reactions are tooth sensitivity and gingival irritation, which mostly subside once the course is finished. Research also indicates it may cause temporary roughening of the tooth surface, increase the potential for demineralisation, and degrade existing restorations. It is therefore best assessed at an examination before deciding.

How long does the effect last?

The effect is not permanent; the colour gradually returns over time, and how fast differs markedly according to diet, smoking and how well the teeth are cleaned. Because individual variation is wide, how long it will hold cannot be promised in advance.

Can I whiten if I have crowns or fillings?

The natural teeth can be whitened, but porcelain veneers, crowns, composite fillings and other artificial materials do not change colour with them, so a mismatch with the natural teeth may appear afterwards. Where restorations are already present, the usual advice is to whiten first, wait for the colour to stabilise, and then remake the restorations to match — a sequence that needs to be planned in advance.

One tooth is noticeably darker — why?

A single darker tooth is often seen where that tooth has been injured in the past or has had root canal treatment, and it is a form of intrinsic discolouration. These situations are handled differently from whitening the whole arch: the state of that particular tooth has to be established first, and then a suitable approach decided.

本頁的主要依據

下列為本頁內容的來源。文中引用的統計數字皆為文獻或官方公開資料，反映的是整體族群，不是本診所的治療成效。

Carey CM: tooth whitening — what we now know, safety and efficacy assessedJ Evid Based Dent Pract 2014
Li Y, Greenwall L: safety issues in tooth bleachingDent Clin North Am 2011
Department of Oral Health, MOHW: prevention of periodontal disease (including the scaling interval covered by National Health Insurance and daily cleaning advice)Ministry of Health and Welfare

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Why Do Teeth Turn Yellow?