Why a tooth darkens or yellows and what to do about it

If all your teeth have yellowed together, it is almost always external pigment plus age-related thinning of the enamel; professional hygiene and whitening help. If a single tooth has darkened, the cause is quite different: most often the pulp inside has died, and what is needed is treatment, not whitening.

When all the teeth yellow

Two processes are at work at once here, and they are worth telling apart, because they are treated differently.

Staining from outside

Pigments from coffee, black tea, red wine, berries, turmeric and tobacco settle on the enamel surface and in its micropores. Add ordinary plaque and calculus to that, and teeth look darker than they are.

This comes off with professional hygiene. Patients who came in «for whitening» often decide after a cleaning that they no longer need it.

Discolouration from within

Enamel is semi-translucent, and the colour of a tooth is largely set by the dentine underneath — which is naturally yellowish. Over the years enamel thins and new, darker dentine forms, so teeth gradually yellow even with impeccable hygiene.

Hygiene is powerless here: there is nothing to remove, the colour is the tooth tissue itself. This is the case where whitening works.

When a single tooth darkens

This is a different story, and it is the one most often googled as «one tooth has gone dark». The causes, by frequency:

• Death of the pulp. After an injury or deep decay the neurovascular bundle dies, breakdown products penetrate the dentinal tubules and stain the tooth from within — grey, brownish or pinkish. The tooth may not hurt for years.
• Previously treated root canals. Some older filling materials cause discolouration over time.
• An old filling. A darkened restoration, or a marginal gap beneath it, often looks like «the tooth has gone dark».
• A crack in the enamel after an injury, in which pigment accumulates.

All these variants have one thing in common: none of them is solved by whitening until the cause is known. An examination and a periapical X-ray are needed — to check the canals and the tissues around the root.

If death of the pulp is confirmed, the tooth is treated endodontically — under a microscope, from UAH 6,600 for a single-rooted tooth. After that the colour can be restored with internal bleaching, or the tooth can be covered with a veneer or a crown. More on the page endodontics.

Particular cases

A tooth darkened after an injury but does not hurt

The absence of pain proves nothing. The pulp can die quietly, and inflammation at the root apex can develop for years without symptoms until it shows up as an abscess. A tooth that has darkened after a knock should be shown to a dentist even if it does not bother you.

White or yellow patches in a child

Patches on permanent teeth in children and teenagers are most often linked to fluorosis or enamel hypoplasia — a disturbance in how the enamel formed before the tooth erupted. Whitening is not indicated here; the approach is decided by the doctor after an examination.

Lines and darkening near the gum

A dark line along the gum margin is usually not the colour of the tooth but calculus. It is removed by hygiene. More in the article about dental calculus.

What not to do on your own

Baking soda, activated charcoal, lemon juice and «folk» abrasive pastes do lighten a tooth — by wearing the enamel away. The effect does not last, and thinned enamel then lets through more yellow from the dentine, so the teeth end up darker than they started.

A separate word about over-the-counter strips and one-size-fits-all trays: a standard tray does not fit closely, gel gets onto the gums, and undetected decay causes sharp pain during whitening.

How we work at Houston

• Examination and finding the cause — external pigment, age-related change, or a problem inside one particular tooth. A periapical X-ray if needed.
• Professional GBT hygiene — the starting point. Often it settles the matter on its own.
• Whitening where it is indicated — in-office BEYOND II Ultra or a home course in ART Whitening trays. More on the page whitening.
• Treatment if the dark tooth is dead — endodontics under a microscope, then internal bleaching or a restoration.

Frequently asked questions