Discoloration falls into broad categories, and they respond very differently to treatment. Surface staining sits on the outside of the enamel and comes from what you consume. Internal discoloration comes from within the tooth. And some colour changes are not staining at all — they are existing dental work that no longer matches, or a tooth that has changed after an injury.
Whitening works well on the first category and poorly on the others. That is worth knowing before you spend money, because the difference is not something you can judge reliably by looking in a mirror.
Possible causes
- Coffee, tea, red wine, and dark-coloured foods staining the enamel surface
- Tobacco use, which stains persistently
- Enamel thinning with age, letting the naturally yellower dentin beneath show through
- A tooth that darkened after an injury, or after root canal treatment
- Certain medications, including tetracycline exposure during tooth development
- Fluorosis, which typically appears as white or mottled patches rather than overall yellowing
- Old fillings, crowns, or veneers that no longer match the teeth around them
- Decay, which can appear as a dark spot or shadow on a specific tooth
When to seek prompt care
- A single tooth that has darkened noticeably compared with its neighbours
- A dark spot or shadow accompanied by sensitivity or pain
- Discoloration that appeared after a knock or injury to the tooth
- Colour change alongside gum swelling or a bad taste
For life-threatening emergencies — trouble breathing or swallowing, severe uncontrolled bleeding — call 911 first.
How a dentist assesses it
A dentist distinguishes surface staining from internal discoloration, checks whether a dark area is actually decay, and assesses whether existing restorations are contributing. That matters because it determines which treatments can help: a tooth that darkened from the inside will not respond to the same approach as coffee staining, and a dark spot that turns out to be decay needs treating rather than bleaching.
Treatment paths this may lead to
Questions patients ask
Why is only one of my teeth dark?
A single darkened tooth often points to something specific — a past injury, changes inside the tooth, or decay. It is a different situation from overall yellowing and generally does not respond to standard whitening, so it is worth having examined.
Will whitening work on grey teeth?
Grey discoloration tends to respond less predictably than yellow. It is one of the situations where an honest conversation before you start saves disappointment afterward.
Do my crowns and veneers whiten?
No. Restorations hold the shade they were made in. If you whiten the teeth around them, they can end up looking darker by comparison — which is why sequencing matters when cosmetic work is planned.
Can teeth get too white?
They can end up looking artificial relative to your face and your remaining natural teeth. A consultation includes talking about a shade that will look like you rather than like dental work.
This guide is general dental-health information, not a diagnosis or individualized medical advice. Only an examination can determine what's happening in your mouth and which treatment fits.