Key takeaways
- A single darker tooth usually means internal change: nerve damage from trauma, a dead nerve, an old metal filling, or a failed root canal.
- A tooth that has gone grey or brown after injury may have a damaged or dying nerve, even if it caused no immediate pain.
- Internal discolouration does not respond to normal whitening; a veneer, crown or internal bleaching gives better results.
- A dead tooth with no symptoms can still abscess over time; getting it assessed sooner is better than waiting for pain.
One tooth noticeably darker than the others stands out in a way that general yellowing does not, and for good reason: it usually signals something specific to that tooth rather than an overall staining problem. Getting the cause right matters because the treatment is different for each one.
Quick answer: The most common causes are internal bleeding from a knock (the tooth darkens as the blood breaks down), a dead or dying nerve, or an old metal filling casting a grey shadow. Standard whitening does not fix internal discolouration; a veneer, crown or internal bleaching gives much better results.
Trauma: the tooth took a knock
This is the most common cause in younger patients. A blow to a tooth can rupture the tiny blood vessels inside the pulp. The haemoglobin slowly breaks down and stains the dentinal tubules from the inside, turning the tooth progressively grey or brown. This can appear weeks or months after the original injury, long after any pain has settled. The tooth may or may not still have a live nerve. If the nerve is dead, it needs treatment: leaving a dead tooth untreated risks eventual infection and abscess. A dentist can confirm nerve status with a simple sensitivity test.
A dead or dying nerve
A tooth whose nerve dies, whether from trauma, decay that reached the pulp, or a previous root canal that did not fully resolve, can darken over time. The discolouration comes from the breakdown products of necrotic (dead) pulp tissue. Even if the tooth is not painful, it is worth treating because a dead tooth is more brittle and can still harbour bacteria that cause infection. After root canal treatment, the tooth can be internally bleached and then protected with a crown or veneer.
Old metal fillings
Silver amalgam fillings can cause a grey or dark shadow in the tooth around them, particularly as the filling ages and oxidises. The tooth itself is not damaged, but the appearance can be significant. Replacing the filling with tooth-coloured composite and placing a veneer if needed typically resolves this. Our post on replacing old silver fillings covers when it makes sense to do this and when to leave them alone.
Can standard whitening fix it?
No, for internal discolouration. Whitening agents work by penetrating the enamel surface from outside; they cannot reach internal staining caused by blood breakdown products or old filling materials. Internal bleaching, which involves placing a whitening agent inside the tooth through the root canal access point, can help. For most internally discoloured teeth, however, a veneer or crown gives a more reliable and lasting cosmetic result. Our comparison of veneers, bonding and whitening is a useful read before deciding.
Sources & further reading
American Dental Association (MouthHealthy) · NHS, Dental Health · NIDCR, US National Institute of Dental & Craniofacial Research · Indian Dental Association
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One tooth looking dark or discoloured? Get it checked at Prudent Dental. Call +91 70287 22200.
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