When a single tooth turns grey, brown or noticeably darker than its neighbours, the cause is usually inside the tooth rather than on the surface, which is why ordinary whitening toothpaste and trays do little for it. The fix for this specific problem is internal bleaching, also called non vital bleaching or the walking bleach technique, where the whitening agent is placed inside the tooth rather than over it. It is a conservative, lower cost way to lighten one dark tooth without drilling it down for a crown or veneer.
Key takeaways
- A single dark tooth is usually discoloured from the inside, often after a root canal or an old knock.
- Surface whitening does not work well on it because the stain sits within the tooth.
- Internal bleaching places whitening agent inside the tooth to lighten it from within.
- It is most predictable when the discolouration follows trauma or nerve death rather than a filling material.
- It is more conservative and lower cost than a crown or veneer, and those remain options if bleaching is not enough.
Why one tooth goes dark
A tooth can darken on its own when the nerve inside it dies, often years after a knock to the mouth, or after root canal treatment. Blood pigments and breakdown products soak into the dentine from the inside and show through the enamel as a grey or brown cast. Because the colour change comes from within, it cannot be reached by a gel sitting on the outside of the tooth, which is the key difference from whitening the whole smile. If the dark tooth has not had a root canal but the nerve has died, that usually needs treating first.
The one rule: match the method to where the stain sits
The decision rule is simple. If the discolouration is inside a root treated tooth, internal bleaching is the natural first choice because it works from where the stain actually is. If the surface is intact and you simply want a brighter overall shade, external whitening suits. If the tooth is also broken down, heavily filled or misshapen, a crown or veneer may be the better answer because it addresses shape and strength as well as colour. Choosing by where the problem sits avoids over treating a tooth that only needs its colour corrected.
How internal bleaching works
The tooth must already have a healthy, well sealed root canal, because the whitening agent is placed into the space the nerve once occupied. The steps are usually as follows.
- The dentist checks the root filling is sound and seals the canal off to protect it.
- A small amount of whitening agent is sealed inside the crown of the tooth.
- The agent is left to work over several days. Because it sits inside while you go about your day, it is nicknamed the walking bleach technique.
- You return so the dentist can assess the shade. The process may be repeated once or twice to reach a good match.
- Once the colour is right, the access point is filled neatly.
Some dentists use an in chair version that works faster in a single visit, and the two approaches are reported to be similarly effective. Results tend to be more predictable when the darkening followed trauma or a dead nerve than when it came from an old filling material.
How it compares with the alternatives
| Option | Best for | Tooth structure removed | General market range (AUD) |
|---|---|---|---|
| Internal bleaching | A single dark root treated tooth | Minimal | $300 to $700 |
| Composite veneer or bonding | Colour plus minor shape correction | Little to none | $250 to $600 per tooth |
| Porcelain veneer | Colour, shape and a durable finish | Some | $1,200 to $2,500 per tooth |
| Crown | A weak or heavily filled dark tooth | Most | $1,500 to $3,000 per tooth |
These are general market ranges, not a quote. The appeal of internal bleaching is that it is the most conservative of the four and keeps the door open to the others if the colour does not lighten enough. Our guide to composite bonding versus veneers compares the covering options if bleaching alone is not the answer.
What to expect afterwards
Internal bleaching can lighten a tooth well, though like all whitening the result can fade gradually over years and may need a top up. The dentist will keep the bleaching agent away from the very base of the tooth and seal the root properly, because careful technique reduces the small risk of irritation to the root over time. A review some months later checks the shade has held and the tooth remains healthy.
Frequently asked questions
Why is only one of my teeth dark?
A single dark tooth usually means the nerve inside it has died or it has had a root canal, and pigments have stained the tooth from within. This is why it looks different from the teeth around it.
Will normal whitening fix a dark tooth?
Not well. External whitening lightens surface and overall shade, but a tooth discoloured from the inside needs the whitening agent placed inside it.
Does the tooth need a root canal first?
Internal bleaching is done on a tooth that already has a sound root canal. If the nerve has died but the tooth has not been treated, that step usually comes first.
How long does internal bleaching last?
Results often hold for years, but some fading is normal and a top up may be needed later. A crown or veneer gives a more permanent colour if that matters to you.
Is internal bleaching safe?
It is a well established technique. A careful dentist seals the root first and keeps the agent away from the root base to keep the small risks low.
The takeaway
A single dark tooth is an inside job, and internal bleaching treats it where the stain sits, conservatively and at lower cost than a crown or veneer. It works best on a root treated tooth that darkened after trauma or nerve death, and the covering options remain available if needed. The team at Lumi Dental can assess a dark tooth and explain which approach suits it. See our current deals page or read about cosmetic options at our Melrose Park practice. This article is general information and not a substitute for personal dental advice.
