Internal bleaching is the treatment for a single dark tooth after a root canal or an injury, because the stain sits inside the dentine and whitening applied to the outside surface has little effect on it. The bleaching agent is placed into the hollow pulp chamber and sealed in, so it works outwards from the inside. It is usually the most conservative option on the table, and it keeps the tooth intact.
Key takeaways
- A tooth darkens after a root canal or trauma because blood breakdown products and pulp remnants stain the dentine from within.
- The walking bleach technique seals a bleaching agent inside the tooth between visits, usually refreshed weekly over two to four appointments.
- A protective barrier is placed over the root filling at about gum level before any bleaching agent goes in, and no heat is used.
- Reported success is high, commonly quoted between 85 and 95 per cent for discolouration from trauma or a dead nerve, with initial results at the upper end of that range.
- Some colour rebound is expected, often between two and eight years, so a top-up may be needed later.
- Existing composite fillings do not lighten, so they usually need replacing afterwards to match the new shade.
Why one tooth goes dark
What happens inside the tooth
When the nerve inside a tooth dies, whether from a knock to the mouth, deep decay or a crack, red blood cells break down and release iron-containing compounds. Those products soak into the dentinal tubules, the microscopic channels that run through the body of the tooth, and they stain it from the inside out. A root canal removes the source of the problem but does not remove the stain that has already spread into the dentine. The same discolouration can happen in children, and our article on a child's tooth turning black or grey covers that situation.
Why external whitening does not fix it
Take-home trays and in-chair whitening work on stains held within the enamel and outer dentine, and they treat every tooth they touch. A dark non-vital tooth is stained more deeply and more heavily than its neighbours, so external whitening tends to lighten the healthy teeth around it and leave the dark one looking, if anything, more obvious. Occasionally a mild greyness responds partly, but the difference usually remains.
What it is not
Not every discoloured tooth is a dead one. Surface staining, an old and darkened filling, fluorosis and developmental marks all look different up close, and so do the chalky patches discussed in our guide to white spots on teeth. An X-ray and a vitality test sort out which problem you actually have, and the answer changes the treatment completely.
The walking bleach technique
Step by step
First the root canal is checked. It has to be well sealed and free of symptoms or signs of infection, and if it is not, that is dealt with before anything else. Then the access cavity is reopened and any old filling material and stained debris are cleared from the pulp chamber. A protective barrier, commonly a glass ionomer cement, is placed over the root filling to roughly the level of the gum, sealing the root canal off from the bleaching agent. The bleaching material, most often sodium perborate mixed with water or a carbamide peroxide preparation, is placed into the chamber. A temporary filling seals the tooth, and you go home with the agent working quietly inside, which is where the name walking bleach comes from.
How many visits
The dressing is typically refreshed about weekly. Most teeth take two to four visits, and the tooth is compared against its neighbours each time. Because rebound is expected, many clinicians deliberately take the tooth slightly lighter than the target before stopping. Once the colour is right, the temporary filling is removed and the access cavity is restored properly, usually after a short delay to let the tooth settle so the bonding is not compromised by residual peroxide.
Why heat is no longer used
Older thermocatalytic techniques used strong hydrogen peroxide with heat applied to speed the reaction. That combination is associated with a higher risk of external root resorption, and the modern protocol of sodium perborate, a properly placed cervical barrier and no heat is specifically designed to reduce it.
How well it works, honestly
Success rates
Published series report high initial success for internal bleaching of teeth discoloured by trauma or pulp necrosis, commonly quoted between 85 and 95 per cent, with immediate results at the top of that band. That is a strong result for a treatment that removes no additional tooth structure.
Rebound and top-ups
The honest caveat is that colour is not permanent. Longer follow-up studies show a meaningful proportion of teeth darken again over time, most often somewhere between two and eight years, and a repeat dressing or two is a straightforward way to bring the shade back. Anyone considering internal bleaching should plan on the possibility of a top-up rather than treat it as a one-off.
The risk to know about
The recognised complication is cervical external root resorption, where the body begins to break down the root surface near the neck of the tooth. It is reported in under about 2 per cent of cases with modern technique. It is usually silent early on, which is why a follow-up X-ray at review appointments is worth keeping.
Comparing your options
Internal bleaching is not the only way to deal with a dark front tooth, but it is the only one that changes nothing about the tooth's structure. The table below sets out the usual alternatives. Cost figures are general market ranges reported across Australia and internationally, not a quote, and the only way to know what applies to your tooth is to have it assessed and receive a written estimate. If you would like one, get in touch with the practice.
| Option | Tooth structure removed | Typical longevity | Reversible | General market cost range per tooth |
|---|---|---|---|---|
| Internal bleaching | None beyond the existing root canal access cavity | Often several years, with rebound commonly between two and eight years | Largely, and top-ups are possible | Roughly $150 to $600, often quoted around $250 to $400, sometimes across several sessions |
| Composite bonding or composite veneer | Little to none | Around five to seven years before repair or repolishing | Mostly | Roughly $250 to $700 |
| Porcelain veneer | Moderate, enamel reduced across the front surface | Often ten to fifteen years | No | Roughly $1,200 to $2,500 |
| Crown | Substantial, the whole tooth is reduced | Often ten to fifteen years or more | No | Roughly $1,500 to $2,500 |
When bleaching is not the right call
A tooth with a large existing filling, a crack, or significant loss of structure may be better restored than bleached, because bleaching does nothing for strength. In those cases a bonded restoration or a crown is often the sounder plan. Where the tooth is largely intact, though, taking the conservative route first costs you very little, since the other options remain available afterwards. If an existing veneer is the problem rather than the tooth beneath, our guide on repairing or replacing a porcelain veneer is the more relevant read.
The filling that gives it away
Bleaching has no effect on composite, so any existing white filling on the tooth will stay the shade it was and will start to look darker as the surrounding tooth lightens. Replacing it after the shade has settled is a normal and expected part of finishing the treatment, and sometimes a little tooth reshaping is done at the same time to tidy the edge.
Frequently asked questions
Does internal bleaching hurt?
The tooth has no living nerve, so the procedure itself is generally comfortable and local anaesthetic is often not needed. Some people notice mild tenderness in the gum around the tooth between visits.
How long until I see a change?
Many people notice a difference after the first dressing, usually within about a week. The full result is judged once all the dressings are complete and the tooth has settled.
Will the tooth ever go dark again?
Some rebound is common over a period of years. A repeat dressing can usually restore the shade, and knowing that upfront makes the result easier to live with.
Can internal bleaching be done on a tooth without a root canal?
No. The technique requires access to the pulp chamber, so the tooth must already be root filled. A discoloured tooth with a living nerve needs a different assessment.
Is it safe for the tooth?
With a well-placed cervical barrier, sodium perborate rather than heated high-concentration peroxide, and a sealed temporary filling, the risk of cervical root resorption is low, reported under about 2 per cent. Review X-rays are the sensible precaution.
What if the root canal is old or was never finished properly?
The root filling is assessed first. If it is inadequate or the tooth shows signs of ongoing infection, that is addressed before bleaching is considered.
Talk it through at a complimentary cosmetic consultation
If one tooth has darkened and you are not sure what your options are, the team at Lumi Dental in Melrose Park offers a complimentary cosmetic consultation to assess the tooth, take the X-rays needed, and explain what conservative treatment could realistically achieve before anything is committed to.
This article is general information only and is not a substitute for personal dental advice. Whether internal bleaching suits your tooth depends on an examination and radiographs taken by a dentist.
