Whitening a root-filled tooth means internal bleaching of a single darkened tooth. The dentist makes a small opening at the back of the tooth, places a protective barrier over the root filling, puts the whitening agent inside the tooth and seals it with a temporary filling. The agent is usually renewed every few days, and in most cases the desired shade is approached in 1–4 sessions. Suitability is decided by examination and X-ray.
Why does a root-filled tooth darken?
A root-filled tooth usually darkens because of blood and tissue remnants left inside the tooth, certain root canal materials or internal changes after trauma. Because the discolouration comes from inside the tooth, external whitening is usually not enough for it.
- Trauma: In a tooth that has been knocked, bleeding inside the pulp can pass into the dentinal tubules and, over time, create a grey-brown shade.
- Tissue remnants: Organic remnants left in the pulp chamber can cause discolouration over time.
- Materials: Some root canal sealers and filling materials can cause staining in the crown of the tooth.
- Ageing: Root-filled teeth may look more opaque and darker over time.
You can find other causes of tooth discolouration on our tooth yellowing and stains page.
Who is internal bleaching suitable for?
Internal bleaching is used on one or a few darkened teeth whose root canal treatment is successful and well sealed and whose structure is sound enough. Suitability is decided by examination and X-ray.
Situations that may be suitable
- A tooth with completed root canal treatment and no problems on the X-ray
- Most of the tooth is sound, with no large filling or crown
- The discolouration comes from inside the tooth
- The gums and surrounding tissues are healthy
Situations that may not be suitable
- The root canal treatment is inadequate or there is infection at the root; the root canal treatment must be redone first
- The tooth has major loss of structure or a crack
- The discolouration comes from metal-containing fillings
- The patient is under 18, pregnant or breastfeeding; these situations are assessed separately
We explain general contraindications in detail on our who should not have teeth whitening page.
How is internal bleaching done?
Internal bleaching relies on a whitening agent placed inside the tooth working over several days. This technique is also called "walking bleach".
- Examination and X-ray: The condition of the root filling and the area around the root are checked, and the starting shade is recorded.
- Access opening: The old filling on the back (tongue side) of the tooth is removed.
- Reducing the root filling: The root filling is removed to slightly below gum level.
- Protective barrier: A protective material about 2 mm thick is placed over the root filling. This barrier limits the whitening agent from moving towards the root.
- Placing the whitening agent: A peroxide-based agent is placed in the pulp chamber.
- Temporary seal: The opening is sealed tightly with a temporary filling.
- Review and renewal: The colour is checked a few days later and the agent is renewed if needed.
- Permanent filling: Once the desired shade is reached, there is a waiting period and the back of the tooth is sealed with a permanent filling.
How many sessions does it take?
In most cases internal bleaching takes 1–4 sessions, usually 3–7 days apart. The exact number depends on how dark the tooth is and how it responds.
| Stage | Approximate time |
|---|---|
| First appointment (preparation and placing the agent) | 30–60 minutes |
| Agent renewal appointments | 15–30 minutes each |
| Interval between sessions | Usually 3–7 days |
| Wait before the permanent filling | Usually 1–2 weeks |
Straight after bleaching, oxygen remaining on the tooth surface temporarily reduces bonding strength. That is why there is usually a waiting period before the permanent composite filling. Sometimes the dentist may aim for slight over-whitening so the tooth matches its neighbours, as some colour may return over time.
What are the risks of internal bleaching?
Internal bleaching is a widely used method when carried out for the right indication and according to protocol; even so, it has some risks, which should be discussed in advance.
- External root resorption: A rare but important complication. It is the breakdown of the root surface at the neck of the tooth. It has been linked particularly to high concentrations, the use of heat and not using a barrier. The protective barrier and regular X-ray checks aim to reduce this risk.
- Colour relapse: Some darkening of the tooth may recur over the years.
- Weakening of the tooth: A root-filled tooth is already more brittle; removing too much tissue can increase the risk of fracture.
- Temporary filling leakage: If the temporary filling falls out or leaks, the agent can escape into the mouth; in this case you should contact your dentist.
- Less change than expected: Some types of discolouration, especially those caused by metal, respond only partly to bleaching.
A tooth that has had internal bleaching should have clinical and X-ray check-ups at the intervals your dentist recommends. This way any problem can be spotted early.
Can internal and external whitening be combined?
Yes, internal and external whitening can be planned together when needed. If a single tooth is dark and the other teeth are generally yellowish, all the teeth can be whitened externally first and the darkened tooth then bleached internally, or the order can be reversed.
For external methods, see our teeth whitening methods page. The right order is decided at the examination, according to the colour of the teeth and the result you are aiming for.
Alternatives: veneers, crowns and composite
If internal bleaching is not suitable or does not give a sufficient result, the colour problem can be solved with restorative methods such as veneers, crowns or composite. These methods do not change the tooth's colour; they cover it.
| Option | What does it do? | When is it considered? |
|---|---|---|
| Internal bleaching | Lightens the tooth's own colour, with little tissue removal | Tooth structure is sound and the colour comes from inside |
| Composite veneer or bonding | Covers the front surface of the tooth with filling material | Slight colour difference, small shape corrections |
| Porcelain veneer | A thin ceramic shell covers the front surface | When colour and shape are to be corrected together |
| Crown | A restoration that covers the whole tooth | When the tooth is weak or has lost a lot of structure |
For very dark teeth, internal bleaching may also be chosen before a veneer or crown, because a lighter base helps thin restorations look natural. For information on the porcelain option, see our porcelain veneers page.
Frequently asked questions
Can a root-filled tooth be whitened?
Yes, if the root canal treatment is successful and the tooth structure is sound enough, its colour can be lightened with internal bleaching. Suitability is decided by examination and X-ray.
How many sessions does internal bleaching take?
In most cases 1–4 sessions are enough, usually 3–7 days apart. The exact number depends on how the tooth responds.
Does internal bleaching damage the tooth?
Although rare, there are risks such as external root resorption and weakening of the tooth. A protective barrier, an appropriate concentration and regular check-ups aim to reduce these risks.
Does ordinary whitening work on a root-filled tooth?
Because the discolouration comes from inside the tooth, external whitening usually has a limited effect on it. That is why internal bleaching is preferred.
Is internal bleaching permanent?
The result can last for many years, but some darkening may occur over time. If needed, the procedure can be repeated or a restorative option considered.
Related pages
Why Do Teeth Turn Yellow? Tooth Discolouration and Types of StainsTell external and internal discolouration apart; find out which stains lighten with whitening and which need other treatment.
Do Crowns and Fillings Whiten? Shade Matching in WhiteningWhitening gel only works on natural tooth tissue; the right sequence is needed to match the shade of restorations.
Porcelain VeneersCorrecting colour, shape and small gaps with thin porcelain shells bonded to the front of the teeth.
Teeth Whitening Methods: Which One Suits You?Compare in-office, at-home, combined and internal whitening, pharmacy products and scale and polish side by side using the same criteria.
Who Should Not Have Teeth Whitening?Situations in which whitening is not recommended or should be postponed, and what needs to be done before treatment.Suitability is decided at an examination. Fill in the form or call us to book an appointment.
Last updated: 2026-11-03 · This page is for general information only and does not replace an examination or diagnosis.