Why do root canal treated teeth discolour?
It is not uncommon for teeth that have had root canal treatment to darken or discolour over time. The discolouration originates from within the tooth itself — not on its outer surface — which is why standard teeth whitening products have no effect on it.
Several factors contribute to this internal darkening:
- Breakdown products from blood and pulp tissue remaining inside the tooth after treatment — haemoglobin degrades into dark pigments that stain dentine
- Residual pulp tissue in the dentinal tubules that was not fully removed during treatment
- Some older root canal sealer materials that were widely used in the past and are known to cause significant dentine staining over time
- Natural changes in the dentine structure following removal of the pulp
Because the source of discolouration is inside the tooth, external whitening products — including professional-strength tray bleaching and in-chair whitening — simply cannot reach it. Internal bleaching is the only reliably effective approach.
What is non-vital (internal) bleaching?
Non-vital bleaching — also known as the walking bleach technique or internal bleaching — is a procedure in which a bleaching agent is placed inside the crown of the tooth to lighten it from within. Unlike external whitening, which acts on the enamel surface, the bleaching agent here is in direct contact with the stained dentine, working on the discolouration at its source.
The agent used is typically sodium perborate or a hydrogen peroxide-based preparation. It is sealed inside the tooth between appointments and left to work gradually — which is why the technique is called the "walking bleach": the patient leaves the practice with the bleaching agent in place and returns a week or two later to assess the result.
Treatment typically requires two to three visits. Once the desired shade is achieved, the bleaching agent is removed and the tooth is permanently sealed with a tooth-coloured restoration.
Expected results
Most discoloured non-vital teeth respond well to internal bleaching. In the majority of cases, significant lightening is achieved — bringing the tooth noticeably closer to the shade of the adjacent natural teeth. Results develop gradually, and the multi-visit approach allows controlled lightening without over-bleaching.
A small number of very severely discoloured teeth — particularly those with longstanding metallic staining from older sealers — may not achieve an adequate result from bleaching alone. In these cases, a porcelain veneer or full-coverage crown may produce a better aesthetic outcome. We will always give you an honest assessment of what is achievable before treatment begins, and will advise if we feel bleaching is unlikely to meet your expectations.
Is internal bleaching safe?
When performed correctly, internal bleaching is a safe and conservative treatment that preserves natural tooth structure. The main recognised risk is external cervical resorption — a rare but serious complication in which bleaching agent leaks through dentinal tubules at the cemento-enamel junction and triggers an inflammatory resorptive response in the surrounding tissues.
This risk is minimised through:
- Careful placement of a protective base over the root filling and at the cemento-enamel junction before the bleaching agent is placed
- Use of appropriate bleaching agent concentrations — avoiding unnecessarily high-strength preparations
- Regular monitoring throughout the treatment course
The specific risk profile for your tooth — based on its anatomy, history, and the degree of discolouration — will be discussed with you before treatment commences. We recommend internal bleaching only when we are confident it is the most appropriate and safe option.
The procedure step by step
- Visit 1: The existing coronal filling is removed. A protective base is carefully placed over the root filling and at the cemento-enamel junction. The bleaching agent is placed in the pulp chamber and sealed in with a temporary filling.
- Between visits (1–2 weeks): The bleaching agent works gradually. Avoid staining foods and drinks (coffee, red wine, tea) during this period to support the best possible result.
- Visit 2: The colour change is assessed. If further lightening is needed, the bleaching agent is replaced and the process repeated for another week or two.
- Final visit: The bleaching agent is removed completely, the access cavity is cleaned, and a permanent tooth-coloured composite restoration is placed to seal the tooth.
Is non-vital bleaching right for your patient?
Internal bleaching is most suitable when:
- There is a single discoloured tooth following root canal treatment
- The crown of the tooth is largely intact with no major structural compromise
- The patient is seeking a conservative option before committing to a crown or veneer
Internal bleaching may not be appropriate when:
- There is insufficient remaining coronal tooth structure to hold a restoration
- Evidence of previous or active resorption is present
- An extensive coronal restoration is required regardless of the bleaching outcome
If you are unsure whether your patient is a candidate for internal bleaching, call us to discuss — we are happy to advise before you refer formally.
Refer for internal bleaching assessment
Online referral with clinical notes and radiographs — we will assess and advise on suitability at the consultation.
Frequently asked questions
Can external teeth whitening fix a discoloured root canal tooth?
No. External whitening products — including professional tray bleaching and in-chair whitening — work on the outer tooth surface and cannot penetrate into the dentine where the discolouration originates in a root canal treated tooth. The only effective approach for a tooth that is dark from within is internal bleaching, where the bleaching agent is placed inside the crown of the tooth to work from the inside out.
How many appointments does internal bleaching take?
Internal bleaching typically requires two to three appointments. At the first visit the existing coronal filling is removed, a protective base is placed over the root filling, and the bleaching agent is placed and sealed inside the tooth. At the second visit (usually one to two weeks later) the colour change is assessed and the bleaching agent replaced if further lightening is needed. At the final visit the bleaching agent is removed and a permanent tooth-coloured restoration is placed.
How long do the results last?
Results from internal bleaching are generally long-lasting. Some gradual re-darkening can occur over the years, particularly if the original cause of discolouration was not fully addressed. In most cases the improvement is sustained for many years. If significant re-darkening does occur, the procedure can generally be repeated.
Is there any pain or sensitivity involved?
Non-vital bleaching is generally well tolerated. The tooth has no living pulp, so the sharp sensitivity associated with external whitening of vital teeth does not typically occur. Some patients experience mild discomfort from the restoration work during the procedure, but the bleaching process itself is usually painless. Any concerns should be discussed with your specialist before treatment begins.
What if bleaching does not work well enough?
If internal bleaching does not achieve the desired result — which is uncommon but can occur with very severely discoloured teeth — alternative options include a porcelain veneer or a full-coverage crown placed by your general dentist. Your specialist will discuss the realistic outcome of internal bleaching before commencing treatment, and will advise if a crown or veneer is likely to produce a better aesthetic result for your specific tooth.