Internal Whitening: Lightening a Dark Root-Filled Tooth
If a tooth has darkened after root canal treatment, this page explains internal whitening (non-vital bleaching): how it works, why the root filling must be sound first, the risk of external cervical resorption, relapse and the alternatives. At Deepcar Dental Care, internal whitening for a dark root-filled tooth takes 2 to 4 sessions. Results vary from tooth to tooth.
5.0 from 550+ Google reviews
Open 8am to 8pm, seven days
Free parking at the door
CQC & GDC registered
No referral needed
Clinically reviewed by Dr Ibraheem Ijaz, dentist · GDC 301711
Medical disclaimer: This page is for general information only. It does not replace an examination or treatment by a dentist.
This page was reviewed by Dr Ibraheem Ijaz, principal dentist at Deepcar Dental Care, a General Dental Practitioner registered with the GDC under number 301711.
What is internal whitening?
Internal whitening aims to lighten a single dark root-filled tooth by placing a whitening agent inside it. It is also called internal teeth whitening, internal bleaching or non-vital bleaching, because the tooth's nerve is no longer alive; such a tooth is sometimes called a dead tooth.
NHS guidance says whitening can only lighten natural teeth, so a crown on the tooth will not change colour. The main page on professionally whitening your teeth explains why whitening is a dental treatment in the UK.
Why does a root-filled tooth darken?
A root-filled tooth can darken because of changes inside it, often linked to an earlier injury or to the root canal treatment itself.
A 2022 review in the International Endodontic Journal explains that a tooth with bleeding inside it after an injury often discolours as blood components spread into the dentine, and iron released as the blood breaks down can stain it brown, reddish or black. Pulp tissue left after root canal treatment and some root canal materials can also discolour it.
Not every dark tooth has had root canal treatment. The page on the causes of a dark or dead tooth covers the other possibilities.
How does internal whitening work?
Internal whitening works by placing a whitening agent inside the pulp chamber, the hollow space in the tooth where the nerve used to be.
In the walking bleach technique, published reviews describe a paste of sodium perborate and water sealed in the pulp chamber under a temporary filling. It releases hydrogen peroxide, which helps break down the coloured pigments.
Where sodium perborate is prohibited, 18% carbamide peroxide can be used instead, the 2022 review notes.
Why does the seal over the root filling matter?
A seal over the root filling, called a cervical barrier or coronal seal, helps stop the whitening agent reaching the root and nearby tissues.
The 2022 review recommends a barrier at least 2 mm thick, and concludes that it is prudent to avoid heat-activated methods and to cover the root filling with a protective base or sealer. Losing the temporary filling between visits, it notes, would allow the inside of the tooth to become contaminated again.
Why must the root filling be checked first?
The root filling must be sound first: the 2022 review says an X-ray showing an adequate root filling is mandatory before bleaching is discussed.
The review describes that X-ray as showing the likely absence of root canal disease, and Leeds Teaching Hospitals NHS Trust's guidance says dental X-rays may be needed to check the root filling before bleaching.
Defective fillings need replacing first, the review says, and fillings will not lighten, so they may not match afterwards. If the root filling itself is not adequate, that comes first, and the page about root canal treatment explains that treatment.
Questions about this treatment? Book online or call the practice.
How many sessions does internal whitening take at Deepcar Dental Care?
At Deepcar Dental Care, internal whitening for a dark root-filled tooth takes 2 to 4 sessions.
Internal whitening for a dark root-treated tooth is one of the whitening treatments offered at the practice.
What are the risks of internal whitening?
External cervical resorption is a reported risk of internal whitening. In this condition, the body's own cells break down part of the root near the gum line.
A 2022 International Endodontic Journal review calls it a serious complication of bleaching with peroxide compounds that can result in tooth loss, and notes that the European Society of Endodontology advises an X-ray after bleaching and regular follow-up X-rays.
The 2022 review suggests the risk depends partly on the method. It reports resorption in 6% to 8% of cases in studies from 1979 to 1997 that used 35% hydrogen peroxide, and in 18% to 25% where the peroxide was heated. In one study of 204 teeth bleached with heat and 30% hydrogen peroxide, with no barrier over the root filling, 4 teeth (1.96%) developed resorption during follow-up of 1 to 19 years, and all four had a history of injury.
In another study of 255 teeth bleached with 35% hydrogen peroxide and sodium perborate, with a 2.5 mm seal over the root filling, none developed it during follow-up of 6 months to 5 years.
The review says modern procedures likely carry a lower risk than older studies using heat and higher hydrogen peroxide concentrations, and that walking bleach is considered a safe protocol with a low risk of resorption. It also says the link between bleaching and resorption remains unclear, though likely related to previous injury.
Some teeth are at higher risk. Studies link resorption after bleaching with young patients, and the review lists previous injury, damage to the ligament around the root, and gaps in the root's protective surface layer. About 10% of teeth have a gap at the neck of the tooth that leaves the dentine underneath exposed, it adds. It also says a higher risk is reasonable to expect where root filling is removed to bleach a root whose discolouration shows through the gum.
Other reported risks include chemical burns to the gums or other soft tissues, rare according to a university dental hospital leaflet, and gum irritation from the gel, which a Leeds Teaching Hospitals NHS Trust leaflet mentions. If any side effect bothers you, NHS guidance is to speak to your dentist.
How long do internal whitening results last?
Internal whitening results can fade, because a whitened root-filled tooth may darken again over time; this is called relapse.
The 2022 review says bleaching outcomes are not predictable, complete restoration of colour is not always possible, and studies have shown colour regression with time. In one study of 58 teeth bleached with 30% hydrogen peroxide, some with heat, and followed for 8 years, most colour failures occurred 2 to 8 years after bleaching.
How closely the tooth will match the teeth next to it cannot be promised in advance. A university dental hospital leaflet says success depends on the cause, extent and duration of the discolouration and on existing fillings, and that the colour may not be stable, sometimes needing re-bleaching after one to two years.
What are the alternatives if internal whitening does not work?
In general, if a root-filled tooth stays dark after internal whitening, a veneer or a crown may be used to cover the discoloured tooth instead.
The 2022 review lists direct composite veneers, porcelain veneers and crowns as alternatives, with more loss of tooth structure than bleaching, expense, risks, and repair or replacement over time. Direct composite veneers are less invasive and easier to repair than porcelain veneers, it says, but more likely to lose colour.
The review adds that an ideal result is especially hard to achieve consistently on a discoloured tooth, because of the dark tooth structure underneath. The page on porcelain veneers explains that treatment, and the page on matching the colour of a restoration explains how a new restoration is matched to natural teeth.
How much does internal whitening cost?
Internal whitening has no line on the practice's current fee list.
What does UK law say about teeth whitening?
In the UK, teeth whitening is the practice of dentistry, so only people registered with the General Dental Council (GDC) may provide it.
For tooth whitening in general, only a dentist can prescribe it, according to the GDC. It is then provided by the dentist or, working to the dentist's prescription, by another dental professional the GDC permits to provide it, such as a dental therapist.
According to the GDC's 2016 position statement, conditions for products containing or releasing between 0.1% and 6% hydrogen peroxide include that they can only be sold to dental practitioners, need an appropriate clinical examination first to rule out risk factors or other oral pathology concerns, and cannot be used on anyone under 18, except where the use is intended wholly for treating or preventing disease. Above 6%, they remain prohibited in oral products unless wholly for treating or preventing disease.
European cosmetics rules of this kind also affect the agents used inside root-filled teeth, the 2022 review notes, raising legal and ethical concerns for younger patients, though there appears to be some latitude where a dentist considers treatment safe and necessary.
When should you speak to your dentist?
Speak to your dentist if a tooth has darkened, because the cause of the darkening decides which treatment, if any, suits it.
Also tell your dentist if the tooth has been injured before, because reviews link previous injury with resorption. If a temporary filling is placed during treatment, tell the dentist treating you if it comes loose or falls out.
Frequently asked questions
Is internal whitening available on the NHS?
Sometimes. NHS Business Services Authority guidance says internal bleaching of a non-vital tooth can be provided under the NHS if the clinician deems it clinically necessary, as a Band 2 course of treatment. Like any Band 2 course, it requires an examination and completion of the planned treatment the patient is willing to undergo. External bleaching cannot be NHS treatment.
Can a dark tooth be whitened if it has not had root canal treatment?
Not by internal whitening, which is for root-filled teeth. A 2025 review notes that whether the nerve is alive decides the approach, and a 2022 review adds that teeth which keep their vitality after an injury may regain their normal colour. The cause of the darkening is diagnosed first.
What usually happens when internal whitening is finished?
In general, the access hole at the back of the tooth is closed with a tooth-coloured filling. Published protocols place it 1 to 3 weeks after the last whitening visit, because fillings bond less well to freshly bleached tooth for a while.
Book a consultation.
Online in under a minute, or call and speak to a real person.
Call 0114 288 2121 or book online to ask about internal whitening. Deepcar Dental Care, at 334 Manchester Road, Deepcar, Sheffield, S36 2RH, is open 8am to 8pm, Monday to Sunday.
Internal whitening is one of several teeth whitening treatments, and the options in this section each have their own page.
334 Manchester Road
Deepcar, Sheffield S36 2RH
0114 288 2121
Contact us
Opening hours
Open 8am to 8pm, seven days
Free parking at the door