A dark tooth after root canal treatment: internal tooth bleaching, a veneer or a crown

Bleaching from the inside, a veneer or a crown: what is really at stake

• A dark tooth after root canal treatment changes colour from the inside, so whitening toothpastes and strips, which act on the enamel surface, will change nothing here. The methods described in the text on teeth whitening at the dentist and at home are for vital teeth.
• The first-choice method is internal tooth bleaching, that is, bleaching the tooth from the inside: the agent is sealed for several days inside the pulp chamber (the empty space in the middle of the crown where the pulp used to be). No grinding of the tooth is required.
• A pooled analysis of studies shows that the tooth lightens on average by about six shades on the shade guide. The evidence on how long the effect lasts is weak.
• A veneer and a crown give a more predictable result, but at the cost of irreversibly ground tissue. Dark dentine shows through thin ceramic, so the darker the tooth, the thicker the veneer has to be.
• It is worth starting with colour: a tooth lightened before a veneer should allow less to be taken off it.
• A veneer is better decided on only once it is clear that the colour has held.

"This tooth does not hurt. It is simply grey, and it shows when I laugh. Can it be lightened, or does it have to be ground down?"

The question usually concerns a central incisor treated endodontically after an injury years earlier, one that stood out in no way for a long time and then began to differ in colour from its neighbour. The answer is: it can usually be lightened, and whether any grinding happens at all will become clear only once bleaching is finished. This text is about colour alone; the mechanical indications are covered by a separate text on when a crown on a tooth after root canal treatment is necessary.

Where does a dark tooth after root canal treatment come from?

Tooth discolouration arises either on the enamel surface or beneath it. This discolouration has a deeper source: dentine that has changed colour under intact enamel. Enamel is translucent and almost colourless in itself; we see the colour of the tooth through it much as we see through a pane of glass.

The most common cause is bleeding into the pulp after an injury. Blood penetrates the dentinal tubules, and iron from breaking-down red cells stains the dentine brown, reddish or black. The second source is the procedure itself. Pulp remnants in the horns of the pulp chamber, medicaments and root canal sealers discolour the dentine from within. Calcium silicate materials used for perforation repair can also discolour the crown.

Hence a practical conclusion: a dark tooth after root canal treatment can be the result of what was left in the pulp chamber, so cleaning it thoroughly is an aesthetic procedure as well. Magnification helps with this, as discussed in the text on root canal treatment under a microscope.

What does internal tooth bleaching involve?

In short: the bleaching agent is placed inside the tooth and sealed there for several days.

The sequence has been settled for several decades. The tooth is isolated with a rubber dam, and the dentist opens the pulp chamber and removes old fillings and material remnants from it, but not the discoloured dentine. The root filling is reduced below the gingival margin and covered with a cement barrier about two millimetres thick. Only then does the bleaching agent go in - in the European Union, carbamide peroxide - and a temporary dressing closes the chamber. The patient returns after three to seven days to have the agent changed; one to four applications are usually enough.

Leaving the agent in longer usually does not lighten the tooth any further: the peroxide is released most intensively in the first days. The risk lies in a leaking or lost dressing, through which the inside of the tooth becomes contaminated again. Cervical resorption has been reported more often in young people and after dental trauma.

How much does the colour change? The tooth lightens on average by 6.27 shades on the shade guide. That is what emerged when six clinical studies with different agents were pooled. A shade guide is a row of reference tooth shades arranged from lightest to darkest. Six shades therefore mean a jump of several positions along that row; one shade is one position.

Whether that is enough for the tooth to stop standing out from its neighbour depends on how far from it the tooth started. Studies report average lightening, not the proportion of teeth that came to match the adjacent tooth in colour: that figure simply does not exist. The aim, in any case, is not to hit the neighbour's shade exactly, but to stop slightly lighter: part of the lightening regresses over time. When to stop is judged by the dentist at each change of agent: a tooth lightened well beyond its neighbours also stands out.

Two reservations have to be added to that number, and both need to be known. The risk of bias in the pooled studies was moderate to high. Data on how long the colour holds were simply missing. A more recent comparative trial on 50 non-vital teeth gave a slightly weaker result than bleaching performed in the surgery, although the colour improved in both groups; the observation there lasted a month, however, so nothing follows from it about the durability of either method.

There is one precondition, and it is not negotiable: internal bleaching is performed only in a tooth with a correctly filled root canal and without inflammatory changes at the root apex. A tooth that hurts or shows a lesion on the radiograph needs treatment first. The procedure is carried out in the surgery as part of dental hygiene and whitening, which covers whitening of a non-vital tooth; whitening of vital teeth is covered by the text on teeth whitening at the dentist and at home.

The protocol calls for waiting twice more. Patients sometimes take this for slowness. The bleaching agent is not heated; the thermocatalytic technique has been abandoned because of the risk of cervical resorption. Nor is the definitive filling placed in the access cavity straight away: it is deferred by one to three weeks, because oxygen released during bleaching temporarily weakens the bonding of composite, and a leaking filling is a frequent cause of the discolouration returning.

When is bleaching alone not enough?

Usually when the problem has stopped residing in the dentine itself. Internal tooth bleaching will not help in four recurring situations.

• An extensive old filling in the crown of the tooth. Bleaching acts on tissue, not on composite. A dark filling margin will stay dark.
• Very dark discolouration. A grey tooth and a light yellow tooth lighten better than a dark yellow or black one; with the latter, the effect can be partial.
• Discolouration from a calcium silicate material reaching deep into the crown. It can be resistant; in a laboratory study, removing the material worked better than bleaching. The patient will not recognise this alone: it is visible on the radiograph and in the records of the earlier treatment.
• • A tooth with a fractured incisal edge or a large loss of tissue. Here the structure of the tooth decides, not the colour.

Stronger evidence does not mean a better first choice

The balance of evidence here looks unusual, and it is worth saying so plainly. Internal bleaching conserves tissue, but its efficacy has been described in studies that are few and carry a risk of bias, and many historical series used hydrogen peroxide concentrations that are no longer used in cosmetic products in the European Union. The veneer has stronger evidence: more studies, longer follow-up, calculated survival rates. That does not make it a better first choice. It means that bleaching is a less predictable method, but a reversible one, and the veneer the other way round.

A veneer: what you gain and what you pay with

You gain a predictable colour and well-documented durability. You pay with enamel the tooth will not get back.

Ceramic veneers hold at ten years and beyond in 93.7 to 96.8 percent of cases, depending on the type of ceramic. This was calculated across 29 studies.

The fact of root canal treatment alone does not rule out a veneer. Non-vital teeth with veneers survived in 95.0%, and vital teeth in 96.0%, and the difference was not clear; the observation covered 672 veneers and lasted from one to fifteen years. That figure is weaker, however, than it looks. There were only 38 endodontically treated teeth in the study, so nobody will say on that basis that the risk is identical.

The biological cost, by contrast, has been calculated precisely. At the neck of the tooth the enamel is only 0.3-0.5 mm thick, and preparation for a veneer takes roughly the same amount away in that spot. Dentine is therefore exposed easily, and that changes the prognosis: in the same observation, survival fell to 93.9% where exposed dentine covered more than 30% of the surface. How much tissue preparation takes is described in the text on whether veneers damage teeth. Procedures in this group are carried out as part of veneers and composite bonding.

Dark dentine shows through a veneer. A strongly discoloured substrate was masked in the laboratory by none of the twelve material combinations tested, even though three degrees of ceramic translucency were set against four cement shades. The colour of the substrate alone accounted for close to nine tenths of the variation in the result, with ceramic translucency and cement shade together accounting for the rest. Another laboratory study showed the price of masking: the best coverage came from low-translucency ceramic 1.2 mm thick, which is thicker than a typical veneer, and a thicker veneer means more tooth has to be removed. This is worth remembering: lightening the tooth before a veneer is not a redundant stage - it should allow a thinner veneer. It is worth knowing what that conclusion rests on: both measurements were made in a laboratory, and nobody has so far compared clinically veneers placed on lightened and on unlightened substrates.

Is it better, then, to go straight to a crown?

No, not if colour alone were the reason. A crown is not a thicker veneer: it is a restoration that encircles the tooth, and the indication for it follows from how much healthy tissue is left. The full selection criteria are described in a separate text: veneers or crowns. Colour does return here as an aesthetic argument, though. A very dark tooth, already prepared, is a difficult substrate under a crown as well, for the same reason as under a veneer: translucent materials, which look best, mask most poorly, and a masking layer needs room. A metal post in the root canal darkens the substrate further; covered with an opaque composite, it gives a better starting point.

Nor does a crown solve the problem of a dark root. It ends at the gingival margin, so it has no influence on the colour of what lies below: with a thin gingiva, or if the gingiva recedes, the dark root shows through regardless of what stands above it.

A crown is not made in order to change the colour of a tooth whose structure does not require a crown. That is trading an aesthetic problem, which is reversible, for a mechanical one, which cannot be undone.

Decision table: discolouration, method and what you lose from the tooth

Situation	First choice	What you lose from the tooth
Grey or light yellow tooth, crown of the tooth entirely sound	internal bleaching	nothing beyond the filling in the access cavity
Dark yellow or black tooth, crown sound	internal bleaching, with notice that the effect can be partial	as above
Discolouration persists after a full cycle of bleaching	veneer on a lightened substrate	0.3-0.7 mm of enamel
Dark margin of an old filling, which bleaching will not touch	composite restoration or a veneer	depending on the extent of the restoration
Dark prepared tooth restored with a post	the type of restoration is decided by structure, not colour: see veneers or crowns licówka czy korona	preparation of the tooth around its whole circumference

"After a full cycle" in the third row means: the colour stopped improving despite further applications.

Timeline: from the first appointment to assessing durability

1. Day 0: the dentist opens the pulp chamber, protects the root canal and places the bleaching agent.
2. After 3-7 days: the first visible change of colour and a change of agent.
3. One to four applications: the full bleaching cycle, at intervals of three to seven days.
4. One to three weeks after the last application: the definitive filling of the access cavity.
5. After a year: usually the first assessment of how durable the colour is, and only then the decision about a veneer.
6. From 2 to 8 years: the period in which recurrences of discolouration have been described.

The whole of internal tooth bleaching - from the first appointment to the definitive filling - usually falls within two to seven weeks.

How long does the effect last, and does the discolouration come back?

Usually for years, though in some patients the discolouration returns. This is the least well studied part of the whole matter, and it is better to say so plainly than to quote a single figure.

In an observation of 58 teeth conducted over eight years, roughly half the results remained good, close to a third acceptable, and one fifth came out as failures. When those failures appeared matters too: between the second and the eighth year after the procedure. There is also a series of 40 teeth observed over a quarter of a century, in which success held in 85% of cases. Both describe treatment from years ago and protocols that differ from today's, so neither figure should be treated as a prognosis for an individual tooth.

Patients themselves were also asked how they rated the result. In series from that period, close to nine in ten rated the effect as good, and a few percent were dissatisfied. That is a different endpoint from measured colour, though: the patient judges whether the tooth has stopped catching the eye, while the shade guide measures how many shades it moved. These measures diverge, and that is one of the reasons why internal tooth bleaching is hard to compare between studies.

Internal tooth bleaching can, moreover, be repeated, and a repeat cycle requires no greater intervention than the first.

Frequently asked questions

How many appointments does internal tooth bleaching take?

Usually three to six. The first appointment is the opening of the pulp chamber, protection of the root canal and placement of the bleaching agent. The agent is changed every three to seven days; one to four applications are usually enough. The last appointment, one to three weeks after bleaching ends, is the restoration of the access cavity.

Does internal bleaching hurt?

The procedure is performed in a tooth after root canal treatment, that is, one without pulp, so the tooth itself does not feel the bleaching agent and anaesthesia is usually not needed. Any discomfort, if it appears, concerns the gum next to the tooth rather than the tooth. Pain that was not there before is a reason to contact the surgery earlier.

Is anything visible on the tooth during that time?

The cavity through which the agent is placed is usually opened from the palatal side, that is, from behind the tooth, and after each appointment it is closed with a temporary dressing. From the smile side, then, no opening is visible, only the tooth itself, growing lighter from appointment to appointment. The definitive filling is placed in the same spot once bleaching is finished.

Is internal bleaching safe for the tooth?

The complication that has to be known about is external cervical resorption: a loss of tissue at the neck of the root. Older reports concerned protocols with heating or with a high concentration of hydrogen peroxide, both now discouraged. For today's protocol, with a barrier and without heating, nobody has calculated how often it occurs. In place of a figure, a rule of observation applies: report pain, swelling or a pinkish discolouration at the neck of the tooth in the months after the procedure to your dentist.

How long does the effect last?

For years, but not in everyone. In an observation of 58 teeth conducted over eight years, roughly half the results remained good, and one fifth came out as failures. Recurrences were described most often between the second and the eighth year. The study is old and its protocol differed from today's, so it speaks to an order of magnitude, not to a prognosis for an individual tooth. Repeat bleaching is usually possible.

Will whitening strips and toothpastes lighten a non-vital tooth?

No. A discoloured non-vital tooth is dark from within, while home preparations act on the enamel surface. They will lighten the neighbouring teeth along the way, which will make the grey central incisor stand out even more clearly. A dark tooth after root canal treatment requires an agent introduced into the inside of the crown.

Can a tooth covered by a crown be whitened?

No. Neither ceramic nor composite can be lightened by any bleaching agent, so changing the colour of a finished prosthetic restoration means, in practice, replacing it. It is different when what is dark is the exposed part of the root at the gum, rather than the crown itself: there the solution is sought on the side of gum surgery or replacement of the restoration.

Will a veneer hold on a tooth after root canal treatment?

In an observation lasting from one to fifteen years, endodontically treated teeth with veneers survived in 95%, and vital teeth in 96%; veneers on endodontically treated teeth numbered only 38 out of the 672 counted. Durability is decided mainly by whether the veneer adheres to enamel or to exposed dentine.

What if the tooth is additionally weakened?

Then the order reverses. First it is established which restoration will hold the tooth, and only within that plan is the colour planned. Internal bleaching remains possible in such a tooth as well, and is sometimes performed in order to lighten the substrate for the future restoration, not as a stand-alone treatment.

Order matters: lighten the tooth first, cover it only afterwards

Internal tooth bleaching is the only one of the methods discussed that does not require grinding the tooth, so it is where one starts even when a veneer is the eventual plan.

Finally, a matter of safety. A dark tooth after root canal treatment is a problem of appearance. Pain, swelling or a pinkish discolouration at the neck of a bleached tooth are no longer that: they require a check-up with a dentist, regardless of how much time has passed since the procedure.

Read more:

• Veneers and Composite Bonding in Warsaw
• Veneers or crowns — when to choose which restoration
• A crown on a tooth after root canal treatment - when it is necessary
• Do veneers damage teeth? Facts, myths and scientific evidence
• Central incisor bonding — what does the procedure on the front teeth look like?

Content and liability disclaimer

This article is informational and educational in nature and does not constitute medical advice, a diagnosis or a therapeutic recommendation — it does not replace a consultation with a specialist. If you are experiencing symptoms, have doubts or are facing a decision about treatment, consult a dentist. The methods described and the data cited are general in nature. The results of scientific studies relate to populations, not to an individual patient. The course and outcome of therapy depend on the individual clinical situation and may vary between patients. No information contained in this article constitutes a guarantee of result. The content has been prepared with due care, based on publicly available medical knowledge and the scientific publications indicated in the Sources section. We do not advise taking or refraining from any health-related action solely on the basis of the content of this article, without prior consultation with a doctor.

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