Internal Tooth Discolouration: When Whitening Won’t Work (And Why)

When people think about teeth whitening, they often assume it can address any form of discolouration. For surface stains caused by food, drink, or smoking, that assumption is often reasonable. But not all tooth colour changes originate on the surface. Some discolouration comes from within the tooth itself — and in these cases, professional teeth whitening may have limited or no visible effect. Understanding this distinction is important for anyone considering whitening, because it helps set honest expectations and avoids unnecessary frustration.

This article explains what internal (intrinsic) tooth discolouration is, why it behaves differently from surface staining, and how dentists assess whether whitening is likely to help. The aim is to provide clarity — not to discourage patients, but to support genuinely informed decision-making.

What Is Internal (Intrinsic) Tooth Discolouration?

Internal tooth discolouration — also referred to as intrinsic staining — is colour change that originates from within the tooth structure itself, rather than on the surface.

Difference between internal and surface stains

Surface (extrinsic) stains sit on or just below the enamel surface. They are typically caused by pigmented foods, drinks, tobacco, or certain mouthwashes, and they generally respond well to professional cleaning and whitening. Internal (intrinsic) stains, by contrast, are located within the dentine or deeper enamel layers. They are part of the tooth’s internal structure and cannot be reached or removed in the same way.

Where intrinsic discolouration occurs

Intrinsic discolouration can affect the dentine, the inner enamel layers, or — in some cases — the dental pulp area. The colour may be distributed throughout the tooth or concentrated in specific areas, depending on the cause. Because it exists within the tooth rather than on its surface, it is not accessible to the whitening agents used in standard whitening treatments.

Why colour appears from within the tooth

Enamel is semi-translucent, which means the colour of the underlying structures shows through to varying degrees. When the dentine is darker, discoloured, or stained internally, the tooth may appear grey, brown, yellow, or uneven in colour — even if the enamel surface itself is clean and free of extrinsic staining. This is why some patients notice persistent discolouration despite having excellent oral hygiene.

Common Causes of Internal Tooth Discolouration

Several factors can lead to intrinsic discolouration. Understanding the cause is important because it directly affects what whitening can and cannot do.

Tooth trauma

A knock or injury to a tooth can damage the blood supply to the dental pulp, leading to internal bleeding and gradual darkening of the affected tooth. This is one of the most common causes of single-tooth discolouration. The tooth may turn grey, brown, or dark yellow over time. Because the colour change comes from within the pulp and dentine, surface whitening has very limited effect on this type of discolouration.

Developmental changes

Conditions that affect tooth development — such as enamel hypoplasia, amelogenesis imperfecta, or dentinogenesis imperfecta — can alter the internal structure and colour of the teeth from an early age. These developmental variations produce discolouration that is built into the tooth from the time it forms. Whitening cannot change the fundamental composition of the enamel or dentine in these cases.

Medication-related staining

Certain medications, most notably tetracycline antibiotics taken during childhood, can become permanently incorporated into the tooth structure during development. This produces characteristic banded or uniform discolouration that ranges from yellow to grey-brown. Other medications and medical treatments can also contribute to intrinsic colour changes. These stains are deeply embedded and highly resistant to whitening.

Age-related dentine changes

As teeth age, the dentine naturally becomes darker and more yellow. At the same time, the enamel gradually thins through normal wear. The combination of darker dentine and thinner enamel means that teeth tend to appear more yellow or dull over time. While whitening can partially counteract these changes, there are natural limits — and in some patients, the degree of change may be modest. Understanding the costs associated with professional whitening helps patients make informed decisions about whether pursuing treatment is worthwhile for age-related changes.

Why Teeth Whitening Doesn’t Work on Internal Stains

Understanding why whitening is limited in these cases requires a basic knowledge of how whitening works.

Whitening gel penetration limits

Whitening gels contain active ingredients — typically hydrogen peroxide or carbamide peroxide — that penetrate the enamel and break down stain molecules through a chemical oxidation process. This is effective for extrinsic stains and some superficial enamel discolouration. However, the gel’s ability to penetrate deeply enough to reach intrinsic staining within the dentine is limited. The deeper the discolouration, the less likely whitening is to produce a visible change.

Tooth structure and translucency

Even if the enamel surface is lightened through whitening, the underlying intrinsic colour of the dentine still shows through. Because enamel is translucent, the internal colour of the tooth remains visible regardless of how effectively the enamel has been treated. This is why some patients notice that their teeth look slightly brighter but the underlying grey, brown, or dark tone persists.

Biological colour constraints

Every tooth has a biological colour determined by its internal structure. Whitening can lighten the tooth to some degree, but it cannot change the fundamental colour of the dentine or alter developmental changes to the enamel. These biological constraints set a natural ceiling on what whitening can achieve — and for teeth with significant intrinsic discolouration, that ceiling may be quite low.

How Internal Discolouration Can Look Different

Internal discolouration does not always present in the same way. Recognising the different appearances can help patients understand what they may be dealing with.

Grey or brown tones

Intrinsic discolouration often presents as a grey, brown, or dusky tone rather than the typical yellow associated with surface staining. This is particularly common after dental trauma or with medication-related staining. The greyish quality of the colour is a strong indicator that the discolouration originates from within the tooth rather than on the surface.

Single-tooth discolouration

When only one tooth appears noticeably darker than the surrounding teeth, it is often a sign of internal discolouration — frequently caused by trauma to that specific tooth. Whitening the surrounding teeth may make the contrast more noticeable rather than less, which is an important consideration during treatment planning.

Patchy or uneven colour

Some forms of intrinsic discolouration produce patchy, mottled, or banded patterns across the teeth. This is common with fluorosis or tetracycline staining. Whitening may lighten the less affected areas more than the heavily stained zones, potentially making the unevenness more prominent in some cases. A dentist can assess whether whitening is likely to improve or worsen the visual uniformity.

Can Internal Discolouration Improve at All With Whitening?

While whitening is generally limited for intrinsic discolouration, there are situations where a modest improvement may occur.

Situations with minimal surface improvement

In some cases, teeth with intrinsic discolouration also have a degree of extrinsic staining on top. Removing the surface component through whitening may produce a slight visual improvement, even though the underlying internal colour remains unchanged. The result is typically a cleaner, slightly brighter appearance rather than a fundamental colour shift.

Why dramatic change is unlikely

For patients whose discolouration is predominantly intrinsic, whitening is unlikely to produce the kind of dramatic shade change that patients with surface staining often experience. The internal colour of the tooth sets a firm baseline that whitening cannot move past. Understanding this before starting treatment is essential for avoiding disappointment.

Importance of expectation-setting

The most valuable thing a dentist can do for a patient with intrinsic discolouration is provide an honest, realistic assessment. If some improvement is likely, explaining the probable degree of change helps the patient decide whether treatment is worthwhile. If improvement is unlikely, saying so clearly prevents unnecessary treatment and the frustration that comes with unmet expectations.

How Dentists Identify Internal vs Surface Discolouration

Distinguishing between extrinsic and intrinsic discolouration is a key part of any whitening assessment.

Visual assessment

A dentist will visually examine the teeth, noting the colour, distribution, and pattern of any discolouration. Surface stains tend to be concentrated in areas where food and drink contact the teeth, while intrinsic discolouration often follows different patterns — such as uniform darkening of a single tooth, horizontal banding, or mottled patches that do not correspond to typical staining sites.

Clinical history

Understanding the patient’s dental and medical history is important. Questions about childhood medication use, dental trauma, developmental conditions, and fluoride exposure can provide valuable clues about the likely cause of discolouration. This history, combined with the visual examination, helps the dentist form an accurate picture of what is driving the colour change.

Shade pattern evaluation

The way colour is distributed across the teeth can reveal a great deal. Extrinsic staining typically responds to cleaning and lightens predictably with whitening. Intrinsic colour tends to be more persistent, evenly distributed within the tooth, and resistant to surface treatments. A dentist can assess these patterns and explain what they mean for the patient’s whitening prospects.

Why Repeating Whitening Usually Doesn’t Help

When whitening does not produce the expected result, patients sometimes wonder whether repeating the treatment will make a difference. In many cases involving intrinsic discolouration, it will not.

Diminishing returns

If the remaining colour is intrinsic, further whitening sessions are targeting the same biological limitation. The enamel may have already been lightened to its maximum extent, and additional applications of whitening gel are unlikely to penetrate deeply enough to affect the dentine colour. Continuing beyond this point produces diminishing returns — the effort and cost increase, but the visible improvement does not.

Sensitivity risks

Extended or repeated whitening can increase the risk of tooth sensitivity. If the teeth have reached their whitening ceiling, continuing treatment exposes the patient to unnecessary discomfort without corresponding aesthetic benefit. A responsible, dentist-led approach involves recognising when to stop — a decision that protects both dental health and patient wellbeing.

Avoiding overtreatment

Over-whitening can lead to a chalky, translucent, or unnaturally bright appearance in the enamel, while the underlying colour remains unchanged. This can actually make the contrast with the intrinsic discolouration more visible rather than less. A measured, professionally guided approach ensures that treatment stops at the right point and that the patient’s expectations are managed throughout.

Home Whitening vs Other Whitening Methods (Educational Comparison)

Patients with internal discolouration sometimes wonder whether a different whitening approach would produce better results. It is useful to understand why the limitations are consistent across methods.

Same limitations for intrinsic stains

Regardless of the delivery method, the fundamental challenge with intrinsic discolouration remains the same: the staining is located within the tooth structure and cannot be fully reached by whitening agents applied to the enamel surface. No external whitening method — whether home-based, professionally supervised, or otherwise — can change the internal colour of the dentine.

Why faster methods don’t change outcomes

More intensive or rapid whitening approaches may lighten surface stains more quickly, but they face the same biological barriers when it comes to intrinsic discolouration. Speed of application does not overcome the depth limitation. The intrinsic colour of the tooth remains the same regardless of how the whitening gel is delivered or activated.

Importance of honest planning

The most valuable aspect of any whitening consultation is honesty. A dentist-led approach to home whitening includes an assessment of whether whitening is likely to help in the first place. For patients with intrinsic discolouration, this honest evaluation can prevent wasted time, unnecessary expense, and avoidable disappointment — and can guide the patient towards a more realistic understanding of their options.

Teeth Whitening Consultations in London

If you are unsure whether your tooth discolouration is internal or surface-related, a professional consultation is the most reliable way to find out.

Assessment-led explanation

At our London clinic, every whitening discussion begins with a careful examination of the teeth. We assess the type, location, and likely cause of any discolouration before recommending treatment. If the discolouration appears to be intrinsic, we will explain this clearly and discuss what whitening can and cannot realistically achieve.

Honest discussion of whitening limits

We do not promise results that are unlikely to be achieved. If whitening is not the right option for your situation, we will tell you so honestly. Our priority is always to ensure that patients make informed decisions based on accurate clinical information rather than unrealistic expectations.

Taking a realistic first step

If you are unsure whether whitening is suitable for your tooth discolouration, a consultation can help explain what is realistic in your situation. Contact us to arrange a consultation and receive honest, personalised guidance from a dentist who will explain your options clearly and without pressure.

Frequently Asked Questions

What is internal tooth discolouration?

Internal (intrinsic) tooth discolouration is colour change that originates from within the tooth structure — typically from the dentine or deeper enamel layers. Unlike surface stains caused by food, drink, or smoking, intrinsic discolouration is part of the tooth itself and is not removable through standard cleaning or whitening. Common causes include dental trauma, childhood medication use, developmental conditions, and natural ageing.

Why won’t my tooth whiten like the others?

If one tooth appears darker or does not respond to whitening in the same way as the others, it is likely affected by intrinsic discolouration. This is most commonly caused by trauma to that specific tooth, which can damage the internal blood supply and lead to gradual darkening. Whitening gel works on the enamel surface and cannot effectively change the internal colour of an individually affected tooth.

Can intrinsic stains ever be removed?

Intrinsic stains cannot be removed through standard whitening treatments. In some cases, a very modest lightening of the overall shade may occur, but the underlying internal colour typically remains. For significant intrinsic discolouration, a dentist may discuss alternative approaches, but whitening alone is unlikely to produce a satisfactory result. A professional assessment is the best way to understand your specific situation.

Is repeated whitening safe if it’s not working?

Continuing to whiten teeth that have reached their natural shade limit is generally not advisable. Repeated whitening beyond this point can increase the risk of sensitivity, weaken enamel, and produce an unnatural appearance without meaningful colour improvement. A dentist can advise when further whitening is unlikely to be beneficial and when it is appropriate to stop.

Why does one tooth look darker than the rest?

A single dark tooth is often the result of internal discolouration, most commonly caused by past trauma to that tooth. The injury may have occurred years or even decades earlier, and the darkening can develop gradually over time. This type of discolouration is within the tooth’s internal structure and does not respond to surface whitening in the same way as the surrounding teeth.

Does internal staining mean whitening failed?

No. If your teeth have been whitened and some discolouration remains, it does not necessarily mean the treatment failed. It may simply mean that the remaining colour is intrinsic — part of the tooth’s internal structure — and was never going to respond to surface-applied whitening gel. Whitening may have successfully removed extrinsic staining while the underlying internal colour remained unchanged. A dentist can explain what has changed and what has not.

Disclaimer: This article provides general information only and does not constitute personalised medical or dental advice. Internal tooth discolouration varies in cause, severity, and appearance, and whitening outcomes are highly individual. No specific shade results or stain removal outcomes are guaranteed. Not all patients are suitable for whitening, and whitening may not be effective for intrinsic discolouration. Always follow the specific guidance provided by your treating dental professional.