The distinction that determines what will work
| Extrinsic | Intrinsic |
|---|
| Where | On the outer surface | Within dentin or enamel |
| Typical cause | Coffee, tea, red wine, tobacco, calculus | Ageing, trauma, dead pulp, tetracycline, fluorosis |
| Pattern | Generalised, worse between teeth and at gumline | Uniform, banded, or a single dark tooth |
| Responds to cleaning? | Yes | No |
| Responds to bleaching? | Yes, readily | Variably — depends on cause |
Why teeth naturally darken with age
Two changes happen simultaneously. Enamel thins with wear, becoming more translucent; and the pulp keeps depositing dentin on the inside, so the dentin layer thickens. Since dentin is yellower than enamel, you end up looking through less white and at more yellow. This is a structural change, not a hygiene failure, and it is why an adult's teeth are legitimately darker than a child's.
Practical implication: age-related yellowing responds reasonably well to bleaching because the colour sits in dentin, which peroxide can reach. Discoloration from tetracycline exposure during tooth development, by contrast, responds poorly and is usually addressed with veneers instead — see
our veneers page.
When ONE tooth goes dark — treat this differently
Generalised yellowing is a cosmetic question. A single tooth that darkens relative to its neighbours is a clinical finding, and the most common explanation is that its pulp has died. Blood breakdown products from the dead tissue diffuse into the dentin and stain it from inside.
- Common trigger: trauma — often years earlier, sometimes forgotten.
- Also: deep decay that reached the pulp, or a large old restoration.
- Watch for: a periapical lesion developing at the root tip, frequently with no pain at all.
Do not whiten a single dark tooth without an examination first. External bleaching will not correct a colour change originating inside the tooth, and more importantly it does nothing about the dead pulp or the infection that may be forming in the bone. The correct sequence is: examine and radiograph, treat the pulp if needed, then address colour — often with internal bleaching, which works from inside the tooth.
Causes checklist
- Dietary chromogens — coffee, tea, red wine, curry, berries, soy sauce.
- Tobacco — tar produces particularly tenacious brown staining.
- Chlorhexidine mouthwash — effective antiseptic, but causes brown staining with prolonged use.
- Iron supplements, especially liquid formulations in children.
- Dental fluorosis — white or brown mottling from excess fluoride during development.
- Tetracycline antibiotics taken during tooth formation — grey-brown horizontal banding.
- Amalgam restorations — can impart a grey cast to surrounding tooth structure.
- Root canal treatment, particularly older techniques or residual material in the crown.
Choosing an approach
- Professional cleaning first. A meaningful share of patients who ask about whitening actually have extrinsic staining and calculus. Cleaning is cheaper, faster, and sometimes sufficient.
- Bleaching for genuine intrinsic yellowing. Options and fees are on our English price list.
- Internal bleaching for a single root-canal-treated dark tooth — the agent is placed inside the tooth.
- Veneers where bleaching cannot work: tetracycline banding, severe fluorosis, or discoloration combined with shape or position concerns.
One caution on expectations: bleaching does not change the colour of existing crowns, veneers, or composite fillings. If you have restorations on your front teeth, whitening the natural teeth around them can create a visible mismatch — which is why the restorations often need replacing afterwards. Raise this before starting, not after.
Frequently asked questions
Why are my teeth getting yellower as I age even though my hygiene is good?
Two structural changes cause it. Enamel thins and becomes more translucent with years of wear, while the pulp continuously deposits new dentin on the inside, thickening that layer. Because dentin is naturally yellower than enamel, you are progressively seeing less white and more yellow. It is a normal anatomical change and not a reflection of your cleaning.
One of my front teeth has gone noticeably darker. What does that mean?
A single darkening tooth most often means its pulp has died, with blood breakdown products staining the dentin from inside. The trigger is frequently trauma, sometimes years earlier and often forgotten. This needs examination and a radiograph rather than whitening, because a periapical infection may be developing silently at the root tip.
Will whitening fix a single dark tooth?
External bleaching generally will not, because the colour originates inside the tooth. More importantly, whitening ignores the underlying cause — a non-vital pulp and possible infection in the bone. The usual sequence is to treat the pulp first, then use internal bleaching, which places the agent inside the tooth where the stain actually is.
Can tetracycline staining be whitened?
Poorly. Tetracycline incorporates into the tooth structure during development and produces grey-brown banding that responds inconsistently to peroxide, even with extended treatment. Veneers are the more predictable solution for these cases, which is why an honest assessment before starting matters more here than with ordinary age-related yellowing.
Do my crowns and fillings whiten too?
No. Bleaching acts on natural tooth structure only. Crowns, veneers, and composite fillings keep their original shade, so whitening the surrounding natural teeth can leave restorations looking conspicuously darker. If you have restorations on visible teeth, plan for possible replacement afterwards and discuss it before treatment rather than being surprised by the result.
Should I get a cleaning or whitening first?
Cleaning first, always. A substantial proportion of patients who request whitening have extrinsic staining and calculus, which cleaning removes at lower cost and with no sensitivity. Only after the surface is genuinely clean can you judge the true underlying shade — and some patients find they no longer want whitening at that point.