Hardly anyone notices it while it is happening. It tends to turn up in an old photo, or in the bathroom mirror on a bright morning, and you find yourself thinking your teeth looked whiter than that a few years ago.
It is easily the thing I am asked about most, and there is rarely a single answer. Teeth change colour for all sorts of reasons. Some come down to what we eat and drink, some to the structure of the tooth itself, and some simply to getting older. Working out which one applies to you matters, because it decides whether whitening will help at all.
Here is a straightforward explanation of what actually causes teeth to yellow, from an AHPRA-registered Oral Health Therapist.
A Quick Look at What a Tooth Is Made Of
Discolouration makes far more sense once you know how a tooth is built.
The outer layer is enamel. It is the hardest substance in the body, only partly see-through, and sitting somewhere close to white. Underneath it is dentine, which is softer and naturally a yellowish to light brown shade. Because enamel is semi-translucent, whatever colour the dentine happens to be shows through to some degree.
That one detail explains most of what follows. Thick, bright enamel makes teeth look lighter. Once enamel thins, or the dentine beneath it darkens, more of that natural yellow comes through. So a tooth can look yellower for two quite different reasons. Either something has settled on the outside, or something has changed on the inside.
Extrinsic Discolouration: Staining on the Surface
Extrinsic staining sits on the enamel, or just inside its outer layer. It is by far the most common sort, and it is the sort that responds best to whitening.
Enamel looks smooth but it is not. It is covered in microscopic pores, and pigment from the things we eat and drink works its way in and builds up. Coffee and tea are the usual offenders, along with red wine, dark soft drinks, curries and deeply coloured sauces, berries, beetroot, and smoking or vaping.
Tannins deserve a mention. They turn up in tea, coffee and red wine, and they help pigment grip the tooth surface, which is why a daily flat white leaves more of a mark than the occasional cup. Acidic drinks make it worse again, because they soften enamel for a short while and give pigment an easier path in.
Plaque plays its part too. Left sitting on the tooth, it holds pigment against the surface, and it can harden into calculus, which takes up stain readily and will not shift with a toothbrush at home.
The encouraging part is that this is exactly the sort of discolouration professional whitening is built for. It is also the sort most affected by everyday habits, which I have written about in Keep Your Teeth White Longer.
Intrinsic Discolouration: Colour Coming From Inside the Tooth
Intrinsic discolouration starts within the tooth rather than on it. It behaves differently, and it does not always respond to whitening in the same way.
The usual causes:
Ageing. The most common of the lot, and entirely normal. Enamel wears thinner over the decades while the dentine underneath grows thicker and darker, so more yellow shows through. It happens to everyone to some degree, and it does not mean anything has gone wrong.
Medications. Tetracycline antibiotics taken in childhood, while the teeth were still forming, can leave banding or a grey to brown cast inside the tooth. A handful of other medications can affect tooth colour as well.
Dental fluorosis. Too much fluoride while teeth are developing can leave white flecks, or in stronger cases brown mottling, within the enamel.
Trauma. A decent knock can cause bleeding inside the tooth or damage the nerve, and it may darken over the months or years that follow. This usually affects one tooth rather than the whole smile.
Erosion thinning the enamel. Regular acid exposure, whether from soft drinks, citrus, reflux, or scrubbing too hard with a toothbrush, wears enamel away and lets more dentine colour through.
Intrinsic discolouration can sometimes be improved, but it is far less predictable than surface staining, and some kinds will not budge at all. This is exactly why the assessment before treatment matters.
What Whitening Will and Will Not Change
I would rather be upfront about the limits than have someone book in expecting something whitening cannot do.
Whitening works on natural tooth structure. It generally does well on surface staining from food, drink and tobacco, and on the gradual yellowing that comes with age.
It does nothing at all to dental work. Crowns, veneers, composite fillings and bonding will not change colour, because they are not natural tooth. If you have restorations among your front teeth, whitening everything around them can leave an obvious mismatch, so it is something to plan for rather than discover afterwards.
It also struggles with heavy intrinsic staining such as tetracycline banding, and it will not correct discolouration caused by decay or another underlying problem. In those cases whitening is simply the wrong tool, and sorting out the cause comes first.
The oral health assessment at the start of every appointment is how all of this gets picked up beforehand rather than afterwards. There is more about how I work on the About page.
When Yellowing Is Worth Getting Checked
Most discolouration is harmless and purely cosmetic. Some of it is worth a closer look.
It is worth booking a check-up if one tooth darkens noticeably against the others, particularly after a knock, or if the change arrives alongside sensitivity, pain or gum trouble. The same goes for dark spots or patches that look different to general yellowing, for teeth turning translucent or wearing at the edges, which can point to acid erosion, and for any rapid change in colour over a short stretch of time.
None of this means something is definitely wrong. It simply means the cause is worth identifying properly before anyone starts thinking about cosmetic treatment.
Can You Slow It Down?
Ageing cannot be stopped, but the staining that builds up on top of it certainly can be reduced.
A rinse with water after coffee, tea, wine or anything strongly coloured genuinely helps, since it clears pigment before it has a chance to settle. A straw keeps iced coffee and dark soft drinks away from the front teeth. And leaving about half an hour before brushing after anything acidic protects enamel while it is still soft.
Past that, the basics outperform anything on the chemist shelf. Brushing twice a day with a fluoride toothpaste and cleaning between the teeth stops plaque holding pigment against the surface, and a regular professional clean removes the hardened build-up a toothbrush cannot reach. Cutting down or giving up smoking makes the single biggest difference on this list, and the benefits go a good deal further than appearance.
So Which One Do You Have?
For most people it is a mixture. A few years of coffee on the surface, the slow natural change that comes with age underneath, and occasionally an intrinsic factor on top of both.
That mixture is why results differ from person to person, and why one treatment plan does not suit everybody. Some teeth respond quickly to an in-chair session such as the Signature Smile. Others do better with something gentler and more gradual, like the Smile Refresh or the take-home Glow Kit, particularly where sensitivity is involved.
Whitening is elective. It is a personal choice rather than something anyone is obliged to do, and there is nothing wrong with naturally shaded teeth. But if it has been on your mind, working out what is actually causing the colour change is the sensible place to start.
Frequently Asked Questions
Yes. Enamel thins gradually over the years while the dentine underneath thickens and darkens, so more natural yellow shows through. It is a normal part of ageing rather than a sign of poor oral health.
No. It works well on surface staining from food, drink and tobacco, and on the normal yellowing that comes with age. It will not change the colour of crowns, veneers or fillings, and heavy intrinsic staining such as tetracycline banding responds far less predictably.
Brushing clears plaque, but it cannot lift pigment that has settled into the microscopic pores of the enamel, and it cannot alter the colour of the dentine underneath. Good oral hygiene slows staining considerably, though it does not prevent it altogether.
Usually not, but occasionally. One tooth darkening, dark patches, or discolouration alongside pain or sensitivity are all worth having assessed by a dental professional rather than treated cosmetically.
Some gradual return of colour is normal, since the same habits and the same ageing process carry on. With good aftercare, results typically last between 6 and 12 months, and a take-home maintenance kit can help stretch that out.
Not Sure What Is Behind Yours?
If you would like to know what is causing your tooth colour, and whether whitening would genuinely help, an assessment is the place to start. I will tell you honestly if whitening is not the right option for your teeth.
Book a consultation or call 0485 938 584 to talk it through.
Smiles by Seanne: dental-grade teeth whitening by an AHPRA-registered Oral Health Therapist, based in Greenwood and mobile across Perth.
