Why do teeth change color even when you brush them?

Two kinds of color change

Tooth color comes from two layers. Enamel, the outer shell, is hard and slightly translucent. Underneath it sits dentin, which is naturally more yellow. What you see is the warmth of dentin filtered through enamel, plus whatever has collected on or inside the enamel over the years. A tooth can therefore look darker for two very different reasons: something has been added to the surface, or the tooth itself has changed.

Surface stain (extrinsic)

Pigments from coffee, tea, red wine, dark sodas, berries, curries and tobacco attach to the tooth surface and to the plaque film that forms between brushings. Fresh stain of this kind is what a toothbrush and a professional polish remove well. Left alone, it builds up in the grooves of back teeth, along the gum line and between teeth, where bristles rarely reach, and once it is held in tartar a brush can no longer lift it.

Color from inside the tooth (intrinsic)

• Thinning enamel. Over the years the enamel layer gets thinner with age and wear, so more of the yellowish dentin underneath shows through. This is a common reason that teeth look more yellow in middle age than they did at twenty, and it happens in mouths that are cleaned very well.
• Medications. Antibiotics in the tetracycline family taken in early childhood, while the permanent teeth were still forming, can leave gray, brown or banded discoloration. Some antihistamines, antipsychotic medications and blood pressure medications are also associated with darkening, as are chemotherapy and radiation treatment to the head and neck.
• Excess fluoride during development. Taking in more fluoride than needed in the years when enamel is forming can cause fluorosis. In the United States it is usually mild and shows as faint white lines or specks rather than yellowing.
• An old injury. A tooth that was hit may darken months or years later. The tooth reacts to the injury by laying down extra dentin, which makes it look more opaque and yellow or gray than its neighbors.
• Early decay. A chalky white spot that does not brush away can be an early cavity, where minerals have been lost from the enamel; a brown or dark spot that does not brush away should be checked for decay as well. It usually causes no pain at this stage.

What brushing can and cannot do

Brushing twice a day with a fluoride toothpaste is still the right habit. It removes plaque, which is where most fresh stain settles, and the mild abrasives in any toothpaste polish away some surface stain. Whitening toothpastes contain abrasives or mild chemical agents that remove surface stain, but they work on the outside of the tooth only.

Brushing cannot:

• Change the color of dentin, which is why well-brushed teeth still warm in tone with age.
• Rebuild enamel that has worn thin.
• Reach stain held in tartar or in places bristles do not go, or color that was built into the tooth by medication, fluorosis or injury.
• Lighten fillings, crowns or veneers, which keep the shade they were made in.

Brushing harder does not help and can make the problem worse. Forceful brushing with a firm brush is commonly suspected of contributing to receding gums, although the research evidence for that link is not conclusive. When gums recede, they expose root surfaces, which are covered by cementum rather than enamel. That band near the gum line usually looks more yellow than the crown of the tooth, and it is softer and more vulnerable to decay. If you notice yellowing mainly at the gum line, technique is worth a look: a soft brush, light pressure and small circular movements are the recommended technique.

What helps, by cause

For surface stain

• A professional cleaning. The hygienist removes tartar and polishes away stain that home brushing leaves behind, particularly between the teeth and along the gum line. For many people this alone restores a noticeably brighter shade.
• Cleaning between the teeth daily, since stain between teeth is invisible to a brush but obvious in a smile.
• Changing exposure. Drinking coffee, tea or wine with meals rather than sipping over hours, rinsing with water afterwards, and stopping tobacco can all help slow the return of stain.
• Whitening toothpaste can help maintain the result, within its limits.

For enamel that has thinned

Whitening is often the first option to consider, because peroxide passes through the enamel into the dentin and breaks down color molecules inside the tooth. That is why whitening can lighten teeth that have no surface stain at all. Results vary with how thin the enamel is and how dark the dentin has become. The most common side effects are temporary sensitivity and gum irritation, and overuse of whitening products can harm enamel and gums, so an examination that checks how much enamel remains matters more than the product. Protecting the enamel that remains matters too: a soft brush, gentle pressure and a fluoride toothpaste. Where enamel is very worn or chipped, bonding or veneers may be the better conversation; the guide on veneers, bonding or whitening walks through that choice.

For color built into the tooth

Discoloration from medications, fluorosis or an old injury is less predictable. In general, yellow tones respond well to whitening, brown tones less so, and gray tones may barely change; color caused by medication or injury may not respond at all. White fluorosis specks are a different problem from yellowing and need their own plan. A single tooth that darkened after root canal treatment can in selected cases be whitened from the inside by the dentist. When whitening cannot deliver the change, bonding or a veneer can cover the color instead. If you are weighing whitening options, the guide on professional whitening or strips explains how each approach works, and the practice's teeth whitening page lists the in-office, custom-tray and combined options offered.

When a color change needs an examination

Gradual, even yellowing across all the teeth is usually cosmetic and can be discussed at a routine check-up. Some patterns deserve a prompt look:

• One tooth darkening on its own, especially a front tooth that was once hit. The tooth may be reacting to the old injury, or the nerve inside may have been damaged, which can lead to infection. It does not always hurt, so do not wait for pain.
• A white, brown or dark spot that does not brush away, which may be early decay. Found early, it can often be managed without a filling; see can you have a cavity without tooth pain?
• A darkened tooth with pain, a swollen or tender gum, a pimple-like bump on the gum, or a bad taste, which can mean infection at the root. Contact a dentist the same day.
• A yellow or dark band at the gum line on many teeth, which may be exposed roots or tartar stain, each with its own fix.
• A change over weeks rather than years, which is worth mentioning along with any new medications.

If a discolored tooth comes with facial swelling and fever, swelling that is spreading toward the eye, under the jaw or into the neck, or any difficulty breathing or swallowing, go to the nearest emergency department or call 911 first; the guide on facial swelling with tooth pain explains why.

The next step

Bring three things to a check-up: when you first noticed the change, whether it affects one tooth or all of them, and a list of your medications, including any long courses of antibiotics in childhood if you know of them. The examination determines which kind of color change you have, whether any spot is early decay, and whether a tooth has been affected by an old injury. From there the options run from a cleaning to whitening to covering a tooth, and the right one follows from the cause rather than from the shade alone. If you have not had an examination in a while, book a check-up and mention the color change when you do.