Discolouration on the teeth

Whether teeth look lighter or darker has two completely different causes — and only one of them can be brushed away. Anyone who confuses them buys products that cannot work, or brushes their enamel thin.

External discolouration: deposited

It sits on the tooth surface, usually on a thin film of plaque. Colouring substances from coffee, black tea, red wine, curry, berries and tobacco deposit there; in smokers components of tar are added. Chlorhexidine, the active ingredient in many medical mouthwashes, also discolours with longer use — brown and clearly visible, but completely removable.

A professional tooth cleaning takes this discolouration off, as a rule completely. Afterwards the tooth has its own colour again.

Internal discolouration: inside the tooth

It lies in the dentine, the layer beneath the enamel, and cannot be reached from outside. The causes include:

• Age. Over the decades the enamel becomes thinner and more translucent, and the yellower dentine beneath shows through more strongly. That is the most common reason why teeth look darker over the years.
• A dead tooth nerve after an accident or a root canal treatment. Usually a single tooth is affected, noticeably darker than its neighbours.
• Medication — above all tetracyclines, if they were taken during the period of tooth formation.
• Too much fluoride during the phase of tooth formation (dental fluorosis): white to brownish spots.
• Molar incisor hypomineralisation, colloquially chalky teeth: cream-coloured to brown areas on permanent molars and incisors whose enamel is softer than normal.

Cleaning does not help here. Depending on the cause and the extent, bleaching, a composite veneer or a ceramic shell may be considered — all decisions that belong in the hands of a dentist and not in the chemist's shop.

Why whitening toothpastes change little

Toothpastes cannot bleach the tooth. What they can do is remove what has been deposited — and they do that through their abrasiveness. The higher that is, the more effective against discolouration and the harder on the enamel. The measure for it is the RDA value. Pastes with high abrasiveness do not belong in continuous use and certainly not on exposed tooth necks: dentine is softer than enamel and does not grow back.

Some products work instead with blue pigments that create an optical effect. That lasts until the next brushing.

What actually helps

• Deposited discolouration: professional tooth cleaning. Afterwards a toothpaste with medium abrasiveness, not maximum.
• Slowing down new formation: rinse the mouth with water after coffee or tea. That removes part of the colouring substances before they settle.
• Do not brush straight after something acidic. The enamel is then softer for a short time; wait about half an hour.
• Never cover a single dark tooth cosmetically without having the cause clarified. A dead nerve needs treatment, not whitening.