There are three things that may cause a tooth to become darker:
The normal ageing process can make teeth look darker or yellower than they once were. This is because the yellow-coloured part of the tooth, the dentine, usually increases in thickness as we age, while the overlying translucent enamel (which makes the tooth look white), either remains the same thickness or becomes thinner through wear and tear.
Whitening can make a difference in these cases, but sometimes other methods, such as veneers, are needed to mask the yellow colour.
The enamel surface is quite porous, so it can absorb dark stains from coffee, tea, nicotine, red wine, grapes, berries and other darkly-coloured foods and drinks. Regular brushing can’t always remove this discolouration from within the minute pores, and even so called “whitening toothpastes” can struggle to remove all of this sub-surface stain.
Whitening is often very successful to treat this type of discolouration.
A tooth can sometimes develop stains deep within the dentine, which is the layer underneath the hard outer enamel shell. These stains can be caused by a number of things:
- Trauma – a blow to the tooth can cause a tooth to become yellow or greyish colour
- Nerve infection and death – a diseased nerve can stain the dentine, usually causing a grey-black discolouration which doesn’t always disappear after root canal therapy
- Antibiotics – antibiotics such as tetracyclines can cause internal staining of a tooth if they are taken for extended periods during childhood when the teeth are forming.
Whitening has a limited effect on this type of staining; however, teeth which have darkened because of nerve infection can be internally bleached after root canal treatment.