Black lines on teeth are the external stains firmly attached to the teeth. There are several causes for these black lines. The appearance, location (the surface and teeth effected) and patient’s habits help diagnose the exact cause of black lines.
The black lines are a form of extrinsic discoloration which are superficial stains and affect outer enamel of the teeth. The chemical compounds produce stain either due to their basic colour or as a result of a chemical reaction at the tooth surface. On the other hand, intrinsic discoloration occurs when the tooth structure is exposed to pigmented compounds during the tooth development.
Here are the list of reasons for black stains on teeth:
Tartar on teeth
A predominant cause of black lines on teeth are tartar buildup on teeth, however, its colour is different from the usual plaque. It appears as dots or lines along the gum line. It is noticed both in baby teeth and the permanent teeth and it always affects more than one tooth.
The black lines on teeth are formed by a black insoluble iron compound, known as ferric sulfide, deposited on the tooth surface. It is formed because of a chemical reaction between the hydrogen sulfide produced by chromogenic bacteria (stain producing bacteria) and the increase levels of iron present in saliva. Iron and other metal compounds like copper and sulphur are responsible for the black lines on teeth.
The elevated levels of iron in saliva could result from any bleeding disorder. The excess iron produced from bleeding deposits in different cells and body fluids like saliva in the presence of an inflammatory substance called IL-6 (several inflammatory substances are released in defence to combat the damage).
Poor oral hygiene results in green, black-brown and orange staining, produced by chromogenic bacteria. Black stains show less plaque buildup and contains a smaller number of a tooth decay causing bacteria and therefore less potential to form cavities.
Dietary sources of pigments involved in the black lines on teeth
Here are the foods and beverages that can cause black staining in teeth:
- Regular consumption of iron rich foods and vitamin supplements during pregnancy or early childhood promotes staining through the multiplication of chromogenic bacteria and the reaction between salivary iron and hydrogen sulphide.
- The black pigmentation can also result from the proline rich salivary protein. They have a high affinity for phenolic and polyphenolic compounds widely present in plant foods and beverages, for instance, tea, coffee, cola and red wine.
- More consumption of vegetables, fruits, dairy products, eggs, and soy sauce also support black stain development. For instance, protein lactoferrin found in dairy products has an affinity to bind to iron in the saliva.
- Children who had never been fed with nursing bottle tend to get them more than the bottle-fed children.
- Drinking tap water instead of bottled mineral or natural well water also seems to be associated with higher prevalence of staining. Black or brownish-black staining on teeth indicates the presence of higher levels of manganese in water. Manganese, like iron, is a naturally occurring metal in soils and water.
One of the adverse effects of smoking is the staining of teeth. This is caused by the tar and nicotine in the cigarettes. Smoking can make your teeth yellow in a short period of time and people who smoke for many years often complain of black discoloration in teeth.
Betel nut chewing
Betel quid chewing stains the teeth and gums. The colour of the stain varies from deep red to black, depending on its preparation and the duration of use.
Another common cause of a black line on tooth is from the metal layer showing from the porcelain fused to metal crowns.
A decade ago, crowns were prepared as porcelain fused to metal where opaque white porcelain was adapted over the metal coping to strengthen the crown.
Although you might have not noticed it when the crown was placed because it was probably hidden under the gum line. However, if the crown is not prepared properly, or the gum line recedes, the metal in the crown will show.