Discolouration of the teeth can be caused by several factors.

It can be due to habitual smoking and drinking of coffee, tea and wine, or intake of certain antibiotics like tetracycline, doxycycline and antihistamines.

For dark teeth discolouration, amalgam restorations are usually the culprit because the silver leaches into the tooth. Patients now days prefer tooth coloured fillings.

Tooth whitening is usually done to treat teeth discolouration. The dentist would also recommend proper dental hygiene, cessation of smoking and reduction of dark-coloured beverage consumption. Tooth whitening is usually performed using a laser or halogen lamp and or bleaching gel. New treatments include combining laser and formulated gels to achieve optimum whitening results. There is also the option to have custom trays and take home whitening kits that you apply daily as per your dentist instructions 

Another teeth whitening option is composite resin or porcelain veneers. A dental composite material is poured into the cavity or on the surface of the tooth and then sculpted into shape.