What causes tooth discoloration?

As you age, your teeth can become darker due to changes in the structure of teeth as the enamel becomes less porous. This means your teeth will stain more easily. There are several causes of tooth discoloration:

Medication. Some medications, such as tetracycline and doxycycline, are known for their ability to discolor teeth if given to children with developing teeth. Additionally, some mouthwashes, antihistamines, antipsychotic drugs and antihypertensive medications can stain teeth.
Food stuff. Coffee, tea, red wine, soda drinks
Tobacco use. Whether smoked or chewed, tobacco can stain teeth.
Disease. Several diseases and radiation to the head and neck can cause reduction in saliva output which in turn can cause defects in the tooth's enamel allowing staining substances to accumulate.
Poor dental hygiene. Poor dental hygiene allows food particles to linger longer between teeth, plaque to build up and tartar to form which creates brown or black stains.
High concentration of fluoride. Drinking water or oral hygiene products containing high fluoride levels can cause staining of teeth, producing a mottled appearance.
Dental work. Centain types of dental work such as amalgam restorations that contain silver can cause teeth to turn a grayish color.
Injury. Any fall or injury that damages the nerves to the teeth can cause discoloration.
Genetics. Some people have naturally brighter enamel than others.

What options do you have to whiten your teeth?

Teeth Whitening in the dentist office
Teeth Whitening at home with bleaching agents, gels or strips.

Tooth Discoloration Prevention

Good oral hygiene includes proper brushing and flossing after meals and washing out your mouth after consuming coffee, wine or cola.
Use an ultrasonic tooth brush
Visit your dentist regularly
Cut back or quit smoking or chewing tobacco products.
Cut back or quit drinking coffee, wine and colas.
Minimize use of other products, particularly those with high fluoride content, known to stain teeth.