Over time, your teeth can go from white to not-so-bright for a number of reasons:
1.Food and Drink
Coffee, tea and red wine are some major staining culprits. What do they have in common? Intense color pigments called chromogens that attach to the white, outer part of your tooth (enamel).
Two chemicals found in tobacco create stubborn stains: Tar and nicotine. Tar is
naturally dark. Nicotine is colorless until it’s mixed with oxygen. Then, it turns into a yellowish, surface-staining substance.
Below the hard, white outer shell of your teeth (enamel) is a softer area called dentin. Over time, the outer enamel layer gets thinner with brushing and more of the yellowish dentin shows through.
If you’ve been hit in the mouth, your tooth may change color because it reacts to an injury by laying down more dentin, which is a darker layer under the enamel.
Tooth darkening can be a side effect of certain antihistamines, antipsychotics and high blood pressure medications. Young children who are exposed to antibiotics like tetracycline and doxycycline when their teeth are forming (either in the womb or as a baby) may have discoloration of their adult teeth later in life. Chemotherapy and head and neck radiation can also darken teeth.