There are a number of factors that can cause your teeth to lose their luster. The most common culprits of teeth staining are coffee, tea and red wine. These drinks contain intense pigmentation that has a tendency to stick to the enamel (the white outer part) or the tooth. Tobacco use also darkens teeth, as tar and nicotine form a surface-staining substance.
In addition, teeth naturally fade with age. Over time, the outer layer of enamel thins, allowing more of the yellowish area below, called dentin, to show through. Certain medications can also cause teeth to fade. Antihistamines, antipsychotics and medications for high blood pressure contribute to tooth discoloration.
In addition, trauma to a tooth can cause it to produce more yellow dentin as a reaction to the injury, darkening the overall color of the tooth.