1) Extrinsic stains: Extrinsic stains are mainly caused by the daily intake of foods and beverages such as coffee, tea or the use of tobacco products, etc. These substances tend to adhere to the enamel and thereby discolor and reduce the brightness of the teeth.
2) Intrinsic stains: Intrinsic stains are caused by excessive intake of fluoride, certain drugs like tetracycline or due to dental pulp necrosis or developmental abnormalities. With time and age, the teeth accumulate more stains and tartar, causing them to look dull and discolored. In addition, as people grow older, the enamel that protects the teeth gets eroded, revealing the underlying deeper yellow color of dentin.