Teeth will gradually discolor depending on your habits, such as a smoker and the foods and drinks you consume. When the enamel erodes, it can create a yellow appearance. Poor dental hygiene, such as not brushing regularly or flossing, can also cause a build-up of plaque, contributing to discoloration. A great-looking smile is a white one, but you also need to pay attention to cavities and gum infections, which can still be present despite brightening your teeth.