Tooth decay occurs when bacteria in dental plaque damages the enamel of your teeth, leaving a hole or cavity. Any part of a tooth can decay, from the roots below the gum line to the chewing surface. If plaque bacteria reach and damage the pulp, the tooth will likely die, because the pulp contains nerves and blood vessels that supply the tooth. Tooth decay can occur due to a number of issues, including poor brushing and flossing habits, diets rich in sugar, the presence of risk factors such as smoking and lack of fluoride in the water supply.