Dental decay is a disease that can damage your tooth's structure. Decay starts by damaging your tooth's protective coating, also known as enamel, causing a hole (cavity) to develop in your tooth. If the cavity is left untreated, it can get bigger and besides causing pain can lead to the loss of a tooth.
Everyday you have a thin sticky substance forming on your teeth and gums called plaque. A cavity is caused when the bacteria living in the plaque react with sugars from the food or drink that you eat, resulting in an acid. This acid then attacks the surface of your tooth. If the cavity is left untreated, it can get bigger. This causes pain and possible lead to the loss of a tooth.