Tooth decay. Coloured scanning electron micrograph (SEM) of plaque bacteria (brown) in a cavity in a decaying tooth. Plaque is a sticky substance made of food remains and the bacteria that naturally occur in the mouth. Bacteria feed on the sugars in the food particles and produce acid as a waste product. This acid corrodes the enamel coating of each tooth. Eventually a hole (known as a cavity) is produced which exposes the pain receptors in the tooth's sensitive interior. Cavities are prevented by brushing and treated by fillings. Magnification: x1200 at 4x4 inch size.