Tooth plaque. Coloured Scanning Electron Micrograph (SEM) of plaque on the surface of a tooth. Plaque, the main cause of tooth decay, is seen here as a yellow coating over the grey enamel of the tooth. Plaque is a sticky substance made of food remains and the bacteria that naturally occur in the mouth (such a Streptococci). 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: x4200 at 6x6cm size.