Used toothbrush bristle. Coloured scanning electron micrograph (SEM) of a bristle from a used toothbrush. It is covered in dental plaque and epithelial cells. Plaque consists of a film of bacteria embedded in a glycoprotein matrix. The matrix is formed from bacterial secretions and saliva. Plaque is the main cause of tooth decay. The bacteria feed on sugars in food, producing acid as a waste product. This acid corrodes the teeth's enamel coating, resulting in dental caries. A build-up of dental plaque can also lead to inflamed and infected gums. Severe gum disease can lead to teeth falling out. Magnification: x1000 when printed at 10 centimetres high.