Human tooth with accumulation of bacterial plaque (smooth areas) and calcified tartar (rough areas) on enamel surface, coloured scanning electron micrograph (SEM). Plaque is the sticky, colourless film of bacteria that forms on teeth. You can sense this film due to your tongue feeling a silky surface on your teeth. It is noticeable when teeth are not brushed. Plaque develops when foods containing carbohydrates (sugars and starches), such as milk, soft drinks or candy are frequently left on the teeth. Bacteria that live in the mouth survive on these foods, producing acids as a result. Over time, these acids destroy tooth enamel, resulting in tooth decay. Plaque can also develop on the tooth roots under the gum and cause breakdown of the bone supporting the tooth. Tartar, or calculus, is plaque that has hardened on your teeth. Tartar can also form at and underneath the gum line and can irritate gum tissues. Magnification: x415 when shortest axis