Dental decay. Animation showing dental caries (tooth decay). Dental caries is the decay and crumbling of the teeth. It is caused by the bacteria (rod-shaped) in plaque (yellow), a substance which covers the surface of unclean teeth. The bacteria break down sugar in the mouth, producing an acid which progressively destroys the teeth and eventually causes cavities (black). Also shown is gingivitis (red), or inflammation of the gums. This condition is also caused by dental plaque.HD master is flattened onto a black background, as seen in this preview. The original file has a transparent alpha channel and is available as the HD master of clip K003 3746.