Formation of plaque on teeth, illustration. Plaque is a bacterial biofilm that can form on teeth and can cause tooth decay. It can develop into tartar, a mineralised and hardened form of dental plaque. If not treated, the condition can lead to gingivitis, peridontitis and tooth loss. This sequence runs from left to right. At left, bacteria on the teeth metabolise sugar and oxygen (red), producing carbon dioxide (CO2) and the bacterial enzyme glucosyltransferase (GTF, blue). At centre, GTF binds the sugar and bacteria in layers on the tooth surface. At right, the bacteria on the surface metabolise by aerobic combustion, but the bacteria trapped below the surface without oxygen metabolise by anaerobic combustion. This produces lactic acid (green) that erodes the enamel, leading to tooth decay. An example of a bacterium that metabolises sugar in the mouth in this way is Streptococcus mutans. For this illustration without labels, see image C047/7640.