Tooth decay. Polarised light micrograph (PLM) of a longitudinal section through a molar tooth with dental caries, or tooth decay. The tooth consists of enamel (orange) covering the dentine (blue) and the pulp (at bottom centre) with its nerve fibres and blood vessels. Tooth decay (red & black, at centre) is caused by the build-up of plaque, which consists largely of food remains and bacteria. The bacteria feed on the food particles, producing acids as they break them down. If untreated the acid will destroy the enamel and dentine, exposing the pulp and causing intense pain. Eventually the tooth will die. Magnification: x15 at 4.5x6.5cm size.