Tooth dentine-pulp boundary. Coloured scanning electron micrograph (SEM) of the boundary between the grey dentine at left (substantia eburnea) and the red pulp at right. Dentine is mineralised connective tissue found under a tooth's enamel and pulp is soft tissue, containing nerves and blood vessels, that makes up the inner part of the tooth. The yellow layer (centre) is new and partially formed dentine. Also seen are the dentinal tubules (dental canaliculi), minute holes which have been formed by the cytoplasmic extensions of odontoblast cells (red tubes). The odontoblast cells, dentine-producing cells, originate in the pulp and allow the dentine to rebuild itself, unlike enamel. Magnification: x550 when printed 10 centimetres wide.