Dentine is the tissue that makes up the bulk of a tooth. It forms a thick shell around the central pulp cavity and is capped with enamel. Dentine is a tough tissue, mineralized with calcium phosphate. It is permeated by a network of tunnels, whose entrances you can see here. These carry extensions of the dentine-producing cells as well as blood vessels and nerve endings sensitive to touch and extremes of temperature. The dentine in this scanning electron micrograph image is magnified 2,500 times.