Dentine (or dentin) and pulp cavity. Light micrograph of a section through dentine (left) and pulp cavity (right) of a human tooth. Dentine, or ivory, makes up the greater part of a tooth, both in the crown and in the root. It is composed of a mixture of organic and inorganic substances (largely lime salts), and is interspersed with fine tubes (dentinal tubules - black dots) which run from pulp cavity to the enamel. The tubules allow some permeability, which can increase the sensitivity of the tooth, and the rate of decay, once the protective enamel is compromised. The pulp cavity contains blood vessels and nerves which keep the tooth alive.