Dentine. Light micrograph of a section through dentine (or dentin) from 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 - dark lines) 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. Magnification: x240 when printed at 10cm wide.