Tooth dentine. Coloured scanning electron micrograph (SEM) of a vertical fracture through the tooth of a domestic cat (Felis catus). The bulk of a tooth is formed of dentine (green), a mineralised tissue with a similar composition to bone. Within the dentine are channels called dental tubules (brown), containing odontoblasts, cells which produce new dentine. The visible part of a tooth (the crown) consists of enamel- covered dentine. Exposed dentine is sensitive to heat, cold and touch because it contains nerve endings.