Tooth dentine. Coloured scanning electron micrograph (SEM) of dentine from a milk tooth. The bulk of a tooth is formed of dentine, a mineralised connective tissue with a similar composition to bone. Within the dentine are channels, called tubules (yellow), that contain odontoblasts, cells that produce new dentine. The arrangement of the tubules is less regular in milk teeth, or deciduous teeth, than it is in permanent teeth.