Tooth dentine. Coloured scanning electron micrograph (SEM) of a section through a human tooth showing dentine, the hard tissue that forms the bulk of a tooth. The visible part of a tooth (the crown) consists of enamel-covered dentine. Running through the dentine are fine tubules. Near the centre of the tooth they contain material from the core pulp tissue. Exposed dentine is sensitive to heat, cold and touch. Magnification unknown.