Dentin tooth tissue. Coloured scanning electron micrograph (SEM) of dentin tooth tissue. Dentin is mineralised connective tissue that makes up the majority of a tooth. The holes in the dentin are dental tubules (or canaliculi) formed by the cytoplasmic extensions (green) of odontoblast cells (dentin-producing cells). Magnification: x425 when printed at 10 centimetres wide.