Developing tooth. Light micrograph of a vertical section through a developing tooth. At bottom is the pulp (white). Successive layers overlying this are the odontoblasts (also white, just below the red layer), the dentine (red), the enamel (white and brown, upper centre), and the ameloblasts (green). The odontoblasts are cells that secrete dentine. The ameloblasts are cells that secrete the minerals that harden to form enamel. Enamel forms the strong outer surface of a tooth, and dentine the inner layer. The pulp is the sensitive inner core of a tooth, which includes nerve endings. As teeth develop, they erupt through the gums and continue to grow until they are the required size. Magnification: x330 when printed 10 centimetres wide.