The papilla occurs mainly during tooth development and plays an important role in determining the shape of the teeth. The dental papilla can induce the formation of enamel-forming apparatus from non-odontogenic oral epithelium, with the combination of the papilla of a molar with the enamel-forming apparatus of an incisor can form a molar, and the combination of the papilla of an incisor with the enamel-forming apparatus of a molar will form an incisor. The papilla cells are undifferentiated mesenchymal cells, which are protected and surrounded by the enamel-forming apparatus. Under the induction of epithelial cells the outer cells of the papilla can differentiate into high columnar dentin-forming cells, which constitute the dentin layer that surrounds and protects the pulp cavity.