Each tooth passes through 4 morphological stages: initiation, bud, cap, bell.
The initiation of tooth development begins at 37 days of development with formation of a continuous horseshoe-band of thickened epithelium in the location of upper and lower jaws – Primary Epithelial Band Each band of epithelium will give rise to 2 sub divisions:
1. Dental lamina
2. Vestibular lamina
Bud Stage This stage occurs between the 7th and 9th weeks of human gestation. It is represented by the first epithelial invagination into the oral ectomesenchyme. The internal part of the tooth bud contains star-like shaped, glycosaminoglycan synthesizing stellate reticulum cells.
Condensation of the ectomesenchyme immediately subjacent to the tooth bud caused by lack of extracellular matrix secretion by the cells thus preventing separation. Histodifferentiation begins at the end of cap stage. Epithelial outgrowth called Enamel Organ because it will eventually form the enamel.
Some structure could be seen at this stage:
Dental Papilla: Ball of condensed ectomesenchymal cells (it will form dentin and pulp). The peripheral cells adjacent to the inner dental epithelium will enlarge and later differentiate into odontoblasts.
Lateral Lamina: extension from the dental lamina that is connected to the enamel organ
Enamel Knot: Densely packed accumulation of cells projecting from the inner enamel epithelium into dental papilla. Exact role not known, but currently believed to be the organizational center for cusp development.
Terminal differentiation of ameloblastsand odontoblasts from mesenchymal cells of dental papilla, and the formation of two principal hard tissues of the tooth, enamel, and dentin, are initiated during the bell stage. Ameloblast and odontoblast differentiation is regulated by interactions between the epithelium and mesenchyme .
While dental papilla is the origin of the future dental pulp, dental follicles give rise to cementoblasts, osteoblasts, and fibroblasts.
Future crown patterning also occurs in the bell stage, by folding of the inner dental epithelium. Cessation of mitotic activity within the inner dental epithelium determines the shape of a tooth.