oral histo week 2

• The union of ectodermal cells and endodermal cells at the bottom of the stomodeum or primitive oral cavity ruptures at the 4th to 5th week of fetal life, thus establishing a connection with the foregut.
• In the oral ectoderm, basal cells begin to proliferate leading to the formation of a band of epithelium (dental lamina) that lines along the outline of the future dental arches.
• Dental lamina and tooth bud are the site of tooth formations.
• Proliferation results in the increase in size of the tooth germ.
• Formative cells of the tooth germs develop into Ameloblasts (enamel) and Odontoblasts (dentin).
• Morphodifferentiation establishes the form and size of the future tooth.
• Apposition is the additive growth as a result of deposition of matrix.
• Dental lamina contains the developing tooth germs/tooth buds.
• Three parts of a tooth germ are enamel organ, dental papilla, and dental follicle.
• As cell proliferation occurs within the tooth germ, the enamel organ increases in size and changes in shape.
• Initiation occurs at the 6th week when there is an interaction between embryonic tissues.
• Bud stage occurs at the 8th week when there are round or ovoid swellings of cells within the dental lamina.
• Cap stage occurs at the 9th to 10th week when there is the formation of a tooth germ and tooth buds continue to proliferate with unequal growth in the different parts of the tooth germ.
• Shallow invagination of the deep surface of the bud occurs during the cap stage.
• Proliferation, Differentiation, Morphogenesis occur during the cap stage.
• Abnormalities during the cap stage can include dens in dente, gemination, fusion, tubercle, and distinct cell layers in the tooth germ.
• Enamel organ is ectodermal in origin and will give rise to the enamel.
• Outer enamel epithelium is a peripheral cell of the enamel organ and lines the convexity of the cap.
• Inner enamel epithelium is a cell in the concavity of the cap and is tall columnar.
• Dental Papilla: Outer cells that are close to enamel organ differentiate into odontoblasts which are initially cuboid cells that later become columnar cells - central cells are primordium of pulp.
• Dental Sac: Circular arrangement of fibers and resemble a capsular structure.
• HERTWIG’S EPITHELIAL ROOT SHEATH: Inner and outer enamel epithelium forms the cervical loop or epithelial diaphragm - diaphragm elongates and becomes the HERS - dictates the shape, length, and number of roots of a tooth.
• Stratum intermedium: Layers of squamous cells between inner enamel epithelium and stellate reticulum.
• MATURATION: Mineralization of calcified tissues - abnormalities: fluorosis, enamel hypocalcification, mottled enamel.
• Outer enamel epithelium: Cells flatten to a low cuboidal form.
• Inner enamel epithelium: Cells elongate and differentiate into ameloblasts.
• Dental Papilla: Ectomesenchymal cells which will form the dentin and pulp.
• Stellate reticulum: Cells in the center of enamel organ between inner and outer enamel epithelium, star-shaped cells separated by abundant intercellular fluid.
• Enamel organ: Organ involved in enamel formation.
• BELL STAGE: 11th to 12th week - Enamel organ continues to invaginate and its margin continues to grow and assume a bell shape - Proliferation, Differentiation, Morphogenesis - differentiation of enamel organ into bell with four cell types and dental papilla into two cell types.
• Dental follicle/dental sac: Ectomesenchymal cells that will form the cementum, periodontal ligament, and alveolar bone.
• APPOSITION: Enamel, dentin, and cementum are secreted in successive layers - Induction, Proliferation, root development - abnormalities: enamel pearls, enamel hypoplasia, concrescence, dilaceration, accessory roots.