Oral Histology Lec 4 PDF

# Oral Histology Lec 4 ## Tooth Development (ODONTOGENESIS) - The complex process by which teeth form from embryonic cells, grow, and erupt into the oral cavity. - In the human 20 primary and 32 permanent teeth develop from the interaction of the oral epithelial cells derived from the first arch an...

# Oral Histology Lec 4 ## Tooth Development (ODONTOGENESIS) - The complex process by which teeth form from embryonic cells, grow, and erupt into the oral cavity. - In the human 20 primary and 32 permanent teeth develop from the interaction of the oral epithelial cells derived from the first arch and the underlying ectomesenchymal cells derived from neural crest cell. ### ODONTOGENESIS (TEETH DEVELOPMENT) | Time Period | Teeth | |---|---| | Weeks 6-7 In-Utero | Deciduous Teeth (Milk or Baby) | | Week 14 | Birth| | ~ 6 years | Permanent Teeth| - At the 6th week of gestation period, certain areas of basal cells of the oral ectoderm proliferate more rapidly. This leads to the formation of the **primary epithelial band**. - At about the 7th week the primary epithelial band quickly give rise to 2 subdivisions: - **Lingual process** called **dental lamina**. - **Buccal process** called **vestibular lamina**. #### Key Definitions - **A-oral epithelium** - **B-primary epithelial band** - **A-primary epithelial band** - **B-dental lamina** - **C-vestibular lamina** #### Dental Lamina - Lingual (inner) process of the primary epithelial band, is a band of epithelium that has invaded the underlying ectomesenchyme. #### Function of Dental Lamina - The dental laminae serve as the primordium for the ectodermal portion of the deciduous teeth. - Later, during the development of the jaws, the permanent molars arise directly from a distal extension of the dental lamina. #### Vestibular Lamina - Buccal (outer) process of the primary epithelial band. - Cells rapidly enlarge to become the vestibule between the lips and cheek & the tooth-bearing area. ## Stages of Tooth Development 1. **Bud Stage:** The epithelium of the dental laminae is separated from the underlying ectomesenchyme by a basement membrane. Round or ovoid swellings arise from the basement membrane at 10 different points, corresponding to the future positions of the deciduous teeth. These are the primordia of the enamel organs, the tooth buds. 2. **Cap Stage:** As the tooth bud continues to proliferate, it does not expand uniformly into a larger sphere. Instead, unequal growth in different parts of the tooth bud leads to the cap stage. The peripheral cells of the cap stage are cuboidal, cover the convexity of the ‘cap’, and are called the **outer enamel epithelium**. The cells in the concavity of the ‘cap’ become tall, columnar cells and represent the **inner enamel epithelium**. 3. **Bell Stage:** As the invagination of the epithelium deepens and its margins continue to grow, the enamel organ assumes a bell shape. In the bell stage, crown shape is determined. * Four different types of epithelial cells can be distinguished on light microscopic examination of the bell stage of the enamel organ. 1. Inner enamel epithelium. 2. Outer enamel epithelium. 3. Stratum intermedium. 4. Stellate reticulum. ## Further Details of Each Stage **Bud Stage:** - The enamel organ consists of peripherally located low columnar cells and centrally located polygonal cells. - Many cells of the tooth bud and the surrounding mesenchyme undergo mitosis. - As a result of the increased mitotic activity and the migration of neural crest cells into the area the ectomesenchymal cells surrounding the tooth bud condense. - The area of ectomesenchymal condensation immediately subjacent to the enamel organ is the **dental papilla.** - The condensed ectomesenchyme that surrounds the tooth bud and the dental papilla is the **dental sac.** **Cap Stage:** - **Stellate reticulum** Polygonal cells located in the center of the epithelial enamel organ, between the outer and inner enamel epithelia, acts as a shock absorber that may support and protect the delicate enamel-forming cells. **Bell Stage:** - **Dental papilla:** The dental papilla is enclosed in the invaginated portion of the enamel organ. Before the inner enamel epithelium begins to produce enamel, the peripheral cells of the mesenchymal dental papilla differentiate into odontoblasts under the organizing influence of the epithelium. - First, they assume a cuboidal form; later they assume a columnar form and acquire the specific potential to produce dentin - The dental papilla ultimately gives rise to **dental pulp**. - **Dental sac:** Before formation of dental tissues begins, the dental sac shows a circular arrangement of its fibers and resembles a capsular structure. With the development of the root, the fibers of the dental sac differentiate into the **periodontal fibers** that become embedded in the developing **cementum** and **alveolar bone**. ## Diagram Descriptions - **Page 4:** This page showcases the development stages of a tooth bud. - **A:** The tooth bud and dental lamina, which eventually develops into enamel and dentin. - **B:** The enamel organ, a crucial structure for tooth development. - **C:** The primordium of the tooth bud, a nascent structure for the development of the first permanent tooth. - **Page 7:** This image further depicts the intricacies of the bell stage. - The **outer enamel epithelium** is highlighted. It is responsible for initiating enamel formation. - **Ameloblasts**, the specialized cells that create enamel, are also illustrated. - **Odontoblasts**, the cells that manufacture dentin, are showcased. - **Page 8:** This image provides a detailed view of the tooth components in the bell stage. - **Dental papilla** and the surrounding enamel organ are shown. - **Dental sac** is visible, which plays a crucial role in tooth development. - **Page 9:** This image shows the primordium of a permanent tooth, which has a similar structure to the development of the tooth bud in the bud stage. - **Dental lamina** forms two branches: - **Lateral dental lamina**, involved in permanent tooth development. - **Enamel cord**, which signifies the initiation of enamel formation.