Lecture 10- Periodontium (Part 4) PDF

The Periodontium (Part 4) Periodontal tissue and root development By the end of this lecture, you should be able to: Summarise the developmental origins of the periodontal tissues Identify the epithelial and mesenchymal tissues involved in root development Describe key events during root development...

The Periodontium (Part 4) Periodontal tissue and root development By the end of this lecture, you should be able to: Summarise the developmental origins of the periodontal tissues Identify the epithelial and mesenchymal tissues involved in root development Describe key events during root development that lead to the formation of the periodontal tissues The development of the dental tissues Periodontal tissue and tooth root development involve the following cell layers and types. By the end of this lecture, you should know where these structures are located at different stages of tooth development, their roles in tooth development, their appearance, etc. Ten Cate’s Oral Histology (8th Edition); Fig. 5-35 Tooth development- a quick reminder Bud stage (~8th week of embryonic development) Cap stage (~9-10th week of embryonic development) Bell stage (~11th week of embryonic development) Periodontal tissue development Bud stage (~8th week of embryonic development) Enamel organ Ectomesenchyme condensation Periodontal tissue development Dental follicle Cap stage (~8th week of embryonic development) Dental papilla (ectomesenchyme) Dental follicle Periodontal tissue development Dental follicle Cementum, PDL, and alveolar bone originate from the dental follicle: a sac-like structure made of ectomesenchymal cells surrounding a developing tooth. The follicle cells give rise to cementoblasts, fibroblasts, osteoblasts, and the other cells needed to make the periodontium. Dental follicle Periodontal tissue development- key events Root formation and elongation begins with the formation of the cervical loop: Extension of the inner and outer enamel epithelia and the stellate reticulum. Elongates during crown formation, but will stick around as another structure during root formation… Cervical loop Dental follicle Periodontal tissue development- key events Root formation and elongation begins with the formation of the cervical loop: Extension of the inner and outer enamel epithelia and the stellate reticulum. Elongates during crown formation, but will stick around as another structure during root formation… Dental follicle Cervical loop Periodontal tissue development- key events Once crown formation is complete, the cervical loop collapses into a twolayered epithelial structure, called Hertwig’s Epithelial Root Sheath (HERS): Pulp Dental follicle Extension of the inner and outer enamel epithelia that forms the tooth root. Elongates and induces dentine formation on the pulp-side, but initially inhibits cementum formation on the follicle side. Ten Cate’s Oral Histology (8th Edition); Fig. 5-28 HERS Periodontal tissue development- key events Dentine HERS then breaks up into a network of epithelial cells à the epithelial rests of Malassez HERS Begins to Break down Pulp This breakup of HERS allows the follicle cells to reach the dentine surface of the developing tooth root, initiating cementum formation. HERS Ten Cate’s Oral Histology (8th Edition); Fig. 5-28 Periodontal tissue development- key events The breakup of HERS allows the surrounding dental follicle cells to reach the root surface. This allows them to differentiate into cementum-producing cells (cementoblasts). Or these leftovers of HERS become the first cementoblasts? Ten Cate’s Oral Histology (8th Edition); Fig. 9-3; 9-27 Periodontal tissue development- key events Several features of periodontal tissue developmental are still unknown, but it is likely that: Dental follicle cells also differentiate into fibroblasts (PDL development). Dental follicle cells also differentiate into osteoblasts (alveolar bone). Ten Cate’s Oral Histology (8th Edition); Fig. 9-1 Dental follicle HERS Periodontal tissue development- key events Rests of Malassez Following HERS breakup: Cementoblasts begin forming cementum along the root dentine. This also traps collagen fiber bundles from the developing PDL, forming Sharpey’s fibers. PDL fiber bundles Cementum Ten Cate’s Oral Histology (8th Edition); Fig. 9-1 By the end of this lecture, you should be able to: Summarise the developmental origins of the periodontal tissues Identify the epithelial and mesenchymal tissues involved in root development Describe key events during root development that lead to the formation of the periodontal tissues