Tooth development -2
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Malabar Dental College Malabar Academic City
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Tooth development -2
- 1. DR VINOD KUMAR R.B PROF & HEAD DEPT OF ORAL PATHOLOGY & MICROBIOLOGY MALABAR DENTAL COLLEGE & RESEARCH CENTRE
- 2. 3. Bell Stage (Early) Inner dental epithelium: Short columnar cells bordering the dental papilla. These will eventually become ameloblasts that will form the enamel of the tooth crown by differentiating into tall columnar cells. Outer dental epithelium: Cuboidal cells that cover the enamel organ. Their function is to organize a network of capillaries that will bring nutrition to the ameloblasts. Stellate reticulum Inner dental epithelium Stratum intermedium Dental papilla Outer dental epithelium http://www.usc.edu/hsc/dental/ohisto/
- 3. 3. Bell Stage (Early) Stellate reticulum Inner dental epithelium Stratum intermedium Dental papilla Stellate reticulum: Star-shaped cells with processes, present between the outer and the inner dental epithelium. These cells secrete glycosaminoglycans, which attract water, thereby swelling the cells and pushing them apart. Stratum intermedium: Cell layer between the inner dental epithelium and stellate reticulum which have high alkaline phosphatase activity. They assist inner dental epithelium (ameloblasts) to form enamel. Outer dental epithelium http://www.usc.edu/hsc/dental/ohisto/
- 4. Bell stage-the invagination of the enamel organ deepens and it attains a bell shape and 4 layers can be identified in the enamel organ 1. Tooth shape is identifiable. 2. Further differentiation of enamel organ 1) outer enamel ep. 2) inner enamel ep. 3) stellate reticulum 4) stratum intermedium 3 2 1 4 http://www.iob.uio.no/studier/undervisning/histologi/index.php
- 5. Bell stage 1. Tooth shape is identifiable. 2. Further differentiation of enamel organ 1) outer enamel ep. 2) inner enamel ep. 3) stellate reticulum 4) stratum intermedium 3 2 1 4 http://www.iob.uio.no/studier/undervisning/histologi/index.php
- 6. stratum intermedium inner enamel ep basement membrane dental papilla http://www.iob.uio.no/studier/undervisning/histologi/index.php
- 7. cap stage bell stage appositional stage Inner enamel epithelium undergoes continous differentiation under the influence of dental papilla (ectomesenchyme derived )
- 9. Epithelial and mesenchymal cells interact throughout tooth formationoral epithelium dental lamina mesenchymal cells budCapmineralizationbell 1 signal proliferation 1 epithelium mesenchyme Due to continued induction by IEE ,superficial cells of dental papilla differentiate to form odontoblasts and they secrete the first layer of dentin .This triggers the final transformation of IEE cells into ameloblasts and they secrete enamel.
- 10. Appositional stage is the late/advanced bell stage during which dental hard tissue formation takes place. 1. oral ep. 2. outer enamel ep. 3. stellate reticulum 4. inner enamel ep. 5. dental papilla 6. cervical loop 3 2 1 5 4 6 blood vessels http://www.iob.uio.no/studier/undervisning/histologi/index.php Stage of mineralization Cervical loop is the apical extension of IEE and OEE preparatory to root formation
- 11. 1. dental papilla 2. preameloblasts 3. Preodontoblasts 4. odontoblasts 5. predentin 6. ameloblasts 7. dentin 8. stratum intermedium 9. enamel 3 2 8 5 4 67 9 1 http://www.iob.uio.no/studier/undervisning/histologi/index.php Appositional stage
- 12. Dental lamina activity takes place in 3 phases 1st phase-formation of enamel organs of primary teeth.2nd phase-formation of enamel organs of succedaneous permanent teeth.3rd phase –formation of enamel organs of permanent molar teeth(non succedaneous teeth) Embryonic age 0 1 2 3 4 5 6 7 8 months Primary incisor Permanent incisor bud Cap mineralization of crownbell bud Cap mineralizationbell dental lamina tooth germs of primary teeth tooth germs of permanent teeth
- 16. DECIDOUS PREDECESSOR PERMANENT SUCCEDANEOUS TEETH NON SUCCEDANEOUS TOOTH
- 17. Root Formation Development of root begins after the enamel and dentin formation has reached the future cementoenamel junction Epithelial cells of the inner and outer dental epithelium proliferate from the cervical loop of the enamel organ to form the Hertwig’s epithelial root sheath. The root sheath determines if a tooth has single or multiple roots, is short or long, or is curved ir straight Hertwig’s epithelial root sheath http://www.usc.edu/hsc/dental/ohisto/
- 18. 1. Formation of root dentin by odontoblasts 2. Disintegration of HERS 3. Migration of ectomesenchymal cells from dental sac to the root dentin through the disintegrated HERS 4. Differentiation of ectomesenchymal cells into cementoblasts and fibroblasts 5. Formation of cementum and collagen fibers - cementoblasts : secret cementoid (matrix) and mineralize cementum on root dentin - fibroblasts : synthesis of collagen fibers of periodontal ligament * Sharpey’s fiber : collagen fibers embedded in cementum Formation of roots odontoblasts cementoblasts cementum dentindental sac HERS dental sac cells becoming cementoblasts 4 1 3 2 5
- 19. Primary apical formen Epithelial diaphragm: the proliferating end of the root sheath bends at a near 45-degree angle. The epithelial diaphragm will encircle the apical opening of the dental pulp during root development http://www.usc.edu/hsc/dental/ohisto/ Formation of epithelial diaphragm
- 21. Secondary apical foramen form as a result of two or three tongues of epithelium growing inward toward each other resulting in multirooted teeth Essentials of Oral Histology and Embryology, Ed: James Avery, 2nd edition. 2000 Tongue like extensions arise from epithelial diaphragm and start growing towards the centre.Once they fuse the single opening gets divided into 2 or 3 depending on the number of roots and thereafter root formation proceeds as if in a single tooth 2 rooted tooth 3 rooted tooth
- 22. Hertwig’s epithelial root sheath Inner dental epithelium Outer dental epithelium Stratum intermedium Eventually the root sheath will fragment to form several discrete clusters of epithelial cells known as epithelial cell rests of malassez. These will persist in adults within the periodontal ligament http://www.usc.edu/hsc/dental/ohisto/
- 23. The epithelial rests appear as small clusters of epithelial cells which are located in the periodontal ligament adjacent to the surface of cementum. They are cellular residues of the embryonic structure known as Hertwig's epithelial root sheath. Epithelial Cell Rests of Malassez http://www.usc.edu/hsc/dental/ohisto/
- 24. After completing enamel formation the ameloblasts loose their shape and form and along with the remaining enamel organ cells forms the reduced enamel epithelium Reduced enamel epithelium protects the mature enamel by separating it from the connective tissue till the tooth erupts
- 25. Summary of tooth development Oral epithelium Dental lamina ameloblastsInner enamel ep Stellate reticulum Stratum intermedium Outer enamel ep HERS Ectomesenchyme Dental sac Dental papilla odontoblasts cementoblasts fibroblasts fibroblasts osteoblasts dentin cementum pulp periodontal ligament alveolar bone enamel guide root formation oral epithelium reduced enamel ep junctional ep.
Editor's Notes
- Proliferation and differentiation of epithelial and ectomesenchymal cells continue and form a larger tooth germ with more complicated structures.
- Enamel organ is further differentiated into four distinct layers.
- Stratum intermedium - several layers of cells between the inner enamel epithelium and stellate reticulum may be derived from the retraction of stellate reticulum. show exceptionally high activity of alkaline phosphatase, an enzyme essential for mineralization
- * Note the relative distance from inner enamel epithelium to outer enamel epithelium become shorter as the tooth germ develops. * The absolute size of the tooth germ become bigger as the development continues. The presented examples are scaled to the similar size for better contrast of the morphological changes.
- Epithelial and mesenchymal cells interact each other throughout the tooth formation. 1. Mesenchymal cells underlying oral epithelium induce the proliferation of oral epithelium to form dental lamina.
- At the appositional stage, the mineralization starts at the deepest part of the enamel organ. Note that blood vessel does not exist within the enamel organ but outside outer enamel epithelium. Blood vessels supply oxygen and nutrients required for the mineralization. The oxygen and nutrients diffuse into outer enamel epithelium and stellate reticulum to reach inner enamel epithelium. Therefore, the distance from the blood vessels to inner enamel epithelium has to be short. Vascularization close to the tooth germ can be seen in bell stage as well. It increases greatly during appositional stage.
- Please remember the order of differentiation. Preameloblasts preodontoblasts odontoblasts dentin ameloblasts enamel
- Although permanent teeth begin to erupt at the age of 6, they begin to develop when the primary teeth develop. The tooth germs of permanent teeth are located at the lingual side of primary tooth germs. Some of the permanent teeth are formed next to the primary teeth (succedaneous teeth) but the tooth buds of molars are formed at the dental lamina that has grown distally without predecessors (accessional teeth). The tooth buds of succedaneous teeth roughly start to begin at the bell stage of the primary tooth germ.
- Some cells in dental papilla remain to be undifferentiated within tooth pulp. These cells are pleuripotent stem cells that have a potential to differentiate into variety of cell types even following the completion of tooth formation.