12. Tooth Development Flashcards
List 3 stages of tooth development
- initiation
- morphogenesis
- histogenesis
Summary of initiation
- determination of tooth position
- appearance of tooth germs
Summary of morphogenesis
- determination of tooth shape
- cell proliferation and movement
Summary of histogenesis
- formation of dental tissues
- cell differentiation and specialisation
What happens in tooth initiation?
- formation of primary epithelial band (6 weeks in utero)
- thickening of oral epithelium
- condensation of mesenchymal cells
- formation of dental and vestibular lamina (7 weeks in utero)
- epithelial cells continue to proliferate and primary epithelial band divides
- into dental lamina (arrowheads) - tooth germs and vestibular lamina (arrows) - vestibule of mouth
- epithelial cells proliferate and central cells subsequently enlarge and degenerate to form sulcus of vestibule
How does formation of primary epithelial band occur?
result of change in orientation of cleavage plane of dividing cells
What happens in tooth morphogenesis?
- formation of tooth bud (8 weeks in utero)
- elongation of dental lamina
- formation of localised swellings on deep surface (tooth buds)
- condensation of mesenchymal cells surrounding tooth bud
- early cap stage at 11 weeks in utero
- late cap stage at 12 weeks
- early bell stage at 14 weeks
- stratum intermedium
- dental papilla and dental follicle
Explain ‘late cap stage’
- dental epithelium forms cap-shaped structure termed dental organ/enamel organ
- group of non-dividing cells form enamel knot (transient molecular signalling centre)
- change in epithelial shape
- condensed mesenchymal cells underlying enamel organ form dental papilla
- mesenchymal cells surrounding enamel organ form dental follicle
Explain ‘early bell stage’
IN LAYERS
- enamel organ
distinguished by outer enamel epithelium and cuboidal epithelial cells
- stellate reticulum (star-shaped)
- epithelial cells become separated but still in contact with desmosomes - intercellular spaces filled with hydrophilic glycosaminoglycans and collagens I,II and III
- inner enamel epithelium (columnar epithelial cell)
- mesenchymal cells on dental papilla and dental follicle continue proliferating
Columnar epithelial cells in early bell stage elongate to form …
(pre)ameloblasts
What is stratum intermedium? Role
- 2-3 layers of flat epithelial cells
- form between inner enamel epithelium and stellate reticulum
- produces alkaline phosphatase - mineralisation of enamel matrix
- protein synthesis, transport of substances to and from inner enamel epithelium (ameloblasts) - ameloblast supporting function
Role of dental papilla
- generate fibroblasts, mesenchymal stem cells of pulp and odontoblasts (dentine producing cells)
Role of dental follicle
- inner layer is condensed, vascular area contacting outer enamel epithelium
- outer layer is loose, vascular area contacting developing alveolar bone
- to support enamel organ with nutrients and generate tooth supporting tissue (periodontal ligament, cementoblasts and osteoblasts of alveolar bone)
What happens in tooth histogenesis?
- late bell stage (18 weeks in utero)
- reciprocal tissue interactions in crown formation
- crown completion
- successional permanent tooth formation
What happens in late bell phase?
- tooth has acquired future shape
- odontoblasts secrete dentine matrix (predentine)
- ameloblasts secrete enamel matrix (preenamel)
- stellate reticulum moves downwards to protect cellular area of developing tooth
- cervical loop is growing end of enamel organ for cell interactions and determination
- located with internal enamel epithelium and outer meet
- breakdown of dental lamina - enamel organ loses contact with oral epithelium
