Tooth Development 1 Flashcards
What are the 3 developmental phases?
1) Initiation
2) Morphogenesis
3) Histogenesis
What occurs during Tooth development Initiation?
- Locations of the teeth are established with the appearance of tooth germs
- Tooth germs appear along the dental lamina (invagination of the oral mucosa)
What occurs during Tooth development Morphogenesis?
- This stage determines the shape of the teeth
- Cell proliferation and movement determine the shapes of teeth
What occurs during Tooth development Histogenesis?
- Differentiation of cells takes place to produce the fully formed dental tissues
- Histogenesis begins during morphogenesis as all the phases are overlapping
What happens in the primitive oral cavity at the start of tooth development?
- Mesenchymal condensation occurs underneath the dental epithelium
- Has a Ectomesenchymal origin which came from the neural tube
What happens 6 weeks in utero?
- Thickening of the oral epithelium
- Followed by invagination of the epithelium into the underlying mesenchyme to form the PRIMARY EPITHELIAL BAND
What happens 7 weeks in utero?
- The PRIMARY EPITHELIAL BAND DIVIDES INTO:
+ Vestibular lamina (buccally)
+ Dental lamina (lingually)
7 weeks in utero: What does the Vestibular lamina contribute to?
- Development of the vestibule
- Delineates the lips and cheeks form the tooth bearing regions
- The degeneration of the central epithelial cells produces the sulcus
7 weeks in utero: What does the Dental lamina contribute to?
- Formation of the teeth
8 weeks in utero: What happens along the Dental lamina?
- A swelling (tooth bud) develops on the deep surface of the Dental lamina
- The Tooth buds are surrounded by a mesenchymal condensation
Tooth Germ Formation (odontogenesis): What are the different stages of development?
- Bud
- Cap
- Early Bell
- Late Bell
Odontogenesis: What happens during the Bud stage)
- Enamel organ appears as a simple ovoid epithelial mass/Epithelial invagination
- Surrounded by the Ectomesencymal condensation
Enamel organ and the Ecotomesencymal condensation are separated by a basement membrane
Odontogenesis: What happens during the Cap stage (11 weeks in utero)?
- Invagination progression
- Peripheral cells start to arrange and differentiate into EXTERNAL and INTERNAL ENAMEL EPITHELIUM
Odontogenesis: What happens during the Cap stage (12 weeks in utero)?
- Central cells within the enamel organ become separated = STELLATE RETICULUM
- EXTERNAL ENAMEL EPITHELIUM becomes CUBOIDAL
- INTERNAL ENAMEL EPITHELIUM becomes COLUMNAR
- Surrounding Ectomesencymal cells proliferation into the :
+ Dental Papilla
+ Dental Follicle
Odontogenesis: What happens during the Early Bell stage (14 weeks in utero)?
- INTERNAL ENAMEL EPITHELIUM alters shape and this determines crown shape
- The Dental lamina breaks down
- Dental Follicle undergoes differentiation:
+ Inner vascular fibrocellular condensation
+ Loose CT layer
+ Outer vascular layer lining the alveolus
Odontogenesis: What happens during the Early Bud stage (14 weeks in utero)?
4 distinct layers of enamel organ are present:
- External Enamel epithelium
- Stellate reticulum
- Stratum intermedium
- Internal Enamel epithelium
What’s the External Enamel Epithelium?
- Outer enamel epithelium which forms the outer later of cells in the enamel organ
- Cuboidal in shape
- Separated from the Dental Follice via a basement membrane
- Possess large central nuclei and relatively little amounts of organelles for protein synthesis
What’s the Cervical Loop?
- The growing margin of the enamel organ
- Lies at the junction between the inner and outer enamel epithelium
What’s the Stellate Reticulum?
- Fills the space between the Inner and Outer dental epithelium
- Star shaped cells with branching processes
- Extracellular material secretion - Alkaline Phosphatase (important)
- Protects the underlying tissues and maintains the tooth shape
Effect on crown outline
What’s the Stratum Intermedium?
- 2-3 layers of flat cells
- Lies over the Internal Enamel Epithelium
- Resembles stellate cells but with smaller spaces
What’s the Internal Enamel Epithelium?
- Columnar cells
- Rich in RNA but contain no Alkaline Phsphatase
- Separated from the dental papilla by a basement membrane and a cell free zone
What happens during the Late Bell Stage?
- Lingual downgrowths of the external enamel epithelium give rise to the permanent anterior teeth buds (5 months utero)
- Dental lamina grows posteriorly to give rise to the tooth buds of the permanent posterior teeth (4 months utero)
What happens during the Late Bell stage (2)?
- Also known as the Appositional stage: formation of the dental hard tissues
- Dentine always precedes enamel!!!
- Hard tissue formation starts at the cusp tips
What do the Internal enamel epithelial cells differentiate into?
- Pre-ameloblasts
- Pre-ameloblasts induce adjacent mesenchymal cells to differentiate into Odontoblasts
- Odontoblasts produce pre-dentine and dentine
- Dentine induces Ameloblasts to form enamel
What are the Transitory structures in Odontogenesis?
- Enamel Knot
- Enamel Cord
- Enamel Niche
What’s an Enamel Knot?
- Localised mass of cells in the centre of the internal enamel epithelium
- Non proliferative cells
- Outline of the future fissures
- Signalling centre*
- Potentially an inducer of odontoblast differentiation
What’s the Enamel Cord?
- Strands of cells extending from the Stratum Intermedium into the Stellate Reticulum
Enamel Septum:
+ Enamel cord that completely splits the stellate reticulum
Enamel Navel:
+ The invagination where the enamel cord meets the external enamel epithelium
- Focus for Stellate cell formation
