OB D2- Tooth development 1 Flashcards
what is histogenesis?
differentiation of undifferentiated cells to make new tissues
what are mineralised dental tissues?
enamel, dentine and cementum
what are unmineralised dental tissues?
dental pulp and periodontium
what does the dental lamina contribute to?
the development of teeth
what does the vestibular lamina contribute to?
the vestibule of the mouth, delineating the lips and
cheek from the teeth formation of sulcus
what is the initation stage?
first stage of tooth development
what is the bud stage?
second stage simple, spherical to ovoid, epithelial condensation poorly morphodifferentiated and histodifferentiated
what is the cap stage ?
third stage of tooth development, in which the tooth
germ grows into cap shape
what is the bell stage?
Fourth stage, in which differentiation occurs to furthest extent and starts to resemble a bell
what is the crown stage?
Some text books count as a stage-some call it late bell stage-this is with fully developed tooth
what is the external enamel epithelium?
outer layer of cuboidal cells that limits the enamel organ.
what is the stellate reticulum?
of epithelial origin but behave like mesenchymal cells-synthesis of Collagen I, II and III
what is stratum intermedium?
two or three layers of cells sitting above IEE. Express Alkaline Phosphatase like SR but not IEE
what is the inner enamel epithelium?
Columnar shaped cells rich in RNA. Connected by desmosomes to each other
what is the ectomesenchyme?
interesting group of cells whose origin is very controversial. Some think neural crest others mesodermal somites
what occurs at 6 weeks?
condensation of ectomesenchyme
Describe the formation of the sulcus.
-Primary epithelial band gives rise to:
◦ Dental Lamina
◦ Vestibular lamina
Vestibular lamina grows then and then breaks down to forms vestibule between teeth and lips/cheeks
what are the 3 overlapping phases of tooth development?
- initiation
- morphogenesis
- histogenesis
what is tooth development an interaction between?
epithelium and mesenchyme (ectomesenchyme)
what does epithelium give rise to?
- enamel
- hyaline layer of the root
what does mesenchyme give rise to?
- dentine
- pulp
- cementum
- periodontium (PDL and bone)
when does initation of tooth development start?
6 weeks i.u
what happens in initiation?
Localised epithelial thickening in incisor and molar regions
which tissue initiates tooth development?
◦ Epithelium, ectomesenchyme or nerve?
◦ Evidence from tissue recombination experiments…..
◦ Epithelium initially has the odontogenic potential, then the ectomesenchyme
In what circumstances will a tooth grow?
Dental epithelium + non-dental ecto-mesenchyme
In what circumstance will a tooth not grow?
- dental epithelium + non-dental mesenchyme
- non-dental epithelium + dental ectoderm-mesenchyme
what are the stages of the tooth germ?
- bud stage
- cap stage
- bell stage
- crown stage
what happens to the dental lamina during stages of the tooth germ?
- continues to lengthen
- changes shape
what happens to the ectomesenchymal during stages of the tooth germ?
condensation
what is classification of the stages based on?
appearance
what are the components of tooth germ?
- enamel organ
- dental papilla
- dental follicle
what happens in the bud stage (8th week)?
- Spherical/ovoid epithelial condensation
- Cell proliferation
- No histodifferentiation or morphogenesis
what happens in the cap stage (11th week)?
- Cap shaped enamel organ - Poorly histodifferentiated
- Little morphogenesis
what happens in the early bell stage (14th week)?
Morpho- and histo-differentiation Enamel Organ: ◦ Inner enamel epithelium ◦ Stratum Intermedium ◦ Stellate reticulum ◦ Outer enamel epithelium Ectomesenchyme: ◦ Dental Papilla ◦ forms odontoblasts (dentine) and pulp ◦ Dental Follicle ◦ forms cementum, PDL and bone
what is inner enamel epithelium (enamel organ component)?
◦ Basal lamina conforms to future ADJ ◦ Columnar cells at cusp tips
◦ Role: forms ameloblasts -> enamel
what is stratum intermedium (enamel organ component)?
◦ Flattened cells
◦ Role: Synthesis and transport to and from IEE
what is stellate reticulum (enamel organ component)?
◦ Star shaped
◦ Fluid filled extracellular space
◦ Osmotic gradient due to extracellular GAGs.
◦ Role: maintenance of shape and protection
what is outer enamel epithelium (enamel organ component)?
◦ Cuboidal cells
◦ Role: maintenance of shape and exchange
what happens at bell stage (week 17)?
-Breakdown of dental lamina -> formation of cell rests, cell nest (cystic potential )
What is the Extracellular matrix and what happens in development?
- Important in morphogenesis and differentiation.
- Adhesion, migration, proliferation, polarisation and differentiation.
- Expression of type I, III, IV collagens, laminin, various proteoglycans- basement membrane of developing tooth
- Changes in fibronectin, tenascin, type I and type III collagen and syndecan.
- Changes in integrin expression especially alpha v beta 5.
- Need intact basement membrane for differentiation of mesenchyme to odontoblast.
