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When do primary tooth buds appear?
8 week embryo
What are the stages of tooth dev?
- crown formation
- root formation and eruption
- root completion
What happens in the initial step of tooth dev?
oral epithelium (ectoderm) thickens in future mandible/maxillary arches (mesenchyme)
Where is echtomesenchyme derived from?
migration of neural crest cells(ectoderm) migrating into mesenchyme (embryonic CT)
What happens during the bud stage and what problems could arise?
- dental lamina proliferates into ectomesenchyme (10 buds(primary) each arch)
- supernumerary, missing
Which layer determines bud fate?
mesenchyme (self-signaling, gradient?) NOT epithelium
What is the role of the basement membrane or basal lamina?
- interface between epitheliual and mesenchymal tissues (laid by both sides)
- MEDIATOR of molecular signaling that controls differentiation
- becomes DEJ
What happens during cap stage?
enamel organ cap from ectoderm surrounds (ectomesenchyme) dental sac and papilla inside developing bone
What happens during bell stage?
- enamel organ forms 4 layers (OEE, IEE, stellate reticulum, stratum intermedium)
- IEE->preameloblasts (cuboidal to columnar)
- dental papilla outer cells->odontoblasts (secrete predentin which causes further differentiation of preameloblasts to ameloblasts)
- dental lamina disintegrates
Which organelles are numerous in ameloblasts and odontoblasts?
- RER, Golgi, mitochondria
- nuclei opposite from secreting side
- tomes process-ameloblasts
- odontoblastic process-odontoblasts
What are the protein matrices named?
- predentin(extracellularly min by Ca2+ and PO4- from matrix vacuoles)
- amelogenin & enamelin (Extracellulary mineralized by HA)
When does tetracycline staining occur?
Which dentin/enamel is the oldest?
oldest cusp tips of DEJ
What happens during crown formation?
enamel organ collapse as enamel & dentin formation proceed to cusp tip the future CEJ
How is the root initially formed?
- late bell stage
- OEE+IEE => Hertwig's Epithelial Root Sheath (ectoderm)
- guides shape and number or roots.
When does enamel pearl form?
What are epithelial rests of Malassez?
- remnants of Hertwig's Root sheath in PDL
- allow pre-cementoblasts(ectomesenchyme) to lay down cementum
- sometimes become cystic (periapical inflammation)
What are the variations of CEJ?
- 60% overlapping
- 30% edge-to-edge
- 10% exposed dentin (leads to hypersensitivity)
When do multiple roots form?
- root sheath stage
- outer cells divide faster
What happens during cementogenesis?
- HRS breakup allows dental sac to contact root dentin and differentiate to cementoblasts
- cementoid matrix mineralized to cementum
What is the reduced enamel epithelium?
- remnants of enamel organ
- secretes enzymes for eruption
- fuses with oral epithelium to form initial junctional epithelium
- analogous to HRS.
What are the 2 main stages of tooth formation?
- 1. Morphogenesis: prolif & migration
- 2. Cytodifferentiation (bell, crown on)
Explain the relationship of dental papilla and IDE or IEE?
IEE trigger dental papillae to become odondtoblasts which through predent cause IEE to become ameloblasts
What are some factors important for tooth dev?
- TGF-beta(binds receptor) & BMP - high in lamina stage-> thickening of oral epi
- Smads (signal cascade, translocates to nucleus) determin size & shape
- CBFa (gene expression) downstream of smad (req for tooth dev)