Tooth development Flashcards
What are the 8 stages of tooth development in early intra-uterine life?
1) Primary epithelial band
2) Dental lamina formation
3) Bud stage
4) Cap stage
5) Early bell stage
6) Late bell stage
7) Root sheath and root formation
8) Root formation and formation of periodontal ligament and alveolar bone
At the beginning of week 6 what is the primitive mouth lined by?
Ectoderm
How does the primary epithelial band form?
Thickening of the embryo’s oral epithelium which lies above mesenchyme
What are the two primary epithelial bands shaped like?
Horse shoe
What is ectomesenchyme derived from?
Neural crest cells that have migrated to the region from neuroectoderm of the embryo
What is the primitive oral cavity called?
Stomodeum
How is the dental lamina formed?
Further thickening and growth of the arch shaped epithelial band into the underlying ectomesenchyme.
Where does the dental lamina begin to form?
Initially in the midline then progresses posteriorly
What are the two processes that the primary epithelial band divides into?
1) Buccal placed vestibular lamina - lips, buccal sulcus, cheeks
2) Lingual placed vestibular lamina - development of the teeth is ARCH shaped
What is initiation?
The development of individual tooth sites along the dental lamina with 10 deciduous tooth germs developing sequentially along each arch
What is morphogenesis?
The process that gives rise to the individual tooth shape under the influence of genetic programming and cell signalling from interactions between the epithelial and mesenchymal cells
What is histogenesis?
Differentiation of different cell types (ameloblast/odontoblast) to give rise to either mineralised tissue - enamel, dentine or cementum or non-mineralised such as pulp and periodontal tissues
What do oral epithelium signal to underlying mesenchyme via?
Bone morphogenic factors and fibroblast growth factors - these regulate gene expression
What do bone morphogenic factors induce?
The expression of mesenchymal homeobox gene transcription factors Msx 1 and Msx2 - Msx1 is found in the bud stage epithelium and Msx2 possibly a regulator in morphogenesis
Where do bioactive signalling molecules pass between?
Epithelium and mesenchyme, where they bind to cell receptors and set of a series of intracellular cascades that regulate gene expression thereby altering cell behaviour
In the superficial layer of the adult oral mucosa what are cells like?
Large and flattened
In the intermediate layer of the adult oral mucosa what are cells like?
Start to enlarge and become flattened in shape
In the basal layer of the adult oral mucosa what are cells like?
Cells are tall columnar, actively reproducing and cells move over the superficial layer over time
What cell layers make up the embryonic oral epithelium/?
Superficial and basal
What creates the primary epithelial band?
Multiplication of basal and superficial cells to increase tissue thickness and complex cell signalling and gene expression
What characterises the early bud stage?
- Spherical condensation of epithelial condensation surrounded by mesenchyme
- No morphodifferentiation visible
- No histodifferentiation visible
- Ectodermal tissue origin
What does the oval mass in the early bud stage penetrate into?
Surrounding ectomesenchyme which surrounds the enamel organ and is growing and condensing
What characterises the cap stage?
Enamel organ looks like a cap
Morphodifferentiation is still not visible
- Early histodifferentiation is visible with recognisable:
Stellate reticulum
Outer enamel epithelium
Inner enamel epithelium
What is the stellate reticulum?
Star shaped cells derived from the superficial cell layer
What are the basal cell layers continuous with in the cap stage?
Outer and inner enamel epithelium
What will the inner enamel epithelium become?
Ameloblast cell layer that lays down the tooth enamel
What role does the stellate reticulum have?
Cushioning and nutrient role for the inner and outer enamel epithelium, supports production of enamel matrix
What shape is the external enamel epithelium in the late cap stage?
Cuboidal
What shape is the inner enamel epithelium in the late cap stage?
More columnar
What is the dental follicle?
Mesenchymal cells proliferating and surrounding enamel organ
What is the dental papilla?
Mesenchymal cells located beneath inner enamel epithelium and condensed into a mass within the concavity of the cap of the enamel organ
What are the three embryological features we can see by the late cap stage?
Dental papilla, dental follicle and enamel organ
What is the enamel organ derived from?
Ectoderm
What is the dental papilla derived from?
Ectomesenchyme, derived from NCC’s, producing future dentine and pulp
What is the dental follicle derived from?
Ectomesenchyme, produces the periodontium, cementum, periodontal ligament, alveolar bone
What is the basement membrane?
It is between the enamel organ and dental papilla and is the site of the future ADJ
What is the early bell stage characterised by?
Morphodifferentiation visible
Histodifferentiation visible (IEE cells become tall columnar)
Development of successional lamina from which permanent incisor, canine and premolar teeth develop after their deciduous tooth predecessor
Permanent molar teeth develop directly from the dental lamina as there is no deciduous teeth to be replaced
What are the histologic features of stratum intermedium?
More inner compressed layer of flat cells
What are the dental papilla and dental follicle characterised by in the bell stage?
Morphodifferentiation is very visible
Both composed of mesodermal/mesenchymal cells
Dental papilla differentiates into odontoblast layer and produces dentine
Dental follicle composed of flattened
What is the late bell stage characterised by?
Morphodifferentiation of crown is complete
Ameloblast differentiation from IEE causes ectomesenchymal peripheral cells of the dental papilla to differentiate into tall columnar odontoblast cells
Enamel and dentine formation starts at the tips of future cusps/incisal edges occurring incrementally
Alveolar bone is deposited around the developing tooth
What are the two main groups of proteins in enamel?
Amelogenins and non-amelogenins
What is root formation characterised by?
Root sheath Dental papilla Dental follicle Odontoblast layer Epithelial rests of malassez Cementoblasts Developing alveolar bone Developing cementum, periodontal ligament and root dentine
What interactions are there in root formation?
Epithelial root sheath, dental follicle and dental papilla
