Tooth Development Flashcards
What happens straight after fertilisation?
Zygote undergoes mitosis and secretes fluids by cells becoming a BLASTOCYST
Blastocyst travels to become implanted in the endometrium of the uterus
What happens during the second week of prenatal development?
The implanted blastocyst grows
Bilaminar embryonic disk develops
When do the neural crest cells develop?
In the third week
Where do the neural crest cells (NCCs) develop from?
Neuroectoderm
Where do neural crest cells migrate from and to?
They migrate from the crests of the neural folds and join the MESODERM to form mesenchyme
What is the mesenchyme do?
It is involved in the development of many face and neck structures (like the branchial arches)
Mesenchyme differentiates to form most of the connective tissue of the head
When do trilaminar disks form?
At the beginning of week 3
What two things make up the neuroectoderm?
Neural plate
Neural grooves
What happens in week 4?
Development of the face begins in the 4th week of prenatal development
5 facial processes for around the primitive mouth
What are the 5 facial processes that form around the primitive mouth in the 4th week?
Stomodeum Frontonasal process Maxillar process Mandibular process Mandibular symphysis
When do ectoderm begin to line the primitive mouth?
Week 6
What gives rise to the oral epithelium?
The outer part of the ectoderm
When does primary tooth development begin?
Week 6
What happens in week 6 in regard to tooth development
Primary tooth development begins with the formation of the epithelial band
The embryo’s oral epithelium thickens (by thickening cells in the superficial layer)
Thickening cells grow down into the mesenchyme forming a horseshoe shaped band in each developing arch
When does dental lamina formation begin?
Week 7
What happens BY week 7?
The primary epithelial bands have divided into 2 processes beginning the development of the lip and jaw
What happens in week 7 in regard to dental lamina formation?
The oral epithelium of the band grows deeper into the ectomesenchyme
Ectomesenchyme is induced to divide and produce 2 types of lamina:
1. Buccal placed vestibular lamina
2. Lingual placed dental lamina
What are the 2 lamina the ectomesenchyme are induced to produce in week 7?
- Buccal placed vestibular lamina which contributes to development of the vestibule of the mouth (lining of lips, cheeks and buccal sulcus)
- Lingual places dental lamina which is an arched shape thickening of the epithelium in the primitive oral cavity which contributes to the development of teeth . Dental lamina begins to form initially in the midline for both arches and progresses posteriorly. underlying ectomesenchyme can be observed to be
condensing
How can development of the dental lamina be seen?
It will increase in length
What can we observe by week 8 in regard to dental lamina formation?
We can observe the development of a series of swelling on the deep surface of the lamina
These are early developing tooth germs each surrounded by mesenchymal condensation
What does the term induction describe in relation to ectodermal-mesenchymal interactions?
The term induction describes the effect of one cell layer on another
What passes between epithelium and mesenchyme binding? What do these substances do?
Bioactive signalling molecules like transcription factors, growth factors and cytokines are produced in a specific sequence
They pass between epithelium and mesenchymal binding sites to cel receptors
They set off a series of intracellular cascades
What do intracellular cascades, between epithelial and mesenchyme binding, do?
They regulate gene expression thereby altering cell behaviour
Which arch is responsible for the imitation of tooth development at the early stages?
The first pharyngeal arch (branchial arch) epithelium
To what does the instructive capacity of development get transferred after the first pharyngeal nerve?
The mesenchyme
ectomesenchyme derived from the neural crest
What can the mesenchyme do during tooth development?
It can induce the epithelium to further develop
What substance may have an important role in the inductive process and how?
The extracellular matrix may have an important role in inductive process by enabling interactions between bioactive molecules
OR by providing a surface for the attachment of cells
State which to components are responsible for the initiation of both development
- The first pharyngeal arch epithelium is responsible for initiation in the early stages
- The mesenchyme takes over to initiate the thickening of the epithelium in the later stages
How may it be possible to engineer dental tissue from stem cells?
By understanding early odontogenic signals
What does growing enamel look like at the ‘bud’ stage?
The enamel organ looks like simple spherical to ovoid epithelial condensations
Poorly morphodifferentiated and histodifferentiated
At the bud stage what is happening to the ectomesenchyme?
It is undergoing proliferation
It surrounds the enamel organ and is going and confessing
What happens at week 10?
The early cap stage begins
Deeper surface of the enamel organ invaginates to form a cap shape
What is a key characteristics of the early cap stage?
Poor histodifferentiation as you can see the round cells in the central portion
Peripheral cells become arranged to form external and internal enamel epithelia
What are the key characterises of the early bud stage?
- Spherical or ovoid shaped epithelium condensation surrounded by mesenchyme
- No morphodifferentiation visible ie no recognisable tooth shapes visible
- No histodifferentiation visible ie no recognisable cell types visible
- Ectodermal tissue origin
What are some key characteristics of the cap stages?
- Crossections of enamel organ looks like a cap
- Morphodifferention not yet visible but progressing
- Early histodifferentaion is visible with recogniable cells such as stellate reticulum, outer enamel, inner enamel epitheium
What happens at week 12?
The late cap stage begins
What happens during the late cap stage?
- Enamel organ enlarges with apparent histodifferentiation
2. Central cells within the organ separate and are held together by desmosomes forming STELLATE RETICULUM •
What happens to the epithelium cells in the late cap stage?
- External enamel epithelium remains cuboidal
2. Internal enamel epithelium becomes more columnar
What do the stellate reticulum do?
They have a cushioning effect
They have a nutrient role for the cells of the inner and outer epithelium
What happens to mesenchymal cells in the late bell stage?
The mesenchymal cells continue to proliferate and surround the enamel organ = This forms the dental follicle
Mesenchymal feels located beneath the internal enamel epithelium condense into a mass wishing the concavity of the cap of the enamel organ to form the dental papilla
What happens BY the late cap stage?
The 3 embryonic structures are considered together to be the tooth germ and sit within the crypt of developing bone
What are the 3 embryonic structures?
The enamel organ
The dental follicle
The dental papilla
How does further development of the dental lamina occur?
- Increasing length
2. Development of a series of swelling on the deep surface of the lamina by week 8
What creates the primary epithelial band and when?
By week 6 complex cell signalling and gene expression occurs within cells to create the primary epithelial band
How and when is the dental lamina formed?
By week 7 increased selective multiplication of basal layers forms the dental lamina
What does tooth development depend on?
Depends on the complex reciprocal interaction between the epithelium and mesenchyme
This ensures an ordered and controlled development of the individual tooth germs.
When does the bud stage occur?
Mostly in week 8
What happens in week 14 and why?
The early bell stage occurs
This is due to further morpho and histodifferentiation
What are some key characteristics of the bell stage?
- Morphodifferentation is visible (recognisable tooth shape beginning to form)
- Histodifferentation is visible (start of cell differentiation)
- Development of successional lamina from which the permanent incisor canine and premolar teeth. develop after their deciduous tooth predecessor
- Permanent molar teeth develop directly from the dental lamina and not from the successional lamina a
Why do permanent molar teeth develop directly from the dental lamina and to from the successional lamina
As there are no deciduous teeth to replace (no baby pre molars)
How is histodifferentation visible in the bell stage at week 14?
Start of cell differentiation as the internal enamel epithelium cells become tall columnar cells
How is morphodifferentation visible in the bell stage at week 14?
recognisable tooth shape beginning to form
By week 14 what happens?
The tooth crown assumes its final shape through morphodifferentation
The cells that will be making up the hard tissue of the crown undergo further histodifferentiaiton into ameloblast and odontoblasts
Name the cells layers that make up the bell stage structures (From outer to inner)
- Dental sac
- Outer enamel epithelium
- Stellate reticulum
- Stratum intermedium
- Inner enamel epithelium
- Outer cells of the dental papilla
- Central cells of the dental papilla
What are some histological features of the dental sac?
Increasing amount of collagen fibres forming around the enamel organ
What are some histological features of the outer enamel epithelium?
Outer cuboidal cells of the enamel organs
What are some histological features of the stellate reticulum?
More outer star-shapes cells in many layers forming a network within the enamel organs
What are some histological features of the stratum intermedium?
More inner compressed layer of flat to cuboidal cells
What are some histological features of the inner enamel epithelium?
Innermost tall, columnar cells of dental enamel
What are some histological features of the outer cells of the dental papilla?
Outer layer of cells of the dental papilla nearest the inner enamel epithelium of the enamel organ
A basement membrane is between the outer layer and inner enamel epithelium
What are some histological features of the central cells of the dental papilla?
Central cell mass of the dental papilla
What is the role of the dental sac in the tooth?
It will differentiate into cementum, periodontal ligament and alveolar process
What is the role of the outer enamel epithelium in the tooth?
Serves as a protective barrier for enamel organs
What is the function of the stellate reticule in the tooth?
Supports the production of the enamel matrix
What is the function the stratum intermedium in the tooth?
Supports the production of the enamel matrix
What is the function of the inner enamel epithelium in the tooth?
Will differentiate into ameloblasts that form the enamel matrix
What is the function of the outer cells of the dental papilla in the tooth/
It will differentiate into odontoblasts that form the dental matrix
What is the function of the central cells of the dental papilla in the tooth?
Will differentiate into pulp tissue
What are the key characteristics of the dental sac and papilla?
- Morphodifferentiation is very visible
- They are coposedof mesodermal and mesenchymal cells
- The dental papilla will differentiate into the odontoblast layer and cells of the pulp which will produce dentine and the dental pulp
- The dental follicle is composed of several layers of flattened cells from which the cementum, periodontal ligament and some alveolar bone will be formed
What does the dental papilla start of as?
A small area of condensed mesenchymal cells
What changes occur to for the dental papilla fro the bud towel stage?
The dental papilla cells begin to proliferate and become more compact as the enamel organ develops
Where does the dental papilla sit?
Within the shape of the inner enamel epithelium and bulges out of the enamel organ
What results after histodifferentation occurs to the dental papilla in the bell stage?
2 types of tissue layers form:
- The outer cells of the dental papilla will differentiate into dentine secreting cells (Odontoblasts)
- Central cells of the dental papilla become the primordium of the pulp
What is the dental follicle composed of?
Several layers of flattened cells
What does the dental follicle surround?
The part of the dental papilla not in contact with the internal enamel epithelium
What type of origin does the dental follicle have?
Mesenchymal origin
Where are the cells of the inner layer of the dental follicle derived from?
The neural crest
What os the cervical loop?
It forms at the growing margins of the enlarging enamel organ
It is the cite of cell division and will become the root sheath of Hertwig
What are the names of the 3 stages that bring about the sequence of histological changes?
- Initiation
- Morphogenesis
- Histogenesis
Describe the Initiation stage that brings about the sequence of histological changes
Involves the physiological process of induction which is an active interaction between the embryonic tissue types
It results in a series of epithelial swelling appearing on the deep surface of epithelial
Describe the Morphogenesis stage that brings about the sequence of histological changes
Tooth germs are classified into buds, caps and bells according to the degree of morphodifferentiation and histodifferentiation of their enamel organs
This process results to the individual tooth shapes
Describe the Histogenesis stage that brings about the sequence of histological changes
Tooth germs rapidly change in size and shape
Differentiation of the cells types (E.g. ameloblasts and odontoblasts) give rise to mineralised and non mineralised tissues
What is the enamel organ derived from?
the ectoderm which makes enamel and ectodermal product
What is the dental papilla formed from?
Ectomesenchyme derived from the neural crest cells
What does the dental papilla form?
The future dentin and pulp for the inner part of the tooth
What origin is the dentin and pulp
Mesenchymal as it is derived from the dental papilla with is formed fro ectomesenchyme
What is the dental follicle formed from?
Ectomesenchyme
What does the dental follicle produce?
Produces the periodontium and the supporting tissues of the tooth including the cementum, periodontal ligament and some alveolar bone
what is the origin of the cementum, periodontal ligament and some alveolar bone?
Of mesenchymal origin as they are derived from the dental follicle which was formed from the ectomesenchyme
What forms the future. amelo dentinal junction (ADJ)
The basement membrane between the enamel organ and the dental; papilla
What is the enamel knot?
The transitionary structure seen as a localised mass of cells in the centre of the inner enamel,el epithelium coming a bulge not the papilla at the centre of the enamel organ
What are some characteristics of he enamel knot?
It can sometimes be seen at the cap stage but disappears before the bell stage
May represent an important signaling centre during tooth development
Cells in this structure DO NOT proliferate