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
- 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
- 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
- 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:
1. The outer cells of the dental papilla will differentiate into dentine secreting cells (Odontoblasts)
2. 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
When does the late cell stage begin?
Week 18
What are some of the key characteristics of the last bell stage
1.Morphodifferentiation of the crown is complete
Histodifferentiation occurs. Ameloblasts differentiate from the inner enamel epithelium which has an inductive effect upon the ectomesenchymal peripheral cells of the dental papilla causingt them to differentiate into tall columnar odontoblast cells
3. Enamel and dentine formation starts at the tip of the future cusps and incised edges
What is the formation of dental hard tissues during which enamel and dentine are deposited in successive layer, initially as a matrix called?
apposition
What do developing ameloblasts induce in the late bell stage at week 18?
They induce adjacent mesenchymal cells of the dental papilla to differentiate into tall columnar odontoblast cells
Which is deposited first: the enamel or dentine matrix?
The dentine matrix
What is happening to the ectodermal tissue in week 18?
The process of induction continues to occur between the ectodermal tissue and the enamel organ and the mesenchymal tissue of the dental papilla and dental sac. This is called reciprocal induction
What is reciprocal induction?
induction occurring between the ectodermal tissue and the enamel organ and the mesenchymal tissue of the dental papilla and dental sac
What does the presence do dentine do to the ameloblats?
Induces them to secrete enamel
What happens after the hard tissue forms?
The dental lamina starts to break down releasing the enamel organs from the oral epithelium
What are pearls of serres and what do they contain?
They are remnants of the dental lamina that may persisting adult mucosa as epithelial pearls
They contain keratin which may be involved in the aetiology of cysts
What are the 8 layers that make up the late bell stage?
- Odontoblast layer
- Ameloblast layer
- Stratum intermedium
- Stellate reticulum
- External epithelium layer
- Developing dental pulp
- Dentine matrix
- Enamel matrix
What is enamel formation called?
Ameolgenesis
What are the 5 stages that characterise amelogenesis?
- Pre-secretory phase
- Secretory phase 3. Transition phase
- Maturation phase
- Postmauratio
What are Tomes processes?
Short coned shapes where secretion and modification of the enamel matrix occurs
What are Tomes processes responsible for?
The prismatic structure of enamel
Where does crystal formation begin?
Within the organic protein matrix and continues as the ameloblasts move away from the future amelo dentine junction
When does the transition to the mature phase in ameolgenesis start?
When enamel has reached its full thickness
As cells lose their tomes process in the transition phase what does this mean they can’t do anymore?
They can’t secrete anymore enamel matrix
How much longer is the maturation phase in comparison to the secretory phase?
Maturation phase os 2-3 time longer than the secretory phase
What happens in the pre secretory phase of amelogeneis?
Internal epithelial enamel starts to differentiate and elongate developing into columnar secretory cells (pre ameloblasts)
These differentiating pre ameloblasts induce the outer/peripheral dental papilla cells to begin differentiating into odontoblasts
Following this the basal lamina is degraded and resorbed by pre ameloblasts
Odontoblasts are the first to lay down dentine matrix (pre dentine)
Pre-ameloblasts then secrete initial enamel matrix.
How do cells in the internal epithelium differentiate into pre ameloblasts?
Cells elongate
They develop secreting organelles and display reverse polarity (Ie nucleus moves to the end of the cell away from the basal lamina)
What happens in the secretory phase of amelogeneis?
Further elongation is seen
Aneloblasts are now tall columnar cells (over 60um height x 2-4um width) with nuclei away from forming enamel
Ameloblasts develop Tomes processes at which secretion and modification occurs
Secretion of the both organic matrix and minerals is also taking place
What happens to crystallite structure during the secretory phase?
Crystallite elongation continues
The crystallites become long ribbons arranged in bundles that form enamel prisms or rods
These enamel prisms elongate incrementally
What happens during the transition phase in amelogensis?
Half the cells die once enamel has reached its full thickness
Cells lose their Tomes process and shrink in size with smooth or riffles cell bass
Enamel matrix is degraded with continuous mineralisation and crystal growth
Selective reabsorption occurs
What happens during the maturation phase in amelogensis?
Cycling of ruffled and smooth ended ameloblasts may indicate alternation between resorptive and secretory activity.
Final degradation and withdrawal of matrix takes place.
Enamel crystallites grow in length as well as increase in thickness and width as further mineral is added to calcium hydroxyapatite crystallites (increase in thickness to 25nm) reducing inter-crystallite space until they contact each other.
Enamel reaches its final level of mineralization
How do enamel crystallites grow in length in the maturation phase of amelogenesis?
As further minerals are added to the crystal hydroxyapatite crystallites
What are the 4 features associated with the presecretory phase of amelogenesis
- Crystodifferentation: differentiation of ameloblasts
- Morphodifferentation : bell stage including formation of the enamel knot
- Resorption of the basal lamina of the internal enamel epithelium
- Epithelium-mesenchymal interactions
What are the 7 features associated with the secretory phase of amelogenesis?
- Initial layer of aprismatic enamel formed
- Ameloblasts develop Tomes processes
- Matrix secretion to final thickness
- Initiation and continuation of mineralisation to 30% by weight
- Crystallite elongation
- Matrix degradation
- Development of prismatic structure
What are the 6 features associated with the transition phase of amelogenesis?
- Ameloblasts shorten (50% die)
- Vascular invagination of the enamel organs
- Re-formation of ameloblast basal lamina
- end of matrix secretion
- Continued matrix degradation
- Selective matrix withdrawal
What are the 4 features associated with the maturation phase of amelogenesis?
- Cycling of ruffles and smooth ended ameloblasts
- Final degradation and withdrawal of matrix
- Crystal growth continues to completion
- Final third of mineralisation after protein removal complete
What are the 4 features associated with the post maturation phase of amelogenesis?
- Enamel organ degenerates
- Enamel coverings established
- Eruption
- Exposure to oral environment and post eruptive changes
What separated the core of the prism and the prisms boundaries?
The orientation of the crystallites
What determines the orientation of the crystallites?
The shape of the tomes process
Which direction do prism core crystallites travel in?
They are parallel to the long axis of the prism
What type of appearance does developing enamel have?
A pit like surface appearance
These pits are surrounded by rod enamel
Why does developing enamel have the appearance it does?
It has a pit like surface appearance because crystallites are formed at the surfaces of the tomes process at different rates
What given enamel is prismatic structure
The tomes process infills the central pits as the ameloblasts retreat to form the main core of the enamel prisms giving enamel is prismatic structure
What is dentine formation called?
Dentiogenesis
When does dentine formation occur?
When the tooth germ has reached the bell stage
The enamel organ is fully formed with differentiated internal enamel epithelium but no enamel has been laid down
What initiates the differentiation of odontoblasts and what do the odontoblasts differentiate from?
Initiated by a series of epithelial signals
Odontoblasts are differentiates from ectoesenchyme of the dental papilla
What are the 7 stages that characterise dentinogenesis?
- Internal epithelium cells start to differentiate and elongate developing into columnar secretory cells (the pre ameloblats)
- Peripheral ectomesenchymal cells divide into pre odontoblasts in contact with the basement membrane and some daughter cells
- Pre-odontoblasts begin to differentiate
- Pre-odontoblast cells develop into columnar secretory cells with an increase in size and number of Golgi apparatus and rough endoplasmic reticulum
- Ameloblasts degrade the basal lamina and allows inductive signalling to the odnotblasts. The nucleus migrates to the base of the cell. Odontoblast processes develops and dentine matrix starts to be laid down
- Once a thin strip of dentine matrix is disposited it then starts to mineralise t and the odontoblasts start to retreat (this leaves behind one main process)
- Ameloblasts develop tomes processes with numerous secretory vacuoles to deposit enamel matrix proteins with subsequent mineralisation to form crystallites and prisms
Columnar secretory cells are called what
Pre ameloblasts
What happens to pre odontoblast cells during dentinogenisis?
They divide into columnar secretory cells
What happens to the peripheral ectomesenchymal cells during dentinogenisis?
They divide into pre-odontoblast in contact with th basement membrane and some daughter cells migraine below this layer
What degrades the basal lamina?
Ameloblasts
What does the degrading of the dental lamina allow
Allow inductive signalling to the odontoblasts
Nucleous migrates to the base of the cell
Odontoblaastic processes develop and dentine matrix starts to be laid down
What is the dentine matrix formed in dentinogenisis made up of?
Mainly compromised of type 1 collagen fibrils
What is the first formed dentine called?
The mantle dentine
What is the first formed dentine call and what is it formed by?
It is called the mantle dentine and it is formed by odontoblasts that are still differentiation
This dentine has a slightly different structure
What follows the formation of the mantle dentine?
Following the formation of the mantle dentine the blue of the primary circumpulpal dentine is laid down in regulation incremental patterns
What are the names of the 6 stages of dentinogenesis?
- Differentiation
- Deposition of organic matrix
- mineralisation and modification of the matrix
- Pertibular dentine formation
- Secondary dentine
- Tertiary dentine formation
What happens in the differentiation stage of dentinogenesis?
- Differentiation: of the odontoblasts from the ectomesenchyme of the dental papilla, this is initiated and controlled by a series of epithelial signals. Development of secretory organelles and polarisation are accompanied by the redistribution of intracellular skeletal proteins. As differentiation progresses the small processes extending from the differentiating odontoblast reduce and one will dominate
What happens in the Deposition of organic matrix stage of dentinogenesis?
Deposition of organic matrix by fully differentiated odontoblasts. The matix formed is comprised mainly of type one collagen fibrils with dentine phosphoprotein (DPP) as the second most abundant constituent. The first formed dentine is called the mantel dentine which is formed by odontoblast that are still differentiating. Following this the bulk of the primary circumpupal dentine is laid down un a regular incremental pattern
What happens in the Mineralisation and modification of the matrix stage of dentinogenesis?
The first layers of the dentine matrix are un mineralised but when it reached a certain width mineralisation begins at the same rate as matrix formation. Hence there is always a layer of mineralised dentine on the pulpal surface called the pre dentine. Odontoblasts control the initiation of mineralization and rate of deposition via controlling the release/level of DPP. They actively transport CA ions from serum to the mineralization front. Under the control of DPP protein, Ca becomes a crystalline mineral (nucleation) following deposition on to type 1 collagen fibril template.
What happens in the Peritubular dentine formation stage of dentinogenesis?
Has a different composition but is structurally continuous with inter-tubular dentine. With age deposition leads to reduction in size of tubules. The degree of tubular occlusion can be used to determine the age of teeth in forensic investigations. Structure= small crystals in amorphous (non fibrillar) matrix.
What happens in the Secondary dentine formation stage of dentinogenesis?
Secondary dentine formation is the continued, slow, age related deposition, by the original odontoblasts of dentine through life following completion of tooth formation. Deposition leads to reduction in pulp chamber size and root canals becoming narrower with accompanying reduction in odontoblast population
What happens in the Tertiary dentine formation stage of dentinogenesis?
Tertiary dentine formation is deposited in response to injury.
Why is there always a layer of un mineralised dentine on the plural surface?
What is it called?
Because when the dentine matrix reaches a certain width mineralisation occurs at the same rate as matrix formation. Hence there is always a layer of un- mineralized dentine on the pulpal surface called pre-dentine
What are the similarities between Amelogenesis and dentinogenesis?
Secretory cells involved
Mineral content changed
Periodic depositions occur
What is coronal dentine formation?
Odontoblasts differentiate and dentine formation begins where the cusps will later form and continues uniformly down the slopes of the cusps and the wall of the crown to the cervical root
What is coronal dentine formation?
It occurs as the epithelium root sheath extends and initiates odontoblast differentiation on its plural surface
The process continues to thicken the dentine and then slows down once the predetermined length of the root is reached
Radicular odontoblasts differ in that they develop looping and branching processes this may give rise o appearance of the granular later near the amelo dentine junction
When does tooTH development occur?
After crown formation
Interaction occur between which components in root formation?
- Dental follicles
- Dental papilla
- Epithelial root sheath of hertwig
Go through the steps of root formation
- After crown formation the internal and outer enamel epithelium at the cervical loop of the enamel organ form a double layered epithelial root sheath (contains NO stellate reticulum or stratum intermedium)
- The root sheath encloses the dental papilla and grows apically to outline the shape of future root and form of the apical foramen
- The dental follicle is seen next to the outer surface of this sheath and for the cementum, periodontal ligament and the alveolar bone
- Dentinogenesis occurs
- Ectomesenchyme cells of dental follicles adjacent to the root dentine differentiate into cemnetoblasts like cells and ceentogenesis starts with the formation of acellular cementum. This is extrinsic fibre cementum
- Cementoblasts form a more distinct layer of cuboidal cells that secret collagen parallel to the surface forming the matrix of the cellular cementum which is intrinsic fibre cementum
- Once cemntogeneis has started cells of the remaining dental follicle become obliquely orientates becoming fibroblasts of the PDL. These secrete collagen which becomes embedded as Sharpeys fibres into developing acellular cementum and developing bone
- Finally the epithelial remnants of the root sheath may be retained and sometimes seen histologically as epithelial rest of Malassez in the PDL
How long does root formation take post eruption?
Approx 1 and a half in deciduous teeth
Approx 3 in permanent teeth
When does the bilaminar embryonic disk develop?
In the second week
What are blastocysts?
A structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo.
What develops from the neuroectoderm?
Neural crest cells (NCCs)
How is the mesenchyme formed?
When the neural crest cells migrate and join the mesoderm
‘Innermost tall, columnar cells of dental enamel’ is a histological feature of which cell layer in the bell stage?
Inner enamel epithelium
What happen in week 3 in regard to specialised cells?
A specialised group of cells called the neural crest cells develop from the neuroectoderm
These cells migrate from the neural folds to join the mesoderm to form mesenchyme
Also trilaminar embryonic disks also form in the third week
Which lamina contributes to the development of the teeth?
The lingual places dental lamina
Will differentiate into ameloblasts that form the enamel matrix’ is the tooth function for which cell layer in the bell stage?
Inner enamel epithelium
Where does the lingual placed dental lamina initially begin to form from?
The midline for both the arches and then progresses posteriorly
By week 8 we can see a series of swellings on the deep surface of the lamina. What are these swellings?
Early developing tooth germs surrounded by mesenchymal condensation
What are the branchial arches in the face and neck developed from?
Mesenchyme is involved in their development
What differentiates to form most of the connective tissue in the head?
Nueral crest cells fused with mesoderm to form mesenchyme
The neural groove and neural plates make up what?
The neurectoderm
When does development of the face begin?
In week 4
Stomodeum
Frontonasal process
Maxillar process
Mandibular process
Mandibular symphysis
Are all what?
The 5 facial processes that form around the primitive mouthin week 4
‘It will differentiate into odontoblasts that form the dental matrix’ is the tooth function for which cell layer in the bell stage?
The outer cells of the dental papilla
What are MSX1 and MSX2?
The 2 mesenchymal homeobox gene transcription factors
What do ectoderm do in week 6?
Begin lining the primitive mouth
‘Supports the production of the enamel matrix’ is the tooth function for which 2 cell layers in the bell stage?
The stratum intermedium and the stellate reticulum
What are each developing tooth germ surrounded by by week 8?
Mesenchymal condensation
Which lamina contributes to the development of the vestibule of the mouth?
The buccal places vestibular lamina
‘More inner compressed layer of flat to cuboidal cells’ is a histological feature of which cell layer in the bell stage?
Stratum intermedium
What is the vestibule of the mouth?
The linings of the lips cheeks and buccal sulcus
What happens in week 6 in regard to facial development?
The primitive mouth is lined by ectoderm
‘Will differentiate into pulp tissue’ is the tooth function for which cell layer in the bell stage?
The central cells of the dental papilla
What does the outer part of the ectoderm give rise to?
The oral epithelium
What does primary tooth development begin with?
The formation of the epithelial band in week 6
Where do thickening epithelium grow to in week 6 of primary tooth development?
Down towards the mesenchyme forming. A horse shoe shaped band in each developing arch
By which week have the primary epithelial bands divided into 2 processes
Week 7
‘More outer star-shapes cells in many layers forming a network within the enamel organs’ is a histological feature of which cell layer in the bell stage?
Stellate reticulum
What does the dividing of the primary epithelial bands into 2 processses lead to?
Begins the development of the lip and jaw
‘Serves as a protective barrier for enamel organs’ is the tooth function for which cell layer in the bell stage?
The outer enamel epithelium
Which lamina is the arch shaped thickening of the epithelium ?
The lingual placed dental lamina
What are the underlying ectomesenchyme doing when dental lamina formation is occurring in week 7?
They are condensing
‘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’ is a histological feature of which cell layer in the bell stage?
Dental papilla
Describe how developing tooth germs look by week 8
They are a series of swellings on the deep surface of the lamina
Each tooth germ is surrounded by mesenchymal condensation
‘It will differentiate into cementum, periodontal ligament and alveolar process’ is the tooth function for which cell layer in the bell stage?
The dental sac
What 2 types of tissue layer is the dental papilla made of?
1.The outer cells of the dental papilla will differentiate into dentin-secreting cells (Odontoblasts)
2.Central cells of the dental papilla become the primordium of the pulp
What initiates the intracellular cascade that regulates gene expression?
Bioactive signalling molecules, such as transcription factors, growth factors and cytokines, are produced in a specific sequence and pass between epithelium and mesenchyme binding to cell receptors setting off a series of intracellular cascades
What is the first pharyngeal arch epithelium (branchial arch) responsible for?
Initiation of tooth development at early stages of tooth development
When does the late cap stage begin?
12th week
What are BMPs?
Bone morphogenic factors. They send signals to underlying mesenchyme
‘Outer cuboidal cells of the enamel organs’ is a histological feature of which cell layer in the bell stage?
Outer enamel epithelium
What are the 2 mesenchymal homeobox gene transcription factors?
MSX1 and MSX2
What can induce the epithelium to further develop?
The mesenchyme
What might we be able to do if we understand early odontogenic signals?
May be possible to engineer dental tissue from stem cells
‘Central cell mass of the dental papilla’ is a histological feature of which cell layer in the bell stage?
Central cells of the dental papilla
Peripheral cells arrange to form what in the early cap stage?
Arrange to form external and internal enamel epithelia
Which cells hold together the separated central cells in the late cap stage?
Desmosomes forming stellate reticulum
How and when is the dental follicle formed?
In the 12th week during the late cap stage. The mesenchymal cells continue to proliferate and surround the enamel organ to form the dental follicle
‘Increasing amount of collagen fibres forming around the enamel organ’ is a histological features of which cell layer in the bell stage?
The dental sac
How and when is the dental papilla formed?
In the 12th week during the late cap stage. The mesenchymal cells beneath the internal epithelium condenses into a mass within the concavity of the cap of the enamel to form the dental papilla
Where do the bioactive signals passing between the epithelium and mesenchymal come from?
They are sent via bone morphogenic factors (BMPs) and fibroblast growth factors
What to bone morphogenic factors (BMPs) induce?
They induce the expression of mesenchymal homeobox gene transcription factors (MSX1 and MSX2)
Where is MSX2 found and what does it do?
In the bud stage epithelium and is possibly a regulator of morphogenesis
What does further morpho and histodifferentiation lead to in week 14?
The early bell stage in week 14
Where do premolar teeth develop from?
The dental lamina
Describe the dental papilla
Starts off as a small area of condensed mesenchymal cells
Cells of the dental papilla cells proliferate and become more compact as the enamel organ develops from the bud to the bell
Dental papilla sits within the shape of the inner enamel epithelium and bulges out of the enamel organ
Describe the dental follicle
Is composed of several layers of flattened cells
Surrounds the part of the dental papilla not in contact with the IEE and part of the enamel organ
Is mesenchymal in origin
Cells of the inner layer of the dental follicle may be derived from the neural crest
What does the ectoderm form?
The enamel organs
What does the ectomessenchyme derived from neural crest cells form?
The dental papilla
What does the ectomesenchyme form?
The dental follicle
What is the basement membrane between the enamel organ and the dental papilla site for?
The future amelo dentinal junction
What happens in week 18?
The late bell stage begins and dental tissue starts forming
What is apposition?
Apposition is the formation of dental hard tissues during which enamel and dentine are deposited in successive layer, initially as a matrix
induction occurring between the ectodermal tissue and the enamel organ and the mesenchymal tissue of the dental papilla and dental sac is called what?
Reciprocal induction
What may be involved in the aetiology of cysts?
The keratin in the epithelial pearls of Serres
What are remnants of the dental lamina that may be found in adult mucosa called?
Epithelial pearls of Serres
Which cells are the first to lay down the dentine matrix?
Odontoblasts
What is the height and width of fully grown columnar cells?
60 micrometre height
2.4 micrometres width
What is dentinogenesis?
Dentine formation
What are the pre ameloblasts?
columnar secretory cells
What do the ameloblasts do in dentinogenisis?
They degrade the dental lamina
