Tooth Development Flashcards
The _______ is the only portion of the tooth we can see.
Enamel
Describe the mature tooth structure.
Enamel
Dentin
Pulp Cavity- Innervation and Vascularization
The tooth rests in a _______ and held in place by the ________ called the ______.
boney socket , connective tissue
Periodontal pocket
What innervates and vascularizes a tooth?
Pulp chamber in dentin
What are the 5 stages of tooth development?
Initiation
1. Bud
2. Cap
3. Bell
4. Apposition
5. Maturation
Which stage of tooth development is enamel and dentin laid?
Bell stage is the earliest point of the first enamel and dentin while a majority is laid during the Apposition Stage
Early tooth development results from interactions between_________.
What is this process called?
Ectoderm of the stomodeum
Ectomesenchyme
INDUCTION
What is ectomesenchyme?
Derived from neural crest cells that migrate into the the developing head
What is stomodeum?
The embryonic mouth
What is induction?
Inductions of process were one tissue directed development of another adjacent tissue. It is mediated by cell contact or factors released by the inducing tissue.
The induction signals usually regulate gene transcription, thereby leading the target cell toward differentiating into a specific cell type.
Induction can be serial and reciprocal.
For example tissue A can influence B and then C.
Or tissue A can influence tissue B and tissue B can induce tissue A
What mediates induction?
It is mediated by cell contact or factors released by the inducing tissue.
What is the major embryologic feature that gives rise to teeth?
When does it appear in the embryo?
At 37 days, the primary epithelial band is present on the maxilla and the mandible of the embryo mouth. (NOT ON EXAM)
It gives rise to the dental lamina and the vestibular lamina as a result of mitosis and a change of orientation of mitotic cells.
What is dental lamina?
Formed by primary epithelial band to give rise to teeth
What is vestibular lamina?
Formed by primary epithelial band to give rise to skin between cheeks and teeth (gums)
What indicates the tooth formation?
In the initiation stage, the formation of a placode in the primary epithelial band due to an increase of mitosis is what indicates the site of tooth formation
What are Meckel’s Cartilage?
Meckel’s Cartilage are small circular rings on either side of the mandibular arch in an embryo. It gives rise to parts of the inner ear and portion of the mandible.
It is also part of the ectomesenchyme.
What directs tooth development?
The ectomesoderm
What two things are REQUIRED for proper teeth development?
Neural Crest AND mandibular epithelium
Neural and limb epithelium will result in
NO Teeth
Yes to bone, cartilage ,neural crest
Neural Crest alone will result in
NO teeth or bone
Yes to cartilage and neural crest
Mandibular epithelium alone will result in
NO teeth,bone, cartilage or neural crest
The mandibular epithelium induces the neural crest to make teeth. True or False
True
Does neural crest have to come from the cranial region to allow tooth development as long as there is mandibular epithelium?
NO! Any neural crest can be used AS LONG AS mandibular epithelium is present
Initiation Stage
In certain regions of the primary epithelial band and increase in mitosis and change of orientation of mitotic cells, create a placode code, which is a thickening of tissue in a localized area.
This is what indicates sites of tooth formation.
First the dental lamina forms by invaginating into the arch. There will be an accumulation of EMS cells by the invagination
The EMS cells will eventually give rise to the dental sac and papilla
EMS cells come from the __________.
Mandibular epithelium comes from the ________.
Neural Crest
Ectoderm
What are two key players in tooth development that regulate pattern of gene expression?
How does it regulate gene expression?
Fibroblast Growth Factors (FGF)
Bone Morphogenetic Proteins (BMP)
Induction of signals by tissues to release ligand that bind to a receptor to initiate a signal transduction cascade. This triggers transcription factor activity in the nucleus.
FGF-8 is derived from the ___________ and regulates gene expression in _________ by triggering transcription factors ______.
Ectoderm, Ectomesenchyme
LHX-6 and LHX-7
Why is FGF-8 important?
FGF-8 is produced by the ectoderm to induce the ectomesenchyme cells to begin tooth development.
ONLY FIRST ARCH ECTODERM can be used. Second arch ectoderm is not relevant to jaw development. It has LOW FGF-8 expression and placodes do not form.
What is first arch ectoderm?
What is second arch ectoderm?
First arch ectoderm consists of the maxillary and mandibular process and is responsible for giving rise to structures, such as oral epithelium, enamel lips and teeth.
Second arch ectoderm has nothing to do with tooth development. It is responsible for giving rise to part of the external ear lining of the faring and facial muscles.
Primary dentition consists of how many teeth?
20
How is the positioning of teeth determined?
Expression of the Pax9 transcription factor in ECM cells is required to differentiate into DENTAL ectomesenchymal cells after induction of FGF8.
Which transcription factor is responsible for tooth position?
Pax9
Differentiates ectomesenchyme to DENTAL version
Which transcription factor is responsible for inducing tooth formation in ECM cells?
LHX-6 and LHX-7 TF induced by FGF8
_____ turns ON Pax9 transcription factor while ______ turns it off.
FGF8
BMP4
What ligand and transcription factor are required to induce tooth formation.
FGF8 and Pax 9
Dental Placode formation requires
p63 TF for Mitosis
TNF for apoptosis and cell division
Ectodysplasin involved in morphogenesis
A loss of Ectodysplasin results in _______ while an over activation results in __________.
fewer teeth
extra teeth
Describe the interaction between FGF8 , LHX6 and LHX7 and Pax 9 transcription factors.
The binding of FGF8 to its receptors on ectomesenchymal cells leads to the activation of downstream signaling pathways, including those that regulate the expression of transcription factors such as Lhx6 and Lhx7.
Lhx6 and Lhx7 are important for the differentiation of cells within the dental papilla and for orchestrating the epithelial-mesenchymal interactions necessary for tooth formation.
FGF8 also induces the expression of Pax9, another transcription factor that plays a significant role in tooth development.
Pax9 is crucial for determining the position and development of teeth along the dental arch. It regulates the expression of genes involved in the formation and development of the tooth structures, including enamel and dentin
Bud Stage
The dental lamina (epithelium) is invaginating into the ectomesenchyme ECM cells are continuing to build up around dental lamina.
What is sonic hedgehog?
shh is an extracellular signal important in the early formation of the bud from the dental lamina.
Less FGF will result in _______.
Less stratification
Less SHH will result in ______.
Less invagination of dental lamina
Once the ectomesenchyme has been induced it becomes an __________.
Induction Signal!
It can use skin epithelium along with its own molar ECM cells to drive tooth formation.
What is the type of induction found between ectomesenchyme and epithelia?
RECIPROCAL
Epithelia induces tooth formation in ectomesenchyme. When ECM is mature (induced), it can induce epithelial cells to drive tooth development from places other than the mandibular epithelium.
Development is faster in the maxillary true or false?
FALSE
MANDIBULAR IS FASTER
What is tooth germ
Ectoderm of dental lamina plus underlying ectomesenchyme
Cap Stage
As the ectoderm develops and invaginate into the ectomesenchyme it begins to surround the cells that will become the dental Papilla.
The ectoderm appears as a cap. The “curve” of the cap will border the accumulation of ectomesenchymal cells.
This is when ECM cells will differentiate into dental papilla.
What are dental papilla and where are the cells initially located?
Dental papilla are cells that give rise to the DENTIN of tooth.
They are located under the cap in the Cap stage.
What happens to ECM cells on the periphery of the cap during the cap stage?
Dental follicle/sac is formed that will eventually create the periodontum.
What are the two types of ECM cells present during the cap stage?
Dental Papilla - Dentin
Dental Follicle/Sac- Periodontum
What molecules are required for transition from bud to cap?
Msx-1 TF in mesenchyme. The lack of this will arrest teeth in bud stage
BMP-4 in mesenchyme which maintains BMP2 and SHH. SHH is needed for cap stage epithelium formation
Activin BA and Pax 9 in mesenchyme to move beyond bud stage.
In the early cap stage, epithelial cells (dental lamina) is referred to as the _______ because it will generate _______.
Enamel Organ
Enamel of tooth
What is the earliest sign of development of permanent dentition?
A lingual protrusion of the dental lamina during the cap stage called the primordium of the succadaneous tooth.
What is the enamel knot?
A thickening of cells on the enamel organ (dental lamina) that is important for signaling tooth development on the INNER enamel epithelium.
Cells are NON-dividing epithelial cells
It determines tooth shape! (Cusps)
What 2 layers does the enamel organ consist of?
Inner and outer enamel epithelium
The enamel organ is attached to the _______ by the __________.
ectoderm, dental lamina
What is the difference between the dental lamina and the enamel organ?
Nothing!
The enamel organ is derived from the dental lamina during early cap stage when dental lamina is ready to make enamel.
Which enamel organ layer forms enamel?
Inner enamel epithelium
What is Stellate Reticulum?
Squishy water filled epithelium area located within the enamel organ.
Cells secrete GAGs which draw in water. This forms the iconic star pattern by separating cells that remain attached via desmosomes.
Does the stellate reticulum dissappear?
YES! After enamel formation
The enamel knot has high expression of _______.
FGF4
p21
SHH
BMP2,4,6 + some more
What happens to enamel knots on teeth with complex morphology
Enamel knows can split to give rise to each cusp of the tooth creating a contour.
Bell Stage is the earliest signs of _____________.
What does it look like?
enamel and dentin formation
The cap has elongated slightly; almost triangular.
Describe the interaction between inner enamel epithelium and dental papilla during the bell stage.
Describe the cellular structure of inner enamel epithelium. (Where are nuclei located)
Inner enamel epithelium have cells that are cuboidal with centrally placed nuclei.
They will differentiate into preameloblast epithelium. These cells are with nuclei closer to the stratum intermedium.
Cells of the inner dental papilla are lining up opposite to all the preameloblast.
What happens to the dental lamina connected to the epithelium during the Bell stage?
While earlier the tooth germ maintains contaact with the ectoderm via the dental lamina, now it will start to break down. and fragment.
What is the stratum intermedium?
A layer of cells between the stratum reticulum and the Inner Enamel Epithelium
What is the shape of preameloblasts and where do they come from?
Inner Enamel epithelium cells differentiated during Bell stage
columnar, nuclei located near stratum intermedium
______ content is high in the inner enamel epithelium.
Glycogen
What compound is found in the Stratum intermedium?
Alkaline phosphatase
What is the junction of the inner and outer enamel epithelium called at the bell stage?
What is its significance?
Cervical loop
Root formation
Roots have dentin and enamel. True or false
FALSE- DENTIN ONLY
A _______ membrane separate the _____________ and the dental follicle.
A ______ membrane separates the inner dental epithelium and __________.
acellular basement membrane, OEE
acellular basement membrane, dental papilla
Apposition Stage
The cells that will give rise to enamel and cells that will give rise to dentil will oppose each other.
Basement membrane that separate IEE from dental papilla breaks down. The pre-ameoloblast cells of the IEE tell the dental papilla cells to differentiate into odontoblasts.
Odontoblasts secrete pre-dentin. This signals the ameloblasts of the IEE to secrete enamel.
Ameloblasts become __________.
Enamel
Every time a cell becomes secretory its nuclei moves ________.
AWAY from site of secretion.
Where are nuclei of ameloblasts and odontoblasts located during secretion?
Ameloblast nuclei are closer to stratum intermedium and odntoblast nuclei is furthest away from preameloblast layer.
AMN _____I______OBN
NOT ______AMN I OBN______
Enamel and dentin are secreted first at the ________.
Tip of the bell
What is amelogenesis?
Enamel formation
During amelogenesis, what key feature do ameloblasts create ?
Tomes processes, finger like projections that lay the enamel around dentinal tubules.
Amelogenesis imperfecta
A hereditary type of an enamel dysplasia where the teeth have either milk enamel or a very thin enamel that chips off.
Yellow dentin is visible
Dentinogenesis imperfecta
A hereditary type of dentin dysplasia that results in blue gray teeth with an opalescent she chipped, enamel and crowns of dentin with severe attrition
Enamel can break and fracture more easily without dentin support.
What is responsible for root formation of the teeth?
Describe the the first step of root formation.
Cervical loop
The inner enamel epithelium of Hertwig Root Sheath induces odontoblast of roots.
After dentin formation, HERS disintegrates.
Some epithelial cells may remain as Cell rests of Malassex which may become cystic and prone to infection. They will be located in periodontal ligament.
Cementum is formed by the ________.
Cells of dental follicle
Cells of dental follicle/sac contact root dentin and cells become cementoblasts.
Describe the time of development in humans and characteristics of teeth development during this time.
42-48 days: Dental Lamina
55-56 Days: Bud stage for incisors, canines, molars
14 weeks: Bell stage for deciduous teeth, bud for permanent
18 week: Dentin and functional ameoblasts in deciduous teeth
32 weeks: Dental and ameloblast in permanent first molars
Where does permanent dentition come from ?
Permanent dentition development occurs around the same time as deciduous.
Successional Lamina gives rise to permanent incisors canine and premolars
Molars, premolars, canine, and incisors all come from successional lamina. True or false
NOT MOLARS
NOT succedaneous teeth
Molars develop as your jaw grows from the regular dental lamina
Reduced enamel epithelium appears as the tooth ________.
What is it made of?
Moves to erupt.
Fused layer of
OEE
Stellate reticulum
Stratum intermediete
Ameloblasts
forms as the tooth moves to erupt.
Eventually the tooth will break through epithelium.
Tooth development start in the ______ of the mouth and goes _______.
Mesial, Lateral
The type of tooth that develops past the bud stage is dependent of the _______.
ectomesenchyme
