Embryology Flashcards
At week 4 a membrane covering the primitive mouth separates the outer ectoderm layer of the developing face with the inner endoderm of the pharynx. Which best identifies this membrane?
oropharyngeal
Around day 15-17 during gastrulation these cells differentiate into the 3 germ layers. What are the names of these cells?
epiblast cells
During the development of the mandible, this cartilage forms a template for the bone which is made by intramembranous ossification. What is the name of the cartilage?
Meckel’s cartilage
After coronal dentine formed and tooth eruption commences, when the cervical loop, outer enamel epithelium and inner enamel epithelium fuse to determine root shape. What does this then become known as?
Hertwig’s epithelial root sheath
What is this tooth known as?
mesiodens
What are these teeth known as?
What teeth does it most commonly affect?
supernumerary teeth
premolar region
What stage of development are supernumerary teeth formed?
initiation stage
What stage of development does macrodontia/microdontia occur?
bud stage
At what stage does dens in dente develop?
cap stage
At what stage does germination/fusion occur?
cap stage
At what stage does tubercle occur?
cap stage
At what stage does concrescence occur?
apposition/maturation stage
What are the two main eruption models called?
continuous and limited eruption
What are the 3 phases of eruption?
- pre-eruptive
- pre-functional
- functional
What phase of eruption is being described?
- localised movements of the socket and movements due to growth
pre-eruptive phase of eruption
What phase of eruption is described?
“major period of axial movement of tooth from developmental to functional position”
pre-functional phase of eruption
What phase of eruption is being described?
“axial movements to accommodate for occlusal wear”
functional phase of eruption
Crown completes … eruption (at approx. 3 years in adult)
before
Root completes … eruption (at approx 3 years in adult)
after
Teeth normally erupt when … of root length formed
2/3
How prevalent is prenatal eruption?
1 in 2000 births
Term used for when patients teeth are at rest and should not be meeting
vertical dimension at rest (RVD)
Term used for when patients teeth are meeting
vertical dimension at occlusion (OVD)
Term used for the space when patient is at RVD
free way space (FWS)
What happens when there is an increase in free way space?
functional eruption
What is being described?
- shedding of the deciduous teeth - root resorption
- bone remodelling
- PDL, cementum and dentine resorbed
- movement of the tooth germ
- root growth
- development of the cementum and PDL
some of the physical changes that happen during eruption
What is being described?
- bone resorption
- sub epithelial connective tissue thins
- reduced enamel epithelium fuses with oral epithelium (compressed enamel organ)
- tooth erupts through epithelial cuff
- Nasmyths membrane, thin membrane of the reduced enamel epithelium that covers the tooth ones it has erupted (reminence of the compressed enamel organ)
some of the tissue changes during eruption
Name 3 factors that eruption depends upon?
- space in the eruption course created by the crown follicle
- eruption pressure triggered by innervation in the apical root membrane
- the ability of the PDL to adapt to eruptive movements
What role does the periodontal ligament play in tooth eruption?
- myofibroblasts in PDL have contractile potential
- turnover of collagen in PDL recorded
What is shown on the image? And how do they occur?
eruption cyst
where the tooth bud tries to push through the epithelial cuff and has not succeeded so therefore creates a cyst
What can cause a disturbance in tooth formation?
- follicle - trauma
- virus
- failure to initiate resorption
- genetic conditions
What systemic causes can then cause eruption deviations? (failure and delayed eruption)
- endocrine and various syndromes
What factors can cause local eruption deviations such as failure, ectopic, impaction or transposition space? (5 points)
- tumours
- supernumerary teeth
- cysts
- primary tooth not shed
- ankylosis - a condition where a tooth fuses to the bone
What is shown on the image? And how is it managed?
- dentigerous cyst - fluid filled cyst - an example of a local eruption deviation that can affect tooth erupting
- can be surgically removed or cut into and deflated
What condition is shown on the image? And how is it caused?
- cherubism
- caused by multiple cysts inside the jaw
What is shown on the image? And what symptoms could a patient have?
- complex odontoma (benign tumour) - can contain teeth in some cases
- can apply pressure to the inferior alveolar nerve and cause pt to have numbness
What is shown on the image? And how can it be treated?
- mesiodens
- remove the supernumerary
What is the name of the tooth on the image? And how is it caused?
- divergent root
- disturbance in the formation of Hertwigs root epithelial sheet
- trauma
What is meant by the term Anodontia?
- missing teeth
What is meant by the term Hypodontia?
- complete or partial missing teeth
What is meant by the term Oligodontia?
- more than 6 teeth missing
What are the 4 main factors that cause disturbances in tooth formation?
- hereditary
- endocrine dysfunction, systemic disease
- excess radiation
- disturbance during the initiation stage
What are the most common groups of teeth that are more prone to being missing?
- upper incisors and laterals
- lower premolars
- wisdom teeth
What are some conditions that cause missing teeth?
- cleft lip/palate
- ectodermal dysplasia
- down syndrome
- amelogenesis imperfecta
What are some conditions that can cause multiple supernumerary teeth?
- Ehlers-danlos syndrome (also pulp stones and roots that are deformed)
- gardner syndrome (multiple polyps, autosomal dominant)
- cleidocranial dysostosis (poorly developed or no collarbones)
What are some systemic conditions that can cause eruption disturbances?
- malnutrition
- hypothyroidism
- hypopituitarism
- hypoparathyroidism
- anaemia
- renal failure
What is this a description of?
- in these bands, enamel prisms are arranged in layers of varying thickness at about right angles to each other
- strengthen the enamel and prevent cracks from propagating through the tooth
Hunter-Schreger bands
What are the 3 periods of prenatal development and when do they occur?
- preimplantation period, first week
- embryonic period, second to eighth week
- fetal period, third to ninth month
What happens during the preimplantation period of development?
Zygote - fertilised egg divides early on, then develops into blastocyst
- Zygote undergoes mitotic cleavage (cell division) in the first few days after it has been fertilised
- It then compacts and then will move down through the Fallopian tubes to the side of the uterus and become implanted
What happens during the embryonic period of development?
Implantation of the blastocyst into uterus during 2nd week
Disc of the embryo starts to develop
Embryo starts to develop features of a human baby
What happens during fetal period of development?
Embryo develops into foetus
What is the name of this process?
Description - One cell group act on another, leads responding tissue to develop
Induction
What is the name of this process?
Description - Controlled cellular growth and accumulation of by-products
Proliferation
What is the name of this process? Description - Change in identical embryonic cells to become distinct structurally and functionally
Differentiation
What is the name of this process? Description - Development of specific tissue structure or differing from due to embryonic cell migration or proliferation and inductive interactions
Morphogenesis
What is the name of this process? Description - Attainment of adult function and size due to proliferation, differentiation and morphogenesis
Maturation
What are the names of the three germ layers?
- Ectoderm (outer layer)
- Mesoderm (middle layer)
- Endoderm (inner layer)
What germ layer do the following derive from? - Epithelial linings of the aero and digestive tracts, gut, liver, stomach and pancreas
Endoderm cells
What germ layer do the following derive from? - Muscle and connective tissue, cartilage, blood, bone, serous membranes
Mesoderm cells
What germ layer do the following derive from? - Skin and nerves, epidermis, nervous system, tooth enamel, neural crest cells
Ectoderm cells
What germ layer do neural crest cells derive from?
Both ectoderm and mesoderm, migration happens from ectoderm cells to mesoderm cells
What does the blastocyst contain that then becomes the foetus?
Inner cell mass
What happens to the inner cell mass once the blastocyst has implanted into the uterus wall?
- Moves to one side and becomes classified as epiblast cells
What are the names of the two types of cells that are formed within the blastocyst and migrate to opposite sides?
epiblast and hypoblast cells
What is the term used for a disc with two sides?
bilaminar disc
What does the yolk sack of the embryo become?
the supporting structure of the uterus
A (embryo)
What structure is labelled A?
yolk sack
B (embryo)
What type of cells are shown on the image labelled B?
hypoblast cells
C (embryo)
What structure is shown on the image labelled C?
bilaminar disc
D (embryo)
What type of cells are shown on the image labelled D?
epiblast cells
What is the term used to describe this process ‘‘the purpose of … is to position the 3 germ layers endoderm, mesoderm and ectoderm which later develop into certain bodily systems’’ ?
gastrulation
What part of the foetus develops at the primitive streak and the primitive node?
spinal cord
When does gastrulation occur?
Day 15-17
During gastrulation, we now have the distinction of the 3 germ layers and there is an invagination of the tissues at the … ?
primitive streak (midline)
During gastrulation, epiblast cells turn into the … ?
ectoderm layer
During gastrulation, there is an ingrowth of the germ layer in the middle which will become the future … ?
mesoderm layer
During gastrulation, on the other side of the disc where the hypoblast cells will disappear, the … will emerge?
endoderm layer
What is meant by the term ‘trilaminar embryo’ ?
there are 3 layers, endoderm, ectoderm and mesoderm
What is the name of the process when the central nervous system is developed?
neurulation
When does neurulation occur?
Day 18-28
What is an example of a neural tube defect? (where it does not close all the way during neurulation)
spina bifida
What supplement do pregnant women take to encourage closure of the neural tube during neurulation?
folic acid
During neurulation, there is the disc of 3 layers, in the midline there is a joining of the cells that become known as the … ?
neural plate
During neurulation, the process of the 3 layers folding in on themselves is called … ?
invagination
During neurulation, neural plate cells become the … ?
neural groove (a groove down the midline of the disc)
During neurulation, the neural groove comes together at the top and becomes the …
neural tube
The neural tube is the future …
spinal cord
After neurulation, when there has been closure of the groove and the neural tube is developed, some of the cells from the ectoderm layer start to migrate, these are called the … ?
neural crest cells
After neurulation, the neural crest cells move into the tissues and become a tissue called … ?
ectomesenchyme
In the head and neck, … contribute to the traditionally mesodermal tissues
neural crest cells
The cranial end of the embryo indicates the region of the future … ?
brain
The caudal end of the embryo indicates the region of the future … ?
spinal cord
What is the name of the membrane that separates the 3 germ layers once the body has reached full growth as an adult?
basal membrane
What are two examples of when the basal membrane is broken down and you have ectodermal tissues cross over?
- squamous cell carcinoma
- formation of enamel
How far into development does the formation of the pharyngeal arches begin?
4 weeks
During formation of the pharyngeal arches, sensory organs are described in the foetal stage as … ?
placodes
The mandible is formed from the … pharyngeal arch?
first
Just above the first pharyngeal arch, there is something called the maxillary prominence, which becomes the … ?
maxilla
During formation of the pharyngeal arches, … come from the ectodermal area and migrate into the pharyngeal arches
neural crest cells
What condition can a baby have if the maxilla does not fuse at the midline?
cleft palate
During the contribution of the germ layers to the pharyngeal arches, there is an inside and an outside of the arches, the inside lining is … ?
endoderm
During the contribution of the germ layers to the pharyngeal arches, there is an inside and an outside of the arches, the outside lining is … ?
ectoderm
During the contribution of the germ layers to the pharyngeal arches, there is an inside and an outside of the arches, the middle lining is … ?
neural crest cells and mesoderm
What are the 4 components of the pharyngeal arches?
1 - central cartilage rod (forms skeleton)
2 - muscular component
3 - vascular component (aortic arch artery)
4 - nervous component (cranial nerves)
On the inside of the pharyngeal arches is the endoderm and on the outside is the ectoderm, normally these are separated by the tissues in the arch, but where they meet in between each arch, they come together, so the endodermal tissue will touch the ectodermal tissues. From the outside, we call this area a … ?
cleft
On the inside of the pharyngeal arches is the endoderm and on the outside is the ectoderm, normally these are separated by the tissues in the arch, but where they meet in between each arch, they come together, so the endodermal tissue will touch the ectodermal tissues. From the inside, we call this area a … ?
pouch
Where the pharyngeal arches meet, they form a membrane and those membranes end up being tissues that that make up the foetus. What pharyngeal arches do they derive from?
first and second
What is the name of the early oral cavity?
the stomodeum
At the early stage of development, the early oral cavity is separated from the amniotic fluid by a membrane and this is called the … which breaks down
oropharyngeal membrane
What does the otic placode become in early development?
the ear
What cranial nerve is associated with the 2nd pharyngeal arch?
facial
What cranial nerve is associated with the 1st pharyngeal arch?
trigeminal
What cranial nerve is associated with the 3rd pharyngeal arch?
glossopharyngeal
What cranial nerve is associated with the 4th pharyngeal arch?
vagus
What cells do the cranial nerves derive from?
neural crest cells and ectoderm cells
What component of the oral cavity comes from more than one of the pharyngeal arches?
the tongue
What are the stages of final position of the tongue?
- Tongue takes up the whole of the oral cavity
- Due to there being no nasal septum, there is an open space where the tongue will develop into
- Then the maxilla will develop, tongue will retract and sit into its final position
What develops in the 1st membrane that separates the endoderm and ectoderm of the pharyngeal arches?
ear/eardrum
What develops in the 2nd membrane that separates the endoderm and ectoderm of the pharyngeal arches?
palatine tonsil
What develops in the 3rd membrane that separates the endoderm and ectoderm of the pharyngeal arches?
thymus and inferior parathyroids - before migrating to the area they will eventually end up
What develops in the 4th membrane that separates the endoderm and ectoderm of the pharyngeal arches?
superior parathyroids
What pharyngeal arch does the maxillary prominence derive from?
first
The … in the pharyngeal arches are there for support and will disappear later on, only there as a scaffold
cartilage rods
What is the name of the cartilage in the second pharyngeal arch?
Reicherts cartilage
What is the name of the second pharyngeal arch?
hyoid
What structures does the 1st pharyngeal arch form?
jaws
middle ear bones
What structures does the second pharyngeal arch form?
facial muscles
middle ear bones
hyoid bone
tongue
What structures does the 3rd pharyngeal arch form?
hyoid bone
tongue
What structures does the 4th pharyngeal arch form?
laryngeal cartilages
tongue
What are the name of the two parts that the neurocranium can be divided into?
calvaria
chondrocranium
What is connective tissue?
- A group of tissues in the body that maintains the form of the body and its organs
All dental tissues (except enamel) come from which germ layer?
mesoderm
What germ layer does enamel come from?
ectoderm
What are the 3 components of connective tissue?
- Cells
- Extracellular matrix
- Ground substance - gel-like substance
A lot of the cells that came up connective tissue will produce a protein that will come out of the cell membrane called … that will form a structure
extracellular matrix
What happens to the cells in connective tissue once they have formed a tissue?
some will sit in the connective tissue and some will retract and disappear
What is the role of connective tissue?
- scaffolding and support
- mobility and stretching
- homeostasis
What is the term used for maintenance or keeping balance in the tissues?
homeostasis
What is homeostasis?
- harbours stem cells for wound healing
- reservoirs of nutrients
- holds water
When thinking about cells in connective tissue.
What are the cells called that secrete collagen for wound healing and maintain structure?
fibroblasts
When thinking about cells in connective tissue.
What are the cells called that produces muscle tissue and fibres?
myofibroblasts
When thinking about the cells in connective tissue.
What are the cells called that are fat producing cells?
lipoblasts
When thinking about cells in connective tissue.
What are the cells called that are the cartilage producing cells?
chondroblasts
When thinking about the cells in connective tissue.
What are the cells called that produces bone matrix?
osteoblasts
When thinking about cells in connective tissue.
What are the cells called that create stem cells for specific tissues?
tissue specific stem cells
When thinking about cells in connective tissue.
What are the cells called that produce something, secretes extra-cellular matrix?
a blast cell
When thinking about cells in connective tissue.
What are the cells called that when it has produced something, the cell will become dormant?
a cyte cell
When thinking about cells in connective tissue.
What are the cells called that break down something?
a clast cell
What is a monocyte cell?
a white blood cell
What are the 3 components of the extra-cellular matrix?
- fibrous structural proteins
- cell-surface proteins
- glycoproteins
What is type 1 collagen produced by and where is it found?
Produced by fibroblasts, osteoblasts or odontoblasts
Found in scar tissue, bone, teeth, tendons and ligaments
What does type 2 collagen make up?
50% hyaline cartilage
What is type 3 collagen produced by and where is it found?
Produced by fibroblasts
Found in arteries and skin
Where is type 4 collagen found?
basement membranes lining cavities and surfaces of organs
What is the role of ground substance?
provide a route for communication and transport between tissues
What are the names of the 2 mechanisms involved in bone differentiation and formation?
intramembranous ossification
endochondral ossification
Most of the structures in the head are formed by … apart from the base of the skull
intramembranous ossification
Most of the long bones in the body are formed by …
endochondral ossification
What is the difference between intramembranous ossification and endochondral ossification?
intramembranous - doesn’t start with cartilage
endochondral - starts with hyaline cartilage
… bone is the hard, outside of the bone
cortical
… is the middle of a bone which is the spongy part
trabecular
What is inside the inner most space of a bone?
stem cells
How is bone formed?
- made from osteoblast cells that secrete osteoid matrix
- osteoid is mineralised to become bone, 60% organic
What are the cellular components of bone and their roles in formation?
- osteoblasts - lay down the osteoid matrix
- osteocytes - osteoblasts in bone matrix lay dormant
- osteoclasts - break down some of the bone in order to keep it healthy
How does alendronic acid work?
Stops the osteoclasts from breaking down bone, making the bones become denser and less likely to fracture in patients with brittle bones
What are the risks of alendrotnic acid in dentistry?
Osteonecrosis of the jaw, after an XLA it can prevent the tissues from healing
How is cartilage formed?
- Cartilage develops with chondroblast cells secreting cartilage matrix
- Once trapped within the matrix, chondroblasts differentiate into chondrocytes
What are the two types of growth in which cartilage is formed and what are they?
- Appositional growth, layered growth
- Interstitial growth, deep in tissues
What is perichondrium? And what does it provide for cartilage?
A membrane that lies outside of the bone
Cartilage relies on this as it is avascular
What are the 3 main types of cartilage?
- Hyaline cartilage
- White fibrocartilage
- Yellow elastic fibrocartilage
What description of cartilage does this most describe? ‘most common, contains only collagen, weakest, all cartilage starts as this’
hyaline
What description of cartilage does this most describe? ‘never found alone but with hyaline, TMJ, has no perichondrium, strong’
white fibrocartilage
What description of cartilage does this most describe? ‘numerous elastic fibres as well as collagen, ear, larynx, epiglottis’
yellow elastic fibrocartilage
All of the bones of the skull are formed from what process?
intramembranous ossification
What part of the skull does the following description of the development best apply? ‘the bones are formed from growth centres from intramembranous ossification, condensation of the connective tissues then occurs, bone cells enter into these areas and start to lay down the bone matrix which then becomes calcified, this is then the centre where the bone expands towards the periphery, forming the joins of the suture as it matures’
the calvaria
What are the following stages describing the cellular development of?
- Mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification centre
- Osteoblasts make an extracellular matrix ‘osteoid’
- Osteoid matrix becomes mineralised, rudimentary bone tissue is formed
intramembranous ossification of the calvaria
What is the periosteum?
fibrous membrane, providing protection and blood supply to bone
When does the process of blood vessels being developed into the bone tissues begin?
when the bone matrix is being laid down
What feature of the skull is being described? ‘contain actively dividing cells, allow the skull to grown to accommodate expanding brain, unique to the cranium’
sutures
What part of the skull is the only part to be developed by endochondral ossification?
the base of the skull (chondrocranium)
What week of foetal development do the endochondral ossification centres sit in order to make the structure for all the different foramina in the base of the skull?
5th and 8th week
What are the 5 zones involved in the endochondral ossification formation of the chondrocranium?
- Resting zone
- Proliferating zone
- Hypertrophic zone
- Ossification or mineralisation zone
- Primary spongiosa
What is the name of the process described and what is being developed?
- All of the cells in the resting zone are cartilage cells, then something starts to happen in the tissues
- The cells then start to expand and become balloon-like in the hypertrophic zone
- Once this has occurred, the osteoblasts come into the tissues and the chondrocytes in the hypertrophic zone die off
- They are then replaced by the matrix that the osteoblasts laid down and this is how the bone formation/endochondral ossification takes place
endochondral ossification formation of the chondrocranium
What part of the skull does this summary of development describe?
- plates of membranous bone
- separated by fontanelles and sutures
- formed by intramembranous ossification
calvaria
What part of the skull does this summary of development describe?
- begins as small cartilage plates
- formed by endochondral ossification
chondrocranium
What does the frontonasal process/prominence develop into?
forehead and front of the nose
What does the lens placode later become?
future eye
What does the nasal placode later become?
future nose
What are being described? ‘On outer surface, sitting laterally on the face, specialised thickened ectoderm at location of special sense organs’
placodes
Is the mandible formed by intramembranous or endochondral ossification?
intramembranous
What is this the formation of? Fill in the blanks
- In the mandibular arch, there is Meckel’s cartilage, the cartilage sits there as a template to provide structure and rigidity to support the bone process of the …
- The bone tissues will form by intramembranous ossification for the majority of the …, so connective tissue cells are laid down which will become osteoblast cells and produce osteoid matrix.
mandible
What is the following stages describing the end of development of?
- When the bone is formed, you have growth of the bone towards the midline, this is where the chin is and where the growth finishes
- Meckel’s cartilage disappears after bone formation
mandible
Is the maxilla formed by intramembranous or endochondral ossification?
intramembranous
When does foetal development of the maxilla begin?
4 weeks
When does foetal development of the mandible begin?
4 weeks
Stages of the … of development
- The maxilla grows towards the front, but also grows on the inside to form the palate in the oral cavity, at this stage there is no divide between the nasal and oral cavity.
- … moves forward towards the midline but doesn’t join up fully, they form a junction with the frontonasal process which goes down and fuses with the …
maxillary process (where the maxilla joins with the palate and the frontonasal process)
What parts of the face come from the medial nasal process?
the midline and philtrum
What part of the face comes from the lateral nasal process?
side of the nostril
What part of the mouth comes from the frontonasal process?
where the maxillary incisors are
Stages of the … of development
- Can be divided into different sections, where the nasal placodes, there is something called the medial nasal process and the lateral nasal process
- The lateral nasal process will join up to the maxillary process and also the medial nasal process and grow towards the midline and will become the tip of the nose
frontonasal process (where the frontonasal process joins up with the maxillary process)
What is a consequence to the baby if there is failure of the fusion of the maxillary process with the medial nasal process?
unilateral or bilateral cleft lip
What is the following a summary of the development of?
- follows Meckel’s cartilage
- formed mainly by intramembranous ossification
- woven bone turning to lamellar bone
mandible
What is the following a summary of the development of?
- formed by intramembranous ossification
- midline palatine suture for lateral growth
maxilla
What week of foetal development does palate formation begin?
5 weeks
What week of foetal development is the palate fully completed?
12 weeks
What are the 3 stages of palate formation?
- primary formation
- secondary formation
- final completion
What part of the palate is meant by the following statement? ‘anterior segment that comes from the frontonasal process, grows down and joins up to the maxilla’
primary palate
What part of the palate is meant by the following statement? ‘the back of the palate, the junction of the plates at the back’
secondary palate
What part of the palate is meant by the following statement? ‘where the bone is fully developed, but also all the structures that sit behind the palate like the muscles, uvula etc.’
final palate
What structure is being developed in this process?
- inter maxillary segment formation from fusion of the two medial nasal processes.
primary palate
What structure is being developed in this process?
- maxillary processes form two separate palatal ‘shelves’, they fuse together and join in the midline at the front first to form the … and this is where you have the closing of the oral cavity from the nasal cavity’
secondary palate
What 2 things have to happen during palate formation in order to have fusion at the midline?
- tongue has to move down posteriorly of the oral cavity
2. two palatal process have to change direction and start growing towards midline
Is the palate developed by endochondral ossification or intramembranous ossification?
intramembranous
What part of the palate is not developed by intramembranous ossification?
posterior of the secondary palate (soft palate and uvula)
Fill in the blanks
There is a condensation, almost like a horseshoe shape arch in the maxilla and the mandible ad this is called the …, from this you have dental buds where the stage of tooth development is initiated and this determines where the tooth is going to go which is genetically pre-programmed
dental lamina
What stage of foetal development does the initiation stage of tooth development happen?
Week 6
What is the term used to define the following?
‘cell changes, change function, change into different types of cells’
proliferation
What is the term used to define the following? ‘describes the form of how the tooth is shaped’
morphogenesis
What is the term used to describe the following? ‘tissues being laid down’
apposition
What is the term used to describe the following? ‘fully mineralises and becomes functional tooth’
maturation
What does the vestibular lamina become?
future sulcus
What stage of tooth development is being described?
- 6th week in utero
- Ectodermal epithelium develops horseshoe shape thickening, which will becomes the dental lamina, next to deeper ectomesenchyme
- Neural tube marginal cells called neural crest cells migrate into the mesenchyme beneath the dental lamina, to form ectomesenchyme
- Ectoderm informs ectomesenchyme that a tooth will form, but the ectomesenchyme dictates which tooth and where
initiation stage
Complex interaction between epithelial and mesenchymal tissues in tooth development.
Finish the sentence..
Between the formation of the enamel and dentine, growth factors and transcription factors signalling between the tissues, have to have … there first before the …
DENTINE there first before the ENAMEL
What stage of tooth development is being described?
- 8th week in utero
- proliferation
- down growth of the dental lamina with 10 buds per arch for deciduous arch and lingually placed for permanent buds starting anteriorly of the mandible
- ectomesenchyme responds by proliferating
- leads to early enamel organ surrounding mesenchyme
bud stage
What stage of foetal development does the bud stage of tooth development happen?
8th week
What stage of foetal development does the cap stage of tooth development happen?
Week 9-10
What stage of tooth development is being described?
- 9th to 10th week in utero
- further proliferation of epithelium, dictates shape of crown morphogenesis
- epithelium differentiates to form the enamel organ
- enamel organ forms a cap shape that surrounds the ectomesenchyme which is now called the dental papilla
- a surrounding mass of ectomesenchyme is named dental sac
cap stage
What does the dental papilla develop into?
the pulp and dentine
What does the dental sac develop into?
the cementum and periodontal ligament
What is meant by the description?
- the cells that will produce the crown of the tooth
enamel organ
In the cap stage of tooth development, what are the 3 elements that the tooth germ comprises of?
- enamel organ
- dental papilla
- dental sac
What week of foetal development does the following happen?
- At this stage, there is a big change inside the mouth, at this point there is another dental lamina being laid down or there is another bud coming along and this is attached to some of the tooth germs in there and this is where the permanent teeth come from
Week 10 (cap stage)
What stage of tooth development is being described?
- 11th-12th week in utero
- no mineralised tissues at this point
- enamel organ now comprised of: outer enamel epithelium, stellate reticulum, stratum intermedium, inner enamel epithelium
Dental papilla differentiates into:
- outer cells (future odontoblasts)
- central cells (future pulp)
bell stage
What week of foetal development does the bell stage occur?
Week 11 and 12
During the bell stage of foetal development, what 4 elements does the tooth germ become comprised of?
- outer enamel epithelium
- stellate reticulum
- stratum intermedium
- inner enamel epithelium
In the appositional/secretory stage of tooth development, what do you need to have the presence of for the formation of enamel and dentine?
enamel organ and dentine matrix
What stage of tooth development is being described?
- enamel, dentine and cementum laid down as a matrix
- preameloblasts and preodontoblasts formed
- preodontoblasts lay down predentine, basement membrane disintegrates forming EDJ and then become ameloblasts and secrete enamel matrix from Tomes process
appositional stage
What are the key elements in the enamel matrix (organic)?
- amelogenin
- enamelin
The tooth root, made of root dentin and root canals (where dental pulp lives), forms from a combination of three structures: …, … and another important group of cells known as …
- dental papilla
- dental sac
- hertwigs epithelial root sheath
What is the name given for the following?
They are discrete clusters of residual cells from Hertwig’s epithelial root sheath (HERS) that didn’t completely disappear
epithelial rests of Malssez
Cementum provides attachment for the periodontal ligament via …
sharpey’s fibres
What condition is shown on the image?
What teeth does it commonly affect?
microdontia (abnormally small teeth)
permanent maxillary lateral incisors (peg laterals) and third molars with partial microdontia (peg molar)
What condition is shown on the image?
macrodontia (abnormally large teeth)
What condition is shown on the image?
What teeth does it usually affect?
dens in dente
permanent upper lateral incisors
What condition is shown on the image?
gemination/fusion
What condition is shown on the image?
tubercle
What condition is shown on the image?
concrescence
What condition is shown on the image?
enamel dysplasia
What condition is shown on the image?
amelogenesis imperfecta
What condition is shown on the image?
dentinogenesis imperfecta
What condition is shown on the image?
enamel pearl
What dental tissue is being described?
- hard, non vascular and no sensation
- 96% mineralised, hydroxyapatite crystals, surrounded by amelogenin protein, enamelin and water
- cannot replace itself, but very hard to destroy
- rods are 5 microns diameter, getting wider nearer the surface
enamel
What process is being described?
A histologic landmark identified on an ameloblast, cells involved in the production of tooth enamel. During the synthesis of enamel, the ameloblast moves away from the enamel, forming a projection surrounded by the developing enamel.
Tomes process
The production of what dental tissue is being described?
- ameloblasts secrete enamel protein matrix, which mineralises due to addition of calcium phosphate crystals
- ameloblasts secrete through Tomes process
- crystals laid down in 2 different orientations (rod and interod)
- ameloblasts travels away from the EDJ, rods intertwine increasing the strength (hunter-schreger bands)
enamel production
What dental tissue is being described?
- incompletely mineralised ribbon-like structures that run longitudinally to the tooth axis and extend from the dentinoenamel junction (DEJ)
enamel tufts
… are fissure-like defects that extend along the longitudinal axis of the tooth down to the dentin layer (also get their name when enamel tufts are at full thickness)
enamel lamellae
What element of enamel structure is being described?
- incremental growth lines, oblique from EDJ to surface, also in cross sections seen as rings
- possibly due to Tomes process restriction at end of secretory phase
- prominent … line is called neonatal line, but other variations may reflect illness, fever and may cause hypoplasia
- on surface they are represented as shallow waves called perikymata
striae of Retzius
What dental tissue is being described?
- produced by odontoblasts
- by weight 70% inorganic (hydroxyapatite)
- softer than enamel but harder than bone
- 20% organic and 10% water
- elastic and flexible, underpins enamel and prevents it from fracturing, yellow giving teeth colour depending on enamel thickness
dentine
The production of what dental tissue is being described?
- Formed by odontoblasts and composed of tubules with odontoblast process within
- Odontoblast end up within and form outermost layer
- Vital like bone and very sensitive
- Vascular connective tissue providing nourishment
pulp
What microscopic dental structure is being described?
- dentinal tubules
- 2.5 micrometers wide at pulpal surface
- occlusally directed S shaped curves, as odontoblasts get crowded as they retreat towards pulp space, finer secondary curves
dentine structure
What are the 4 types of dentine?
- mantle
- primary
- secondary
- tertiary
What type of dentine is being described?
- First formed 30-150 micrometers of the primary dentine, first formed, less mineralised, loose collagen and trapped odontoblast terminal branches
mantle dentine
What type of dentine is being described?
- Most of the tooth
primary dentine
What type of dentine is being described?
- After root formation is completed, throughout life at pulpal edge, reducing pulp size
secondary dentine
What type of dentine is being described?
- Induced by stimuli
- (reparative), responsive to events e.g. caries, fracture, cavity prep, irregular tubules, less permeable and protects the pulp, osteodentin (fast formed), type I and III collagen
tertiary dentine
What are the 3 types of microscopic dentine?
- peri/intratubular
- intertubular
- interglobular
… contains dentinal tubules that have become completely obliterated by the deposition of peritubular dentin. This reaction by irritated odontoblasts forms a protective wall between themselves and noxious stimuli
sclerotic dentine
What component of dentine is being described?
- an area of empty dentinal tubules beneath a carious lesion where the odontoblasts have died and not laid down sclerotic dentin
dead track
What are the incremental growth lines of dentine called?
lines of Von Ebner
Metabolic disturbances (birth, fever, infections) accentuate Von Ebner lines called…
contour line of Owen
What tooth structure is being described?
- attached to the root dentine
- provides anchorage for collagen fibres of the PDL (sharpeys fibres)
cementum
What are the two types of cementum?
- acellular: first formed over root dentine, covered by cellular cementum
- cellular: contains cementum forming cells
What is being described?
- epithelial remnants of the Hertwig’s epithelial root sheath (HERS) that are involved in the formation of tooth roots
epithelial rests of Malassez
What are the 4 functions of the periodontal ligament?
- support
- sensory
- nutritive via blood supply
- homeostasis
What are the 3 elements of the periodontal ligament?
- cells
- fibres
- ground substance
What are the 5 elements of the pulp?
- collagen
- ground substance
- blood vessels
- rudimentary lymphatics
- nerves
What 2 types of nerves are in the pulp?
- myelinated nerves - sensory, in dentinal tubules
2. unmyelinated nerves - are associated with the blood vessels
What dental structure is being described?
- supports and protects the maxillary and mandibular teeth
- made up of both compact lamina dura and woven or spongy bone
alveolar bone
What is being described?
thin membrane of the reduced enamel epithelium that covers the tooth once it has erupted (reminence of the compressed enamel organ)
nasmyths membrane
