Lecture 10 Flashcards
A 5-6 week embryo has a thickened epithelium at the maxillary and mandibular processes. What is this thickened epithelium called?
Primary epithelial band
What does the primary epithelial band rest on?
basal lamina
What is the underlying connective tissue under the basal lamina of the primary epithelial band called?
Ectomesenchyme
Which cells from the ectoderm migrate into the mesoderm-derived mesenchyme to make it the ectomesenchyme?
NCC
What is the name of the embryonic band where teeth will develop?
Primary epithelial band
The primary epithelium thickens in response to what genes expressed by the underlying embryonic CT?
Homeobox domain genes
Sonic hedgehog (Shh) is part of over _____ genes which are expressed in cells of the developing oral epithelium and mesenchyme.
90
What are the two well supported models that explain how teeth develop into different shapes?
The field model and the clone model
Which tooth-determination model states that there are distinct, graded and overlapping fields of ectomesenchymal cells for each tooth family?
The field model
The clone model states that each tooth class is derived from a clone of _____________ cells programmed to produce teeth of a given pattern.
ectomesenchymal
The primary epithelial band of a 6-7 week embryo begins to grow into the underlying ectomesenchyme forming what two invaginations?
Vestibular lamina and dental lamina
What will the vestibular lamina become?
The space between the cheek and gingiva
What will parts of the dental lamina develop into?
teeth
T/F Primary epithelial band development proceeds from distal to mesial.
FALSE. It proceeds from mesial to distal or midline of the arch to the posterior
What will the base of the dental lamina form?
The bud of the developing enamel organ
What will the condensation of ectomesenchymal cells surrounding the dental lamina become?
The dental papilla and dental follicle
The bud will develop into what enamel producing cells?
ameloblasts
The crescent-shaped condensation that forms the dental papilla will develop into what parts of the tooth?
The dentin and pulp
At week 8, what is the bud stage characterized by?
The folding of the dental lamina into the ectomesenchyme of the jaw
What happens to the bud in a 10 week embryo?
The bud develops into the cap shaped enamel organ
What re the three layers of cells of the enamel organ?
Outer enamel epithelium (OEE), inner enamel epithelium (IEE) and the stellate reticulum in between the other two
How does the stellate reticulum form?
Like a blastocyst water is drawn in the center of the enamel organ becomes fluid-filled
What do the stellate reticulum cells secrete to draw in water inside the enamel organ?
Glycosaminoglycans
Why do stellate reticulum cells become star shaped?
They are interconnected by desmosomes that remain attached as the cells become fluid-filled and stretched around the junctions
Which enamel epithelium encloses around the dental papilla?
IEE
What do elongated ectomesenchymal cells form around the enamel organ and underlying dental papilla?
A dental sac also also a dental follicle
The dental follicle develops into some of the the ______ tissues of the tooth.
supporting
What will eventually enclose the dental follicle?
A bony crypt of alveolar bone
What are enamel-knots?
Clusters of non-dividing epithelial cells in molar cap stage teeth.
What is the probable purpose of the enamel knots?
To serve as an organizational center for cusp development.
What genes do enamel knot precursor cells express?
Shh, Bmp, Fgf, and Wnt genes
What does the enamel knot develop into in the bell stage?
the enamel cord
Around week 14, what does the enamel organ resemble as it expands?
A bell
Where do cells of the stratum intermedium (SI) develop?
Develop between the SR and the IEE
What do the SI cells and the adjacent IEE work together in the formation of?
enamel
The degeneration of the dental lamina frees the developing tooth from what?
The epithelium
What is crown pattern established by?
The folding of the IEE
What will the layer of ectomesenchymal cells next to the IEE develop into?
Odontoblasts
What is between the developing odontoblasts and ameloblasts of the IEE?
A thick basal lamina that becomes the DEJ
Where does the cervical loop of the bell stage form?
It forms where the IEE and OEE are folded into a loop around the cervical region of the developing tooth
What will the cervical loop develop into when the root of the tooth begins to form?
Hertwig’s epithelial root sheat (HERS)
What does the epithelium of the dental lamina also form?
The permanent tooth bud
What do enamel cords correspond to in molar?
Cusps
What does the differential rate of mitotic division of the IEE result in the developing crown?
Results in the contours of the developing crown
What do multiple cusps result from?
Multiple zones of differentiation of the IEE
During what stage does the dental lamina become fragmented?
Bell stage
What are some of the things any remaining DL fragments/scraps may become if they do not degenerate?
Enamel pearls, eruption cysts (may delay eruption), odontomas, or supernumerary teeth
What is the apposition stage?
The production of enamel and dentin
Where is dentin produced by the odontoblasts in the apposition stage? Where is enamel produced by ameloblasts during apposition?
- Dentin is produced in the peripheral most layer of the dental papilla.
- Enamel - in the IEE of the enamel organ
Which cells differentiate first? Odontoblasts or ameloblasts?
Ameloblasts
Which cells lead the way of tooth formation even though they differentiate second?
Odontoblasts lead the way. Ameloblasts have to wait for them to catch up before tooth formation begins in earnest
What is the name of the collar of odontogenic epithelium formed from the apical portion of the enamel organ?
Hertwig’s epithelial root sheath (HERS)
What does HERS do?
IT surrounds and guides the developing root below the cervix of the tooth
What will the HERS sheath eventually form after the root is developed?
the apical foramen
What do the odontoblasts processes extend through to get to the DEJ?
Dentin matrix, dentin and and abut against the enamel
What is the succedaneous lamina?
An epithelial structure that is responsible for the development of permanent teeth
What must odontoblasts secrete to stimulate the ameloblasts to produce enamel?
predentin
What does the deposition of enamel by ameloblasts ultimately do to the stellate reticulum?
It ultimately destroys the SR as it surpasses it and the OEE
What are the six stages of tooth development?
- bud
- cap
- bell
- apposition
- beginning of eruption
- eruption into the oral cavity
Mnemonic: better call betty after being educated
What do nerves travel with during their formation inside the tooth?
Nerves travel with blood vessels
The permanent tooth buds of which teeth develop positioned lingually and of the same dental lamina of the corresponding primary teeth?
All but the molars (incisors, canines, and premolars)
Primary dentition is established during what weeks of embryonic development? During what time is successional permanent dentition established?
- weeks 6-8
2. week 20 of fetal development to 10 months after birth
Which teeth are not succedaneous?
Permanent molars
Which succedaneous tooth replaces the primary molar?
The permanent premolar
When do permanent molars begin to develop?
Between week 20 of fetal development to 5 years after birth
Once the mandible grows long enough, what grows posteriorly into the ectomesenchyme and forms tooth buds for the permanent molars?
Dental lamina
Where is the enamel matrix deposited by ameloblasts at the earliest stage of enamel formation?
On previously formed predentin
What does the maturation of enamel matrix remove from the enamel organ? What mineralizes the maturing enamel matrix?
Organic material (proteins) and water. Calcium and phosphate
What do active ameloblasts have to fuel the transport of organic material out and mineral into the enamel?
Many mitochondria
What structure helps to orient enamel crystals?
Tome’s process.
What are the three basic stages of amelogenesis?
- Presecretory stage
- Secretory stage
- Maturation stage
What happens during the presecretory stage of amelogenesis?
Rough ER and Golgi of ameloblasts develop and produce vesicles of proteins
What happens during the secretory stage of amelogenesis?
ameloblasts deposit the proteins and minerals of the enamel
What happens during the maturation stage of amelogenesis?
Ameloblasts import mineral ions to harden the enamel
What are amelogenins?
A group of low molecular weight proteins that establish and maintain spacing between enamel rods in early stages of enamel development.
Which protein group accounts for 90% of the enamel proteins and lays the scaffolding for early enamel development?
Amelogenins
Which group of proteins accounts for 10% of the enamel proteins and is thought to help the ameloblasts hold on to the underlying layer on which they ride?
Nonamelogenins
Which enamel proteins are not present in mature enamel?
Nonamelogenins
What are three important nonamelogenins?
Ameloblastin, enamelin, and tuftelin
Which specific nonamelogenin is believed to help ameloblasts adhere to the enamel surface during the secretory stage?
Ameloblastin
How does the absence of ameloblastin affect the differentiation of ameloblasts?
Absence of this protein causes the differentiating ameloblasts to detach from dentin and enamel formation stops
Which of the three nonamelogenins is thought to be a crystal promoter?
Enamalin is believed to promote apatite crystal elongation
Which enamel protein is thought to be the least important?
Tuftelin is under contention of even being a functional enamel protein
What does the Tome’s process secrete?
Developing enamel
The enamel rod and interrod enamel is left behind the ameloblast cell and _____ the path taken by the cell
records
What part of the Tome’s process deposits enamel unto dentin?
proximal portion of Tome’s process (ppTP)
What parts of the columnar ameloblasts point into the enamel matrix creating a “stair-step” or “saw-tooth” appearance
Tome’s processes
During enamel maturation, how often do ameloblasts alternate their morphology between smooth and ruffled?
Every 8 hours
What percentage of the time, during enamel maturation, do ameloblasts spend secreting in the ruffled stage?
80% of the time
What do ameloblasts do during the smooth stage of their time?
The re-absorb enamel protein fragments and calcium ions for active crystal growth of enamel
During what enamel hardening stage/phase is the pH of the enamel more acidic? Less acidic or neutral?
- Ruffle-ended stage is more acidic
2. Smooth-ended stage is near neutral
How does the pH of the enamel influence crystal formation?
During the reabsorption of the smooth stage a less acidic pH makes the environment less soluble and allows to crystals to precipitate. A more acidic environment keeps a mineral in solution
During what enamel maturing stage do the ameloblasts incorporate inorganic material into the enamel? During what stage do ameloblasts absorb water and degraded proteins from the enamel matrix?
- Ruffled
2. Smooth
What is perikymata?
Shallow, periodic furrows on the labial surface of enamel
What are the Striae of Retzius thought to be associated with?
Either the weekly rhythm of enamel production during the development of a tooth or the addition of new ameloblast cohorts as the crown of a tooth gets bigger
What is it thought that the neonatal line inside enamel represents?
The great physiological changes occurring during birth
What are von Korff’s fibers? Where do they originate?
- Large type I collagen fibers associated with fibronectin.
2. These fibers originate between the odontoblasts and extend to the inner enamel epithelium.
The odontoblasts produce predentin that will activate the ameloblasts to produce enamel. Which cells release signaling molecules that influence odontoblast differentiation?
Ameloblasts release the signaling molecules. It’s like a back and forth activation: ameloblasts form first, which activate odontoblasts, which make predentin, which activates enamel production by the ameloblasts that started it all
Dentin and enamel both create patterns of incremental lines. What does this suggest about the growth of these two dental tissues?
They undergo pulsed growth and major physiological changes during formation may leave traces not unlike tree-ring growth
What is the main organic component of predentin matrix?
Type I collagen
What does predentin mineralize as?
Hydroxyapatite
Dentin is similar to what matrix of the bone?
osteoid matrix of the bone
What does newly formed dentin surrounding odontoblast processes form?
Dentinal tubule
What is the more mineralized sheath of dentin immediately surrounding the dentinal tubule called?
Peritubular dentin
The dental follicle gives rise to what three cells that are part of the periodontal apparatus?
Osteoblasts, fibroblasts, and cementoblasts
What do the residual portions of Hertwig’s epithelial root sheath (HERS) fragmentation form?
cell rests of Malassez
What is the likely function of cell rests of Malassez
Probably support PDL tissue homeostasis and may even contribute to periodontal tissue regeneration
