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Craniofacial Embryology > Lecture 10 > Flashcards

Lecture 10 Flashcards

1
Q

A 5-6 week embryo has a thickened epithelium at the maxillary and mandibular processes. What is this thickened epithelium called?

A

Primary epithelial band

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2
Q

What does the primary epithelial band rest on?

A

basal lamina

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3
Q

What is the underlying connective tissue under the basal lamina of the primary epithelial band called?

A

Ectomesenchyme

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4
Q

Which cells from the ectoderm migrate into the mesoderm-derived mesenchyme to make it the ectomesenchyme?

A

NCC

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5
Q

What is the name of the embryonic band where teeth will develop?

A

Primary epithelial band

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6
Q

The primary epithelium thickens in response to what genes expressed by the underlying embryonic CT?

A

Homeobox domain genes

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7
Q

Sonic hedgehog (Shh) is part of over _____ genes which are expressed in cells of the developing oral epithelium and mesenchyme.

A

90

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8
Q

What are the two well supported models that explain how teeth develop into different shapes?

A

The field model and the clone model

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9
Q

Which tooth-determination model states that there are distinct, graded and overlapping fields of ectomesenchymal cells for each tooth family?

A

The field model

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10
Q

The clone model states that each tooth class is derived from a clone of _____________ cells programmed to produce teeth of a given pattern.

A

ectomesenchymal

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11
Q

The primary epithelial band of a 6-7 week embryo begins to grow into the underlying ectomesenchyme forming what two invaginations?

A

Vestibular lamina and dental lamina

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12
Q

What will the vestibular lamina become?

A

The space between the cheek and gingiva

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13
Q

What will parts of the dental lamina develop into?

A

teeth

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14
Q

T/F Primary epithelial band development proceeds from distal to mesial.

A

FALSE. It proceeds from mesial to distal or midline of the arch to the posterior

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15
Q

What will the base of the dental lamina form?

A

The bud of the developing enamel organ

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16
Q

What will the condensation of ectomesenchymal cells surrounding the dental lamina become?

A

The dental papilla and dental follicle

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17
Q

The bud will develop into what enamel producing cells?

A

ameloblasts

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18
Q

The crescent-shaped condensation that forms the dental papilla will develop into what parts of the tooth?

A

The dentin and pulp

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19
Q

At week 8, what is the bud stage characterized by?

A

The folding of the dental lamina into the ectomesenchyme of the jaw

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20
Q

What happens to the bud in a 10 week embryo?

A

The bud develops into the cap shaped enamel organ

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21
Q

What re the three layers of cells of the enamel organ?

A

Outer enamel epithelium (OEE), inner enamel epithelium (IEE) and the stellate reticulum in between the other two

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22
Q

How does the stellate reticulum form?

A

Like a blastocyst water is drawn in the center of the enamel organ becomes fluid-filled

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23
Q

What do the stellate reticulum cells secrete to draw in water inside the enamel organ?

A

Glycosaminoglycans

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24
Q

Why do stellate reticulum cells become star shaped?

A

They are interconnected by desmosomes that remain attached as the cells become fluid-filled and stretched around the junctions

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25
Q

Which enamel epithelium encloses around the dental papilla?

A

IEE

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26
Q

What do elongated ectomesenchymal cells form around the enamel organ and underlying dental papilla?

A

A dental sac also also a dental follicle

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27
Q

The dental follicle develops into some of the the ______ tissues of the tooth.

A

supporting

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28
Q

What will eventually enclose the dental follicle?

A

A bony crypt of alveolar bone

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29
Q

What are enamel-knots?

A

Clusters of non-dividing epithelial cells in molar cap stage teeth.

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30
Q

What is the probable purpose of the enamel knots?

A

To serve as an organizational center for cusp development.

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31
Q

What genes do enamel knot precursor cells express?

A

Shh, Bmp, Fgf, and Wnt genes

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32
Q

What does the enamel knot develop into in the bell stage?

A

the enamel cord

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33
Q

Around week 14, what does the enamel organ resemble as it expands?

A

A bell

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34
Q

Where do cells of the stratum intermedium (SI) develop?

A

Develop between the SR and the IEE

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35
Q

What do the SI cells and the adjacent IEE work together in the formation of?

A

enamel

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36
Q

The degeneration of the dental lamina frees the developing tooth from what?

A

The epithelium

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37
Q

What is crown pattern established by?

A

The folding of the IEE

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38
Q

What will the layer of ectomesenchymal cells next to the IEE develop into?

A

Odontoblasts

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39
Q

What is between the developing odontoblasts and ameloblasts of the IEE?

A

A thick basal lamina that becomes the DEJ

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40
Q

Where does the cervical loop of the bell stage form?

A

It forms where the IEE and OEE are folded into a loop around the cervical region of the developing tooth

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41
Q

What will the cervical loop develop into when the root of the tooth begins to form?

A

Hertwig’s epithelial root sheat (HERS)

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42
Q

What does the epithelium of the dental lamina also form?

A

The permanent tooth bud

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43
Q

What do enamel cords correspond to in molar?

A

Cusps

44
Q

What does the differential rate of mitotic division of the IEE result in the developing crown?

A

Results in the contours of the developing crown

45
Q

What do multiple cusps result from?

A

Multiple zones of differentiation of the IEE

46
Q

During what stage does the dental lamina become fragmented?

A

Bell stage

47
Q

What are some of the things any remaining DL fragments/scraps may become if they do not degenerate?

A

Enamel pearls, eruption cysts (may delay eruption), odontomas, or supernumerary teeth

48
Q

What is the apposition stage?

A

The production of enamel and dentin

49
Q

Where is dentin produced by the odontoblasts in the apposition stage? Where is enamel produced by ameloblasts during apposition?

A
  1. Dentin is produced in the peripheral most layer of the dental papilla.
  2. Enamel - in the IEE of the enamel organ
50
Q

Which cells differentiate first? Odontoblasts or ameloblasts?

A

Ameloblasts

51
Q

Which cells lead the way of tooth formation even though they differentiate second?

A

Odontoblasts lead the way. Ameloblasts have to wait for them to catch up before tooth formation begins in earnest

52
Q

What is the name of the collar of odontogenic epithelium formed from the apical portion of the enamel organ?

A

Hertwig’s epithelial root sheath (HERS)

53
Q

What does HERS do?

A

IT surrounds and guides the developing root below the cervix of the tooth

54
Q

What will the HERS sheath eventually form after the root is developed?

A

the apical foramen

55
Q

What do the odontoblasts processes extend through to get to the DEJ?

A

Dentin matrix, dentin and and abut against the enamel

56
Q

What is the succedaneous lamina?

A

An epithelial structure that is responsible for the development of permanent teeth

57
Q

What must odontoblasts secrete to stimulate the ameloblasts to produce enamel?

A

predentin

58
Q

What does the deposition of enamel by ameloblasts ultimately do to the stellate reticulum?

A

It ultimately destroys the SR as it surpasses it and the OEE

59
Q

What are the six stages of tooth development?

A
  1. bud
  2. cap
  3. bell
  4. apposition
  5. beginning of eruption
  6. eruption into the oral cavity
    Mnemonic: better call betty after being educated
60
Q

What do nerves travel with during their formation inside the tooth?

A

Nerves travel with blood vessels

61
Q

The permanent tooth buds of which teeth develop positioned lingually and of the same dental lamina of the corresponding primary teeth?

A

All but the molars (incisors, canines, and premolars)

62
Q

Primary dentition is established during what weeks of embryonic development? During what time is successional permanent dentition established?

A
  1. weeks 6-8

2. week 20 of fetal development to 10 months after birth

63
Q

Which teeth are not succedaneous?

A

Permanent molars

64
Q

Which succedaneous tooth replaces the primary molar?

A

The permanent premolar

65
Q

When do permanent molars begin to develop?

A

Between week 20 of fetal development to 5 years after birth

66
Q

Once the mandible grows long enough, what grows posteriorly into the ectomesenchyme and forms tooth buds for the permanent molars?

A

Dental lamina

67
Q

Where is the enamel matrix deposited by ameloblasts at the earliest stage of enamel formation?

A

On previously formed predentin

68
Q

What does the maturation of enamel matrix remove from the enamel organ? What mineralizes the maturing enamel matrix?

A 
Organic material (proteins) and water.
Calcium and phosphate
69
Q

What do active ameloblasts have to fuel the transport of organic material out and mineral into the enamel?

A

Many mitochondria

70
Q

What structure helps to orient enamel crystals?

A

Tome’s process.

71
Q

What are the three basic stages of amelogenesis?

A
  1. Presecretory stage
  2. Secretory stage
  3. Maturation stage
72
Q

What happens during the presecretory stage of amelogenesis?

A

Rough ER and Golgi of ameloblasts develop and produce vesicles of proteins

73
Q

What happens during the secretory stage of amelogenesis?

A

ameloblasts deposit the proteins and minerals of the enamel

74
Q

What happens during the maturation stage of amelogenesis?

A

Ameloblasts import mineral ions to harden the enamel

75
Q

What are amelogenins?

A

A group of low molecular weight proteins that establish and maintain spacing between enamel rods in early stages of enamel development.

76
Q

Which protein group accounts for 90% of the enamel proteins and lays the scaffolding for early enamel development?

A

Amelogenins

77
Q

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?

A

Nonamelogenins

78
Q

Which enamel proteins are not present in mature enamel?

A

Nonamelogenins

79
Q

What are three important nonamelogenins?

A

Ameloblastin, enamelin, and tuftelin

80
Q

Which specific nonamelogenin is believed to help ameloblasts adhere to the enamel surface during the secretory stage?

A

Ameloblastin

81
Q

How does the absence of ameloblastin affect the differentiation of ameloblasts?

A

Absence of this protein causes the differentiating ameloblasts to detach from dentin and enamel formation stops

82
Q

Which of the three nonamelogenins is thought to be a crystal promoter?

A

Enamalin is believed to promote apatite crystal elongation

83
Q

Which enamel protein is thought to be the least important?

A

Tuftelin is under contention of even being a functional enamel protein

84
Q

What does the Tome’s process secrete?

A

Developing enamel

85
Q

The enamel rod and interrod enamel is left behind the ameloblast cell and _____ the path taken by the cell

A

records

86
Q

What part of the Tome’s process deposits enamel unto dentin?

A

proximal portion of Tome’s process (ppTP)

87
Q

What parts of the columnar ameloblasts point into the enamel matrix creating a “stair-step” or “saw-tooth” appearance

A

Tome’s processes

88
Q

During enamel maturation, how often do ameloblasts alternate their morphology between smooth and ruffled?

A

Every 8 hours

89
Q

What percentage of the time, during enamel maturation, do ameloblasts spend secreting in the ruffled stage?

A

80% of the time

90
Q

What do ameloblasts do during the smooth stage of their time?

A

The re-absorb enamel protein fragments and calcium ions for active crystal growth of enamel

91
Q

During what enamel hardening stage/phase is the pH of the enamel more acidic? Less acidic or neutral?

A
  1. Ruffle-ended stage is more acidic

2. Smooth-ended stage is near neutral

92
Q

How does the pH of the enamel influence crystal formation?

A

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

93
Q

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?

A
  1. Ruffled

2. Smooth

94
Q

What is perikymata?

A

Shallow, periodic furrows on the labial surface of enamel

95
Q

What are the Striae of Retzius thought to be associated with?

A

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

96
Q

What is it thought that the neonatal line inside enamel represents?

A

The great physiological changes occurring during birth

97
Q

What are von Korff’s fibers? Where do they originate?

A
  1. Large type I collagen fibers associated with fibronectin.

2. These fibers originate between the odontoblasts and extend to the inner enamel epithelium.

98
Q

The odontoblasts produce predentin that will activate the ameloblasts to produce enamel. Which cells release signaling molecules that influence odontoblast differentiation?

A

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

99
Q

Dentin and enamel both create patterns of incremental lines. What does this suggest about the growth of these two dental tissues?

A

They undergo pulsed growth and major physiological changes during formation may leave traces not unlike tree-ring growth

100
Q

What is the main organic component of predentin matrix?

A

Type I collagen

101
Q

What does predentin mineralize as?

A

Hydroxyapatite

102
Q

Dentin is similar to what matrix of the bone?

A

osteoid matrix of the bone

103
Q

What does newly formed dentin surrounding odontoblast processes form?

A

Dentinal tubule

104
Q

What is the more mineralized sheath of dentin immediately surrounding the dentinal tubule called?

A

Peritubular dentin

105
Q

The dental follicle gives rise to what three cells that are part of the periodontal apparatus?

A

Osteoblasts, fibroblasts, and cementoblasts

106
Q

What do the residual portions of Hertwig’s epithelial root sheath (HERS) fragmentation form?

A

cell rests of Malassez

107
Q

What is the likely function of cell rests of Malassez

A

Probably support PDL tissue homeostasis and may even contribute to periodontal tissue regeneration

Craniofacial Embryology (10 decks)

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