Lecture 10

Question 1

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

Answer 1

Primary epithelial band

Question 2

What does the primary epithelial band rest on?

Answer 2

basal lamina

Question 3

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

Answer 3

Ectomesenchyme

Question 4

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

Answer 4

NCC

Question 5

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

Answer 5

Primary epithelial band

Question 6

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

Answer 6

Homeobox domain genes

Question 7

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

Answer 7

90

Question 8

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

Answer 8

The field model and the clone model

Question 9

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

Answer 9

The field model

Question 10

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

Answer 10

ectomesenchymal

Question 11

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

Answer 11

Vestibular lamina and dental lamina

Question 12

What will the vestibular lamina become?

Answer 12

The space between the cheek and gingiva

Question 13

What will parts of the dental lamina develop into?

Answer 13

teeth

Question 14

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

Answer 14

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

Question 15

What will the base of the dental lamina form?

Answer 15

The bud of the developing enamel organ

Question 16

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

Answer 16

The dental papilla and dental follicle

Question 17

The bud will develop into what enamel producing cells?

Answer 17

ameloblasts

Question 18

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

Answer 18

The dentin and pulp

Question 19

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

Answer 19

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

Question 20

What happens to the bud in a 10 week embryo?

Answer 20

The bud develops into the cap shaped enamel organ

Question 21

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

Answer 21

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

Question 22

How does the stellate reticulum form?

Answer 22

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

Question 23

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

Answer 23

Glycosaminoglycans

Question 24

Why do stellate reticulum cells become star shaped?

Answer 24

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

Question 25

Which enamel epithelium encloses around the dental papilla?

Answer 25

IEE

Question 26

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

Answer 26

A dental sac also also a dental follicle

Question 27

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

Answer 27

supporting

Question 28

What will eventually enclose the dental follicle?

Answer 28

A bony crypt of alveolar bone

Question 29

What are enamel-knots?

Answer 29

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

Question 30

What is the probable purpose of the enamel knots?

Answer 30

To serve as an organizational center for cusp development.

Question 31

What genes do enamel knot precursor cells express?

Answer 31

Shh, Bmp, Fgf, and Wnt genes

Question 32

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

Answer 32

the enamel cord

Question 33

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

Answer 33

A bell

Question 34

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

Answer 34

Develop between the SR and the IEE

Question 35

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

Answer 35

enamel

Question 36

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

Answer 36

The epithelium

Question 37

What is crown pattern established by?

Answer 37

The folding of the IEE

Question 38

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

Answer 38

Odontoblasts

Question 39

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

Answer 39

A thick basal lamina that becomes the DEJ

Question 40

Where does the cervical loop of the bell stage form?

Answer 40

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

Question 41

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

Answer 41

Hertwig's epithelial root sheat (HERS)

Question 42

What does the epithelium of the dental lamina also form?

Answer 42

The permanent tooth bud

Question 43

What do enamel cords correspond to in molar?

Answer 43

Cusps

Question 44

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

Answer 44

Results in the contours of the developing crown

Question 45

What do multiple cusps result from?

Answer 45

Multiple zones of differentiation of the IEE

Question 46

During what stage does the dental lamina become fragmented?

Answer 46

Bell stage

Question 47

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

Answer 47

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

Question 48

What is the apposition stage?

Answer 48

The production of enamel and dentin

Question 49

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

Answer 49

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

Question 50

Which cells differentiate first? Odontoblasts or ameloblasts?

Answer 50

Ameloblasts

Question 51

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

Answer 51

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

Question 52

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

Answer 52

Hertwig's epithelial root sheath (HERS)

Question 53

What does HERS do?

Answer 53

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

Question 54

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

Answer 54

the apical foramen

Question 55

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

Answer 55

Dentin matrix, dentin and and abut against the enamel

Question 56

What is the succedaneous lamina?

Answer 56

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

Question 57

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

Answer 57

predentin

Question 58

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

Answer 58

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

Question 59

What are the six stages of tooth development?

Answer 59

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

Question 60

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

Answer 60

Nerves travel with blood vessels

Question 61

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

Answer 61

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

Question 62

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

Answer 62

1. weeks 6-8 | 2. week 20 of fetal development to 10 months after birth

Question 63

Which teeth are not succedaneous?

Answer 63

Permanent molars

Question 64

Which succedaneous tooth replaces the primary molar?

Answer 64

The permanent premolar

Question 65

When do permanent molars begin to develop?

Answer 65

Between week 20 of fetal development to 5 years after birth

Question 66

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

Answer 66

Dental lamina

Question 67

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

Answer 67

On previously formed predentin

Question 68

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

Answer 68

``` Organic material (proteins) and water. Calcium and phosphate ```

Question 69

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

Answer 69

Many mitochondria

Question 70

What structure helps to orient enamel crystals?

Answer 70

Tome's process.

Question 71

What are the three basic stages of amelogenesis?

Answer 71

1. Presecretory stage 2. Secretory stage 3. Maturation stage

Question 72

What happens during the presecretory stage of amelogenesis?

Answer 72

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

Question 73

What happens during the secretory stage of amelogenesis?

Answer 73

ameloblasts deposit the proteins and minerals of the enamel

Question 74

What happens during the maturation stage of amelogenesis?

Answer 74

Ameloblasts import mineral ions to harden the enamel

Question 75

What are amelogenins?

Answer 75

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

Question 76

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

Answer 76

Amelogenins

Question 77

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?

Answer 77

Nonamelogenins

Question 78

Which enamel proteins are not present in mature enamel?

Answer 78

Nonamelogenins

Question 79

What are three important nonamelogenins?

Answer 79

Ameloblastin, enamelin, and tuftelin

Question 80

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

Answer 80

Ameloblastin

Question 81

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

Answer 81

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

Question 82

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

Answer 82

Enamalin is believed to promote apatite crystal elongation

Question 83

Which enamel protein is thought to be the least important?

Answer 83

Tuftelin is under contention of even being a functional enamel protein

Question 84

What does the Tome's process secrete?

Answer 84

Developing enamel

Question 85

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

Answer 85

records

Question 86

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

Answer 86

proximal portion of Tome's process (ppTP)

Question 87

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

Answer 87

Tome's processes

Question 88

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

Answer 88

Every 8 hours

Question 89

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

Answer 89

80% of the time

Question 90

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

Answer 90

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

Question 91

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

Answer 91

1. Ruffle-ended stage is more acidic | 2. Smooth-ended stage is near neutral

Question 92

How does the pH of the enamel influence crystal formation?

Answer 92

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

Question 93

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?

Answer 93

1. Ruffled | 2. Smooth

Question 94

What is perikymata?

Answer 94

Shallow, periodic furrows on the labial surface of enamel

Question 95

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

Answer 95

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

Question 96

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

Answer 96

The great physiological changes occurring during birth

Question 97

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

Answer 97

1. Large type I collagen fibers associated with fibronectin. | 2. These fibers originate between the odontoblasts and extend to the inner enamel epithelium.

Question 98

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

Answer 98

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

Question 99

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

Answer 99

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

Question 100

What is the main organic component of predentin matrix?

Answer 100

Type I collagen

Question 101

What does predentin mineralize as?

Answer 101

Hydroxyapatite

Question 102

Dentin is similar to what matrix of the bone?

Answer 102

osteoid matrix of the bone

Question 103

What does newly formed dentin surrounding odontoblast processes form?

Answer 103

Dentinal tubule

Question 104

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

Answer 104

Peritubular dentin

Question 105

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

Answer 105

Osteoblasts, fibroblasts, and cementoblasts

Question 106

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

Answer 106

cell rests of Malassez

Question 107

What is the likely function of cell rests of Malassez

Answer 107

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