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Flashcards in Dentin Deck (58):
1

What are some differences between Dentin and Pulp?

Pulp = soft connective tissue with blood vessels, whole cells, and is non-mineralized
Dentin = minneralized connective tissue covering the pulp with no blood vessels or whole cells. It does have nerve endings and odontoblastic processes

2

Clinical significance of Dentin

Protects both the enamel and pulp

3

How does Dentin protect enamel

It is softer and more compressive, so it can cushion the more brittle enamel

4

Describe the appearance of the DEJ at the crown

It is scalloped, which facilitates adhesion of dentin and enamel to one another

5

When does Dentinogeneis occur?

During the "Bell stage" of tooth development

6

What occurs just prior to dentinogenesis?

Tissue layers of the dental organ are present
Crown outline is present
There are no odontoblasts or ameloblasts

7

What occurs in the late bell stage in regards to dentinogenesis?

Inner enamel cells (which become ameloblasts) are present
Undifferentiated mesenchumal cells are present in the dental papilla (become odontoblasts)
Dentin is secreted, and then enamel is secreted

8

What direction does dentinogenesis occur?

From cusp tip to cervix

9

Odontoblast differentiation

Begin as mesenchymal cells
One cell will divide to become a preodontoblast and a fibroblast
When preodontoblast begins to secrete matrix, it is an odontoblast

10

What induces odontoblast differentiation

Inductive signals for odontoblast differentiation

11

Where do signals for odontoblast differentiation come from?

From the enamel organ - most likely the enamel knot
This signal induces several molecules

12

Wnt10a

One of the growth factors implicated by the enamel knot
First expressed in the not, then in pre-odontoblast at the cusp tip.
Then it is successively expressed in the more cervical parts of the teeth
Expression immediately precedes the wave of odontoblast differentiation

13

T/F - Wnt10a is the only molecule implicated in inducing odontoblast differentiation

False - it is most likely just one of many

14

What is required for dentin mineralization?

Ca+2
Phosphate-
Initiation fo crystal formation

15

Where does Ca+2 come from for dentin mineralizaiton?

Free ions in plasma

16

Where does the phosphate come from for dentin mineralization?

From plasma and cleavage of organic molecules containing phosphate in odontoblasts by alkaline phosphatase

17

How is Ca and phosphate transported?

It is transported into predentin through and between odontoblasts

18

T/F - The presence of requisite ions are sufficient to initiate crystal formation

False - It requires special mechanisms:
Mantle
Circumpulpal

19

Mantle dentin formation

Initial layer of dentin near the DEJ
Principle component is Type I collagen
Secreted by odontoblasts
Relatively large fibrils
Oriented perpendicular to the basal lamina/future DEJ

20

Mantle dentin mineralization

Mineralized by matrix vesicles

21

Matrix vesicles

Membrane bound vesicles synthesized by odontobalsts
Concentrate Ca and PO containing and other organic molecules
Help mineralize Mantle dentin

22

How does dentin form?

Odontobalsts secrete matrix, which then mineralizes
Odontoblasts grow, and their processes elongate - this creates a barrier between dentin and pulp
Odontoblasts migrate toward pulp

23

T/F - Near the end of mantle formation, once odontoblast process becomes dominant

True

24

Circumpulpal dentin formation

Interior to mantle - much thicker
Process is the same as mantle formation

25

What is the difference between formation of Mantle and Circumpulpal dentin formation

Circumpulpal has smaller fibrils than Mantle
Circumpulpal is secreted parrallel to basal lamina, Mantle is perp.
Circumpulpal is mineralized by proteins, Mantle is mineralized by matrix vesicles

26

What are functional consequences of developmental differences between Mantle and Circumpulpal dentin

Mantle is more organic
Mantle is less mineralized
DEJ is more vulnerable to caries

27

Dentin phosphoprotein

Relatively spcific to dentin
Prominent dentin protein
Highly phosphorylated
High in serine/aspartic acid
Acidic
Thought to precipitate Ca to initiate mineralization

28

Dentin constituents by weight

70% inorganic
20% organic
10% water

29

Dentin constituents by volume

45% inorganic
33% organic
22% water

30

Mineral phase of dentin

Hydroxyapatite crystals
1000s of unit cells/crystal
Crystals are randomly oriented - enamel is organized

31

What is the size of dentin crystals and how does that compare to enamel?

10x35x100nm
Much smaller than enamel crystals

32

Organic phase of dentin

Made of collagen and noncollagen proteins (90% type I collagen)

33

What are the types of proteins found in dentin?

Non-tissue specific proteins
Mineralized tissue-specific proteins
Dentin-dominant proteins

34

What are non-tissue specific proteins in dentin?

Proteoglycans
Signaling molecules/growth factors

35

What are mineralized tissue-specific proteins in dentin?

Osteocalcin
Bone sialoprotein

36

What are dentin-dominant proteins

Dentin matrix protein I
Dentin glycoprotein
Dentin sialoprotein
Dentin phosphoprotein

37

Dentin sialoprotein

5-8% of non-collagen proteins in dentin
Function is not well understood

38

Dentin phosphoprotein

>50% of non-collagen proteins in dentin
Anionic
Includes chain of polar amino acid repeates
Serines are phosphoryated

39

What gene codes for Dentin phosphoprotein

DSPP (Dentin sialophosphoprotein)

40

Human hereditary disorder

aka Dentinogenesis Imperfecta
Dentin forms improperly
1:6,000-8,000
Associated with mutations of DSPP

41

How does Dentinogenesis Imperfecta defer in humans and mice?

In mice: there are 2 alleles, and both need to be negative for there to be abnormal dentin
In humams: DI is dominantly inherited with DSPP mutation

42

What are the 2 types of mutations to cause DI in humans?

1) changes in the first 3 amino acids critical for moving DSPP through the rough ER
2) Small base pair deletions produce frameshifts coding the DPP molecule that contain polar AA repeat - they become uncharged

43

What is the result of the mutations that cause DI

Result in abnormal DSPP cannot be released from odontoblasts - also traps normal proteins made by the unaffected chromosome, making it a dominant negative mutaiton

44

Dentinal tubules

At right angles to DEJ
S-shaped in crown, straighter in the root
Have terminal and lateral branches

45

Contents of dentinal tubules

Fluid (mostly water)
Nerve fibers
Odontobalstic processes
Very few collagen fibers
Non-cellular lining sheath

46

How do dentin tubules differ near the DEJ to the PD border?

Diameter of tubule is larger close to PD border
Number of tubules is greater close to PD border
Tubules occupy less area at DEJ than PD border
Permeability and wetness increase toward the PD border

47

What are the different types of dentin based off of?

When they're formed
Location
Histological features

48

Primary dentin

Dentin formed until the completion of root dentin
Comprises most of dentin (both mantle and circumpulpal)
20u-150u at DEJ

49

Secondary dentin

Formed after root development
Forms slowly but throughout life
Central to primary dentin
Similar in structure to primary dentin
In circumpulpal dentin
Likely formed by initial odontoblasts

50

Tertiary dentin

Produced in specific locaiton in response to noxious stimuli
Structurally irregular - may or may not have tubules and may include cells
Thought that initial odontobalsts are killed, and new ones come in for tertiary dentin

51

Intertubular dentin

Between tubules
Found in primary and secondary dentin

52

Intratubular/Peritubular dentin

Lines tubules
Found in primary and secondary dentin

53

What are some differences between intertubular and intratubular dentin?

Intratubular dentin covers less volume
Intratubular dentin is much more mineralized
Intratubular ring is wider near DEJ - tubule is narrower here

54

Translucent dentin

Tubules are completely filed with intratubular dentin
Normal process of aging

55

Sclerotic dentin

Tubules are completely filled with intratubular dentin
Accelerated ddeposition due to caries or attrition

56

Dead tracts

Tubules are dried out and become filled with air

57

Interglobular dentin

Hypomineralized dentin just below the mantle dentin

58

Growth lines

Reflect incremental pattern of deposition
Can be exaggerated due to tetracycline treatment