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Oral Histology > Dentin > Flashcards

Dentin Flashcards

1
Q

What are some differences between Dentin and Pulp?

A 
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
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2
Q

Clinical significance of Dentin

A

Protects both the enamel and pulp

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3
Q

How does Dentin protect enamel

A

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

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4
Q

Describe the appearance of the DEJ at the crown

A

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

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5
Q

When does Dentinogeneis occur?

A

During the “Bell stage” of tooth development

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6
Q

What occurs just prior to dentinogenesis?

A

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

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7
Q

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

A

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

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8
Q

What direction does dentinogenesis occur?

A

From cusp tip to cervix

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9
Q

Odontoblast differentiation

A

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

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10
Q

What induces odontoblast differentiation

A

Inductive signals for odontoblast differentiation

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11
Q

Where do signals for odontoblast differentiation come from?

A

From the enamel organ - most likely the enamel knot

This signal induces several molecules

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12
Q

Wnt10a

A

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

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13
Q

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

A

False - it is most likely just one of many

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14
Q

What is required for dentin mineralization?

A

Ca+2
Phosphate-
Initiation fo crystal formation

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15
Q

Where does Ca+2 come from for dentin mineralizaiton?

A

Free ions in plasma

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16
Q

Where does the phosphate come from for dentin mineralization?

A

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

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17
Q

How is Ca and phosphate transported?

A

It is transported into predentin through and between odontoblasts

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18
Q

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

A

False - It requires special mechanisms:
Mantle
Circumpulpal

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19
Q

Mantle dentin formation

A 
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
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20
Q

Mantle dentin mineralization

A

Mineralized by matrix vesicles

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21
Q

Matrix vesicles

A

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

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22
Q

How does dentin form?

A

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

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23
Q

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

A

True

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24
Q

Circumpulpal dentin formation

A

Interior to mantle - much thicker

Process is the same as mantle formation

25
Q

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

A

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
Q

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

A

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

27
Q

Dentin phosphoprotein

A 
Relatively spcific to dentin
Prominent dentin protein
Highly phosphorylated
High in serine/aspartic acid
Acidic
Thought to precipitate Ca to initiate mineralization
28
Q

Dentin constituents by weight

A

70% inorganic
20% organic
10% water

29
Q

Dentin constituents by volume

A

45% inorganic
33% organic
22% water

30
Q

Mineral phase of dentin

A

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

31
Q

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

A

10x35x100nm

Much smaller than enamel crystals

32
Q

Organic phase of dentin

A

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

33
Q

What are the types of proteins found in dentin?

A

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

34
Q

What are non-tissue specific proteins in dentin?

A

Proteoglycans

Signaling molecules/growth factors

35
Q

What are mineralized tissue-specific proteins in dentin?

A

Osteocalcin

Bone sialoprotein

36
Q

What are dentin-dominant proteins

A

Dentin matrix protein I
Dentin glycoprotein
Dentin sialoprotein
Dentin phosphoprotein

37
Q

Dentin sialoprotein

A

5-8% of non-collagen proteins in dentin

Function is not well understood

38
Q

Dentin phosphoprotein

A

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

39
Q

What gene codes for Dentin phosphoprotein

A

DSPP (Dentin sialophosphoprotein)

40
Q

Human hereditary disorder

A

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

41
Q

How does Dentinogenesis Imperfecta defer in humans and mice?

A

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
Q

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

A

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
Q

What is the result of the mutations that cause DI

A

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
Q

Dentinal tubules

A

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

45
Q

Contents of dentinal tubules

A 
Fluid (mostly water)
Nerve fibers
Odontobalstic processes
Very few collagen fibers
Non-cellular lining sheath
46
Q

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

A

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
Q

What are the different types of dentin based off of?

A

When they’re formed
Location
Histological features

48
Q

Primary dentin

A

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

49
Q

Secondary dentin

A 
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
Q

Tertiary dentin

A

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
Q

Intertubular dentin

A

Between tubules

Found in primary and secondary dentin

52
Q

Intratubular/Peritubular dentin

A

Lines tubules

Found in primary and secondary dentin

53
Q

What are some differences between intertubular and intratubular dentin?

A

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

54
Q

Translucent dentin

A

Tubules are completely filed with intratubular dentin

Normal process of aging

55
Q

Sclerotic dentin

A

Tubules are completely filled with intratubular dentin

Accelerated ddeposition due to caries or attrition

56
Q

Dead tracts

A

Tubules are dried out and become filled with air

57
Q

Interglobular dentin

A

Hypomineralized dentin just below the mantle dentin

58
Q

Growth lines

A

Reflect incremental pattern of deposition

Can be exaggerated due to tetracycline treatment

Oral Histology (12 decks)

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