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Dent 6500 > Dentin > Flashcards

Dentin Flashcards

1
Q

Dentin has an intimate relationship with what?

A

Pulp

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2
Q

What is Pulp?

A

Soft connective tissue in the center of the tooth. It has blood vessels, whole cells, and is non-mineralized.

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3
Q

What is Dentin?

A

It is mineralized connective tissue covering the pulp. No blood vessels or whole cells. It has odontoblast processes, and never endings from Trigeminal ganglion.

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4
Q

Most of the volume of the tooth is taken up by what?

A

Dentin

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5
Q

Dentin protects what?

A

Pulp and enamel

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6
Q

Dentin cushions the overlying enamel because of what property?

A

It is flexible

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7
Q

Conditions that affect the dentin also affect what?

A

enamel

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8
Q

Why is the DEJ scalloped?

A

It facilitates adhesion

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9
Q

When does dentinogenesis begin?

A

During the bell stage

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10
Q

What happens just prior to dentinogenesis?

A

Tissue layers of dental organ present

Crown outline present

No odontoblasts or ameloblasts

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11
Q

In the late bell stage what happens?

A

Inner epithelial cells turn into ameloblasts

Undifferentiated mesenchymal cells (dental papilla) become odontoblasts

Dentin is secreted

Enamel is secreted

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12
Q

Dentinogenesis proceeds from where to where?

A

Cusp tips to cervix

Periphery to pulp center

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13
Q

What happens in odontoblast differentiation?

A

Undifferentiated mesenchymal cell divides. It secretes a type 1 collagen matrix. It grows, elongates, and sends out processes.

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14
Q

What kicks off odontoblast differentiation?

A

Inductive signal for odontoblasts is secreted from enamel organ (likely the enamel knot). There are multiple molecules and several families of signaling/growth factors involved. One is Wnt10a.

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15
Q

Where is Wnt10a found?

A

First in the enamel knot, then in pre-odontoblasts at the cusp tip, then successively more cervical parts of teeth. It’s expression immediately precedes the wave of odontoblast differentiation.

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16
Q

What is Dspp (dentin sialophosoprotein)?

A

a molecule expressed by mature odontoblasts, it gives rise to DPP (and other proteins)

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17
Q

When Wnt10a is added to embryoic mesodermal cell lines in vitro culture what does it induce?

A

Dspp

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18
Q

What is predentin?

A

unmineralized organic matrix of dentin

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19
Q

Odontoblasts secrete organic matrix (prevention( then what happens?

A

The matrix is mineralized

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20
Q

What are the requirements for mineralization?

A

1 - Ca++ and phosphate - Ca++ is from free ions in plasma, phosphate comes from plasma and clevage of organic molecules containing phosphate in odontoblast by alkaline phosphatase. Then it is transported into prevention through and between odontoblasts.
2 - Initiation of crystal formation - Mantle (initation), and Circumpulpal (subsequent)

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21
Q

What is Mantle Dentin Formation?

A

The initial layer of dentin (at DEJ). Collagen Type 1 is the principle of its organic matrix. It is secreted from odontoblasts, has relatively large fibrils and is oriented at right angles to the basal lamina (future DEJ).

22
Q

What mineralizes Mantle Dentin?

A

Matrix Vesticles. Membrane bound vesicles, synthesized by ODB, concentrate Ca++, PO containing and other organic molecules.

23
Q

What is Circumpulpal dentin formation?

A

Interior to mantle dentin. It is much thicker than mantle dentin, but its overall process is similar. Its organic matrix has Type 1 collagen, smaller fibrils, and is parallel to basal lamina . It is not mineralized by Matrix Vesicles.

24
Q

What mineralizes Circumpupal dentin?

A

Proteins. Sythesized and secreted from ODB process. Binds to collagen. Special properties of proteins precipitate Ca++ ions present in interstitial fluid and initiate crystal formation (heterogeneous nucleation).

25
Q

Mantle dentin is more ____.

A

Organic

26
Q

Mantle dentin is less ______.

A

Mineralized

27
Q

T or F: the nature of mantle dentin makes DEJ more vulnerable to caries

A

True!

28
Q

What is Phosphophoryn/Dentin Phosphoprotein?

A

It is a protein that is relatively specific to dentin. It is a prominent dentinal protein (>50% of non collagenous proteins). It is highly phosphorylated and high in serine/apartic acid. It is acidic/anionic. The current hypothesis is that it precipitates Ca++ ions from tissue fluid which initiates mineralization.

29
Q

What is the hydroxyapatite composition of dentin?

A

70%

30
Q

What is the mineral phase of dentin?

A

Hydroxyapatite crystals. The unit cell formula for it is (Ca)10(PO4)6(OH)2 + 4-5% carbonate. It has thousands of unit cells per crystal. The crystal size is ~10x25x100nm and are randomly oriented.

31
Q

What is the organic phase of dentin?

A

Processes of cells.
Extra cellular matrix: Collagen and NCPs. Type 1 collage is 90% of organic matrix.
Non-tissue specific proteins - proteoglycans, signaling molecules, growth factors
Mineralized-tissue specific proteins - osteocalcin, bone sialoprotein
Dentin-dominant proteins - found more in dentin than in other tissues

32
Q

What are Dentin-Dominant proteins?

A 
Dentin Matrix Protein 1
Dentin Glycoprotein
Dentin Sialoprotein
5-8% NCPs
*Their function are not well understood
But Dentin Phosphoprotein (DPP)
>50% NCps
Anionic 
Includes long chain of polar amino acid repeats
>200 serine-serine-aspartic acid
series are phosphorylated
Produced by DSPP gene
33
Q

What is dentino genesis imperfecta (DI)?

A

It is a human hereditary disorder. Dentin forms improperly,, its incidence is 1:6-8k, and is associated with mutation in DSPP gene.

34
Q

What are the 2 types of mutations known to cause DI?

A

1 - changes in first 3 amino acids (iso, pro, val) critical for trafficking DSPP through rER.
2 - Small base pair deletions that produce frameshifts coding the part of the DPP molecule that contain polar AA repeats: polar change to uncharged.

35
Q

What is the result of both mutations that cause DI?

A

Abnormal DSPP cannot be release from the odontoblast. It is stuck in rER or cell membrane. The mutated DSPP traps the normal protein made by the unaffected chromosome in heterozygotes. Thus DI is a dominant negative mutation.

36
Q

What are the content of dentinal tubules?

A 
Fluid (mostly water)
Nerve fibers 
Odontoblastic processes
A few Collagen fibers
Some say there is a mysterious Non-cellular lining sheath (organic composition unknown)
37
Q

Describe dentinal tubule appearance.

A

At right angles to DEJ
S-Shaped in Crown
Straighter in the root
Terminal and lateral branches

38
Q

Why are branches more prominent at DEJ and CEJ?

A

Because “baby” odontoblasts laying down mantle dentin have multiple processes near the DEJ. They eventually have one main process.

39
Q

Why is are the dimensions and number of tubules clinically significant?

A

The number of tubules in the inner dentin is greater than the number in the outer dentin. The tubule diameter in the inner dentin is also larger. Tubules occupy much less surface area at DEJ than at P-D border. Permeability and wetness increase toward P-D border. Tubules create a natural pathway for microorganisms.

40
Q

What are the different types of dentin?

A

Primary
Secondary
Tertiary (reparative and reactive)

41
Q

What is primary dentin?

A

Dentin that is formed up until the completion of root development. It makes up most of the dentin. It has mantle dentin (20u-150u layer at DEJ), which is less mineralized. And Circumpulpal dentin which is more mineralized.

42
Q

What is secondary dentin?

A

Dentin that is formed after root development. It is formed at a slower rate than primary dentin. It is central to primary dentin and present along the entire circumference of the pulp chamber but is heaviest on roof and floor. Similar to primary dentin in structure. It is formed throughout life and shrinks the pulp chamber.

43
Q

What is tertiary dentin?

A

It is produced in specific location in response to a noxious stimulus. It is irregular in structure, may or may not have tubules and may include whole cells.

44
Q

Explain intertubular vs. intratubular dentin.

A

Between vs. lining the tubules.
Both kinds are found in primary and secondary dentin.
Intertubular has more volume than intratubular.
The intratubular ring is wider near the DEJ, which accounts for the narrowing of the tubule.

*The process by which interlobular dentin is formed isn’t well understood, but it is first formed away from the pulp.

45
Q

What is translucent or sclerotic dentin?

A

Tubules that are completely filled with intra/peritubular dentin. Translucent dentin is part of the normal aging process but sclerotic dentin is the product of accelerated deposition due to caries or attrition.

46
Q

What are dead tracts?

A

Tubules that have dried out and become filled with air.

47
Q

What is interglobular dentin?

A

Hypomineralized dentin just below the mantle dentin, because of the changeover in mineralization processes that occurs there.

48
Q

Initial mineralization of dentin occurs in what?

A

Discrete foci of calcification called calcospherites which eventually fuse. If they don’t fuse, interlobular dentin is formed.

49
Q

Growth lines in dentin reflect what?

A

The incremental pattern of deposition. They are 20uM apart which is about 5 days of growth. Pronounced growth lines can occur that reflect perturbations, like the neonatal line commonly observed in teeth mineralizing at birth.

*Growth lines are exaggerated due to tetracycline treatment.

50
Q

What is Tome’s granular layer?

A

A specialized layer of dentin in the root. Don’t know what it’s for.

51
Q

DPP
1 - has a strong negative charge
2 - can precipitate ions from solution
3 - is secreted from cells of the enamel knot

A

1 and 2 are true

Dent 6500 (6 decks)

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