Dentin

Question 1

dentin and pulp have an intimate relationship, but they are distinctive. HOW?

Answer 1

pulp is a non-mineralized soft connective tissue that is covered by the mineralized CT (dentin)

• pulp has blood vessels and whole cells whereas dentin doesn’t have blood vessels or whole cells (OB processes and nerve endings)
• *pulp makes the dentin

Question 2

where are the cell bodies that have their processes in the pulp and dentin

Answer 2

cell bodies from the trigeminal nerve

Question 3

how does dentin protect both enamel and pulp?

Answer 3

covers soft tissue (pulp) and acts a shock absorber for enamel brittle enamel because dentin’s compressive strength (flexibility) is greater than enamel

Question 4

can defects in dentin affect enamel?

Answer 4

yes

ex. dentinogenesis imperfecta

Question 5

why is DEJ scalloped in the crown?

Answer 5

** dentin has finger like projections that extend into the enamel for adhesion

Question 6

where does dentinogenesis begin?

Answer 6

begins during the “bell stage”

Question 7

what do the tissues look like prior to dentinogenesis

Answer 7

prior to dentinogenesis the tissue layers of the enamel organ are present, the outline of the crown is present
**there are NO odontoblasts or ameloblasts

Question 8

what direction does dentinogenesis occur?

Answer 8

cusp tips to cervix and periphery to pulp center

Question 9

explain the how the periphery of the dental papilla cells differentiate into ODB

Answer 9

first the pre-AB start changing and becoming columnar cells (telling the mesenchyme cells to stop dividing). The enamel knot (concentration of epithelial cells in the enamel cap) secretes a signal that allows for the undifferentiated mesenchymal cells to differentiate into ODB

Question 10

what happens to the 2 daughter cells of the pre-odontoblasts?

Answer 10

one becomes fibroblast and the other goes to pulp (to be ODB)

Question 11

what molecular family is said to be a signaling molecule secreted by enamel knot?

Answer 11

Wnt family (specifically Wnt10a)
**expression of Wnt10a immediately proceeds the wave of odotoblast differentiation

Question 12

what experiment proves that wnt10a induces ODB differentiation?

Answer 12

embyonic mesoderm cells subject to wnt10a express Dspp (dentin sialophosphoprotein is expressed by mature ODB)

Question 13

when dentin is secreted is is mineralized?

Answer 13

NO

unmineralized predentin is first

Question 14

what are the requirements for mineralization?

Answer 14

1. Ca and Ph (from free ions in plasma and cut from organic molecules with alkaline phosphatase) that are transported through or btwn ODB in unmineralized matrix
2. initiation of crystal formation (energy process) either through mantle or circumpulpal dentin formation

Question 15

what is the principal component of the organic matrix of dentin?

Answer 15

collagen type I fibers

Question 16

where is mantle dentin formation

Answer 16

at the DEJ (first layer of dentin)

Question 17

how is mantle dentin mineralized?

Answer 17

through matrix vesicles that are synthesized by ODB taking in lots of calcium and Ph through binding proteins where they form crystals (in matrix) burst and then mineralize the LARGE collagen fibers secreted by ODB at RIGHT ANGLES to the basal lamina (aka DEJ)

Question 18

what causes the vesicles to mineralize?

Answer 18

special proteins inside or just a really high number of Ca ions

Question 19

how does circumpulpal dentin formation occur?

Answer 19

the ODB grows towards pulp center, process elongates (until there is only 1) and dentin forms around the processes. Smaller collagen fibrils parallel to basal lamina (DEJ) secreted by ODB cell body and mineralized by PROTEINS (not matrix vesicles) in the ODB processes

Question 20

how do the proteins cause mineralization in circumpulpal dentin?

Answer 20

special properties allow Ca to percipitate out in the interstitial fluid t allow crystalization
**heterogeneous nucleation

Question 21

what are the diff (functionally) in the circumpulpal vs. mantle dentin?

Answer 21

mantle is more organic (more collagen) so softer and less mineralized which means the DEJ is more susceptible to caries

Question 22

dentin phosphoprotein/ phosphoryn

Answer 22

• (relatively) specific to dentin (small amounts elsewhere)
• most prominent dentinal protein (>50% non-collagenous proteins)
• highly phosporylated (anionic)
• high in serine/aspartic acid
• secreted by ODB
• **protein that causes the circumpulpal dentin to mineralize through precipitating (pulling out) calcium ions out of tissue fluid
• comes from gene is DSPP (dentin sialophosphoprotein)

Question 23

what percent of dentin is HA?

Answer 23

70%

Question 24

what is the difference in enamel vs. dentin HA crystals?

Answer 24

enamel is larger, more mineralized, harder and more orderly

** dentin is random

Question 25

what are parts of the organic phase of dentin

Answer 25

- cell processes and ECM * the ECM is 90% type 1 collagen but the non-collagenous proteins are non-tissue specific (ex. growth/signaling factors like bone morphogenic proteins and proteoglycans), mineralized-tissue specific (osteocalcin and bone sialoprotein) and dentin-dominant proteins

Question 26

what are the dentin dominant proteins?

Answer 26

dentin matrix protein 1, dentin glycoprotein, dentin sialoprotein

Question 27

when there is no DSPP what happens?

Answer 27

hypomineralization of dentin (ex. dentinogenesis imperfecta because dentin doesn't form properly) **hard to tell on knockout DSPP mouse if DPP is the cause for hypomineralization because makes DGP and DSP too

Question 28

what are the 2 mutations in humans (not in mice) that lead to DI?

Answer 28

1. changing the first 3 aa that are needed to move DSPP out of the RER (can't leave rer is mutated) 2. base pair deletion leading to the polar molecule to become uncharged (cant leave cell membrane is mutated)

Question 29

why is DI a dominant negative in humans?

Answer 29

because the more abnormal DSPP there is, then more normal DSPP (from normal chromosome) is trapped to decrease its release

Question 30

dentinal tubules content

Answer 30

fluid (water), nerve fibers, ODB processes, collagen fibers and non-cellular lining sheath???

Question 31

why are tubules straighter in the root then the crown (s shape)?

Answer 31

because ODB crowding moving into pulp chamber

Question 32

what angle are the dentinal tubules at?

Answer 32

right angle to DEJ

Question 33

where are the terminal and lateral branches of the dentinal tubules?

Answer 33

DEJ and DCJ

Question 34

why are br. more prominent at the DEJ and DCJ?

Answer 34

because thats where odontoblasts first "form" and baby ODB have many processes that extend out towards the junctions and as they progress down the ECM takes up the place of the processes (not as visible)

Question 35

difference in tubules btwn the inner and outer dentin

Answer 35

inner dentin has more tubules with a larger diameter than the outer dentin (larger to get to "wet" pulp") **less surface area occupied at the DEJ by tubules than at the P-D border

Question 36

primary dentin

Answer 36

until completion of root development | **most of dentin (mantle and circumpulpal)

Question 37

what is the diameter of mantle dentin?

Answer 37

20-150 under layer at DEJ

Question 38

secondary dentin

Answer 38

- formed after rt development - slower rate but throughout life - central to primary dentin - all along the pulp chamber, but heaviest on the roof and floor * *circumpulpal dentin as well - looks like primary dentin

Question 39

tertiary (reparative and reactive dentin)

Answer 39

-produced in a specific location due to noxious stimulus (caries or attrition) -irregular structure (may not have tubules (look like bone), may include whole cells?) reactive - mild stimulus reparative - caries kill ODB

Question 40

intertubular vs. intratubular/peritubular dentin

Answer 40

intertubular dentin is between and intratubular dentin lines the tubules -found in primary and secondary dentin intertubular >> intratubular intratubular is more mineralized than intertubular

Question 41

what accounts for the narrowing of the tubules near the DEJ?

Answer 41

intratubular ring becoming wider * *may even occlude the tubules near the DEJ (so fewer tubules) * ****** all of the dentin we talked about as far as formation (mantle and circumpulpal) is intertubular dentin

Question 42

translucent/sclerotic dentin

Answer 42

- tubules filled with intra/peritubular dentin * *both increase with age - translucent is the normal aging process and sclerotic is because there is accelerated deposition due to caries * *makes the tooth harder and more caries resistant

Question 43

dead tracts

Answer 43

tubules that dry out and fill with air

Question 44

interglobular dentin

Answer 44

individual foci are mineralized first (calcospherites) which will fuse to mineralize. If they do not fuse, then interglobular dentin forms **a lot in DSPP knockout mice

Question 45

Tome's granular layer

Answer 45

looped temrinal br. tubules (looks like sand) always in outer dentin in the root of the tooth ( near the DCJ)

Question 46

growth lines in dentin

Answer 46

pronounced growth lines can occur that reflect perturbations ex. is neonatal line observed in teeth mineralizing at birth **** growth lines are exaggerated due to tetracycline treatment by mother because it binds to collagen fibers