Lecture 4: Dentin: Gross Structure & Composition

Question 1

both dentin and pulp are ____ tissues

Answer 1

connective

Question 2

what is the only part of the tooth that has blood vessels and is NONmineralized?

Answer 2

pulp

Question 3

what does the dentin protect?

Answer 3

BOTH the pulp and enamel

Question 4

____ is has a higher hardness and stiffness but ____ has a higher compressive strength

Answer 4

• enamel

- dentin

Question 5

during what stage of tooth development does dentinogenesis begin?

Answer 5

bell stage

*just prior to this, dental organ and crown outline are present but no ameloblasts or odontoblasts

Question 6

what is the progression of odontoblast formation?

Answer 6

undifferentiated mesencymal cells –> preodontoblasts —> odontoblasts

*odontoblasts secretes organic matrix then the matrix is mineralized
(unmineralized organic matrix = predentin)

Question 7

what molecule is responsible for “kicking off” odontoblasts differentiation?

Answer 7

Wnt10a

• expression immediately precedes “wave” of odontoblast differentiation
• it induces dentin sialophosphoprotein (DSPP)

Question 8

what are the two requirements for mineralization of dentin?

Answer 8

• Ca+++ and phosphate —
• initiation of crystal formation
  
  • mantle (initial)
  • circumpulpal (subsequent)

Question 9

describe the mantle dentin formation

Answer 9

• initial layer of dentin at DEJ
• principle component is COLLAGEN TYPE I
• large fibril oriented at right angles to basal lamina/DEJ
• MINERALIZATION is done by MATRIX VESICLES synthesized by odontoblasts

Question 10

describe the circumpulpal dentin formation

Answer 10

• interior to mantle layer and much thicker
• TYPE ONE COLLAGEN
• smaller fibrils parallel to basal lamina/DEJ
• MINERALIZATION is done by PROTEINS (bind to collagen)(secreted from odontoblast process)

Question 11

what are the two reasons why the DEJ is vulnerable to caries?

Answer 11

• mantle dentin is MORE organic

- mantle dentin is LESS mineralized

Question 12

what is the hypothesis as to what initiates mineralization of dentin?

Answer 12

precipitates Ca+++ ions form the tissue fluid

Question 13

what are the constituents of dentin by WEIGHT and VOLUME?

Answer 13

WEIGHT

• 10% water
• 20% organic
• 70% inorganic

VOLUME

• 22% water
• 33% organic
• 45% inorganic

Question 14

dentin is harder than ___ and ____ but softer than ____

Answer 14

• bone and cementum

- enamel

Question 15

during the mineral phase of dentin the hydroxyapetite crystals have a ____ orientation

Answer 15

random

Question 16

what are the three type of proteins in the organic phase of dentin?

Answer 16

• TYPE ONE COLLAGEN (90% of organic matrix)
• non-tissue specific proteins (signaling molecules and growth factors)
• mineralized-tissue specific proteins
• dentin-dominant proteins

[last three are considered non-collagenous]

Question 17

what are the three types of dentin dominant proteins?

Answer 17

• dentin matrix protein I
• dentin glycoprotein
• dentin sialoprotein

Question 18

> 50% of dentin dominant proteins that is anionic and includes long chains of polar amino acids

Answer 18

dentin phosphoprotein (DSPP)

*MUTATIONS IN THIS GENE CAUSE DENTINOGENESIS IMPERFECTA

Question 19

what are the two types of mutations of the DSPP gene that cause dentinogenesis imperfect?

Answer 19

• changes in the 1rst 3 amino acids which are critical for trafficking (moving) DSPP through the RER
• small base pair deletions that produce frame shifts coding the part of the DPP molecule that contain polar AA repeats: POLAR CHANGED TO UNCHARGED!

Question 20

dentinogenesis imperfecta is a ___ ____ mutation

Answer 20

dominant negative

• abnormal DSPP cannot be released from the odontoblasts afar mutation
• mutated DSPP “traps” the normal protein made by the unaffected protein

Question 21

what are the three contents of dentinal tubules

Answer 21

• fluid (major component is water)
• nerve fibers
• odontoblastic processes
• they are right angles to the DEJ and are S-shaped in root
• they also have terminal and lateral branches

Question 22

what are the major differences between inner dentin and outer dentin?

Answer 22

inner has more tubules as well as a larger diameter for the tubules

*tubules occupy much less surface area at the DEJ than at pulp-dentin border (permeability and wetness inc. toward P-D border

Question 23

dentin formed until completion of root development

-comprises most of dentin

Answer 23

primary dentin

Question 24

dentin formed after root development

• formed at a slower rate but THROUGHOUT LIFE
• present along the entire circumference of the pulp chamber but heaviest on roof and floor

Answer 24

secondary dentin

• central to primary dentin
• bc its formed throughout life, the pulp chamber gets smaller with aging

Question 25

dentin produced in a SPECIFIC LOCATION in response to a noxious stimulus

• structually irregular
• may or may not have tubules
• may include cells

Answer 25

tertiary dentin

• happens after attrition or caries
• also called reparative or reactive dentin

Question 26

what are the differences between INTERtubular dentin vs INTRAtubular dentin

Answer 26

• both types found in primary & secondary dentin
• volume: INTER > INTRA
• mineralization: INTRA&raquo_space;> INTER
• INTRA “ring” is wider near DEJ (accounts for narrowing of tubule)

Question 27

what is the difference between translucent dentin and sclerotic dentin?

Answer 27

transleucent dentin is a NORMAL process of aging whereas sclerotic dentin is accelerated deposition due to caries or attrition

Question 28

occur when dentin tubules dry out or become filled with air

Answer 28

dead tracts

Question 29

hypomineralized dentin just below the mantle dentin that results from the CALCOSHERITES not fusing so initial mineralization of dentin does not occur

Answer 29

interglobular dentin

Question 30

the growth lines in dentin reflect what?

Answer 30

the incremental pattern of deposition

*similar to rings of trees