Lecture 4: Dentin: Gross Structure & Composition Flashcards
both dentin and pulp are ____ tissues
connective
what is the only part of the tooth that has blood vessels and is NONmineralized?
pulp
what does the dentin protect?
BOTH the pulp and enamel
____ is has a higher hardness and stiffness but ____ has a higher compressive strength
- enamel
- dentin
during what stage of tooth development does dentinogenesis begin?
bell stage
*just prior to this, dental organ and crown outline are present but no ameloblasts or odontoblasts
what is the progression of odontoblast formation?
undifferentiated mesencymal cells –> preodontoblasts —> odontoblasts
*odontoblasts secretes organic matrix then the matrix is mineralized
(unmineralized organic matrix = predentin)
what molecule is responsible for “kicking off” odontoblasts differentiation?
Wnt10a
- expression immediately precedes “wave” of odontoblast differentiation
- it induces dentin sialophosphoprotein (DSPP)
what are the two requirements for mineralization of dentin?
- Ca+++ and phosphate —
- initiation of crystal formation
- mantle (initial)
- circumpulpal (subsequent)
describe the mantle dentin formation
- 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
describe the circumpulpal dentin formation
- 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)
what are the two reasons why the DEJ is vulnerable to caries?
- mantle dentin is MORE organic
- mantle dentin is LESS mineralized
what is the hypothesis as to what initiates mineralization of dentin?
precipitates Ca+++ ions form the tissue fluid
what are the constituents of dentin by WEIGHT and VOLUME?
WEIGHT
- 10% water
- 20% organic
- 70% inorganic
VOLUME
- 22% water
- 33% organic
- 45% inorganic
dentin is harder than ___ and ____ but softer than ____
- bone and cementum
- enamel
during the mineral phase of dentin the hydroxyapetite crystals have a ____ orientation
random
what are the three type of proteins in the organic phase of dentin?
- 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]
what are the three types of dentin dominant proteins?
- dentin matrix protein I
- dentin glycoprotein
- dentin sialoprotein
> 50% of dentin dominant proteins that is anionic and includes long chains of polar amino acids
dentin phosphoprotein (DSPP)
*MUTATIONS IN THIS GENE CAUSE DENTINOGENESIS IMPERFECTA
what are the two types of mutations of the DSPP gene that cause dentinogenesis imperfect?
- 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!
dentinogenesis imperfecta is a ___ ____ mutation
dominant negative
- abnormal DSPP cannot be released from the odontoblasts afar mutation
- mutated DSPP “traps” the normal protein made by the unaffected protein
what are the three contents of dentinal tubules
- 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
what are the major differences between inner dentin and outer dentin?
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
dentin formed until completion of root development
-comprises most of dentin
primary dentin
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
secondary dentin
- central to primary dentin
- bc its formed throughout life, the pulp chamber gets smaller with aging
dentin produced in a SPECIFIC LOCATION in response to a noxious stimulus
- structually irregular
- may or may not have tubules
- may include cells
tertiary dentin
- happens after attrition or caries
- also called reparative or reactive dentin
what are the differences between INTERtubular dentin vs INTRAtubular dentin
- both types found in primary & secondary dentin
- volume: INTER > INTRA
- mineralization: INTRA»_space;> INTER
- INTRA “ring” is wider near DEJ (accounts for narrowing of tubule)
what is the difference between translucent dentin and sclerotic dentin?
transleucent dentin is a NORMAL process of aging whereas sclerotic dentin is accelerated deposition due to caries or attrition
occur when dentin tubules dry out or become filled with air
dead tracts
hypomineralized dentin just below the mantle dentin that results from the CALCOSHERITES not fusing so initial mineralization of dentin does not occur
interglobular dentin
the growth lines in dentin reflect what?
the incremental pattern of deposition
*similar to rings of trees
