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
