Dentin Flashcards
What are some differences between Dentin and Pulp?
Pulp = soft connective tissue with blood vessels, whole cells, and is non-mineralized Dentin = minneralized connective tissue covering the pulp with no blood vessels or whole cells. It does have nerve endings and odontoblastic processes
Clinical significance of Dentin
Protects both the enamel and pulp
How does Dentin protect enamel
It is softer and more compressive, so it can cushion the more brittle enamel
Describe the appearance of the DEJ at the crown
It is scalloped, which facilitates adhesion of dentin and enamel to one another
When does Dentinogeneis occur?
During the “Bell stage” of tooth development
What occurs just prior to dentinogenesis?
Tissue layers of the dental organ are present
Crown outline is present
There are no odontoblasts or ameloblasts
What occurs in the late bell stage in regards to dentinogenesis?
Inner enamel cells (which become ameloblasts) are present
Undifferentiated mesenchumal cells are present in the dental papilla (become odontoblasts)
Dentin is secreted, and then enamel is secreted
What direction does dentinogenesis occur?
From cusp tip to cervix
Odontoblast differentiation
Begin as mesenchymal cells
One cell will divide to become a preodontoblast and a fibroblast
When preodontoblast begins to secrete matrix, it is an odontoblast
What induces odontoblast differentiation
Inductive signals for odontoblast differentiation
Where do signals for odontoblast differentiation come from?
From the enamel organ - most likely the enamel knot
This signal induces several molecules
Wnt10a
One of the growth factors implicated by the enamel knot
First expressed in the not, then in pre-odontoblast at the cusp tip.
Then it is successively expressed in the more cervical parts of the teeth
Expression immediately precedes the wave of odontoblast differentiation
T/F - Wnt10a is the only molecule implicated in inducing odontoblast differentiation
False - it is most likely just one of many
What is required for dentin mineralization?
Ca+2
Phosphate-
Initiation fo crystal formation
Where does Ca+2 come from for dentin mineralizaiton?
Free ions in plasma
Where does the phosphate come from for dentin mineralization?
From plasma and cleavage of organic molecules containing phosphate in odontoblasts by alkaline phosphatase
How is Ca and phosphate transported?
It is transported into predentin through and between odontoblasts
T/F - The presence of requisite ions are sufficient to initiate crystal formation
False - It requires special mechanisms:
Mantle
Circumpulpal
Mantle dentin formation
Initial layer of dentin near the DEJ Principle component is Type I collagen Secreted by odontoblasts Relatively large fibrils Oriented perpendicular to the basal lamina/future DEJ
Mantle dentin mineralization
Mineralized by matrix vesicles
Matrix vesicles
Membrane bound vesicles synthesized by odontobalsts
Concentrate Ca and PO containing and other organic molecules
Help mineralize Mantle dentin
How does dentin form?
Odontobalsts secrete matrix, which then mineralizes
Odontoblasts grow, and their processes elongate - this creates a barrier between dentin and pulp
Odontoblasts migrate toward pulp
T/F - Near the end of mantle formation, once odontoblast process becomes dominant
True
Circumpulpal dentin formation
Interior to mantle - much thicker
Process is the same as mantle formation
What is the difference between formation of Mantle and Circumpulpal dentin formation
Circumpulpal has smaller fibrils than Mantle
Circumpulpal is secreted parrallel to basal lamina, Mantle is perp.
Circumpulpal is mineralized by proteins, Mantle is mineralized by matrix vesicles
What are functional consequences of developmental differences between Mantle and Circumpulpal dentin
Mantle is more organic
Mantle is less mineralized
DEJ is more vulnerable to caries
Dentin phosphoprotein
Relatively spcific to dentin Prominent dentin protein Highly phosphorylated High in serine/aspartic acid Acidic Thought to precipitate Ca to initiate mineralization
Dentin constituents by weight
70% inorganic
20% organic
10% water
Dentin constituents by volume
45% inorganic
33% organic
22% water
Mineral phase of dentin
Hydroxyapatite crystals
1000s of unit cells/crystal
Crystals are randomly oriented - enamel is organized
What is the size of dentin crystals and how does that compare to enamel?
10x35x100nm
Much smaller than enamel crystals
Organic phase of dentin
Made of collagen and noncollagen proteins (90% type I collagen)
What are the types of proteins found in dentin?
Non-tissue specific proteins
Mineralized tissue-specific proteins
Dentin-dominant proteins
What are non-tissue specific proteins in dentin?
Proteoglycans
Signaling molecules/growth factors
What are mineralized tissue-specific proteins in dentin?
Osteocalcin
Bone sialoprotein
What are dentin-dominant proteins
Dentin matrix protein I
Dentin glycoprotein
Dentin sialoprotein
Dentin phosphoprotein
Dentin sialoprotein
5-8% of non-collagen proteins in dentin
Function is not well understood
Dentin phosphoprotein
> 50% of non-collagen proteins in dentin
Anionic
Includes chain of polar amino acid repeates
Serines are phosphoryated
What gene codes for Dentin phosphoprotein
DSPP (Dentin sialophosphoprotein)
Human hereditary disorder
aka Dentinogenesis Imperfecta
Dentin forms improperly
1:6,000-8,000
Associated with mutations of DSPP
How does Dentinogenesis Imperfecta defer in humans and mice?
In mice: there are 2 alleles, and both need to be negative for there to be abnormal dentin
In humams: DI is dominantly inherited with DSPP mutation
What are the 2 types of mutations to cause DI in humans?
1) changes in the first 3 amino acids critical for moving DSPP through the rough ER
2) Small base pair deletions produce frameshifts coding the DPP molecule that contain polar AA repeat - they become uncharged
What is the result of the mutations that cause DI
Result in abnormal DSPP cannot be released from odontoblasts - also traps normal proteins made by the unaffected chromosome, making it a dominant negative mutaiton
Dentinal tubules
At right angles to DEJ
S-shaped in crown, straighter in the root
Have terminal and lateral branches
Contents of dentinal tubules
Fluid (mostly water) Nerve fibers Odontobalstic processes Very few collagen fibers Non-cellular lining sheath
How do dentin tubules differ near the DEJ to the PD border?
Diameter of tubule is larger close to PD border
Number of tubules is greater close to PD border
Tubules occupy less area at DEJ than PD border
Permeability and wetness increase toward the PD border
What are the different types of dentin based off of?
When they’re formed
Location
Histological features
Primary dentin
Dentin formed until the completion of root dentin
Comprises most of dentin (both mantle and circumpulpal)
20u-150u at DEJ
Secondary dentin
Formed after root development Forms slowly but throughout life Central to primary dentin Similar in structure to primary dentin In circumpulpal dentin Likely formed by initial odontoblasts
Tertiary dentin
Produced in specific locaiton in response to noxious stimuli
Structurally irregular - may or may not have tubules and may include cells
Thought that initial odontobalsts are killed, and new ones come in for tertiary dentin
Intertubular dentin
Between tubules
Found in primary and secondary dentin
Intratubular/Peritubular dentin
Lines tubules
Found in primary and secondary dentin
What are some differences between intertubular and intratubular dentin?
Intratubular dentin covers less volume
Intratubular dentin is much more mineralized
Intratubular ring is wider near DEJ - tubule is narrower here
Translucent dentin
Tubules are completely filed with intratubular dentin
Normal process of aging
Sclerotic dentin
Tubules are completely filled with intratubular dentin
Accelerated ddeposition due to caries or attrition
Dead tracts
Tubules are dried out and become filled with air
Interglobular dentin
Hypomineralized dentin just below the mantle dentin
Growth lines
Reflect incremental pattern of deposition
Can be exaggerated due to tetracycline treatment
