Dentin Flashcards
Inorganic , water and organic of dentin by volume and weight
Weight In organic 70% Water 10 Organic 20 Vol Inorganic 45% Organic 33 Water 22
Organic content of dentin
consists of fibrils
embedded in an amorphous ground substance.
The fibrils are collagen over
mainly collagen type I
small amount of type III & V
Making up about 90% of organic matrix
. ground substance mucopolysaccharides, glycoseaminoglycans &
content, small inclusion of noncollagenous protein matrix. proteoglycans”
Size of hydroxy appetite crystal
0.05- 0.06 µm
Non collagenous matrix protein function
Regulate the mineral deposition by acting as
Inhibitors Promoters Stabelizers
Their distribution is suggestive for their role
• •
Proteoglycan is conc in predentin …prevent premature mineralization of organic matrix till maturation of the collagen fibers and attanement of their correct position
DPP…. Bind to collagen and initiate hydroxyappetite formation as it binds to large amount of Ca
•
DSP, DMP located in peritubular dentin…. they inhibit its growth and prevent occlusion of dentinal tubules
Dentin is more permeable at ….third
Cervical
Points to talk about in physical properties of dentin
Hardness
Radio opacity
Color
Permeability
Origin of odontoblast
What is meant by post mitotic
produced by the last mitotic division of the mother cell and can’t undergo further mitotic division) • • Originated from neural crest cells. “asymmetrical one”division
Stages of odontoblast
4 stages I-Preodontoblasts II-Secretory odontoblast III-Transitional odontoblast IV-Aging odontoblast
Division of papilla stem cells after induction
:
Large cells in contact with dental lamina become pre-odontoblasts (short columnar in single raw)
B. Smaller cells with stem cell potentials grouped in “Hoehl cell layer.
Secretory odontoblast
The cells continue differentiation and increase in length (large & plump). Open faced & basally situated nucleus. Basophilic cytoplasm. Pronounced Golgi complex, RER, mitochondria
Have junction complexes and gap junction to form a row of cells. The cell exhibit alkaline phosphatase which is necessary for Ca++ transport into the cell.
As the dentin matrix is formed
Odontoblasts begin to move towards the pulp.
The plasma membrane of the odontoblasts adjacent to the IEE pushes out short stubby processes
called odontoblastic processes (tomes fibers).
Existence of secretory granules
Pre odontoblast
Small oval with polarised nucleus
Poorly developed golgi
Few rer
Transitional odontoblasts
- dark closed faced nuclei
- shifted from the basal part of the cell
- narrower
- fewer organelles
- fewer secretory granules
Aging odontoblast
- closed faced nucleus
- apically positioned
- narrow and flat with less cytoplasm
- few organelles
- no secretory granules
Note
Resting odontoblast could turn to active secretory odontoblast
And they normally produce dentin at v slow rate
Terminal branches of odontoblastic process form…..at ADJ
Unit with each other forming a plexus near ADJ.
Number of d tubules per unit area
At pulpal side more than at adj
At pulp it is 59k to 76k per mm square
Ratio is 4:1
More in crown than root
Diameter of d tubules
At adj .9 micron
Mid root 1.2
At pulp 2.5 (3:4)
4:1
Effect of profuse branching of dentinal tubules
Increase permeability, Enhance carious lesions, Increase response of the pulp to restorative procedures.
Ground substance of mantle dentin is made of 2 sources
in ground substance which is the product of odontoblasts incorporated with some of pre-existing substance of the cell free zone to form Mantle dentin.
Mechanism of collagen formation
After odontoblasts differentiated, the collagen formation begins in ribosomes sites of RER as procollagen, then pass to Golgi complex where they are glycosylated to be transferred as secretory vesicles towards the secretory poles of the cells. Once the secretory vesicles secreted outside the cell, the procollagen molecules aggregated as large fibers of collagen fibers
Compare circum pulpal and mantle dentin
Mantle Thickness is 5 to 20 micron Thick fibers .1 to .2 micron GS-- mix of .. Mineralisation-- globular Direction-- acc to crown or root(perpendicular but root is // to adj )
Circum pulpal
Thinner and more tightly aggregated .05 micron
Linear Mineralisation
Direction perpendicular to dentinal tubules and oblique to it and // to surface
Atea where secretion habbens from odontoblast called
Secretory pole of cell
Matrix vesicle content
After rupture it releases a…
Ca - phosphate
And alkaline phosphatase enzyme( Has membrane rich in alkaline phosphatase)
Cluster of crystallites
Mineralization
Of Dentin Hydroxy appetite crystals steps
Initially mineralization starts by deposition of very fine plates of hydroxyapatite on the surface of collagen fibrils and the ground substance.
later crystals are deposited within the fibrils themselves.
Crystals are arranged parallel to the collagen fibers long axis.
Which is more mineralised globular or linear
Linear
Pre dentin thickness
10 to 20 m
Mineralisation and matrix formation at same rate
The 3 patterns of mineralisation
Linear calcification: deposition of crystals along the uninterrupted front and is the principle pattern of mineralization in mantle dentin.
Globular calcification: deposition of crystals in several areas of the matrix, with continue calcification globular masses develops, which enlarge and fuse to form a single mass, usually present in
circumpulpal dentin just below mantle dentin.
Combined pattern of both types: In the rest of circumpulpal dentin
Info about intra tubular dentin
It doesn’t exist in the area of interglobular dentin. Its width is 0.4 µ at pulp end, and 0.75µ at ADJ. Changes the diameter of DTs in some areas. If exposed to external stimuli deposition till obliteration of D.T.
40% more.mineralised
Intra- tubular dentin may fill the tubules as in the area near the ADJ overlying the pulp horn or in the peripheral tubules of the root.
It contains less collagen amount.
Due to the difference in calcification between the peritubular and the inter tubular dentin the interface between them appears very clear in ground section.
It was thought that this interface is an actual structure or sheath and they call it sheath of Neuman but E.M failed to prove it & on contrary the collagen fibrils of both types intermingles with each other.
Interglobular dentin
Ocuur with vit D deficiency OR exposure to high fluoride content
It follows the incremental pattern of dentin
It is seen most frequently in circumpulpal dentin just below mantle dentin in crown next to ADJ
most frequently in cervical and middle third.
Because it is defect in mineralization (not of matrix formation) dentinal tubules pass uninterrupted through interglobular dentin with no peri-tubular dentin exists
Zine of hopewell smith
• • • •
Only in the root Hyaline layer 8-15µ May serve to bond cementum to dentin
Granular Layer of Tomes
THEORIES
: 1-Thought to be true spaces (rejected as it can’t be seen in H&E sections or in E\M)
2-Minute hypomineralized areas of interglobular dentin but differ in that they are smaller & don’t follow any incremental pattern.
3-Section through looped terminal portion of dentinal tubules. in the beginning of dentin root formation the odontoblasts are disoriented and turns to a right angle to
the root surface during its retreat toward the pulp 4- B.V
5- Recently it was considered as special arrangement of collagen and noncollagnenous matrix protein in the dentin cementum interface
2ry dentin notes
Formed through out life “after complete root formation”
Increased by mild stimulus reaching the pulp as slow attrition, slowly progressive caries.
Why there is line of demarcation between both 1ry and 2ry D
moving in a wavier course (less regular) forming+ changing direction and less tubules
2ry and 3ry dentin are they continuous
-May be continuous with 2ry dentin.
Types of 3ry dentin
-osteodentin
Vaso dentin
Atubular dentin
Line of demarcation in 2ry and 3ry D
Line of demarcation Present and stained dark. In 2ry d
But in 3ry it May or may not present
Incremental lines of von ebner
Reflect normal rhythmic formation Linear pattern of dentin deposition At the boundary bet. Daily increment there is change in collagen orientation. The distance between the lines4-8 microns in crown, much less in root represent daily rate of D. formation. Run at right angles to the dentinal tubulesDentin Incremental lines of Dentin
Incremental lines of Von-Ebner (hypocalcefied)
Super imposed on the daily rhythm there is a 5 day cycle in which change in the collagen fiber is greater it is readily seen in ground section
Rate of dentin formation 2mm / 12 h 4mm/day …………..20mm / 5 days
Contour line of Owen
: It is more accentuated incremental lines, resulted from disturbance in mineralization process. It is easily seen in longitudinal ground section.
.
Or due to coincidence between the 2ry curvature of D.T
Neonatal line of dentin
Neonatal line:
Deciduous teeth and the first permanent molar Separates prenatal from post natal enamel, Due to sudden change in the environment during dentinogenesis. Quality of prenatal better than postnatal.
Dead tract
Due to crowding of the odontoblast the narrow pulpal horn leaving empty tubules which may be filled with air
Sclerotic dentin
This dentin has uniform refractive index because dentinal tubules are occluded by widening of peritubular zones and odontoblastic processes become reduced in diameter.
It appear translucent when viewed by transmitted light, it appear dark when transmitted by reflected light.
Sclerotic dentin will leads to occlusion of the dentinal tubules by calcified deposit,
This increased mineralization of the tooth leads to:
Decrease the conductivity of the odontoblastic processes.
Slows down carious process.
Prolong the pulp vitality
Decrease permeability of dentin
Increase the brittleness of dentin
Site of sclerotic dentin that occur as age change
Apical of root
Midway between adj and pulp in crown
Nerve supply of dentin
- sub odontoblastic plexus or raschkow plexus found in the sub odontoblastic zone (in diagram its before the cell rich zone)
Changes to nerves acc to zone
Lose their myelin sheath when reaching cell free zone
And lose schwann cell coat and enter between od. For 100 to 150 micron
Name of theories of dentin sensetivity
Direct neural stimulation
Od transduction
Hydrodynamic
Third argument against direct neural stimulation
about eruption
Newly erupted teeth are sensitive, although plexus of Raschkow do not establish until a tooth had erupted.
What supports argument of odontoblastic transduction
This theory is supported by the neural origin of odontoblasts “neural crest cells”
Why sens at adj is more
The increased sensitivity at ADJ due to profuse branching of tubules in this region
Clinical consideration of dentin
I-Occluding DTs • Adhesive material, desensitizing agents exhibits reduction of dentinal fluid flow rate • Potassium salts “potassium nitrate”, it disrupts nerve impulses transmission
•Laser
Laser, Different mechanisms of action have been proposed for laser 1- Occlusion through coagulation of the proteins of the fluid inside the dentinal tubules 2- Occlusion of tubules through partial submelting 3- Discharging of internal tubular nerve
2-Metallic restorations are excellent thermal conductors. Therefore it is important to replace a cement base under these restorations to protect the pulp by minimizing pain conduction.
3-Sealing of dentinal tubules is a prerequisite of effective restorative dentistry because of the permeability of dentin .
Smear layer
When dentin is cut or abraded by dental instruments, a smear layer develops and covers the surface and obscures the underlying structure .
A:The bur cutting marks and at B: higher magnification C: shows the smear layer thickness from the side and the smear plugs as the cut dentin debris is pushed into the dentin tubule lumen.
Advantages of the smear layer: It reduces permeability and therefore aids in maintaining a drier field and reduces infiltration of noxious agents into the tubules and perhaps the pulp.
Disadvantages It is a hindrance to dentin bonding procedures and, therefore, is normally removed or modified by some form of acid conditioning.
Type 3 dentinogenesis imperfecta
Enlarged pulp chamber Increased thickness of predentin Hypomeneralization
